naga 0.11.0

/*!

Frontend for [SPIR-V][spv] (Standard Portable Intermediate Representation).

## ID lookups

Our IR links to everything with `Handle`, while SPIR-V uses IDs.
In order to keep track of the associations, the parser has many lookup tables.
There map `spv::Word` into a specific IR handle, plus potentially a bit of
extra info, such as the related SPIR-V type ID.
TODO: would be nice to find ways that avoid looking up as much

## Inputs/Outputs

We create a private variable for each input/output. The relevant inputs are
populated at the start of an entry point. The outputs are saved at the end.

The function associated with an entry point is wrapped in another function,
such that we can handle any `Return` statements without problems.

## Row-major matrices

We don't handle them natively, since the IR only expects column majority.
Instead, we detect when such matrix is accessed in the `OpAccessChain`,
and we generate a parallel expression that loads the value, but transposed.
This value then gets used instead of `OpLoad` result later on.

[spv]: https://www.khronos.org/registry/SPIR-V/
*/

mod convert;
mod error;
mod function;
mod image;
mod null;

use convert::*;
pub use error::Error;
use function::*;

use crate::{
    arena::{Arena, Handle, UniqueArena},
    proc::{Alignment, Layouter},
    FastHashMap, FastHashSet,
};

use num_traits::cast::FromPrimitive;
use petgraph::graphmap::GraphMap;
use std::{convert::TryInto, mem, num::NonZeroU32, path::PathBuf};

pub const SUPPORTED_CAPABILITIES: &[spirv::Capability] = &[
    spirv::Capability::Shader,
    spirv::Capability::VulkanMemoryModel,
    spirv::Capability::ClipDistance,
    spirv::Capability::CullDistance,
    spirv::Capability::SampleRateShading,
    spirv::Capability::DerivativeControl,
    spirv::Capability::InterpolationFunction,
    spirv::Capability::Matrix,
    spirv::Capability::ImageQuery,
    spirv::Capability::Sampled1D,
    spirv::Capability::Image1D,
    spirv::Capability::SampledCubeArray,
    spirv::Capability::ImageCubeArray,
    spirv::Capability::ImageMSArray,
    spirv::Capability::StorageImageExtendedFormats,
    spirv::Capability::Sampled1D,
    spirv::Capability::SampledCubeArray,
    spirv::Capability::Int8,
    spirv::Capability::Int16,
    spirv::Capability::Int64,
    spirv::Capability::Float16,
    spirv::Capability::Float64,
    spirv::Capability::Geometry,
    spirv::Capability::MultiView,
    // tricky ones
    spirv::Capability::UniformBufferArrayDynamicIndexing,
    spirv::Capability::StorageBufferArrayDynamicIndexing,
];
pub const SUPPORTED_EXTENSIONS: &[&str] = &[
    "SPV_KHR_storage_buffer_storage_class",
    "SPV_KHR_vulkan_memory_model",
    "SPV_KHR_multiview",
];
pub const SUPPORTED_EXT_SETS: &[&str] = &["GLSL.std.450"];

#[derive(Copy, Clone)]
pub struct Instruction {
    op: spirv::Op,
    wc: u16,
}

impl Instruction {
    const fn expect(self, count: u16) -> Result<(), Error> {
        if self.wc == count {
            Ok(())
        } else {
            Err(Error::InvalidOperandCount(self.op, self.wc))
        }
    }

    fn expect_at_least(self, count: u16) -> Result<u16, Error> {
        self.wc
            .checked_sub(count)
            .ok_or(Error::InvalidOperandCount(self.op, self.wc))
    }
}

impl crate::TypeInner {
    fn can_comparison_sample(&self, module: &crate::Module) -> bool {
        match *self {
            crate::TypeInner::Image {
                class:
                    crate::ImageClass::Sampled {
                        kind: crate::ScalarKind::Float,
                        multi: false,
                    },
                ..
            } => true,
            crate::TypeInner::Sampler { .. } => true,
            crate::TypeInner::BindingArray { base, .. } => {
                module.types[base].inner.can_comparison_sample(module)
            }
            _ => false,
        }
    }
}

#[derive(Clone, Copy, Debug, PartialEq, PartialOrd)]
pub enum ModuleState {
    Empty,
    Capability,
    Extension,
    ExtInstImport,
    MemoryModel,
    EntryPoint,
    ExecutionMode,
    Source,
    Name,
    ModuleProcessed,
    Annotation,
    Type,
    Function,
}

trait LookupHelper {
    type Target;
    fn lookup(&self, key: spirv::Word) -> Result<&Self::Target, Error>;
}

impl<T> LookupHelper for FastHashMap<spirv::Word, T> {
    type Target = T;
    fn lookup(&self, key: spirv::Word) -> Result<&T, Error> {
        self.get(&key).ok_or(Error::InvalidId(key))
    }
}

impl crate::ImageDimension {
    const fn required_coordinate_size(&self) -> Option<crate::VectorSize> {
        match *self {
            crate::ImageDimension::D1 => None,
            crate::ImageDimension::D2 => Some(crate::VectorSize::Bi),
            crate::ImageDimension::D3 => Some(crate::VectorSize::Tri),
            crate::ImageDimension::Cube => Some(crate::VectorSize::Tri),
        }
    }
}

type MemberIndex = u32;

bitflags::bitflags! {
    #[derive(Default)]
    struct DecorationFlags: u32 {
        const NON_READABLE = 0x1;
        const NON_WRITABLE = 0x2;
    }
}

impl DecorationFlags {
    fn to_storage_access(self) -> crate::StorageAccess {
        let mut access = crate::StorageAccess::all();
        if self.contains(DecorationFlags::NON_READABLE) {
            access &= !crate::StorageAccess::LOAD;
        }
        if self.contains(DecorationFlags::NON_WRITABLE) {
            access &= !crate::StorageAccess::STORE;
        }
        access
    }
}

#[derive(Debug, PartialEq)]
enum Majority {
    Column,
    Row,
}

#[derive(Debug, Default)]
struct Decoration {
    name: Option<String>,
    built_in: Option<spirv::Word>,
    location: Option<spirv::Word>,
    desc_set: Option<spirv::Word>,
    desc_index: Option<spirv::Word>,
    specialization: Option<spirv::Word>,
    storage_buffer: bool,
    offset: Option<spirv::Word>,
    array_stride: Option<NonZeroU32>,
    matrix_stride: Option<NonZeroU32>,
    matrix_major: Option<Majority>,
    invariant: bool,
    interpolation: Option<crate::Interpolation>,
    sampling: Option<crate::Sampling>,
    flags: DecorationFlags,
}

impl Decoration {
    fn debug_name(&self) -> &str {
        match self.name {
            Some(ref name) => name.as_str(),
            None => "?",
        }
    }

    const fn resource_binding(&self) -> Option<crate::ResourceBinding> {
        match *self {
            Decoration {
                desc_set: Some(group),
                desc_index: Some(binding),
                ..
            } => Some(crate::ResourceBinding { group, binding }),
            _ => None,
        }
    }

    fn io_binding(&self) -> Result<crate::Binding, Error> {
        match *self {
            Decoration {
                built_in: Some(built_in),
                location: None,
                invariant,
                ..
            } => Ok(crate::Binding::BuiltIn(map_builtin(built_in, invariant)?)),
            Decoration {
                built_in: None,
                location: Some(location),
                interpolation,
                sampling,
                ..
            } => Ok(crate::Binding::Location {
                location,
                interpolation,
                sampling,
            }),
            _ => Err(Error::MissingDecoration(spirv::Decoration::Location)),
        }
    }
}

#[derive(Debug)]
struct LookupFunctionType {
    parameter_type_ids: Vec<spirv::Word>,
    return_type_id: spirv::Word,
}

struct LookupFunction {
    handle: Handle<crate::Function>,
    parameters_sampling: Vec<image::SamplingFlags>,
}

#[derive(Debug)]
struct EntryPoint {
    stage: crate::ShaderStage,
    name: String,
    early_depth_test: Option<crate::EarlyDepthTest>,
    workgroup_size: [u32; 3],
    variable_ids: Vec<spirv::Word>,
}

#[derive(Clone, Debug)]
struct LookupType {
    handle: Handle<crate::Type>,
    base_id: Option<spirv::Word>,
}

#[derive(Debug)]
struct LookupConstant {
    handle: Handle<crate::Constant>,
    type_id: spirv::Word,
}

#[derive(Debug)]
enum Variable {
    Global,
    Input(crate::FunctionArgument),
    Output(crate::FunctionResult),
}

#[derive(Debug)]
struct LookupVariable {
    inner: Variable,
    handle: Handle<crate::GlobalVariable>,
    type_id: spirv::Word,
}

/// Information about SPIR-V result ids, stored in `Parser::lookup_expression`.
#[derive(Clone, Debug)]
struct LookupExpression {
    /// The `Expression` constructed for this result.
    ///
    /// Note that, while a SPIR-V result id can be used in any block dominated
    /// by its definition, a Naga `Expression` is only in scope for the rest of
    /// its subtree. `Parser::get_expr_handle` takes care of spilling the result
    /// to a `LocalVariable` which can then be used anywhere.
    handle: Handle<crate::Expression>,

    /// The SPIR-V type of this result.
    type_id: spirv::Word,

    /// The label id of the block that defines this expression.
    ///
    /// This is zero for globals, constants, and function parameters, since they
    /// originate outside any function's block.
    block_id: spirv::Word,
}

#[derive(Debug)]
struct LookupMember {
    type_id: spirv::Word,
    // This is true for either matrices, or arrays of matrices (yikes).
    row_major: bool,
}

#[derive(Clone, Debug)]
enum LookupLoadOverride {
    /// For arrays of matrices, we track them but not loading yet.
    Pending,
    /// For matrices, vectors, and scalars, we pre-load the data.
    Loaded(Handle<crate::Expression>),
}

#[derive(PartialEq)]
enum ExtendedClass {
    Global(crate::AddressSpace),
    Input,
    Output,
}

#[derive(Clone, Debug)]
pub struct Options {
    /// The IR coordinate space matches all the APIs except SPIR-V,
    /// so by default we flip the Y coordinate of the `BuiltIn::Position`.
    /// This flag can be used to avoid this.
    pub adjust_coordinate_space: bool,
    /// Only allow shaders with the known set of capabilities.
    pub strict_capabilities: bool,
    pub block_ctx_dump_prefix: Option<PathBuf>,
}

impl Default for Options {
    fn default() -> Self {
        Options {
            adjust_coordinate_space: true,
            strict_capabilities: false,
            block_ctx_dump_prefix: None,
        }
    }
}

/// An index into the `BlockContext::bodies` table.
type BodyIndex = usize;

/// An intermediate representation of a Naga [`Statement`].
///
/// `Body` and `BodyFragment` values form a tree: the `BodyIndex` fields of the
/// variants are indices of the child `Body` values in [`BlockContext::bodies`].
/// The `lower` function assembles the final `Statement` tree from this `Body`
/// tree. See [`BlockContext`] for details.
///
/// [`Statement`]: crate::Statement
#[derive(Debug)]
enum BodyFragment {
    BlockId(spirv::Word),
    If {
        condition: Handle<crate::Expression>,
        accept: BodyIndex,
        reject: BodyIndex,
    },
    Loop {
        body: BodyIndex,
        continuing: BodyIndex,
    },
    Switch {
        selector: Handle<crate::Expression>,
        cases: Vec<(i32, BodyIndex)>,
        default: BodyIndex,
    },
    Break,
    Continue,
}

/// An intermediate representation of a Naga [`Block`].
///
/// This will be assembled into a `Block` once we've added spills for phi nodes
/// and out-of-scope expressions. See [`BlockContext`] for details.
///
/// [`Block`]: crate::Block
#[derive(Debug)]
struct Body {
    /// The index of the direct parent of this body
    parent: usize,
    data: Vec<BodyFragment>,
}

impl Body {
    /// Creates a new empty `Body` with the specified `parent`
    pub const fn with_parent(parent: usize) -> Self {
        Body {
            parent,
            data: Vec::new(),
        }
    }
}

#[derive(Debug)]
struct PhiExpression {
    /// The local variable used for the phi node
    local: Handle<crate::LocalVariable>,
    /// List of (expression, block)
    expressions: Vec<(spirv::Word, spirv::Word)>,
}

#[derive(Debug)]
enum MergeBlockInformation {
    LoopMerge,
    LoopContinue,
    SelectionMerge,
    SwitchMerge,
}

/// Fragments of Naga IR, to be assembled into `Statements` once data flow is
/// resolved.
///
/// We can't build a Naga `Statement` tree directly from SPIR-V blocks for two
/// main reasons:
///
/// - A SPIR-V expression can be used in any SPIR-V block dominated by its
///   definition, whereas Naga expressions are scoped to the rest of their
///   subtree. This means that discovering an expression use later in the
///   function retroactively requires us to have spilled that expression into a
///   local variable back before we left its scope.
///
/// - We translate SPIR-V OpPhi expressions as Naga local variables in which we
///   store the appropriate value before jumping to the OpPhi's block.
///
/// Both cases require us to go back and amend previously generated Naga IR
/// based on things we discover later. But modifying old blocks in arbitrary
/// spots in a `Statement` tree is awkward.
///
/// Instead, as we iterate through the function's body, we accumulate
/// control-flow-free fragments of Naga IR in the [`blocks`] table, while
/// building a skeleton of the Naga `Statement` tree in [`bodies`]. We note any
/// spills and temporaries we must introduce in [`phis`].
///
/// Finally, once we've processed the entire function, we add temporaries and
/// spills to the fragmentary `Blocks` as directed by `phis`, and assemble them
/// into the final Naga `Statement` tree as directed by `bodies`.
///
/// [`blocks`]: BlockContext::blocks
/// [`bodies`]: BlockContext::bodies
/// [`phis`]: BlockContext::phis
/// [`lower`]: function::lower
#[derive(Debug)]
struct BlockContext<'function> {
    /// Phi nodes encountered when parsing the function, used to generate spills
    /// to local variables.
    phis: Vec<PhiExpression>,

    /// Fragments of control-flow-free Naga IR.
    ///
    /// These will be stitched together into a proper `Statement` tree according
    /// to `bodies`, once parsing is complete.
    blocks: FastHashMap<spirv::Word, crate::Block>,

    /// Map from block label ids to the index of the corresponding `Body` in
    /// `bodies`.
    body_for_label: FastHashMap<spirv::Word, BodyIndex>,

    /// SPIR-V metadata about merge/continue blocks.
    mergers: FastHashMap<spirv::Word, MergeBlockInformation>,

    /// A table of `Body` values, each representing a block in the final IR.
    bodies: Vec<Body>,

    /// Id of the function currently being processed
    function_id: spirv::Word,
    /// Expression arena of the function currently being processed
    expressions: &'function mut Arena<crate::Expression>,
    /// Local variables arena of the function currently being processed
    local_arena: &'function mut Arena<crate::LocalVariable>,
    /// Constants arena of the module being processed
    const_arena: &'function mut Arena<crate::Constant>,
    /// Type arena of the module being processed
    type_arena: &'function UniqueArena<crate::Type>,
    /// Global arena of the module being processed
    global_arena: &'function Arena<crate::GlobalVariable>,
    /// Arguments of the function currently being processed
    arguments: &'function [crate::FunctionArgument],
    /// Metadata about the usage of function parameters as sampling objects
    parameter_sampling: &'function mut [image::SamplingFlags],
}

enum SignAnchor {
    Result,
    Operand,
}

pub struct Parser<I> {
    data: I,
    data_offset: usize,
    state: ModuleState,
    layouter: Layouter,
    temp_bytes: Vec<u8>,
    ext_glsl_id: Option<spirv::Word>,
    future_decor: FastHashMap<spirv::Word, Decoration>,
    future_member_decor: FastHashMap<(spirv::Word, MemberIndex), Decoration>,
    lookup_member: FastHashMap<(Handle<crate::Type>, MemberIndex), LookupMember>,
    handle_sampling: FastHashMap<Handle<crate::GlobalVariable>, image::SamplingFlags>,
    lookup_type: FastHashMap<spirv::Word, LookupType>,
    lookup_void_type: Option<spirv::Word>,
    lookup_storage_buffer_types: FastHashMap<Handle<crate::Type>, crate::StorageAccess>,
    // Lookup for samplers and sampled images, storing flags on how they are used.
    lookup_constant: FastHashMap<spirv::Word, LookupConstant>,
    lookup_variable: FastHashMap<spirv::Word, LookupVariable>,
    lookup_expression: FastHashMap<spirv::Word, LookupExpression>,
    // Load overrides are used to work around row-major matrices
    lookup_load_override: FastHashMap<spirv::Word, LookupLoadOverride>,
    lookup_sampled_image: FastHashMap<spirv::Word, image::LookupSampledImage>,
    lookup_function_type: FastHashMap<spirv::Word, LookupFunctionType>,
    lookup_function: FastHashMap<spirv::Word, LookupFunction>,
    lookup_entry_point: FastHashMap<spirv::Word, EntryPoint>,
    //Note: each `OpFunctionCall` gets a single entry here, indexed by the
    // dummy `Handle<crate::Function>` of the call site.
    deferred_function_calls: Vec<spirv::Word>,
    dummy_functions: Arena<crate::Function>,
    // Graph of all function calls through the module.
    // It's used to sort the functions (as nodes) topologically,
    // so that in the IR any called function is already known.
    function_call_graph: GraphMap<spirv::Word, (), petgraph::Directed>,
    options: Options,
    index_constants: Vec<Handle<crate::Constant>>,
    index_constant_expressions: Vec<Handle<crate::Expression>>,

    /// Maps for a switch from a case target to the respective body and associated literals that
    /// use that target block id.
    ///
    /// Used to preserve allocations between instruction parsing.
    switch_cases: indexmap::IndexMap<
        spirv::Word,
        (BodyIndex, Vec<i32>),
        std::hash::BuildHasherDefault<rustc_hash::FxHasher>,
    >,

    /// Tracks usage of builtins, used to cull unused builtins since they can
    /// have serious performance implications.
    builtin_usage: FastHashSet<crate::BuiltIn>,
}

impl<I: Iterator<Item = u32>> Parser<I> {
    pub fn new(data: I, options: &Options) -> Self {
        Parser {
            data,
            data_offset: 0,
            state: ModuleState::Empty,
            layouter: Layouter::default(),
            temp_bytes: Vec::new(),
            ext_glsl_id: None,
            future_decor: FastHashMap::default(),
            future_member_decor: FastHashMap::default(),
            handle_sampling: FastHashMap::default(),
            lookup_member: FastHashMap::default(),
            lookup_type: FastHashMap::default(),
            lookup_void_type: None,
            lookup_storage_buffer_types: FastHashMap::default(),
            lookup_constant: FastHashMap::default(),
            lookup_variable: FastHashMap::default(),
            lookup_expression: FastHashMap::default(),
            lookup_load_override: FastHashMap::default(),
            lookup_sampled_image: FastHashMap::default(),
            lookup_function_type: FastHashMap::default(),
            lookup_function: FastHashMap::default(),
            lookup_entry_point: FastHashMap::default(),
            deferred_function_calls: Vec::default(),
            dummy_functions: Arena::new(),
            function_call_graph: GraphMap::new(),
            options: options.clone(),
            index_constants: Vec::new(),
            index_constant_expressions: Vec::new(),
            switch_cases: indexmap::IndexMap::default(),
            builtin_usage: FastHashSet::default(),
        }
    }

    fn span_from(&self, from: usize) -> crate::Span {
        crate::Span::from(from..self.data_offset)
    }

    fn span_from_with_op(&self, from: usize) -> crate::Span {
        crate::Span::from((from - 4)..self.data_offset)
    }

    fn next(&mut self) -> Result<u32, Error> {
        if let Some(res) = self.data.next() {
            self.data_offset += 4;
            Ok(res)
        } else {
            Err(Error::IncompleteData)
        }
    }

    fn next_inst(&mut self) -> Result<Instruction, Error> {
        let word = self.next()?;
        let (wc, opcode) = ((word >> 16) as u16, (word & 0xffff) as u16);
        if wc == 0 {
            return Err(Error::InvalidWordCount);
        }
        let op = spirv::Op::from_u16(opcode).ok_or(Error::UnknownInstruction(opcode))?;

        Ok(Instruction { op, wc })
    }

    fn next_string(&mut self, mut count: u16) -> Result<(String, u16), Error> {
        self.temp_bytes.clear();
        loop {
            if count == 0 {
                return Err(Error::BadString);
            }
            count -= 1;
            let chars = self.next()?.to_le_bytes();
            let pos = chars.iter().position(|&c| c == 0).unwrap_or(4);
            self.temp_bytes.extend_from_slice(&chars[..pos]);
            if pos < 4 {
                break;
            }
        }
        std::str::from_utf8(&self.temp_bytes)
            .map(|s| (s.to_owned(), count))
            .map_err(|_| Error::BadString)
    }

    fn next_decoration(
        &mut self,
        inst: Instruction,
        base_words: u16,
        dec: &mut Decoration,
    ) -> Result<(), Error> {
        let raw = self.next()?;
        let dec_typed = spirv::Decoration::from_u32(raw).ok_or(Error::InvalidDecoration(raw))?;
        log::trace!("\t\t{}: {:?}", dec.debug_name(), dec_typed);
        match dec_typed {
            spirv::Decoration::BuiltIn => {
                inst.expect(base_words + 2)?;
                dec.built_in = Some(self.next()?);
            }
            spirv::Decoration::Location => {
                inst.expect(base_words + 2)?;
                dec.location = Some(self.next()?);
            }
            spirv::Decoration::DescriptorSet => {
                inst.expect(base_words + 2)?;
                dec.desc_set = Some(self.next()?);
            }
            spirv::Decoration::Binding => {
                inst.expect(base_words + 2)?;
                dec.desc_index = Some(self.next()?);
            }
            spirv::Decoration::BufferBlock => {
                dec.storage_buffer = true;
            }
            spirv::Decoration::Offset => {
                inst.expect(base_words + 2)?;
                dec.offset = Some(self.next()?);
            }
            spirv::Decoration::ArrayStride => {
                inst.expect(base_words + 2)?;
                dec.array_stride = NonZeroU32::new(self.next()?);
            }
            spirv::Decoration::MatrixStride => {
                inst.expect(base_words + 2)?;
                dec.matrix_stride = NonZeroU32::new(self.next()?);
            }
            spirv::Decoration::Invariant => {
                dec.invariant = true;
            }
            spirv::Decoration::NoPerspective => {
                dec.interpolation = Some(crate::Interpolation::Linear);
            }
            spirv::Decoration::Flat => {
                dec.interpolation = Some(crate::Interpolation::Flat);
            }
            spirv::Decoration::Centroid => {
                dec.sampling = Some(crate::Sampling::Centroid);
            }
            spirv::Decoration::Sample => {
                dec.sampling = Some(crate::Sampling::Sample);
            }
            spirv::Decoration::NonReadable => {
                dec.flags |= DecorationFlags::NON_READABLE;
            }
            spirv::Decoration::NonWritable => {
                dec.flags |= DecorationFlags::NON_WRITABLE;
            }
            spirv::Decoration::ColMajor => {
                dec.matrix_major = Some(Majority::Column);
            }
            spirv::Decoration::RowMajor => {
                dec.matrix_major = Some(Majority::Row);
            }
            spirv::Decoration::SpecId => {
                dec.specialization = Some(self.next()?);
            }
            other => {
                log::warn!("Unknown decoration {:?}", other);
                for _ in base_words + 1..inst.wc {
                    let _var = self.next()?;
                }
            }
        }
        Ok(())
    }

    /// Return the Naga `Expression` for a given SPIR-V result `id`.
    ///
    /// `lookup` must be the `LookupExpression` for `id`.
    ///
    /// SPIR-V result ids can be used by any block dominated by the id's
    /// definition, but Naga `Expressions` are only in scope for the remainder
    /// of their `Statement` subtree. This means that the `Expression` generated
    /// for `id` may no longer be in scope. In such cases, this function takes
    /// care of spilling the value of `id` to a `LocalVariable` which can then
    /// be used anywhere. The SPIR-V domination rule ensures that the
    /// `LocalVariable` has been initialized before it is used.
    ///
    /// The `body_idx` argument should be the index of the `Body` that hopes to
    /// use `id`'s `Expression`.
    fn get_expr_handle(
        &self,
        id: spirv::Word,
        lookup: &LookupExpression,
        ctx: &mut BlockContext,
        emitter: &mut super::Emitter,
        block: &mut crate::Block,
        body_idx: BodyIndex,
    ) -> Handle<crate::Expression> {
        // What `Body` was `id` defined in?
        let expr_body_idx = ctx
            .body_for_label
            .get(&lookup.block_id)
            .copied()
            .unwrap_or(0);

        // Don't need to do a load/store if the expression is in the main body
        // or if the expression is in the same body as where the query was
        // requested. The body_idx might actually not be the final one if a loop
        // or conditional occurs but in those cases we know that the new body
        // will be a subscope of the body that was passed so we can still reuse
        // the handle and not issue a load/store.
        if is_parent(body_idx, expr_body_idx, ctx) {
            lookup.handle
        } else {
            // Add a temporary variable of the same type which will be used to
            // store the original expression and used in the current block
            let ty = self.lookup_type[&lookup.type_id].handle;
            let local = ctx.local_arena.append(
                crate::LocalVariable {
                    name: None,
                    ty,
                    init: None,
                },
                crate::Span::default(),
            );

            block.extend(emitter.finish(ctx.expressions));
            let pointer = ctx.expressions.append(
                crate::Expression::LocalVariable(local),
                crate::Span::default(),
            );
            emitter.start(ctx.expressions);
            let expr = ctx
                .expressions
                .append(crate::Expression::Load { pointer }, crate::Span::default());

            // Add a slightly odd entry to the phi table, so that while `id`'s
            // `Expression` is still in scope, the usual phi processing will
            // spill its value to `local`, where we can find it later.
            //
            // This pretends that the block in which `id` is defined is the
            // predecessor of some other block with a phi in it that cites id as
            // one of its sources, and uses `local` as its variable. There is no
            // such phi, but nobody needs to know that.
            ctx.phis.push(PhiExpression {
                local,
                expressions: vec![(id, lookup.block_id)],
            });

            expr
        }
    }

    fn parse_expr_unary_op(
        &mut self,
        ctx: &mut BlockContext,
        emitter: &mut super::Emitter,
        block: &mut crate::Block,
        block_id: spirv::Word,
        body_idx: usize,
        op: crate::UnaryOperator,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        let result_type_id = self.next()?;
        let result_id = self.next()?;
        let p_id = self.next()?;

        let p_lexp = self.lookup_expression.lookup(p_id)?;
        let handle = self.get_expr_handle(p_id, p_lexp, ctx, emitter, block, body_idx);

        let expr = crate::Expression::Unary { op, expr: handle };
        self.lookup_expression.insert(
            result_id,
            LookupExpression {
                handle: ctx.expressions.append(expr, self.span_from_with_op(start)),
                type_id: result_type_id,
                block_id,
            },
        );
        Ok(())
    }

    fn parse_expr_binary_op(
        &mut self,
        ctx: &mut BlockContext,
        emitter: &mut super::Emitter,
        block: &mut crate::Block,
        block_id: spirv::Word,
        body_idx: usize,
        op: crate::BinaryOperator,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        let result_type_id = self.next()?;
        let result_id = self.next()?;
        let p1_id = self.next()?;
        let p2_id = self.next()?;

        let p1_lexp = self.lookup_expression.lookup(p1_id)?;
        let left = self.get_expr_handle(p1_id, p1_lexp, ctx, emitter, block, body_idx);
        let p2_lexp = self.lookup_expression.lookup(p2_id)?;
        let right = self.get_expr_handle(p2_id, p2_lexp, ctx, emitter, block, body_idx);

        let expr = crate::Expression::Binary { op, left, right };
        self.lookup_expression.insert(
            result_id,
            LookupExpression {
                handle: ctx.expressions.append(expr, self.span_from_with_op(start)),
                type_id: result_type_id,
                block_id,
            },
        );
        Ok(())
    }

    /// A more complicated version of the unary op,
    /// where we force the operand to have the same type as the result.
    fn parse_expr_unary_op_sign_adjusted(
        &mut self,
        ctx: &mut BlockContext,
        emitter: &mut super::Emitter,
        block: &mut crate::Block,
        block_id: spirv::Word,
        body_idx: usize,
        op: crate::UnaryOperator,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        let result_type_id = self.next()?;
        let result_id = self.next()?;
        let p1_id = self.next()?;
        let span = self.span_from_with_op(start);

        let p1_lexp = self.lookup_expression.lookup(p1_id)?;
        let left = self.get_expr_handle(p1_id, p1_lexp, ctx, emitter, block, body_idx);

        let result_lookup_ty = self.lookup_type.lookup(result_type_id)?;
        let kind = ctx.type_arena[result_lookup_ty.handle]
            .inner
            .scalar_kind()
            .unwrap();

        let expr = crate::Expression::Unary {
            op,
            expr: if p1_lexp.type_id == result_type_id {
                left
            } else {
                ctx.expressions.append(
                    crate::Expression::As {
                        expr: left,
                        kind,
                        convert: None,
                    },
                    span,
                )
            },
        };

        self.lookup_expression.insert(
            result_id,
            LookupExpression {
                handle: ctx.expressions.append(expr, span),
                type_id: result_type_id,
                block_id,
            },
        );
        Ok(())
    }

    /// A more complicated version of the binary op,
    /// where we force the operand to have the same type as the result.
    /// This is mostly needed for "i++" and "i--" coming from GLSL.
    #[allow(clippy::too_many_arguments)]
    fn parse_expr_binary_op_sign_adjusted(
        &mut self,
        ctx: &mut BlockContext,
        emitter: &mut super::Emitter,
        block: &mut crate::Block,
        block_id: spirv::Word,
        body_idx: usize,
        op: crate::BinaryOperator,
        // For arithmetic operations, we need the sign of operands to match the result.
        // For boolean operations, however, the operands need to match the signs, but
        // result is always different - a boolean.
        anchor: SignAnchor,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        let result_type_id = self.next()?;
        let result_id = self.next()?;
        let p1_id = self.next()?;
        let p2_id = self.next()?;
        let span = self.span_from_with_op(start);

        let p1_lexp = self.lookup_expression.lookup(p1_id)?;
        let left = self.get_expr_handle(p1_id, p1_lexp, ctx, emitter, block, body_idx);
        let p2_lexp = self.lookup_expression.lookup(p2_id)?;
        let right = self.get_expr_handle(p2_id, p2_lexp, ctx, emitter, block, body_idx);

        let expected_type_id = match anchor {
            SignAnchor::Result => result_type_id,
            SignAnchor::Operand => p1_lexp.type_id,
        };
        let expected_lookup_ty = self.lookup_type.lookup(expected_type_id)?;
        let kind = ctx.type_arena[expected_lookup_ty.handle]
            .inner
            .scalar_kind()
            .unwrap();

        let expr = crate::Expression::Binary {
            op,
            left: if p1_lexp.type_id == expected_type_id {
                left
            } else {
                ctx.expressions.append(
                    crate::Expression::As {
                        expr: left,
                        kind,
                        convert: None,
                    },
                    span,
                )
            },
            right: if p2_lexp.type_id == expected_type_id {
                right
            } else {
                ctx.expressions.append(
                    crate::Expression::As {
                        expr: right,
                        kind,
                        convert: None,
                    },
                    span,
                )
            },
        };

        self.lookup_expression.insert(
            result_id,
            LookupExpression {
                handle: ctx.expressions.append(expr, span),
                type_id: result_type_id,
                block_id,
            },
        );
        Ok(())
    }

    /// A version of the binary op where one or both of the arguments might need to be casted to a
    /// specific integer kind (unsigned or signed), used for operations like OpINotEqual or
    /// OpUGreaterThan.
    #[allow(clippy::too_many_arguments)]
    fn parse_expr_int_comparison(
        &mut self,
        ctx: &mut BlockContext,
        emitter: &mut super::Emitter,
        block: &mut crate::Block,
        block_id: spirv::Word,
        body_idx: usize,
        op: crate::BinaryOperator,
        kind: crate::ScalarKind,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        let result_type_id = self.next()?;
        let result_id = self.next()?;
        let p1_id = self.next()?;
        let p2_id = self.next()?;
        let span = self.span_from_with_op(start);

        let p1_lexp = self.lookup_expression.lookup(p1_id)?;
        let left = self.get_expr_handle(p1_id, p1_lexp, ctx, emitter, block, body_idx);
        let p1_lookup_ty = self.lookup_type.lookup(p1_lexp.type_id)?;
        let p1_kind = ctx.type_arena[p1_lookup_ty.handle]
            .inner
            .scalar_kind()
            .unwrap();
        let p2_lexp = self.lookup_expression.lookup(p2_id)?;
        let right = self.get_expr_handle(p2_id, p2_lexp, ctx, emitter, block, body_idx);
        let p2_lookup_ty = self.lookup_type.lookup(p2_lexp.type_id)?;
        let p2_kind = ctx.type_arena[p2_lookup_ty.handle]
            .inner
            .scalar_kind()
            .unwrap();

        let expr = crate::Expression::Binary {
            op,
            left: if p1_kind == kind {
                left
            } else {
                ctx.expressions.append(
                    crate::Expression::As {
                        expr: left,
                        kind,
                        convert: None,
                    },
                    span,
                )
            },
            right: if p2_kind == kind {
                right
            } else {
                ctx.expressions.append(
                    crate::Expression::As {
                        expr: right,
                        kind,
                        convert: None,
                    },
                    span,
                )
            },
        };

        self.lookup_expression.insert(
            result_id,
            LookupExpression {
                handle: ctx.expressions.append(expr, span),
                type_id: result_type_id,
                block_id,
            },
        );
        Ok(())
    }

    fn parse_expr_shift_op(
        &mut self,
        ctx: &mut BlockContext,
        emitter: &mut super::Emitter,
        block: &mut crate::Block,
        block_id: spirv::Word,
        body_idx: usize,
        op: crate::BinaryOperator,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        let result_type_id = self.next()?;
        let result_id = self.next()?;
        let p1_id = self.next()?;
        let p2_id = self.next()?;

        let span = self.span_from_with_op(start);

        let p1_lexp = self.lookup_expression.lookup(p1_id)?;
        let left = self.get_expr_handle(p1_id, p1_lexp, ctx, emitter, block, body_idx);
        let p2_lexp = self.lookup_expression.lookup(p2_id)?;
        let p2_handle = self.get_expr_handle(p2_id, p2_lexp, ctx, emitter, block, body_idx);
        // convert the shift to Uint
        let right = ctx.expressions.append(
            crate::Expression::As {
                expr: p2_handle,
                kind: crate::ScalarKind::Uint,
                convert: None,
            },
            span,
        );

        let expr = crate::Expression::Binary { op, left, right };
        self.lookup_expression.insert(
            result_id,
            LookupExpression {
                handle: ctx.expressions.append(expr, span),
                type_id: result_type_id,
                block_id,
            },
        );
        Ok(())
    }

    fn parse_expr_derivative(
        &mut self,
        ctx: &mut BlockContext,
        emitter: &mut super::Emitter,
        block: &mut crate::Block,
        block_id: spirv::Word,
        body_idx: usize,
        axis: crate::DerivativeAxis,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        let result_type_id = self.next()?;
        let result_id = self.next()?;
        let arg_id = self.next()?;

        let arg_lexp = self.lookup_expression.lookup(arg_id)?;
        let arg_handle = self.get_expr_handle(arg_id, arg_lexp, ctx, emitter, block, body_idx);

        let expr = crate::Expression::Derivative {
            axis,
            expr: arg_handle,
        };
        self.lookup_expression.insert(
            result_id,
            LookupExpression {
                handle: ctx.expressions.append(expr, self.span_from_with_op(start)),
                type_id: result_type_id,
                block_id,
            },
        );
        Ok(())
    }

    #[allow(clippy::too_many_arguments)]
    fn insert_composite(
        &self,
        root_expr: Handle<crate::Expression>,
        root_type_id: spirv::Word,
        object_expr: Handle<crate::Expression>,
        selections: &[spirv::Word],
        type_arena: &UniqueArena<crate::Type>,
        expressions: &mut Arena<crate::Expression>,
        constants: &Arena<crate::Constant>,
        span: crate::Span,
    ) -> Result<Handle<crate::Expression>, Error> {
        let selection = match selections.first() {
            Some(&index) => index,
            None => return Ok(object_expr),
        };
        let root_span = expressions.get_span(root_expr);
        let root_lookup = self.lookup_type.lookup(root_type_id)?;
        let (count, child_type_id) = match type_arena[root_lookup.handle].inner {
            crate::TypeInner::Struct { ref members, .. } => {
                let child_member = self
                    .lookup_member
                    .get(&(root_lookup.handle, selection))
                    .ok_or(Error::InvalidAccessType(root_type_id))?;
                (members.len(), child_member.type_id)
            }
            crate::TypeInner::Array { size, .. } => {
                let size = match size {
                    crate::ArraySize::Constant(handle) => match constants[handle] {
                        crate::Constant {
                            specialization: Some(_),
                            ..
                        } => return Err(Error::UnsupportedType(root_lookup.handle)),
                        ref unspecialized => unspecialized
                            .to_array_length()
                            .ok_or(Error::InvalidArraySize(handle))?,
                    },
                    // A runtime sized array is not a composite type
                    crate::ArraySize::Dynamic => {
                        return Err(Error::InvalidAccessType(root_type_id))
                    }
                };

                let child_type_id = root_lookup
                    .base_id
                    .ok_or(Error::InvalidAccessType(root_type_id))?;

                (size as usize, child_type_id)
            }
            crate::TypeInner::Vector { size, .. }
            | crate::TypeInner::Matrix { columns: size, .. } => {
                let child_type_id = root_lookup
                    .base_id
                    .ok_or(Error::InvalidAccessType(root_type_id))?;
                (size as usize, child_type_id)
            }
            _ => return Err(Error::InvalidAccessType(root_type_id)),
        };

        let mut components = Vec::with_capacity(count);
        for index in 0..count as u32 {
            let expr = expressions.append(
                crate::Expression::AccessIndex {
                    base: root_expr,
                    index,
                },
                if index == selection { span } else { root_span },
            );
            components.push(expr);
        }
        components[selection as usize] = self.insert_composite(
            components[selection as usize],
            child_type_id,
            object_expr,
            &selections[1..],
            type_arena,
            expressions,
            constants,
            span,
        )?;

        Ok(expressions.append(
            crate::Expression::Compose {
                ty: root_lookup.handle,
                components,
            },
            span,
        ))
    }

    /// Add the next SPIR-V block's contents to `block_ctx`.
    ///
    /// Except for the function's entry block, `block_id` should be the label of
    /// a block we've seen mentioned before, with an entry in
    /// `block_ctx.body_for_label` to tell us which `Body` it contributes to.
    fn next_block(&mut self, block_id: spirv::Word, ctx: &mut BlockContext) -> Result<(), Error> {
        // Extend `body` with the correct form for a branch to `target`.
        fn merger(body: &mut Body, target: &MergeBlockInformation) {
            body.data.push(match *target {
                MergeBlockInformation::LoopContinue => BodyFragment::Continue,
                MergeBlockInformation::LoopMerge | MergeBlockInformation::SwitchMerge => {
                    BodyFragment::Break
                }

                // Finishing a selection merge means just falling off the end of
                // the `accept` or `reject` block of the `If` statement.
                MergeBlockInformation::SelectionMerge => return,
            })
        }

        let mut emitter = super::Emitter::default();
        emitter.start(ctx.expressions);

        // Find the `Body` that this block belongs to. Index zero is the
        // function's root `Body`, corresponding to `Function::body`.
        let mut body_idx = *ctx.body_for_label.entry(block_id).or_default();
        let mut block = crate::Block::new();
        // Stores the merge block as defined by a `OpSelectionMerge` otherwise is `None`
        //
        // This is used in `OpSwitch` to promote the `MergeBlockInformation` from
        // `SelectionMerge` to `SwitchMerge` to allow `Break`s this isn't desirable for
        // `LoopMerge`s because otherwise `Continue`s wouldn't be allowed
        let mut selection_merge_block = None;

        macro_rules! get_expr_handle {
            ($id:expr, $lexp:expr) => {
                self.get_expr_handle($id, $lexp, ctx, &mut emitter, &mut block, body_idx)
            };
        }
        macro_rules! parse_expr_op {
            ($op:expr, BINARY) => {
                self.parse_expr_binary_op(ctx, &mut emitter, &mut block, block_id, body_idx, $op)
            };

            ($op:expr, SHIFT) => {
                self.parse_expr_shift_op(ctx, &mut emitter, &mut block, block_id, body_idx, $op)
            };
            ($op:expr, UNARY) => {
                self.parse_expr_unary_op(ctx, &mut emitter, &mut block, block_id, body_idx, $op)
            };
            ($axis:expr, DERIVATIVE) => {
                self.parse_expr_derivative(ctx, &mut emitter, &mut block, block_id, body_idx, $axis)
            };
        }

        let terminator = loop {
            use spirv::Op;
            let start = self.data_offset;
            let inst = self.next_inst()?;
            let span = crate::Span::from(start..(start + 4 * (inst.wc as usize)));
            log::debug!("\t\t{:?} [{}]", inst.op, inst.wc);

            match inst.op {
                Op::Line => {
                    inst.expect(4)?;
                    let _file_id = self.next()?;
                    let _row_id = self.next()?;
                    let _col_id = self.next()?;
                }
                Op::NoLine => inst.expect(1)?,
                Op::Undef => {
                    inst.expect(3)?;
                    let (type_id, id, handle) =
                        self.parse_null_constant(inst, ctx.type_arena, ctx.const_arena)?;
                    self.lookup_expression.insert(
                        id,
                        LookupExpression {
                            handle: ctx
                                .expressions
                                .append(crate::Expression::Constant(handle), span),
                            type_id,
                            block_id,
                        },
                    );
                }
                Op::Variable => {
                    inst.expect_at_least(4)?;
                    block.extend(emitter.finish(ctx.expressions));

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let _storage_class = self.next()?;
                    let init = if inst.wc > 4 {
                        inst.expect(5)?;
                        let init_id = self.next()?;
                        let lconst = self.lookup_constant.lookup(init_id)?;
                        Some(lconst.handle)
                    } else {
                        None
                    };

                    let name = self
                        .future_decor
                        .remove(&result_id)
                        .and_then(|decor| decor.name);
                    if let Some(ref name) = name {
                        log::debug!("\t\t\tid={} name={}", result_id, name);
                    }
                    let lookup_ty = self.lookup_type.lookup(result_type_id)?;
                    let var_handle = ctx.local_arena.append(
                        crate::LocalVariable {
                            name,
                            ty: match ctx.type_arena[lookup_ty.handle].inner {
                                crate::TypeInner::Pointer { base, .. } => base,
                                _ => lookup_ty.handle,
                            },
                            init,
                        },
                        span,
                    );

                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx
                                .expressions
                                .append(crate::Expression::LocalVariable(var_handle), span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                    emitter.start(ctx.expressions);
                }
                Op::Phi => {
                    inst.expect_at_least(3)?;
                    block.extend(emitter.finish(ctx.expressions));

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;

                    let name = format!("phi_{}", result_id);
                    let local = ctx.local_arena.append(
                        crate::LocalVariable {
                            name: Some(name),
                            ty: self.lookup_type.lookup(result_type_id)?.handle,
                            init: None,
                        },
                        self.span_from(start),
                    );
                    let pointer = ctx
                        .expressions
                        .append(crate::Expression::LocalVariable(local), span);

                    let in_count = (inst.wc - 3) / 2;
                    let mut phi = PhiExpression {
                        local,
                        expressions: Vec::with_capacity(in_count as usize),
                    };
                    for _ in 0..in_count {
                        let expr = self.next()?;
                        let block = self.next()?;
                        phi.expressions.push((expr, block));
                    }

                    ctx.phis.push(phi);
                    emitter.start(ctx.expressions);

                    // Associate the lookup with an actual value, which is emitted
                    // into the current block.
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx
                                .expressions
                                .append(crate::Expression::Load { pointer }, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::AccessChain | Op::InBoundsAccessChain => {
                    struct AccessExpression {
                        base_handle: Handle<crate::Expression>,
                        type_id: spirv::Word,
                        load_override: Option<LookupLoadOverride>,
                    }

                    inst.expect_at_least(4)?;

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let base_id = self.next()?;
                    log::trace!("\t\t\tlooking up expr {:?}", base_id);

                    let mut acex = {
                        let lexp = self.lookup_expression.lookup(base_id)?;
                        let lty = self.lookup_type.lookup(lexp.type_id)?;

                        // HACK `OpAccessChain` and `OpInBoundsAccessChain`
                        // require for the result type to be a pointer, but if
                        // we're given a pointer to an image / sampler, it will
                        // be *already* dereferenced, since we do that early
                        // during `parse_type_pointer()`.
                        //
                        // This can happen only through `BindingArray`, since
                        // that's the only case where one can obtain a pointer
                        // to an image / sampler, and so let's match on that:
                        let dereference = match ctx.type_arena[lty.handle].inner {
                            crate::TypeInner::BindingArray { .. } => false,
                            _ => true,
                        };

                        let type_id = if dereference {
                            lty.base_id.ok_or(Error::InvalidAccessType(lexp.type_id))?
                        } else {
                            lexp.type_id
                        };

                        AccessExpression {
                            base_handle: get_expr_handle!(base_id, lexp),
                            type_id,
                            load_override: self.lookup_load_override.get(&base_id).cloned(),
                        }
                    };

                    for _ in 4..inst.wc {
                        let access_id = self.next()?;
                        log::trace!("\t\t\tlooking up index expr {:?}", access_id);
                        let index_expr = self.lookup_expression.lookup(access_id)?.clone();
                        let index_expr_handle = get_expr_handle!(access_id, &index_expr);
                        let index_expr_data = &ctx.expressions[index_expr.handle];
                        let index_maybe = match *index_expr_data {
                            crate::Expression::Constant(const_handle) => {
                                Some(ctx.const_arena[const_handle].to_array_length().ok_or(
                                    Error::InvalidAccess(crate::Expression::Constant(const_handle)),
                                )?)
                            }
                            _ => None,
                        };

                        log::trace!("\t\t\tlooking up type {:?}", acex.type_id);
                        let type_lookup = self.lookup_type.lookup(acex.type_id)?;
                        acex = match ctx.type_arena[type_lookup.handle].inner {
                            // can only index a struct with a constant
                            crate::TypeInner::Struct { ref members, .. } => {
                                let index = index_maybe
                                    .ok_or_else(|| Error::InvalidAccess(index_expr_data.clone()))?;

                                let lookup_member = self
                                    .lookup_member
                                    .get(&(type_lookup.handle, index))
                                    .ok_or(Error::InvalidAccessType(acex.type_id))?;
                                let base_handle = ctx.expressions.append(
                                    crate::Expression::AccessIndex {
                                        base: acex.base_handle,
                                        index,
                                    },
                                    span,
                                );

                                if let Some(crate::Binding::BuiltIn(built_in)) =
                                    members[index as usize].binding
                                {
                                    self.builtin_usage.insert(built_in);
                                }

                                AccessExpression {
                                    base_handle,
                                    type_id: lookup_member.type_id,
                                    load_override: if lookup_member.row_major {
                                        debug_assert!(acex.load_override.is_none());
                                        let sub_type_lookup =
                                            self.lookup_type.lookup(lookup_member.type_id)?;
                                        Some(match ctx.type_arena[sub_type_lookup.handle].inner {
                                            // load it transposed, to match column major expectations
                                            crate::TypeInner::Matrix { .. } => {
                                                let loaded = ctx.expressions.append(
                                                    crate::Expression::Load {
                                                        pointer: base_handle,
                                                    },
                                                    span,
                                                );
                                                let transposed = ctx.expressions.append(
                                                    crate::Expression::Math {
                                                        fun: crate::MathFunction::Transpose,
                                                        arg: loaded,
                                                        arg1: None,
                                                        arg2: None,
                                                        arg3: None,
                                                    },
                                                    span,
                                                );
                                                LookupLoadOverride::Loaded(transposed)
                                            }
                                            _ => LookupLoadOverride::Pending,
                                        })
                                    } else {
                                        None
                                    },
                                }
                            }
                            crate::TypeInner::Matrix { .. } => {
                                let load_override = match acex.load_override {
                                    // We are indexing inside a row-major matrix
                                    Some(LookupLoadOverride::Loaded(load_expr)) => {
                                        let index = index_maybe.ok_or_else(|| {
                                            Error::InvalidAccess(index_expr_data.clone())
                                        })?;
                                        let sub_handle = ctx.expressions.append(
                                            crate::Expression::AccessIndex {
                                                base: load_expr,
                                                index,
                                            },
                                            span,
                                        );
                                        Some(LookupLoadOverride::Loaded(sub_handle))
                                    }
                                    _ => None,
                                };
                                let sub_expr = match index_maybe {
                                    Some(index) => crate::Expression::AccessIndex {
                                        base: acex.base_handle,
                                        index,
                                    },
                                    None => crate::Expression::Access {
                                        base: acex.base_handle,
                                        index: index_expr_handle,
                                    },
                                };
                                AccessExpression {
                                    base_handle: ctx.expressions.append(sub_expr, span),
                                    type_id: type_lookup
                                        .base_id
                                        .ok_or(Error::InvalidAccessType(acex.type_id))?,
                                    load_override,
                                }
                            }
                            // This must be a vector or an array.
                            _ => {
                                let base_handle = ctx.expressions.append(
                                    crate::Expression::Access {
                                        base: acex.base_handle,
                                        index: index_expr_handle,
                                    },
                                    span,
                                );
                                let load_override = match acex.load_override {
                                    // If there is a load override in place, then we always end up
                                    // with a side-loaded value here.
                                    Some(lookup_load_override) => {
                                        let sub_expr = match lookup_load_override {
                                            // We must be indexing into the array of row-major matrices.
                                            // Let's load the result of indexing and transpose it.
                                            LookupLoadOverride::Pending => {
                                                let loaded = ctx.expressions.append(
                                                    crate::Expression::Load {
                                                        pointer: base_handle,
                                                    },
                                                    span,
                                                );
                                                ctx.expressions.append(
                                                    crate::Expression::Math {
                                                        fun: crate::MathFunction::Transpose,
                                                        arg: loaded,
                                                        arg1: None,
                                                        arg2: None,
                                                        arg3: None,
                                                    },
                                                    span,
                                                )
                                            }
                                            // We are indexing inside a row-major matrix.
                                            LookupLoadOverride::Loaded(load_expr) => {
                                                ctx.expressions.append(
                                                    crate::Expression::Access {
                                                        base: load_expr,
                                                        index: index_expr_handle,
                                                    },
                                                    span,
                                                )
                                            }
                                        };
                                        Some(LookupLoadOverride::Loaded(sub_expr))
                                    }
                                    None => None,
                                };
                                AccessExpression {
                                    base_handle,
                                    type_id: type_lookup
                                        .base_id
                                        .ok_or(Error::InvalidAccessType(acex.type_id))?,
                                    load_override,
                                }
                            }
                        };
                    }

                    if let Some(load_expr) = acex.load_override {
                        self.lookup_load_override.insert(result_id, load_expr);
                    }
                    let lookup_expression = LookupExpression {
                        handle: acex.base_handle,
                        type_id: result_type_id,
                        block_id,
                    };
                    self.lookup_expression.insert(result_id, lookup_expression);
                }
                Op::VectorExtractDynamic => {
                    inst.expect(5)?;

                    let result_type_id = self.next()?;
                    let id = self.next()?;
                    let composite_id = self.next()?;
                    let index_id = self.next()?;

                    let root_lexp = self.lookup_expression.lookup(composite_id)?;
                    let root_handle = get_expr_handle!(composite_id, root_lexp);
                    let root_type_lookup = self.lookup_type.lookup(root_lexp.type_id)?;
                    let index_lexp = self.lookup_expression.lookup(index_id)?;
                    let index_handle = get_expr_handle!(index_id, index_lexp);

                    let num_components = match ctx.type_arena[root_type_lookup.handle].inner {
                        crate::TypeInner::Vector { size, .. } => size as usize,
                        _ => return Err(Error::InvalidVectorType(root_type_lookup.handle)),
                    };

                    let mut handle = ctx.expressions.append(
                        crate::Expression::Access {
                            base: root_handle,
                            index: self.index_constant_expressions[0],
                        },
                        span,
                    );
                    for &index_expr in self.index_constant_expressions[1..num_components].iter() {
                        let access_expr = ctx.expressions.append(
                            crate::Expression::Access {
                                base: root_handle,
                                index: index_expr,
                            },
                            span,
                        );
                        let cond = ctx.expressions.append(
                            crate::Expression::Binary {
                                op: crate::BinaryOperator::Equal,
                                left: index_expr,
                                right: index_handle,
                            },
                            span,
                        );
                        handle = ctx.expressions.append(
                            crate::Expression::Select {
                                condition: cond,
                                accept: access_expr,
                                reject: handle,
                            },
                            span,
                        );
                    }

                    self.lookup_expression.insert(
                        id,
                        LookupExpression {
                            handle,
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::VectorInsertDynamic => {
                    inst.expect(6)?;

                    let result_type_id = self.next()?;
                    let id = self.next()?;
                    let composite_id = self.next()?;
                    let object_id = self.next()?;
                    let index_id = self.next()?;

                    let object_lexp = self.lookup_expression.lookup(object_id)?;
                    let object_handle = get_expr_handle!(object_id, object_lexp);
                    let root_lexp = self.lookup_expression.lookup(composite_id)?;
                    let root_handle = get_expr_handle!(composite_id, root_lexp);
                    let root_type_lookup = self.lookup_type.lookup(root_lexp.type_id)?;
                    let index_lexp = self.lookup_expression.lookup(index_id)?;
                    let mut index_handle = get_expr_handle!(index_id, index_lexp);
                    let index_type = self.lookup_type.lookup(index_lexp.type_id)?.handle;

                    // SPIR-V allows signed and unsigned indices but naga's is strict about
                    // types and since the `index_constants` are all signed integers, we need
                    // to cast the index to a signed integer if it's unsigned.
                    if let Some(crate::ScalarKind::Uint) =
                        ctx.type_arena[index_type].inner.scalar_kind()
                    {
                        index_handle = ctx.expressions.append(
                            crate::Expression::As {
                                expr: index_handle,
                                kind: crate::ScalarKind::Sint,
                                convert: None,
                            },
                            span,
                        )
                    }

                    let num_components = match ctx.type_arena[root_type_lookup.handle].inner {
                        crate::TypeInner::Vector { size, .. } => size as usize,
                        _ => return Err(Error::InvalidVectorType(root_type_lookup.handle)),
                    };
                    let mut components = Vec::with_capacity(num_components);
                    for &index_expr in self.index_constant_expressions[..num_components].iter() {
                        let access_expr = ctx.expressions.append(
                            crate::Expression::Access {
                                base: root_handle,
                                index: index_expr,
                            },
                            span,
                        );
                        let cond = ctx.expressions.append(
                            crate::Expression::Binary {
                                op: crate::BinaryOperator::Equal,
                                left: index_expr,
                                right: index_handle,
                            },
                            span,
                        );
                        let handle = ctx.expressions.append(
                            crate::Expression::Select {
                                condition: cond,
                                accept: object_handle,
                                reject: access_expr,
                            },
                            span,
                        );
                        components.push(handle);
                    }
                    let handle = ctx.expressions.append(
                        crate::Expression::Compose {
                            ty: root_type_lookup.handle,
                            components,
                        },
                        span,
                    );

                    self.lookup_expression.insert(
                        id,
                        LookupExpression {
                            handle,
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::CompositeExtract => {
                    inst.expect_at_least(4)?;

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let base_id = self.next()?;
                    log::trace!("\t\t\tlooking up expr {:?}", base_id);
                    let mut lexp = self.lookup_expression.lookup(base_id)?.clone();
                    lexp.handle = get_expr_handle!(base_id, &lexp);
                    for _ in 4..inst.wc {
                        let index = self.next()?;
                        log::trace!("\t\t\tlooking up type {:?}", lexp.type_id);
                        let type_lookup = self.lookup_type.lookup(lexp.type_id)?;
                        let type_id = match ctx.type_arena[type_lookup.handle].inner {
                            crate::TypeInner::Struct { .. } => {
                                self.lookup_member
                                    .get(&(type_lookup.handle, index))
                                    .ok_or(Error::InvalidAccessType(lexp.type_id))?
                                    .type_id
                            }
                            crate::TypeInner::Array { .. }
                            | crate::TypeInner::Vector { .. }
                            | crate::TypeInner::Matrix { .. } => type_lookup
                                .base_id
                                .ok_or(Error::InvalidAccessType(lexp.type_id))?,
                            ref other => {
                                log::warn!("composite type {:?}", other);
                                return Err(Error::UnsupportedType(type_lookup.handle));
                            }
                        };
                        lexp = LookupExpression {
                            handle: ctx.expressions.append(
                                crate::Expression::AccessIndex {
                                    base: lexp.handle,
                                    index,
                                },
                                span,
                            ),
                            type_id,
                            block_id,
                        };
                    }

                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: lexp.handle,
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::CompositeInsert => {
                    inst.expect_at_least(5)?;

                    let result_type_id = self.next()?;
                    let id = self.next()?;
                    let object_id = self.next()?;
                    let composite_id = self.next()?;
                    let mut selections = Vec::with_capacity(inst.wc as usize - 5);
                    for _ in 5..inst.wc {
                        selections.push(self.next()?);
                    }

                    let object_lexp = self.lookup_expression.lookup(object_id)?.clone();
                    let object_handle = get_expr_handle!(object_id, &object_lexp);
                    let root_lexp = self.lookup_expression.lookup(composite_id)?.clone();
                    let root_handle = get_expr_handle!(composite_id, &root_lexp);
                    let handle = self.insert_composite(
                        root_handle,
                        result_type_id,
                        object_handle,
                        &selections,
                        ctx.type_arena,
                        ctx.expressions,
                        ctx.const_arena,
                        span,
                    )?;

                    self.lookup_expression.insert(
                        id,
                        LookupExpression {
                            handle,
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::CompositeConstruct => {
                    inst.expect_at_least(3)?;

                    let result_type_id = self.next()?;
                    let id = self.next()?;
                    let mut components = Vec::with_capacity(inst.wc as usize - 2);
                    for _ in 3..inst.wc {
                        let comp_id = self.next()?;
                        log::trace!("\t\t\tlooking up expr {:?}", comp_id);
                        let lexp = self.lookup_expression.lookup(comp_id)?;
                        let handle = get_expr_handle!(comp_id, lexp);
                        components.push(handle);
                    }
                    let ty = self.lookup_type.lookup(result_type_id)?.handle;
                    let first = components[0];
                    let expr = match ctx.type_arena[ty].inner {
                        // this is an optimization to detect the splat
                        crate::TypeInner::Vector { size, .. }
                            if components.len() == size as usize
                                && components[1..].iter().all(|&c| c == first) =>
                        {
                            crate::Expression::Splat { size, value: first }
                        }
                        _ => crate::Expression::Compose { ty, components },
                    };
                    self.lookup_expression.insert(
                        id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::Load => {
                    inst.expect_at_least(4)?;

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let pointer_id = self.next()?;
                    if inst.wc != 4 {
                        inst.expect(5)?;
                        let _memory_access = self.next()?;
                    }

                    let base_lexp = self.lookup_expression.lookup(pointer_id)?;
                    let base_handle = get_expr_handle!(pointer_id, base_lexp);
                    let type_lookup = self.lookup_type.lookup(base_lexp.type_id)?;
                    let handle = match ctx.type_arena[type_lookup.handle].inner {
                        crate::TypeInner::Image { .. } | crate::TypeInner::Sampler { .. } => {
                            base_handle
                        }
                        _ => match self.lookup_load_override.get(&pointer_id) {
                            Some(&LookupLoadOverride::Loaded(handle)) => handle,
                            //Note: we aren't handling `LookupLoadOverride::Pending` properly here
                            _ => ctx.expressions.append(
                                crate::Expression::Load {
                                    pointer: base_handle,
                                },
                                span,
                            ),
                        },
                    };

                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle,
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::Store => {
                    inst.expect_at_least(3)?;

                    let pointer_id = self.next()?;
                    let value_id = self.next()?;
                    if inst.wc != 3 {
                        inst.expect(4)?;
                        let _memory_access = self.next()?;
                    }
                    let base_expr = self.lookup_expression.lookup(pointer_id)?;
                    let base_handle = get_expr_handle!(pointer_id, base_expr);
                    let value_expr = self.lookup_expression.lookup(value_id)?;
                    let value_handle = get_expr_handle!(value_id, value_expr);

                    block.extend(emitter.finish(ctx.expressions));
                    block.push(
                        crate::Statement::Store {
                            pointer: base_handle,
                            value: value_handle,
                        },
                        span,
                    );
                    emitter.start(ctx.expressions);
                }
                // Arithmetic Instructions +, -, *, /, %
                Op::SNegate | Op::FNegate => {
                    inst.expect(4)?;
                    self.parse_expr_unary_op_sign_adjusted(
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                        crate::UnaryOperator::Negate,
                    )?;
                }
                Op::IAdd
                | Op::ISub
                | Op::IMul
                | Op::BitwiseOr
                | Op::BitwiseXor
                | Op::BitwiseAnd
                | Op::SDiv
                | Op::SRem => {
                    inst.expect(5)?;
                    let operator = map_binary_operator(inst.op)?;
                    self.parse_expr_binary_op_sign_adjusted(
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                        operator,
                        SignAnchor::Result,
                    )?;
                }
                Op::IEqual | Op::INotEqual => {
                    inst.expect(5)?;
                    let operator = map_binary_operator(inst.op)?;
                    self.parse_expr_binary_op_sign_adjusted(
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                        operator,
                        SignAnchor::Operand,
                    )?;
                }
                Op::FAdd => {
                    inst.expect(5)?;
                    parse_expr_op!(crate::BinaryOperator::Add, BINARY)?;
                }
                Op::FSub => {
                    inst.expect(5)?;
                    parse_expr_op!(crate::BinaryOperator::Subtract, BINARY)?;
                }
                Op::FMul => {
                    inst.expect(5)?;
                    parse_expr_op!(crate::BinaryOperator::Multiply, BINARY)?;
                }
                Op::UDiv | Op::FDiv => {
                    inst.expect(5)?;
                    parse_expr_op!(crate::BinaryOperator::Divide, BINARY)?;
                }
                Op::UMod | Op::FRem => {
                    inst.expect(5)?;
                    parse_expr_op!(crate::BinaryOperator::Modulo, BINARY)?;
                }
                Op::SMod => {
                    inst.expect(5)?;

                    // x - y * int(floor(float(x) / float(y)))

                    let start = self.data_offset;
                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let p1_id = self.next()?;
                    let p2_id = self.next()?;
                    let span = self.span_from_with_op(start);

                    let p1_lexp = self.lookup_expression.lookup(p1_id)?;
                    let left = self.get_expr_handle(
                        p1_id,
                        p1_lexp,
                        ctx,
                        &mut emitter,
                        &mut block,
                        body_idx,
                    );
                    let p2_lexp = self.lookup_expression.lookup(p2_id)?;
                    let right = self.get_expr_handle(
                        p2_id,
                        p2_lexp,
                        ctx,
                        &mut emitter,
                        &mut block,
                        body_idx,
                    );

                    let result_ty = self.lookup_type.lookup(result_type_id)?;
                    let inner = &ctx.type_arena[result_ty.handle].inner;
                    let kind = inner.scalar_kind().unwrap();
                    let size = inner.size(ctx.const_arena) as u8;

                    let left_cast = ctx.expressions.append(
                        crate::Expression::As {
                            expr: left,
                            kind: crate::ScalarKind::Float,
                            convert: Some(size),
                        },
                        span,
                    );
                    let right_cast = ctx.expressions.append(
                        crate::Expression::As {
                            expr: right,
                            kind: crate::ScalarKind::Float,
                            convert: Some(size),
                        },
                        span,
                    );
                    let div = ctx.expressions.append(
                        crate::Expression::Binary {
                            op: crate::BinaryOperator::Divide,
                            left: left_cast,
                            right: right_cast,
                        },
                        span,
                    );
                    let floor = ctx.expressions.append(
                        crate::Expression::Math {
                            fun: crate::MathFunction::Floor,
                            arg: div,
                            arg1: None,
                            arg2: None,
                            arg3: None,
                        },
                        span,
                    );
                    let cast = ctx.expressions.append(
                        crate::Expression::As {
                            expr: floor,
                            kind,
                            convert: Some(size),
                        },
                        span,
                    );
                    let mult = ctx.expressions.append(
                        crate::Expression::Binary {
                            op: crate::BinaryOperator::Multiply,
                            left: cast,
                            right,
                        },
                        span,
                    );
                    let sub = ctx.expressions.append(
                        crate::Expression::Binary {
                            op: crate::BinaryOperator::Subtract,
                            left,
                            right: mult,
                        },
                        span,
                    );
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: sub,
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::FMod => {
                    inst.expect(5)?;

                    // x - y * floor(x / y)

                    let start = self.data_offset;
                    let span = self.span_from_with_op(start);

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let p1_id = self.next()?;
                    let p2_id = self.next()?;

                    let p1_lexp = self.lookup_expression.lookup(p1_id)?;
                    let left = self.get_expr_handle(
                        p1_id,
                        p1_lexp,
                        ctx,
                        &mut emitter,
                        &mut block,
                        body_idx,
                    );
                    let p2_lexp = self.lookup_expression.lookup(p2_id)?;
                    let right = self.get_expr_handle(
                        p2_id,
                        p2_lexp,
                        ctx,
                        &mut emitter,
                        &mut block,
                        body_idx,
                    );

                    let div = ctx.expressions.append(
                        crate::Expression::Binary {
                            op: crate::BinaryOperator::Divide,
                            left,
                            right,
                        },
                        span,
                    );
                    let floor = ctx.expressions.append(
                        crate::Expression::Math {
                            fun: crate::MathFunction::Floor,
                            arg: div,
                            arg1: None,
                            arg2: None,
                            arg3: None,
                        },
                        span,
                    );
                    let mult = ctx.expressions.append(
                        crate::Expression::Binary {
                            op: crate::BinaryOperator::Multiply,
                            left: floor,
                            right,
                        },
                        span,
                    );
                    let sub = ctx.expressions.append(
                        crate::Expression::Binary {
                            op: crate::BinaryOperator::Subtract,
                            left,
                            right: mult,
                        },
                        span,
                    );
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: sub,
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::VectorTimesScalar
                | Op::VectorTimesMatrix
                | Op::MatrixTimesScalar
                | Op::MatrixTimesVector
                | Op::MatrixTimesMatrix => {
                    inst.expect(5)?;
                    parse_expr_op!(crate::BinaryOperator::Multiply, BINARY)?;
                }
                Op::Transpose => {
                    inst.expect(4)?;

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let matrix_id = self.next()?;
                    let matrix_lexp = self.lookup_expression.lookup(matrix_id)?;
                    let matrix_handle = get_expr_handle!(matrix_id, matrix_lexp);
                    let expr = crate::Expression::Math {
                        fun: crate::MathFunction::Transpose,
                        arg: matrix_handle,
                        arg1: None,
                        arg2: None,
                        arg3: None,
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::Dot => {
                    inst.expect(5)?;

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let left_id = self.next()?;
                    let right_id = self.next()?;
                    let left_lexp = self.lookup_expression.lookup(left_id)?;
                    let left_handle = get_expr_handle!(left_id, left_lexp);
                    let right_lexp = self.lookup_expression.lookup(right_id)?;
                    let right_handle = get_expr_handle!(right_id, right_lexp);
                    let expr = crate::Expression::Math {
                        fun: crate::MathFunction::Dot,
                        arg: left_handle,
                        arg1: Some(right_handle),
                        arg2: None,
                        arg3: None,
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::BitFieldInsert => {
                    inst.expect(7)?;

                    let start = self.data_offset;
                    let span = self.span_from_with_op(start);

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let base_id = self.next()?;
                    let insert_id = self.next()?;
                    let offset_id = self.next()?;
                    let count_id = self.next()?;
                    let base_lexp = self.lookup_expression.lookup(base_id)?;
                    let base_handle = get_expr_handle!(base_id, base_lexp);
                    let insert_lexp = self.lookup_expression.lookup(insert_id)?;
                    let insert_handle = get_expr_handle!(insert_id, insert_lexp);
                    let offset_lexp = self.lookup_expression.lookup(offset_id)?;
                    let offset_handle = get_expr_handle!(offset_id, offset_lexp);
                    let offset_lookup_ty = self.lookup_type.lookup(offset_lexp.type_id)?;
                    let count_lexp = self.lookup_expression.lookup(count_id)?;
                    let count_handle = get_expr_handle!(count_id, count_lexp);
                    let count_lookup_ty = self.lookup_type.lookup(count_lexp.type_id)?;

                    let offset_kind = ctx.type_arena[offset_lookup_ty.handle]
                        .inner
                        .scalar_kind()
                        .unwrap();
                    let count_kind = ctx.type_arena[count_lookup_ty.handle]
                        .inner
                        .scalar_kind()
                        .unwrap();

                    let offset_cast_handle = if offset_kind != crate::ScalarKind::Uint {
                        ctx.expressions.append(
                            crate::Expression::As {
                                expr: offset_handle,
                                kind: crate::ScalarKind::Uint,
                                convert: None,
                            },
                            span,
                        )
                    } else {
                        offset_handle
                    };

                    let count_cast_handle = if count_kind != crate::ScalarKind::Uint {
                        ctx.expressions.append(
                            crate::Expression::As {
                                expr: count_handle,
                                kind: crate::ScalarKind::Uint,
                                convert: None,
                            },
                            span,
                        )
                    } else {
                        count_handle
                    };

                    let expr = crate::Expression::Math {
                        fun: crate::MathFunction::InsertBits,
                        arg: base_handle,
                        arg1: Some(insert_handle),
                        arg2: Some(offset_cast_handle),
                        arg3: Some(count_cast_handle),
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::BitFieldSExtract | Op::BitFieldUExtract => {
                    inst.expect(6)?;

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let base_id = self.next()?;
                    let offset_id = self.next()?;
                    let count_id = self.next()?;
                    let base_lexp = self.lookup_expression.lookup(base_id)?;
                    let base_handle = get_expr_handle!(base_id, base_lexp);
                    let offset_lexp = self.lookup_expression.lookup(offset_id)?;
                    let offset_handle = get_expr_handle!(offset_id, offset_lexp);
                    let offset_lookup_ty = self.lookup_type.lookup(offset_lexp.type_id)?;
                    let count_lexp = self.lookup_expression.lookup(count_id)?;
                    let count_handle = get_expr_handle!(count_id, count_lexp);
                    let count_lookup_ty = self.lookup_type.lookup(count_lexp.type_id)?;

                    let offset_kind = ctx.type_arena[offset_lookup_ty.handle]
                        .inner
                        .scalar_kind()
                        .unwrap();
                    let count_kind = ctx.type_arena[count_lookup_ty.handle]
                        .inner
                        .scalar_kind()
                        .unwrap();

                    let offset_cast_handle = if offset_kind != crate::ScalarKind::Uint {
                        ctx.expressions.append(
                            crate::Expression::As {
                                expr: offset_handle,
                                kind: crate::ScalarKind::Uint,
                                convert: None,
                            },
                            span,
                        )
                    } else {
                        offset_handle
                    };

                    let count_cast_handle = if count_kind != crate::ScalarKind::Uint {
                        ctx.expressions.append(
                            crate::Expression::As {
                                expr: count_handle,
                                kind: crate::ScalarKind::Uint,
                                convert: None,
                            },
                            span,
                        )
                    } else {
                        count_handle
                    };

                    let expr = crate::Expression::Math {
                        fun: crate::MathFunction::ExtractBits,
                        arg: base_handle,
                        arg1: Some(offset_cast_handle),
                        arg2: Some(count_cast_handle),
                        arg3: None,
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::BitReverse | Op::BitCount => {
                    inst.expect(4)?;

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let base_id = self.next()?;
                    let base_lexp = self.lookup_expression.lookup(base_id)?;
                    let base_handle = get_expr_handle!(base_id, base_lexp);
                    let expr = crate::Expression::Math {
                        fun: match inst.op {
                            Op::BitReverse => crate::MathFunction::ReverseBits,
                            Op::BitCount => crate::MathFunction::CountOneBits,
                            _ => unreachable!(),
                        },
                        arg: base_handle,
                        arg1: None,
                        arg2: None,
                        arg3: None,
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::OuterProduct => {
                    inst.expect(5)?;

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let left_id = self.next()?;
                    let right_id = self.next()?;
                    let left_lexp = self.lookup_expression.lookup(left_id)?;
                    let left_handle = get_expr_handle!(left_id, left_lexp);
                    let right_lexp = self.lookup_expression.lookup(right_id)?;
                    let right_handle = get_expr_handle!(right_id, right_lexp);
                    let expr = crate::Expression::Math {
                        fun: crate::MathFunction::Outer,
                        arg: left_handle,
                        arg1: Some(right_handle),
                        arg2: None,
                        arg3: None,
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                // Bitwise instructions
                Op::Not => {
                    inst.expect(4)?;
                    self.parse_expr_unary_op_sign_adjusted(
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                        crate::UnaryOperator::Not,
                    )?;
                }
                Op::ShiftRightLogical => {
                    inst.expect(5)?;
                    //TODO: convert input and result to usigned
                    parse_expr_op!(crate::BinaryOperator::ShiftRight, SHIFT)?;
                }
                Op::ShiftRightArithmetic => {
                    inst.expect(5)?;
                    //TODO: convert input and result to signed
                    parse_expr_op!(crate::BinaryOperator::ShiftRight, SHIFT)?;
                }
                Op::ShiftLeftLogical => {
                    inst.expect(5)?;
                    parse_expr_op!(crate::BinaryOperator::ShiftLeft, SHIFT)?;
                }
                // Sampling
                Op::Image => {
                    inst.expect(4)?;
                    self.parse_image_uncouple(block_id)?;
                }
                Op::SampledImage => {
                    inst.expect(5)?;
                    self.parse_image_couple()?;
                }
                Op::ImageWrite => {
                    let extra = inst.expect_at_least(4)?;
                    let stmt =
                        self.parse_image_write(extra, ctx, &mut emitter, &mut block, body_idx)?;
                    block.extend(emitter.finish(ctx.expressions));
                    block.push(stmt, span);
                    emitter.start(ctx.expressions);
                }
                Op::ImageFetch | Op::ImageRead => {
                    let extra = inst.expect_at_least(5)?;
                    self.parse_image_load(
                        extra,
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                    )?;
                }
                Op::ImageSampleImplicitLod | Op::ImageSampleExplicitLod => {
                    let extra = inst.expect_at_least(5)?;
                    let options = image::SamplingOptions {
                        compare: false,
                        project: false,
                    };
                    self.parse_image_sample(
                        extra,
                        options,
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                    )?;
                }
                Op::ImageSampleProjImplicitLod | Op::ImageSampleProjExplicitLod => {
                    let extra = inst.expect_at_least(5)?;
                    let options = image::SamplingOptions {
                        compare: false,
                        project: true,
                    };
                    self.parse_image_sample(
                        extra,
                        options,
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                    )?;
                }
                Op::ImageSampleDrefImplicitLod | Op::ImageSampleDrefExplicitLod => {
                    let extra = inst.expect_at_least(6)?;
                    let options = image::SamplingOptions {
                        compare: true,
                        project: false,
                    };
                    self.parse_image_sample(
                        extra,
                        options,
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                    )?;
                }
                Op::ImageSampleProjDrefImplicitLod | Op::ImageSampleProjDrefExplicitLod => {
                    let extra = inst.expect_at_least(6)?;
                    let options = image::SamplingOptions {
                        compare: true,
                        project: true,
                    };
                    self.parse_image_sample(
                        extra,
                        options,
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                    )?;
                }
                Op::ImageQuerySize => {
                    inst.expect(4)?;
                    self.parse_image_query_size(
                        false,
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                    )?;
                }
                Op::ImageQuerySizeLod => {
                    inst.expect(5)?;
                    self.parse_image_query_size(
                        true,
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                    )?;
                }
                Op::ImageQueryLevels => {
                    inst.expect(4)?;
                    self.parse_image_query_other(
                        crate::ImageQuery::NumLevels,
                        ctx.expressions,
                        block_id,
                    )?;
                }
                Op::ImageQuerySamples => {
                    inst.expect(4)?;
                    self.parse_image_query_other(
                        crate::ImageQuery::NumSamples,
                        ctx.expressions,
                        block_id,
                    )?;
                }
                // other ops
                Op::Select => {
                    inst.expect(6)?;
                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let condition = self.next()?;
                    let o1_id = self.next()?;
                    let o2_id = self.next()?;

                    let cond_lexp = self.lookup_expression.lookup(condition)?;
                    let cond_handle = get_expr_handle!(condition, cond_lexp);
                    let o1_lexp = self.lookup_expression.lookup(o1_id)?;
                    let o1_handle = get_expr_handle!(o1_id, o1_lexp);
                    let o2_lexp = self.lookup_expression.lookup(o2_id)?;
                    let o2_handle = get_expr_handle!(o2_id, o2_lexp);

                    let expr = crate::Expression::Select {
                        condition: cond_handle,
                        accept: o1_handle,
                        reject: o2_handle,
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::VectorShuffle => {
                    inst.expect_at_least(5)?;
                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let v1_id = self.next()?;
                    let v2_id = self.next()?;

                    let v1_lexp = self.lookup_expression.lookup(v1_id)?;
                    let v1_lty = self.lookup_type.lookup(v1_lexp.type_id)?;
                    let v1_handle = get_expr_handle!(v1_id, v1_lexp);
                    let n1 = match ctx.type_arena[v1_lty.handle].inner {
                        crate::TypeInner::Vector { size, .. } => size as u32,
                        _ => return Err(Error::InvalidInnerType(v1_lexp.type_id)),
                    };
                    let v2_lexp = self.lookup_expression.lookup(v2_id)?;
                    let v2_lty = self.lookup_type.lookup(v2_lexp.type_id)?;
                    let v2_handle = get_expr_handle!(v2_id, v2_lexp);
                    let n2 = match ctx.type_arena[v2_lty.handle].inner {
                        crate::TypeInner::Vector { size, .. } => size as u32,
                        _ => return Err(Error::InvalidInnerType(v2_lexp.type_id)),
                    };

                    self.temp_bytes.clear();
                    let mut max_component = 0;
                    for _ in 5..inst.wc as usize {
                        let mut index = self.next()?;
                        if index == u32::MAX {
                            // treat Undefined as X
                            index = 0;
                        }
                        max_component = max_component.max(index);
                        self.temp_bytes.push(index as u8);
                    }

                    // Check for swizzle first.
                    let expr = if max_component < n1 {
                        use crate::SwizzleComponent as Sc;
                        let size = match self.temp_bytes.len() {
                            2 => crate::VectorSize::Bi,
                            3 => crate::VectorSize::Tri,
                            _ => crate::VectorSize::Quad,
                        };
                        let mut pattern = [Sc::X; 4];
                        for (pat, index) in pattern.iter_mut().zip(self.temp_bytes.drain(..)) {
                            *pat = match index {
                                0 => Sc::X,
                                1 => Sc::Y,
                                2 => Sc::Z,
                                _ => Sc::W,
                            };
                        }
                        crate::Expression::Swizzle {
                            size,
                            vector: v1_handle,
                            pattern,
                        }
                    } else {
                        // Fall back to access + compose
                        let mut components = Vec::with_capacity(self.temp_bytes.len());
                        for index in self.temp_bytes.drain(..).map(|i| i as u32) {
                            let expr = if index < n1 {
                                crate::Expression::AccessIndex {
                                    base: v1_handle,
                                    index,
                                }
                            } else if index < n1 + n2 {
                                crate::Expression::AccessIndex {
                                    base: v2_handle,
                                    index: index - n1,
                                }
                            } else {
                                return Err(Error::InvalidAccessIndex(index));
                            };
                            components.push(ctx.expressions.append(expr, span));
                        }
                        crate::Expression::Compose {
                            ty: self.lookup_type.lookup(result_type_id)?.handle,
                            components,
                        }
                    };

                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::Bitcast
                | Op::ConvertSToF
                | Op::ConvertUToF
                | Op::ConvertFToU
                | Op::ConvertFToS
                | Op::FConvert
                | Op::UConvert
                | Op::SConvert => {
                    inst.expect(4)?;
                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let value_id = self.next()?;

                    let value_lexp = self.lookup_expression.lookup(value_id)?;
                    let ty_lookup = self.lookup_type.lookup(result_type_id)?;
                    let (kind, width) = match ctx.type_arena[ty_lookup.handle].inner {
                        crate::TypeInner::Scalar { kind, width }
                        | crate::TypeInner::Vector { kind, width, .. } => (kind, width),
                        crate::TypeInner::Matrix { width, .. } => (crate::ScalarKind::Float, width),
                        _ => return Err(Error::InvalidAsType(ty_lookup.handle)),
                    };

                    let expr = crate::Expression::As {
                        expr: get_expr_handle!(value_id, value_lexp),
                        kind,
                        convert: if kind == crate::ScalarKind::Bool {
                            Some(crate::BOOL_WIDTH)
                        } else if inst.op == Op::Bitcast {
                            None
                        } else {
                            Some(width)
                        },
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::FunctionCall => {
                    inst.expect_at_least(4)?;
                    block.extend(emitter.finish(ctx.expressions));

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let func_id = self.next()?;

                    let mut arguments = Vec::with_capacity(inst.wc as usize - 4);
                    for _ in 0..arguments.capacity() {
                        let arg_id = self.next()?;
                        let lexp = self.lookup_expression.lookup(arg_id)?;
                        arguments.push(get_expr_handle!(arg_id, lexp));
                    }

                    // We just need an unique handle here, nothing more.
                    let function = self.add_call(ctx.function_id, func_id);

                    let result = if self.lookup_void_type == Some(result_type_id) {
                        None
                    } else {
                        let expr_handle = ctx
                            .expressions
                            .append(crate::Expression::CallResult(function), span);
                        self.lookup_expression.insert(
                            result_id,
                            LookupExpression {
                                handle: expr_handle,
                                type_id: result_type_id,
                                block_id,
                            },
                        );
                        Some(expr_handle)
                    };
                    block.push(
                        crate::Statement::Call {
                            function,
                            arguments,
                            result,
                        },
                        span,
                    );
                    emitter.start(ctx.expressions);
                }
                Op::ExtInst => {
                    use crate::MathFunction as Mf;
                    use spirv::GLOp as Glo;

                    let base_wc = 5;
                    inst.expect_at_least(base_wc)?;

                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let set_id = self.next()?;
                    if Some(set_id) != self.ext_glsl_id {
                        return Err(Error::UnsupportedExtInstSet(set_id));
                    }
                    let inst_id = self.next()?;
                    let gl_op = Glo::from_u32(inst_id).ok_or(Error::UnsupportedExtInst(inst_id))?;

                    let fun = match gl_op {
                        Glo::Round => Mf::Round,
                        Glo::RoundEven => Mf::Round,
                        Glo::Trunc => Mf::Trunc,
                        Glo::FAbs | Glo::SAbs => Mf::Abs,
                        Glo::FSign | Glo::SSign => Mf::Sign,
                        Glo::Floor => Mf::Floor,
                        Glo::Ceil => Mf::Ceil,
                        Glo::Fract => Mf::Fract,
                        Glo::Sin => Mf::Sin,
                        Glo::Cos => Mf::Cos,
                        Glo::Tan => Mf::Tan,
                        Glo::Asin => Mf::Asin,
                        Glo::Acos => Mf::Acos,
                        Glo::Atan => Mf::Atan,
                        Glo::Sinh => Mf::Sinh,
                        Glo::Cosh => Mf::Cosh,
                        Glo::Tanh => Mf::Tanh,
                        Glo::Atan2 => Mf::Atan2,
                        Glo::Asinh => Mf::Asinh,
                        Glo::Acosh => Mf::Acosh,
                        Glo::Atanh => Mf::Atanh,
                        Glo::Radians => Mf::Radians,
                        Glo::Degrees => Mf::Degrees,
                        Glo::Pow => Mf::Pow,
                        Glo::Exp => Mf::Exp,
                        Glo::Log => Mf::Log,
                        Glo::Exp2 => Mf::Exp2,
                        Glo::Log2 => Mf::Log2,
                        Glo::Sqrt => Mf::Sqrt,
                        Glo::InverseSqrt => Mf::InverseSqrt,
                        Glo::MatrixInverse => Mf::Inverse,
                        Glo::Determinant => Mf::Determinant,
                        Glo::Modf => Mf::Modf,
                        Glo::FMin | Glo::UMin | Glo::SMin | Glo::NMin => Mf::Min,
                        Glo::FMax | Glo::UMax | Glo::SMax | Glo::NMax => Mf::Max,
                        Glo::FClamp | Glo::UClamp | Glo::SClamp | Glo::NClamp => Mf::Clamp,
                        Glo::FMix => Mf::Mix,
                        Glo::Step => Mf::Step,
                        Glo::SmoothStep => Mf::SmoothStep,
                        Glo::Fma => Mf::Fma,
                        Glo::Frexp => Mf::Frexp, //TODO: FrexpStruct?
                        Glo::Ldexp => Mf::Ldexp,
                        Glo::Length => Mf::Length,
                        Glo::Distance => Mf::Distance,
                        Glo::Cross => Mf::Cross,
                        Glo::Normalize => Mf::Normalize,
                        Glo::FaceForward => Mf::FaceForward,
                        Glo::Reflect => Mf::Reflect,
                        Glo::Refract => Mf::Refract,
                        Glo::PackUnorm4x8 => Mf::Pack4x8unorm,
                        Glo::PackSnorm4x8 => Mf::Pack4x8snorm,
                        Glo::PackHalf2x16 => Mf::Pack2x16float,
                        Glo::PackUnorm2x16 => Mf::Pack2x16unorm,
                        Glo::PackSnorm2x16 => Mf::Pack2x16snorm,
                        Glo::UnpackUnorm4x8 => Mf::Unpack4x8unorm,
                        Glo::UnpackSnorm4x8 => Mf::Unpack4x8snorm,
                        Glo::UnpackHalf2x16 => Mf::Unpack2x16float,
                        Glo::UnpackUnorm2x16 => Mf::Unpack2x16unorm,
                        Glo::UnpackSnorm2x16 => Mf::Unpack2x16snorm,
                        Glo::FindILsb => Mf::FindLsb,
                        Glo::FindUMsb | Glo::FindSMsb => Mf::FindMsb,
                        _ => return Err(Error::UnsupportedExtInst(inst_id)),
                    };

                    let arg_count = fun.argument_count();
                    inst.expect(base_wc + arg_count as u16)?;
                    let arg = {
                        let arg_id = self.next()?;
                        let lexp = self.lookup_expression.lookup(arg_id)?;
                        get_expr_handle!(arg_id, lexp)
                    };
                    let arg1 = if arg_count > 1 {
                        let arg_id = self.next()?;
                        let lexp = self.lookup_expression.lookup(arg_id)?;
                        Some(get_expr_handle!(arg_id, lexp))
                    } else {
                        None
                    };
                    let arg2 = if arg_count > 2 {
                        let arg_id = self.next()?;
                        let lexp = self.lookup_expression.lookup(arg_id)?;
                        Some(get_expr_handle!(arg_id, lexp))
                    } else {
                        None
                    };
                    let arg3 = if arg_count > 3 {
                        let arg_id = self.next()?;
                        let lexp = self.lookup_expression.lookup(arg_id)?;
                        Some(get_expr_handle!(arg_id, lexp))
                    } else {
                        None
                    };

                    let expr = crate::Expression::Math {
                        fun,
                        arg,
                        arg1,
                        arg2,
                        arg3,
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                // Relational and Logical Instructions
                Op::LogicalNot => {
                    inst.expect(4)?;
                    parse_expr_op!(crate::UnaryOperator::Not, UNARY)?;
                }
                Op::LogicalOr => {
                    inst.expect(5)?;
                    parse_expr_op!(crate::BinaryOperator::LogicalOr, BINARY)?;
                }
                Op::LogicalAnd => {
                    inst.expect(5)?;
                    parse_expr_op!(crate::BinaryOperator::LogicalAnd, BINARY)?;
                }
                Op::SGreaterThan | Op::SGreaterThanEqual | Op::SLessThan | Op::SLessThanEqual => {
                    inst.expect(5)?;
                    self.parse_expr_int_comparison(
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                        map_binary_operator(inst.op)?,
                        crate::ScalarKind::Sint,
                    )?;
                }
                Op::UGreaterThan | Op::UGreaterThanEqual | Op::ULessThan | Op::ULessThanEqual => {
                    inst.expect(5)?;
                    self.parse_expr_int_comparison(
                        ctx,
                        &mut emitter,
                        &mut block,
                        block_id,
                        body_idx,
                        map_binary_operator(inst.op)?,
                        crate::ScalarKind::Uint,
                    )?;
                }
                Op::FOrdEqual
                | Op::FUnordEqual
                | Op::FOrdNotEqual
                | Op::FUnordNotEqual
                | Op::FOrdLessThan
                | Op::FUnordLessThan
                | Op::FOrdGreaterThan
                | Op::FUnordGreaterThan
                | Op::FOrdLessThanEqual
                | Op::FUnordLessThanEqual
                | Op::FOrdGreaterThanEqual
                | Op::FUnordGreaterThanEqual
                | Op::LogicalEqual
                | Op::LogicalNotEqual => {
                    inst.expect(5)?;
                    let operator = map_binary_operator(inst.op)?;
                    parse_expr_op!(operator, BINARY)?;
                }
                Op::Any | Op::All | Op::IsNan | Op::IsInf | Op::IsFinite | Op::IsNormal => {
                    inst.expect(4)?;
                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let arg_id = self.next()?;

                    let arg_lexp = self.lookup_expression.lookup(arg_id)?;
                    let arg_handle = get_expr_handle!(arg_id, arg_lexp);

                    let expr = crate::Expression::Relational {
                        fun: map_relational_fun(inst.op)?,
                        argument: arg_handle,
                    };
                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: ctx.expressions.append(expr, span),
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::Kill => {
                    inst.expect(1)?;
                    break Some(crate::Statement::Kill);
                }
                Op::Unreachable => {
                    inst.expect(1)?;
                    break None;
                }
                Op::Return => {
                    inst.expect(1)?;
                    break Some(crate::Statement::Return { value: None });
                }
                Op::ReturnValue => {
                    inst.expect(2)?;
                    let value_id = self.next()?;
                    let value_lexp = self.lookup_expression.lookup(value_id)?;
                    let value_handle = get_expr_handle!(value_id, value_lexp);
                    break Some(crate::Statement::Return {
                        value: Some(value_handle),
                    });
                }
                Op::Branch => {
                    inst.expect(2)?;
                    let target_id = self.next()?;

                    // If this is a branch to a merge or continue block,
                    // then that ends the current body.
                    if let Some(info) = ctx.mergers.get(&target_id) {
                        block.extend(emitter.finish(ctx.expressions));
                        ctx.blocks.insert(block_id, block);
                        let body = &mut ctx.bodies[body_idx];
                        body.data.push(BodyFragment::BlockId(block_id));

                        merger(body, info);

                        return Ok(());
                    }

                    // Since the target of the branch has no merge information,
                    // this must be the only branch to that block. This means
                    // we can treat it as an extension of the current `Body`.
                    //
                    // NOTE: it's possible that another branch was already made to this block
                    // setting the body index in which case it SHOULD NOT be overridden.
                    // For example a switch with falltrough, the OpSwitch will set the body to
                    // the respective case and the case may branch to another case in which case
                    // the body index shouldn't be changed
                    ctx.body_for_label.entry(target_id).or_insert(body_idx);

                    break None;
                }
                Op::BranchConditional => {
                    inst.expect_at_least(4)?;

                    let condition = {
                        let condition_id = self.next()?;
                        let lexp = self.lookup_expression.lookup(condition_id)?;
                        get_expr_handle!(condition_id, lexp)
                    };

                    block.extend(emitter.finish(ctx.expressions));
                    ctx.blocks.insert(block_id, block);
                    let body = &mut ctx.bodies[body_idx];
                    body.data.push(BodyFragment::BlockId(block_id));

                    let true_id = self.next()?;
                    let false_id = self.next()?;

                    let same_target = true_id == false_id;

                    // Start a body block for the `accept` branch.
                    let accept = ctx.bodies.len();
                    let mut accept_block = Body::with_parent(body_idx);

                    // If the `OpBranchConditional`target is somebody else's
                    // merge or continue block, then put a `Break` or `Continue`
                    // statement in this new body block.
                    if let Some(info) = ctx.mergers.get(&true_id) {
                        merger(
                            match same_target {
                                true => &mut ctx.bodies[body_idx],
                                false => &mut accept_block,
                            },
                            info,
                        )
                    } else {
                        // Note the body index for the block we're branching to.
                        let prev = ctx.body_for_label.insert(
                            true_id,
                            match same_target {
                                true => body_idx,
                                false => accept,
                            },
                        );
                        debug_assert!(prev.is_none());
                    }

                    if same_target {
                        return Ok(());
                    }

                    ctx.bodies.push(accept_block);

                    // Handle the `reject` branch just like the `accept` block.
                    let reject = ctx.bodies.len();
                    let mut reject_block = Body::with_parent(body_idx);

                    if let Some(info) = ctx.mergers.get(&false_id) {
                        merger(&mut reject_block, info)
                    } else {
                        let prev = ctx.body_for_label.insert(false_id, reject);
                        debug_assert!(prev.is_none());
                    }

                    ctx.bodies.push(reject_block);

                    let body = &mut ctx.bodies[body_idx];
                    body.data.push(BodyFragment::If {
                        condition,
                        accept,
                        reject,
                    });

                    // Consume branch weights
                    for _ in 4..inst.wc {
                        let _ = self.next()?;
                    }

                    return Ok(());
                }
                Op::Switch => {
                    inst.expect_at_least(3)?;
                    let selector = self.next()?;
                    let default_id = self.next()?;

                    // If the previous instruction was a `OpSelectionMerge` then we must
                    // promote the `MergeBlockInformation` to a `SwitchMerge`
                    if let Some(merge) = selection_merge_block {
                        ctx.mergers
                            .insert(merge, MergeBlockInformation::SwitchMerge);
                    }

                    let default = ctx.bodies.len();
                    ctx.bodies.push(Body::with_parent(body_idx));
                    ctx.body_for_label.entry(default_id).or_insert(default);

                    let selector_lexp = &self.lookup_expression[&selector];
                    let selector_lty = self.lookup_type.lookup(selector_lexp.type_id)?;
                    let selector_handle = get_expr_handle!(selector, selector_lexp);
                    let selector = match ctx.type_arena[selector_lty.handle].inner {
                        crate::TypeInner::Scalar {
                            kind: crate::ScalarKind::Uint,
                            width: _,
                        } => {
                            // IR expects a signed integer, so do a bitcast
                            ctx.expressions.append(
                                crate::Expression::As {
                                    kind: crate::ScalarKind::Sint,
                                    expr: selector_handle,
                                    convert: None,
                                },
                                span,
                            )
                        }
                        crate::TypeInner::Scalar {
                            kind: crate::ScalarKind::Sint,
                            width: _,
                        } => selector_handle,
                        ref other => unimplemented!("Unexpected selector {:?}", other),
                    };

                    // Clear past switch cases to prevent them from entering this one
                    self.switch_cases.clear();

                    for _ in 0..(inst.wc - 3) / 2 {
                        let literal = self.next()?;
                        let target = self.next()?;

                        let case_body_idx = ctx.bodies.len();

                        // Check if any previous case already used this target block id, if so
                        // group them together to reorder them later so that no weird
                        // falltrough cases happen.
                        if let Some(&mut (_, ref mut literals)) = self.switch_cases.get_mut(&target)
                        {
                            literals.push(literal as i32);
                            continue;
                        }

                        let mut body = Body::with_parent(body_idx);

                        if let Some(info) = ctx.mergers.get(&target) {
                            merger(&mut body, info);
                        }

                        ctx.bodies.push(body);
                        ctx.body_for_label.entry(target).or_insert(case_body_idx);

                        // Register this target block id as already having been processed and
                        // the respective body index assigned and the first case value
                        self.switch_cases
                            .insert(target, (case_body_idx, vec![literal as i32]));
                    }

                    // Loop trough the collected target blocks creating a new case for each
                    // literal pointing to it, only one case will have the true body and all the
                    // others will be empty falltrough so that they all execute the same body
                    // without duplicating code.
                    //
                    // Since `switch_cases` is an indexmap the order of insertion is preserved
                    // this is needed because spir-v defines falltrough order in the switch
                    // instruction.
                    let mut cases = Vec::with_capacity((inst.wc as usize - 3) / 2);
                    for &(case_body_idx, ref literals) in self.switch_cases.values() {
                        let value = literals[0];

                        for &literal in literals.iter().skip(1) {
                            let empty_body_idx = ctx.bodies.len();
                            let body = Body::with_parent(body_idx);

                            ctx.bodies.push(body);

                            cases.push((literal, empty_body_idx));
                        }

                        cases.push((value, case_body_idx));
                    }

                    block.extend(emitter.finish(ctx.expressions));

                    let body = &mut ctx.bodies[body_idx];
                    ctx.blocks.insert(block_id, block);
                    // Make sure the vector has space for at least two more allocations
                    body.data.reserve(2);
                    body.data.push(BodyFragment::BlockId(block_id));
                    body.data.push(BodyFragment::Switch {
                        selector,
                        cases,
                        default,
                    });

                    return Ok(());
                }
                Op::SelectionMerge => {
                    inst.expect(3)?;
                    let merge_block_id = self.next()?;
                    // TODO: Selection Control Mask
                    let _selection_control = self.next()?;

                    // Indicate that the merge block is a continuation of the
                    // current `Body`.
                    ctx.body_for_label.entry(merge_block_id).or_insert(body_idx);

                    // Let subsequent branches to the merge block know that
                    // they've reached the end of the selection construct.
                    ctx.mergers
                        .insert(merge_block_id, MergeBlockInformation::SelectionMerge);

                    selection_merge_block = Some(merge_block_id);
                }
                Op::LoopMerge => {
                    inst.expect_at_least(4)?;
                    let merge_block_id = self.next()?;
                    let continuing = self.next()?;

                    // TODO: Loop Control Parameters
                    for _ in 0..inst.wc - 3 {
                        self.next()?;
                    }

                    // Indicate that the merge block is a continuation of the
                    // current `Body`.
                    ctx.body_for_label.entry(merge_block_id).or_insert(body_idx);
                    // Let subsequent branches to the merge block know that
                    // they're `Break` statements.
                    ctx.mergers
                        .insert(merge_block_id, MergeBlockInformation::LoopMerge);

                    let loop_body_idx = ctx.bodies.len();
                    ctx.bodies.push(Body::with_parent(body_idx));

                    let continue_idx = ctx.bodies.len();
                    // The continue block inherits the scope of the loop body
                    ctx.bodies.push(Body::with_parent(loop_body_idx));
                    ctx.body_for_label.entry(continuing).or_insert(continue_idx);
                    // Let subsequent branches to the continue block know that
                    // they're `Continue` statements.
                    ctx.mergers
                        .insert(continuing, MergeBlockInformation::LoopContinue);

                    // The loop header always belongs to the loop body
                    ctx.body_for_label.insert(block_id, loop_body_idx);

                    let parent_body = &mut ctx.bodies[body_idx];
                    parent_body.data.push(BodyFragment::Loop {
                        body: loop_body_idx,
                        continuing: continue_idx,
                    });
                    body_idx = loop_body_idx;
                }
                Op::DPdx | Op::DPdxFine | Op::DPdxCoarse => {
                    parse_expr_op!(crate::DerivativeAxis::X, DERIVATIVE)?;
                }
                Op::DPdy | Op::DPdyFine | Op::DPdyCoarse => {
                    parse_expr_op!(crate::DerivativeAxis::Y, DERIVATIVE)?;
                }
                Op::Fwidth | Op::FwidthFine | Op::FwidthCoarse => {
                    parse_expr_op!(crate::DerivativeAxis::Width, DERIVATIVE)?;
                }
                Op::ArrayLength => {
                    inst.expect(5)?;
                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let structure_id = self.next()?;
                    let member_index = self.next()?;

                    // We're assuming that the validation pass, if it's run, will catch if the
                    // wrong types or parameters are supplied here.

                    let structure_ptr = self.lookup_expression.lookup(structure_id)?;
                    let structure_handle = get_expr_handle!(structure_id, structure_ptr);

                    let member_ptr = ctx.expressions.append(
                        crate::Expression::AccessIndex {
                            base: structure_handle,
                            index: member_index,
                        },
                        span,
                    );

                    let length = ctx
                        .expressions
                        .append(crate::Expression::ArrayLength(member_ptr), span);

                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle: length,
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                Op::CopyMemory => {
                    inst.expect_at_least(3)?;
                    let target_id = self.next()?;
                    let source_id = self.next()?;
                    let _memory_access = if inst.wc != 3 {
                        inst.expect(4)?;
                        spirv::MemoryAccess::from_bits(self.next()?)
                            .ok_or(Error::InvalidParameter(Op::CopyMemory))?
                    } else {
                        spirv::MemoryAccess::NONE
                    };

                    // TODO: check if the source and target types are the same?
                    let target = self.lookup_expression.lookup(target_id)?;
                    let target_handle = get_expr_handle!(target_id, target);
                    let source = self.lookup_expression.lookup(source_id)?;
                    let source_handle = get_expr_handle!(source_id, source);

                    // This operation is practically the same as loading and then storing, I think.
                    let value_expr = ctx.expressions.append(
                        crate::Expression::Load {
                            pointer: source_handle,
                        },
                        span,
                    );

                    block.extend(emitter.finish(ctx.expressions));
                    block.push(
                        crate::Statement::Store {
                            pointer: target_handle,
                            value: value_expr,
                        },
                        span,
                    );

                    emitter.start(ctx.expressions);
                }
                Op::ControlBarrier => {
                    inst.expect(4)?;
                    let exec_scope_id = self.next()?;
                    let _mem_scope_raw = self.next()?;
                    let semantics_id = self.next()?;
                    let exec_scope_const = self.lookup_constant.lookup(exec_scope_id)?;
                    let semantics_const = self.lookup_constant.lookup(semantics_id)?;
                    let exec_scope = match ctx.const_arena[exec_scope_const.handle].inner {
                        crate::ConstantInner::Scalar {
                            value: crate::ScalarValue::Uint(raw),
                            width: _,
                        } => raw as u32,
                        _ => return Err(Error::InvalidBarrierScope(exec_scope_id)),
                    };
                    let semantics = match ctx.const_arena[semantics_const.handle].inner {
                        crate::ConstantInner::Scalar {
                            value: crate::ScalarValue::Uint(raw),
                            width: _,
                        } => raw as u32,
                        _ => return Err(Error::InvalidBarrierMemorySemantics(semantics_id)),
                    };
                    if exec_scope == spirv::Scope::Workgroup as u32 {
                        let mut flags = crate::Barrier::empty();
                        flags.set(
                            crate::Barrier::STORAGE,
                            semantics & spirv::MemorySemantics::UNIFORM_MEMORY.bits() != 0,
                        );
                        flags.set(
                            crate::Barrier::WORK_GROUP,
                            semantics
                                & (spirv::MemorySemantics::SUBGROUP_MEMORY
                                    | spirv::MemorySemantics::WORKGROUP_MEMORY)
                                    .bits()
                                != 0,
                        );
                        block.push(crate::Statement::Barrier(flags), span);
                    } else {
                        log::warn!("Unsupported barrier execution scope: {}", exec_scope);
                    }
                }
                Op::CopyObject => {
                    inst.expect(4)?;
                    let result_type_id = self.next()?;
                    let result_id = self.next()?;
                    let operand_id = self.next()?;

                    let lookup = self.lookup_expression.lookup(operand_id)?;
                    let handle = get_expr_handle!(operand_id, lookup);

                    self.lookup_expression.insert(
                        result_id,
                        LookupExpression {
                            handle,
                            type_id: result_type_id,
                            block_id,
                        },
                    );
                }
                _ => return Err(Error::UnsupportedInstruction(self.state, inst.op)),
            }
        };

        block.extend(emitter.finish(ctx.expressions));
        if let Some(stmt) = terminator {
            block.push(stmt, crate::Span::default());
        }

        // Save this block fragment in `block_ctx.blocks`, and mark it to be
        // incorporated into the current body at `Statement` assembly time.
        ctx.blocks.insert(block_id, block);
        let body = &mut ctx.bodies[body_idx];
        body.data.push(BodyFragment::BlockId(block_id));
        Ok(())
    }

    fn make_expression_storage(
        &mut self,
        globals: &Arena<crate::GlobalVariable>,
        constants: &Arena<crate::Constant>,
    ) -> Arena<crate::Expression> {
        let mut expressions = Arena::new();
        #[allow(clippy::panic)]
        {
            assert!(self.lookup_expression.is_empty());
        }
        // register global variables
        for (&id, var) in self.lookup_variable.iter() {
            let span = globals.get_span(var.handle);
            let handle = expressions.append(crate::Expression::GlobalVariable(var.handle), span);
            self.lookup_expression.insert(
                id,
                LookupExpression {
                    type_id: var.type_id,
                    handle,
                    // Setting this to an invalid id will cause get_expr_handle
                    // to default to the main body making sure no load/stores
                    // are added.
                    block_id: 0,
                },
            );
        }
        // register special constants
        self.index_constant_expressions.clear();
        for &con_handle in self.index_constants.iter() {
            let span = constants.get_span(con_handle);
            let handle = expressions.append(crate::Expression::Constant(con_handle), span);
            self.index_constant_expressions.push(handle);
        }
        // register constants
        for (&id, con) in self.lookup_constant.iter() {
            let span = constants.get_span(con.handle);
            let handle = expressions.append(crate::Expression::Constant(con.handle), span);
            self.lookup_expression.insert(
                id,
                LookupExpression {
                    type_id: con.type_id,
                    handle,
                    // Setting this to an invalid id will cause get_expr_handle
                    // to default to the main body making sure no load/stores
                    // are added.
                    block_id: 0,
                },
            );
        }
        // done
        expressions
    }

    fn switch(&mut self, state: ModuleState, op: spirv::Op) -> Result<(), Error> {
        if state < self.state {
            Err(Error::UnsupportedInstruction(self.state, op))
        } else {
            self.state = state;
            Ok(())
        }
    }

    /// Walk the statement tree and patch it in the following cases:
    /// 1. Function call targets are replaced by `deferred_function_calls` map
    fn patch_statements(
        &mut self,
        statements: &mut crate::Block,
        expressions: &mut Arena<crate::Expression>,
        fun_parameter_sampling: &mut [image::SamplingFlags],
    ) -> Result<(), Error> {
        use crate::Statement as S;
        let mut i = 0usize;
        while i < statements.len() {
            match statements[i] {
                S::Emit(_) => {}
                S::Block(ref mut block) => {
                    self.patch_statements(block, expressions, fun_parameter_sampling)?;
                }
                S::If {
                    condition: _,
                    ref mut accept,
                    ref mut reject,
                } => {
                    self.patch_statements(reject, expressions, fun_parameter_sampling)?;
                    self.patch_statements(accept, expressions, fun_parameter_sampling)?;
                }
                S::Switch {
                    selector: _,
                    ref mut cases,
                } => {
                    for case in cases.iter_mut() {
                        self.patch_statements(&mut case.body, expressions, fun_parameter_sampling)?;
                    }
                }
                S::Loop {
                    ref mut body,
                    ref mut continuing,
                    break_if: _,
                } => {
                    self.patch_statements(body, expressions, fun_parameter_sampling)?;
                    self.patch_statements(continuing, expressions, fun_parameter_sampling)?;
                }
                S::Break
                | S::Continue
                | S::Return { .. }
                | S::Kill
                | S::Barrier(_)
                | S::Store { .. }
                | S::ImageStore { .. }
                | S::Atomic { .. } => {}
                S::Call {
                    function: ref mut callee,
                    ref arguments,
                    ..
                } => {
                    let fun_id = self.deferred_function_calls[callee.index()];
                    let fun_lookup = self.lookup_function.lookup(fun_id)?;
                    *callee = fun_lookup.handle;

                    // Patch sampling flags
                    for (arg_index, arg) in arguments.iter().enumerate() {
                        let flags = match fun_lookup.parameters_sampling.get(arg_index) {
                            Some(&flags) if !flags.is_empty() => flags,
                            _ => continue,
                        };

                        match expressions[*arg] {
                            crate::Expression::GlobalVariable(handle) => {
                                if let Some(sampling) = self.handle_sampling.get_mut(&handle) {
                                    *sampling |= flags
                                }
                            }
                            crate::Expression::FunctionArgument(i) => {
                                fun_parameter_sampling[i as usize] |= flags;
                            }
                            ref other => return Err(Error::InvalidGlobalVar(other.clone())),
                        }
                    }
                }
            }
            i += 1;
        }
        Ok(())
    }

    fn patch_function(
        &mut self,
        handle: Option<Handle<crate::Function>>,
        fun: &mut crate::Function,
    ) -> Result<(), Error> {
        // Note: this search is a bit unfortunate
        let (fun_id, mut parameters_sampling) = match handle {
            Some(h) => {
                let (&fun_id, lookup) = self
                    .lookup_function
                    .iter_mut()
                    .find(|&(_, ref lookup)| lookup.handle == h)
                    .unwrap();
                (fun_id, mem::take(&mut lookup.parameters_sampling))
            }
            None => (0, Vec::new()),
        };

        for (_, expr) in fun.expressions.iter_mut() {
            if let crate::Expression::CallResult(ref mut function) = *expr {
                let fun_id = self.deferred_function_calls[function.index()];
                *function = self.lookup_function.lookup(fun_id)?.handle;
            }
        }

        self.patch_statements(
            &mut fun.body,
            &mut fun.expressions,
            &mut parameters_sampling,
        )?;

        if let Some(lookup) = self.lookup_function.get_mut(&fun_id) {
            lookup.parameters_sampling = parameters_sampling;
        }
        Ok(())
    }

    pub fn parse(mut self) -> Result<crate::Module, Error> {
        let mut module = {
            if self.next()? != spirv::MAGIC_NUMBER {
                return Err(Error::InvalidHeader);
            }
            let version_raw = self.next()?;
            let generator = self.next()?;
            let _bound = self.next()?;
            let _schema = self.next()?;
            log::info!("Generated by {} version {:x}", generator, version_raw);
            crate::Module::default()
        };

        // register indexing constants
        self.index_constants.clear();
        for i in 0..4 {
            let handle = module.constants.append(
                crate::Constant {
                    name: None,
                    specialization: None,
                    inner: crate::ConstantInner::Scalar {
                        width: 4,
                        value: crate::ScalarValue::Sint(i),
                    },
                },
                Default::default(),
            );
            self.index_constants.push(handle);
        }

        self.layouter.clear();
        self.dummy_functions = Arena::new();
        self.lookup_function.clear();
        self.function_call_graph.clear();

        loop {
            use spirv::Op;

            let inst = match self.next_inst() {
                Ok(inst) => inst,
                Err(Error::IncompleteData) => break,
                Err(other) => return Err(other),
            };
            log::debug!("\t{:?} [{}]", inst.op, inst.wc);

            match inst.op {
                Op::Capability => self.parse_capability(inst),
                Op::Extension => self.parse_extension(inst),
                Op::ExtInstImport => self.parse_ext_inst_import(inst),
                Op::MemoryModel => self.parse_memory_model(inst),
                Op::EntryPoint => self.parse_entry_point(inst),
                Op::ExecutionMode => self.parse_execution_mode(inst),
                Op::String => self.parse_string(inst),
                Op::Source => self.parse_source(inst),
                Op::SourceExtension => self.parse_source_extension(inst),
                Op::Name => self.parse_name(inst),
                Op::MemberName => self.parse_member_name(inst),
                Op::ModuleProcessed => self.parse_module_processed(inst),
                Op::Decorate => self.parse_decorate(inst),
                Op::MemberDecorate => self.parse_member_decorate(inst),
                Op::TypeVoid => self.parse_type_void(inst),
                Op::TypeBool => self.parse_type_bool(inst, &mut module),
                Op::TypeInt => self.parse_type_int(inst, &mut module),
                Op::TypeFloat => self.parse_type_float(inst, &mut module),
                Op::TypeVector => self.parse_type_vector(inst, &mut module),
                Op::TypeMatrix => self.parse_type_matrix(inst, &mut module),
                Op::TypeFunction => self.parse_type_function(inst),
                Op::TypePointer => self.parse_type_pointer(inst, &mut module),
                Op::TypeArray => self.parse_type_array(inst, &mut module),
                Op::TypeRuntimeArray => self.parse_type_runtime_array(inst, &mut module),
                Op::TypeStruct => self.parse_type_struct(inst, &mut module),
                Op::TypeImage => self.parse_type_image(inst, &mut module),
                Op::TypeSampledImage => self.parse_type_sampled_image(inst),
                Op::TypeSampler => self.parse_type_sampler(inst, &mut module),
                Op::Constant | Op::SpecConstant => self.parse_constant(inst, &mut module),
                Op::ConstantComposite => self.parse_composite_constant(inst, &mut module),
                Op::ConstantNull | Op::Undef => self
                    .parse_null_constant(inst, &module.types, &mut module.constants)
                    .map(|_| ()),
                Op::ConstantTrue => self.parse_bool_constant(inst, true, &mut module),
                Op::ConstantFalse => self.parse_bool_constant(inst, false, &mut module),
                Op::Variable => self.parse_global_variable(inst, &mut module),
                Op::Function => {
                    self.switch(ModuleState::Function, inst.op)?;
                    inst.expect(5)?;
                    self.parse_function(&mut module)
                }
                _ => Err(Error::UnsupportedInstruction(self.state, inst.op)), //TODO
            }?;
        }

        log::info!("Patching...");
        {
            let mut nodes = petgraph::algo::toposort(&self.function_call_graph, None)
                .map_err(|cycle| Error::FunctionCallCycle(cycle.node_id()))?;
            nodes.reverse(); // we need dominated first
            let mut functions = mem::take(&mut module.functions);
            for fun_id in nodes {
                if fun_id > !(functions.len() as u32) {
                    // skip all the fake IDs registered for the entry points
                    continue;
                }
                let lookup = self.lookup_function.get_mut(&fun_id).unwrap();
                // take out the function from the old array
                let fun = mem::take(&mut functions[lookup.handle]);
                // add it to the newly formed arena, and adjust the lookup
                lookup.handle = module
                    .functions
                    .append(fun, functions.get_span(lookup.handle));
            }
        }
        // patch all the functions
        for (handle, fun) in module.functions.iter_mut() {
            self.patch_function(Some(handle), fun)?;
        }
        for ep in module.entry_points.iter_mut() {
            self.patch_function(None, &mut ep.function)?;
        }

        // Check all the images and samplers to have consistent comparison property.
        for (handle, flags) in self.handle_sampling.drain() {
            if !image::patch_comparison_type(
                flags,
                module.global_variables.get_mut(handle),
                &mut module.types,
            ) {
                return Err(Error::InconsistentComparisonSampling(handle));
            }
        }

        if !self.future_decor.is_empty() {
            log::warn!("Unused item decorations: {:?}", self.future_decor);
            self.future_decor.clear();
        }
        if !self.future_member_decor.is_empty() {
            log::warn!("Unused member decorations: {:?}", self.future_member_decor);
            self.future_member_decor.clear();
        }

        Ok(module)
    }

    fn parse_capability(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Capability, inst.op)?;
        inst.expect(2)?;
        let capability = self.next()?;
        let cap =
            spirv::Capability::from_u32(capability).ok_or(Error::UnknownCapability(capability))?;
        if !SUPPORTED_CAPABILITIES.contains(&cap) {
            if self.options.strict_capabilities {
                return Err(Error::UnsupportedCapability(cap));
            } else {
                log::warn!("Unknown capability {:?}", cap);
            }
        }
        Ok(())
    }

    fn parse_extension(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Extension, inst.op)?;
        inst.expect_at_least(2)?;
        let (name, left) = self.next_string(inst.wc - 1)?;
        if left != 0 {
            return Err(Error::InvalidOperand);
        }
        if !SUPPORTED_EXTENSIONS.contains(&name.as_str()) {
            return Err(Error::UnsupportedExtension(name));
        }
        Ok(())
    }

    fn parse_ext_inst_import(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Extension, inst.op)?;
        inst.expect_at_least(3)?;
        let result_id = self.next()?;
        let (name, left) = self.next_string(inst.wc - 2)?;
        if left != 0 {
            return Err(Error::InvalidOperand);
        }
        if !SUPPORTED_EXT_SETS.contains(&name.as_str()) {
            return Err(Error::UnsupportedExtSet(name));
        }
        self.ext_glsl_id = Some(result_id);
        Ok(())
    }

    fn parse_memory_model(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::MemoryModel, inst.op)?;
        inst.expect(3)?;
        let _addressing_model = self.next()?;
        let _memory_model = self.next()?;
        Ok(())
    }

    fn parse_entry_point(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::EntryPoint, inst.op)?;
        inst.expect_at_least(4)?;
        let exec_model = self.next()?;
        let exec_model = spirv::ExecutionModel::from_u32(exec_model)
            .ok_or(Error::UnsupportedExecutionModel(exec_model))?;
        let function_id = self.next()?;
        let (name, left) = self.next_string(inst.wc - 3)?;
        let ep = EntryPoint {
            stage: match exec_model {
                spirv::ExecutionModel::Vertex => crate::ShaderStage::Vertex,
                spirv::ExecutionModel::Fragment => crate::ShaderStage::Fragment,
                spirv::ExecutionModel::GLCompute => crate::ShaderStage::Compute,
                _ => return Err(Error::UnsupportedExecutionModel(exec_model as u32)),
            },
            name,
            early_depth_test: None,
            workgroup_size: [0; 3],
            variable_ids: self.data.by_ref().take(left as usize).collect(),
        };
        self.lookup_entry_point.insert(function_id, ep);
        Ok(())
    }

    fn parse_execution_mode(&mut self, inst: Instruction) -> Result<(), Error> {
        use spirv::ExecutionMode;

        self.switch(ModuleState::ExecutionMode, inst.op)?;
        inst.expect_at_least(3)?;

        let ep_id = self.next()?;
        let mode_id = self.next()?;
        let args: Vec<spirv::Word> = self.data.by_ref().take(inst.wc as usize - 3).collect();

        let ep = self
            .lookup_entry_point
            .get_mut(&ep_id)
            .ok_or(Error::InvalidId(ep_id))?;
        let mode = spirv::ExecutionMode::from_u32(mode_id)
            .ok_or(Error::UnsupportedExecutionMode(mode_id))?;

        match mode {
            ExecutionMode::EarlyFragmentTests => {
                if ep.early_depth_test.is_none() {
                    ep.early_depth_test = Some(crate::EarlyDepthTest { conservative: None });
                }
            }
            ExecutionMode::DepthUnchanged => {
                ep.early_depth_test = Some(crate::EarlyDepthTest {
                    conservative: Some(crate::ConservativeDepth::Unchanged),
                });
            }
            ExecutionMode::DepthGreater => {
                ep.early_depth_test = Some(crate::EarlyDepthTest {
                    conservative: Some(crate::ConservativeDepth::GreaterEqual),
                });
            }
            ExecutionMode::DepthLess => {
                ep.early_depth_test = Some(crate::EarlyDepthTest {
                    conservative: Some(crate::ConservativeDepth::LessEqual),
                });
            }
            ExecutionMode::DepthReplacing => {
                // Ignored because it can be deduced from the IR.
            }
            ExecutionMode::OriginUpperLeft => {
                // Ignored because the other option (OriginLowerLeft) is not valid in Vulkan mode.
            }
            ExecutionMode::LocalSize => {
                ep.workgroup_size = [args[0], args[1], args[2]];
            }
            _ => {
                return Err(Error::UnsupportedExecutionMode(mode_id));
            }
        }

        Ok(())
    }

    fn parse_string(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Source, inst.op)?;
        inst.expect_at_least(3)?;
        let _id = self.next()?;
        let (_name, _) = self.next_string(inst.wc - 2)?;
        Ok(())
    }

    fn parse_source(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Source, inst.op)?;
        for _ in 1..inst.wc {
            let _ = self.next()?;
        }
        Ok(())
    }

    fn parse_source_extension(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Source, inst.op)?;
        inst.expect_at_least(2)?;
        let (_name, _) = self.next_string(inst.wc - 1)?;
        Ok(())
    }

    fn parse_name(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Name, inst.op)?;
        inst.expect_at_least(3)?;
        let id = self.next()?;
        let (name, left) = self.next_string(inst.wc - 2)?;
        if left != 0 {
            return Err(Error::InvalidOperand);
        }
        self.future_decor.entry(id).or_default().name = Some(name);
        Ok(())
    }

    fn parse_member_name(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Name, inst.op)?;
        inst.expect_at_least(4)?;
        let id = self.next()?;
        let member = self.next()?;
        let (name, left) = self.next_string(inst.wc - 3)?;
        if left != 0 {
            return Err(Error::InvalidOperand);
        }

        self.future_member_decor
            .entry((id, member))
            .or_default()
            .name = Some(name);
        Ok(())
    }

    fn parse_module_processed(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Name, inst.op)?;
        inst.expect_at_least(2)?;
        let (_info, left) = self.next_string(inst.wc - 1)?;
        //Note: string is ignored
        if left != 0 {
            return Err(Error::InvalidOperand);
        }
        Ok(())
    }

    fn parse_decorate(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Annotation, inst.op)?;
        inst.expect_at_least(3)?;
        let id = self.next()?;
        let mut dec = self.future_decor.remove(&id).unwrap_or_default();
        self.next_decoration(inst, 2, &mut dec)?;
        self.future_decor.insert(id, dec);
        Ok(())
    }

    fn parse_member_decorate(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Annotation, inst.op)?;
        inst.expect_at_least(4)?;
        let id = self.next()?;
        let member = self.next()?;

        let mut dec = self
            .future_member_decor
            .remove(&(id, member))
            .unwrap_or_default();
        self.next_decoration(inst, 3, &mut dec)?;
        self.future_member_decor.insert((id, member), dec);
        Ok(())
    }

    fn parse_type_void(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(2)?;
        let id = self.next()?;
        self.lookup_void_type = Some(id);
        Ok(())
    }

    fn parse_type_bool(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(2)?;
        let id = self.next()?;
        let inner = crate::TypeInner::Scalar {
            kind: crate::ScalarKind::Bool,
            width: crate::BOOL_WIDTH,
        };
        self.lookup_type.insert(
            id,
            LookupType {
                handle: module.types.insert(
                    crate::Type {
                        name: self.future_decor.remove(&id).and_then(|dec| dec.name),
                        inner,
                    },
                    self.span_from_with_op(start),
                ),
                base_id: None,
            },
        );
        Ok(())
    }

    fn parse_type_int(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(4)?;
        let id = self.next()?;
        let width = self.next()?;
        let sign = self.next()?;
        let inner = crate::TypeInner::Scalar {
            kind: match sign {
                0 => crate::ScalarKind::Uint,
                1 => crate::ScalarKind::Sint,
                _ => return Err(Error::InvalidSign(sign)),
            },
            width: map_width(width)?,
        };
        self.lookup_type.insert(
            id,
            LookupType {
                handle: module.types.insert(
                    crate::Type {
                        name: self.future_decor.remove(&id).and_then(|dec| dec.name),
                        inner,
                    },
                    self.span_from_with_op(start),
                ),
                base_id: None,
            },
        );
        Ok(())
    }

    fn parse_type_float(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(3)?;
        let id = self.next()?;
        let width = self.next()?;
        let inner = crate::TypeInner::Scalar {
            kind: crate::ScalarKind::Float,
            width: map_width(width)?,
        };
        self.lookup_type.insert(
            id,
            LookupType {
                handle: module.types.insert(
                    crate::Type {
                        name: self.future_decor.remove(&id).and_then(|dec| dec.name),
                        inner,
                    },
                    self.span_from_with_op(start),
                ),
                base_id: None,
            },
        );
        Ok(())
    }

    fn parse_type_vector(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(4)?;
        let id = self.next()?;
        let type_id = self.next()?;
        let type_lookup = self.lookup_type.lookup(type_id)?;
        let (kind, width) = match module.types[type_lookup.handle].inner {
            crate::TypeInner::Scalar { kind, width } => (kind, width),
            _ => return Err(Error::InvalidInnerType(type_id)),
        };
        let component_count = self.next()?;
        let inner = crate::TypeInner::Vector {
            size: map_vector_size(component_count)?,
            kind,
            width,
        };
        self.lookup_type.insert(
            id,
            LookupType {
                handle: module.types.insert(
                    crate::Type {
                        name: self.future_decor.remove(&id).and_then(|dec| dec.name),
                        inner,
                    },
                    self.span_from_with_op(start),
                ),
                base_id: Some(type_id),
            },
        );
        Ok(())
    }

    fn parse_type_matrix(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(4)?;
        let id = self.next()?;
        let vector_type_id = self.next()?;
        let num_columns = self.next()?;
        let decor = self.future_decor.remove(&id);

        let vector_type_lookup = self.lookup_type.lookup(vector_type_id)?;
        let inner = match module.types[vector_type_lookup.handle].inner {
            crate::TypeInner::Vector { size, width, .. } => crate::TypeInner::Matrix {
                columns: map_vector_size(num_columns)?,
                rows: size,
                width,
            },
            _ => return Err(Error::InvalidInnerType(vector_type_id)),
        };

        self.lookup_type.insert(
            id,
            LookupType {
                handle: module.types.insert(
                    crate::Type {
                        name: decor.and_then(|dec| dec.name),
                        inner,
                    },
                    self.span_from_with_op(start),
                ),
                base_id: Some(vector_type_id),
            },
        );
        Ok(())
    }

    fn parse_type_function(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect_at_least(3)?;
        let id = self.next()?;
        let return_type_id = self.next()?;
        let parameter_type_ids = self.data.by_ref().take(inst.wc as usize - 3).collect();
        self.lookup_function_type.insert(
            id,
            LookupFunctionType {
                parameter_type_ids,
                return_type_id,
            },
        );
        Ok(())
    }

    fn parse_type_pointer(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(4)?;
        let id = self.next()?;
        let storage_class = self.next()?;
        let type_id = self.next()?;

        let decor = self.future_decor.remove(&id);
        let base_lookup_ty = self.lookup_type.lookup(type_id)?;
        let base_inner = &module.types[base_lookup_ty.handle].inner;

        let space = if let Some(space) = base_inner.pointer_space() {
            space
        } else if self
            .lookup_storage_buffer_types
            .contains_key(&base_lookup_ty.handle)
        {
            crate::AddressSpace::Storage {
                access: crate::StorageAccess::default(),
            }
        } else {
            match map_storage_class(storage_class)? {
                ExtendedClass::Global(space) => space,
                ExtendedClass::Input | ExtendedClass::Output => crate::AddressSpace::Private,
            }
        };

        // We don't support pointers to runtime-sized arrays in the `Uniform`
        // storage class with the `BufferBlock` decoration. Runtime-sized arrays
        // should be in the StorageBuffer class.
        if let crate::TypeInner::Array {
            size: crate::ArraySize::Dynamic,
            ..
        } = *base_inner
        {
            match space {
                crate::AddressSpace::Storage { .. } => {}
                _ => {
                    return Err(Error::UnsupportedRuntimeArrayStorageClass);
                }
            }
        }

        // Don't bother with pointer stuff for `Handle` types.
        let lookup_ty = if space == crate::AddressSpace::Handle {
            base_lookup_ty.clone()
        } else {
            LookupType {
                handle: module.types.insert(
                    crate::Type {
                        name: decor.and_then(|dec| dec.name),
                        inner: crate::TypeInner::Pointer {
                            base: base_lookup_ty.handle,
                            space,
                        },
                    },
                    self.span_from_with_op(start),
                ),
                base_id: Some(type_id),
            }
        };
        self.lookup_type.insert(id, lookup_ty);
        Ok(())
    }

    fn parse_type_array(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(4)?;
        let id = self.next()?;
        let type_id = self.next()?;
        let length_id = self.next()?;
        let length_const = self.lookup_constant.lookup(length_id)?;

        let decor = self.future_decor.remove(&id).unwrap_or_default();
        let base = self.lookup_type.lookup(type_id)?.handle;

        self.layouter
            .update(&module.types, &module.constants)
            .unwrap();

        // HACK if the underlying type is an image or a sampler, let's assume
        //      that we're dealing with a binding-array
        //
        // Note that it's not a strictly correct assumption, but rather a trade
        // off caused by an impedance mismatch between SPIR-V's and Naga's type
        // systems - Naga distinguishes between arrays and binding-arrays via
        // types (i.e. both kinds of arrays are just different types), while
        // SPIR-V distinguishes between them through usage - e.g. given:
        //
        // ```
        // %image = OpTypeImage %float 2D 2 0 0 2 Rgba16f
        // %uint_256 = OpConstant %uint 256
        // %image_array = OpTypeArray %image %uint_256
        // ```
        //
        // ```
        // %image = OpTypeImage %float 2D 2 0 0 2 Rgba16f
        // %uint_256 = OpConstant %uint 256
        // %image_array = OpTypeArray %image %uint_256
        // %image_array_ptr = OpTypePointer UniformConstant %image_array
        // ```
        //
        // ... in the first case, `%image_array` should technically correspond
        // to `TypeInner::Array`, while in the second case it should say
        // `TypeInner::BindingArray` (kinda, depending on whether `%image_array`
        // is ever used as a freestanding type or rather always through the
        // pointer-indirection).
        //
        // Anyway, at the moment we don't support other kinds of image / sampler
        // arrays than those binding-based, so this assumption is pretty safe
        // for now.
        let inner = if let crate::TypeInner::Image { .. } | crate::TypeInner::Sampler { .. } =
            module.types[base].inner
        {
            crate::TypeInner::BindingArray {
                base,
                size: crate::ArraySize::Constant(length_const.handle),
            }
        } else {
            crate::TypeInner::Array {
                base,
                size: crate::ArraySize::Constant(length_const.handle),
                stride: match decor.array_stride {
                    Some(stride) => stride.get(),
                    None => self.layouter[base].to_stride(),
                },
            }
        };

        self.lookup_type.insert(
            id,
            LookupType {
                handle: module.types.insert(
                    crate::Type {
                        name: decor.name,
                        inner,
                    },
                    self.span_from_with_op(start),
                ),
                base_id: Some(type_id),
            },
        );
        Ok(())
    }

    fn parse_type_runtime_array(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(3)?;
        let id = self.next()?;
        let type_id = self.next()?;

        let decor = self.future_decor.remove(&id).unwrap_or_default();
        let base = self.lookup_type.lookup(type_id)?.handle;

        self.layouter
            .update(&module.types, &module.constants)
            .unwrap();

        // HACK same case as in `parse_type_array()`
        let inner = if let crate::TypeInner::Image { .. } | crate::TypeInner::Sampler { .. } =
            module.types[base].inner
        {
            crate::TypeInner::BindingArray {
                base: self.lookup_type.lookup(type_id)?.handle,
                size: crate::ArraySize::Dynamic,
            }
        } else {
            crate::TypeInner::Array {
                base: self.lookup_type.lookup(type_id)?.handle,
                size: crate::ArraySize::Dynamic,
                stride: match decor.array_stride {
                    Some(stride) => stride.get(),
                    None => self.layouter[base].to_stride(),
                },
            }
        };

        self.lookup_type.insert(
            id,
            LookupType {
                handle: module.types.insert(
                    crate::Type {
                        name: decor.name,
                        inner,
                    },
                    self.span_from_with_op(start),
                ),
                base_id: Some(type_id),
            },
        );
        Ok(())
    }

    fn parse_type_struct(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect_at_least(2)?;
        let id = self.next()?;
        let parent_decor = self.future_decor.remove(&id);
        let is_storage_buffer = parent_decor
            .as_ref()
            .map_or(false, |decor| decor.storage_buffer);

        self.layouter
            .update(&module.types, &module.constants)
            .unwrap();

        let mut members = Vec::<crate::StructMember>::with_capacity(inst.wc as usize - 2);
        let mut member_lookups = Vec::with_capacity(members.capacity());
        let mut storage_access = crate::StorageAccess::empty();
        let mut span = 0;
        let mut alignment = Alignment::ONE;
        for i in 0..u32::from(inst.wc) - 2 {
            let type_id = self.next()?;
            let ty = self.lookup_type.lookup(type_id)?.handle;
            let decor = self
                .future_member_decor
                .remove(&(id, i))
                .unwrap_or_default();

            storage_access |= decor.flags.to_storage_access();

            member_lookups.push(LookupMember {
                type_id,
                row_major: decor.matrix_major == Some(Majority::Row),
            });

            let member_alignment = self.layouter[ty].alignment;
            span = member_alignment.round_up(span);
            alignment = member_alignment.max(alignment);

            let mut binding = decor.io_binding().ok();
            if let Some(offset) = decor.offset {
                span = offset;
            }
            let offset = span;

            span += self.layouter[ty].size;

            let inner = &module.types[ty].inner;
            if let crate::TypeInner::Matrix {
                columns,
                rows,
                width,
            } = *inner
            {
                if let Some(stride) = decor.matrix_stride {
                    let expected_stride = Alignment::from(rows) * width as u32;
                    if stride.get() != expected_stride {
                        return Err(Error::UnsupportedMatrixStride {
                            stride: stride.get(),
                            columns: columns as u8,
                            rows: rows as u8,
                            width,
                        });
                    }
                }
            }

            if let Some(ref mut binding) = binding {
                binding.apply_default_interpolation(inner);
            }
            members.push(crate::StructMember {
                name: decor.name,
                ty,
                binding,
                offset,
            });
        }

        span = alignment.round_up(span);

        let inner = crate::TypeInner::Struct { span, members };

        let ty_handle = module.types.insert(
            crate::Type {
                name: parent_decor.and_then(|dec| dec.name),
                inner,
            },
            self.span_from_with_op(start),
        );

        if is_storage_buffer {
            self.lookup_storage_buffer_types
                .insert(ty_handle, storage_access);
        }
        for (i, member_lookup) in member_lookups.into_iter().enumerate() {
            self.lookup_member
                .insert((ty_handle, i as u32), member_lookup);
        }
        self.lookup_type.insert(
            id,
            LookupType {
                handle: ty_handle,
                base_id: None,
            },
        );
        Ok(())
    }

    fn parse_type_image(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(9)?;

        let id = self.next()?;
        let sample_type_id = self.next()?;
        let dim = self.next()?;
        let _is_depth = self.next()?;
        let is_array = self.next()? != 0;
        let is_msaa = self.next()? != 0;
        let _is_sampled = self.next()?;
        let format = self.next()?;

        let dim = map_image_dim(dim)?;
        let decor = self.future_decor.remove(&id).unwrap_or_default();

        // ensure there is a type for texture coordinate without extra components
        module.types.insert(
            crate::Type {
                name: None,
                inner: {
                    let kind = crate::ScalarKind::Float;
                    let width = 4;
                    match dim.required_coordinate_size() {
                        None => crate::TypeInner::Scalar { kind, width },
                        Some(size) => crate::TypeInner::Vector { size, kind, width },
                    }
                },
            },
            Default::default(),
        );

        let base_handle = self.lookup_type.lookup(sample_type_id)?.handle;
        let kind = module.types[base_handle]
            .inner
            .scalar_kind()
            .ok_or(Error::InvalidImageBaseType(base_handle))?;

        let inner = crate::TypeInner::Image {
            class: if format != 0 {
                crate::ImageClass::Storage {
                    format: map_image_format(format)?,
                    access: crate::StorageAccess::default(),
                }
            } else {
                crate::ImageClass::Sampled {
                    kind,
                    multi: is_msaa,
                }
            },
            dim,
            arrayed: is_array,
        };

        let handle = module.types.insert(
            crate::Type {
                name: decor.name,
                inner,
            },
            self.span_from_with_op(start),
        );

        self.lookup_type.insert(
            id,
            LookupType {
                handle,
                base_id: Some(sample_type_id),
            },
        );
        Ok(())
    }

    fn parse_type_sampled_image(&mut self, inst: Instruction) -> Result<(), Error> {
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(3)?;
        let id = self.next()?;
        let image_id = self.next()?;
        self.lookup_type.insert(
            id,
            LookupType {
                handle: self.lookup_type.lookup(image_id)?.handle,
                base_id: Some(image_id),
            },
        );
        Ok(())
    }

    fn parse_type_sampler(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(2)?;
        let id = self.next()?;
        let decor = self.future_decor.remove(&id).unwrap_or_default();
        let handle = module.types.insert(
            crate::Type {
                name: decor.name,
                inner: crate::TypeInner::Sampler { comparison: false },
            },
            self.span_from_with_op(start),
        );
        self.lookup_type.insert(
            id,
            LookupType {
                handle,
                base_id: None,
            },
        );
        Ok(())
    }

    fn parse_constant(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect_at_least(4)?;
        let type_id = self.next()?;
        let id = self.next()?;
        let type_lookup = self.lookup_type.lookup(type_id)?;
        let ty = type_lookup.handle;

        let inner = match module.types[ty].inner {
            crate::TypeInner::Scalar {
                kind: crate::ScalarKind::Uint,
                width,
            } => {
                let low = self.next()?;
                let high = if width > 4 {
                    inst.expect(5)?;
                    self.next()?
                } else {
                    0
                };
                crate::ConstantInner::Scalar {
                    width,
                    value: crate::ScalarValue::Uint((u64::from(high) << 32) | u64::from(low)),
                }
            }
            crate::TypeInner::Scalar {
                kind: crate::ScalarKind::Sint,
                width,
            } => {
                let low = self.next()?;
                let high = if width > 4 {
                    inst.expect(5)?;
                    self.next()?
                } else {
                    0
                };
                crate::ConstantInner::Scalar {
                    width,
                    value: crate::ScalarValue::Sint(
                        (i64::from(high as i32) << 32) | ((i64::from(low as i32) << 32) >> 32),
                    ),
                }
            }
            crate::TypeInner::Scalar {
                kind: crate::ScalarKind::Float,
                width,
            } => {
                let low = self.next()?;
                let extended = match width {
                    4 => f64::from(f32::from_bits(low)),
                    8 => {
                        inst.expect(5)?;
                        let high = self.next()?;
                        f64::from_bits((u64::from(high) << 32) | u64::from(low))
                    }
                    _ => return Err(Error::InvalidTypeWidth(width as u32)),
                };
                crate::ConstantInner::Scalar {
                    width,
                    value: crate::ScalarValue::Float(extended),
                }
            }
            _ => return Err(Error::UnsupportedType(type_lookup.handle)),
        };

        let decor = self.future_decor.remove(&id).unwrap_or_default();

        self.lookup_constant.insert(
            id,
            LookupConstant {
                handle: module.constants.append(
                    crate::Constant {
                        specialization: decor.specialization,
                        name: decor.name,
                        inner,
                    },
                    self.span_from_with_op(start),
                ),
                type_id,
            },
        );
        Ok(())
    }

    fn parse_composite_constant(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect_at_least(3)?;
        let type_id = self.next()?;
        let type_lookup = self.lookup_type.lookup(type_id)?;
        let ty = type_lookup.handle;
        let id = self.next()?;

        let mut components = Vec::with_capacity(inst.wc as usize - 3);
        for _ in 0..components.capacity() {
            let component_id = self.next()?;
            let constant = self.lookup_constant.lookup(component_id)?;
            components.push(constant.handle);
        }

        self.lookup_constant.insert(
            id,
            LookupConstant {
                handle: module.constants.append(
                    crate::Constant {
                        name: self.future_decor.remove(&id).and_then(|dec| dec.name),
                        specialization: None,
                        inner: crate::ConstantInner::Composite { ty, components },
                    },
                    self.span_from_with_op(start),
                ),
                type_id,
            },
        );
        Ok(())
    }

    fn parse_null_constant(
        &mut self,
        inst: Instruction,
        types: &UniqueArena<crate::Type>,
        constants: &mut Arena<crate::Constant>,
    ) -> Result<(u32, u32, Handle<crate::Constant>), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(3)?;
        let type_id = self.next()?;
        let id = self.next()?;
        let span = self.span_from_with_op(start);
        let type_lookup = self.lookup_type.lookup(type_id)?;
        let ty = type_lookup.handle;

        let inner = null::generate_null_constant(ty, types, constants, span)?;
        let handle = constants.append(
            crate::Constant {
                name: self.future_decor.remove(&id).and_then(|dec| dec.name),
                specialization: None, //TODO
                inner,
            },
            span,
        );
        self.lookup_constant
            .insert(id, LookupConstant { handle, type_id });
        Ok((type_id, id, handle))
    }

    fn parse_bool_constant(
        &mut self,
        inst: Instruction,
        value: bool,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect(3)?;
        let type_id = self.next()?;
        let id = self.next()?;

        self.lookup_constant.insert(
            id,
            LookupConstant {
                handle: module.constants.append(
                    crate::Constant {
                        name: self.future_decor.remove(&id).and_then(|dec| dec.name),
                        specialization: None, //TODO
                        inner: crate::ConstantInner::boolean(value),
                    },
                    self.span_from_with_op(start),
                ),
                type_id,
            },
        );
        Ok(())
    }

    fn parse_global_variable(
        &mut self,
        inst: Instruction,
        module: &mut crate::Module,
    ) -> Result<(), Error> {
        let start = self.data_offset;
        self.switch(ModuleState::Type, inst.op)?;
        inst.expect_at_least(4)?;
        let type_id = self.next()?;
        let id = self.next()?;
        let storage_class = self.next()?;
        let init = if inst.wc > 4 {
            inst.expect(5)?;
            let init_id = self.next()?;
            let lconst = self.lookup_constant.lookup(init_id)?;
            Some(lconst.handle)
        } else {
            None
        };
        let span = self.span_from_with_op(start);
        let mut dec = self.future_decor.remove(&id).unwrap_or_default();

        let original_ty = self.lookup_type.lookup(type_id)?.handle;
        let mut ty = original_ty;

        if let crate::TypeInner::Pointer { base, space: _ } = module.types[original_ty].inner {
            ty = base;
        }

        if let crate::TypeInner::BindingArray { .. } = module.types[original_ty].inner {
            // Inside `parse_type_array()` we guess that an array of images or
            // samplers must be a binding array, and here we validate that guess
            if dec.desc_set.is_none() || dec.desc_index.is_none() {
                return Err(Error::NonBindingArrayOfImageOrSamplers);
            }
        }

        if let crate::TypeInner::Image {
            dim,
            arrayed,
            class: crate::ImageClass::Storage { format, access: _ },
        } = module.types[ty].inner
        {
            // Storage image types in IR have to contain the access, but not in the SPIR-V.
            // The same image type in SPIR-V can be used (and has to be used) for multiple images.
            // So we copy the type out and apply the variable access decorations.
            let access = dec.flags.to_storage_access();

            ty = module.types.insert(
                crate::Type {
                    name: None,
                    inner: crate::TypeInner::Image {
                        dim,
                        arrayed,
                        class: crate::ImageClass::Storage { format, access },
                    },
                },
                Default::default(),
            );
        }

        let ext_class = match self.lookup_storage_buffer_types.get(&ty) {
            Some(&access) => ExtendedClass::Global(crate::AddressSpace::Storage { access }),
            None => map_storage_class(storage_class)?,
        };

        // Fix empty name for gl_PerVertex struct generated by glslang
        if let crate::TypeInner::Pointer { .. } = module.types[original_ty].inner {
            if ext_class == ExtendedClass::Input || ext_class == ExtendedClass::Output {
                if let Some(ref dec_name) = dec.name {
                    if dec_name.is_empty() {
                        dec.name = Some("perVertexStruct".to_string())
                    }
                }
            }
        }

        let (inner, var) = match ext_class {
            ExtendedClass::Global(mut space) => {
                if let crate::AddressSpace::Storage { ref mut access } = space {
                    *access &= dec.flags.to_storage_access();
                }
                let var = crate::GlobalVariable {
                    binding: dec.resource_binding(),
                    name: dec.name,
                    space,
                    ty,
                    init,
                };
                (Variable::Global, var)
            }
            ExtendedClass::Input => {
                let mut binding = dec.io_binding()?;
                let mut unsigned_ty = ty;
                if let crate::Binding::BuiltIn(built_in) = binding {
                    let needs_inner_uint = match built_in {
                        crate::BuiltIn::BaseInstance
                        | crate::BuiltIn::BaseVertex
                        | crate::BuiltIn::InstanceIndex
                        | crate::BuiltIn::SampleIndex
                        | crate::BuiltIn::VertexIndex
                        | crate::BuiltIn::PrimitiveIndex
                        | crate::BuiltIn::LocalInvocationIndex => Some(crate::TypeInner::Scalar {
                            kind: crate::ScalarKind::Uint,
                            width: 4,
                        }),
                        crate::BuiltIn::GlobalInvocationId
                        | crate::BuiltIn::LocalInvocationId
                        | crate::BuiltIn::WorkGroupId
                        | crate::BuiltIn::WorkGroupSize => Some(crate::TypeInner::Vector {
                            size: crate::VectorSize::Tri,
                            kind: crate::ScalarKind::Uint,
                            width: 4,
                        }),
                        _ => None,
                    };
                    if let (Some(inner), Some(crate::ScalarKind::Sint)) =
                        (needs_inner_uint, module.types[ty].inner.scalar_kind())
                    {
                        unsigned_ty = module
                            .types
                            .insert(crate::Type { name: None, inner }, Default::default());
                    }
                }

                let var = crate::GlobalVariable {
                    name: dec.name.clone(),
                    space: crate::AddressSpace::Private,
                    binding: None,
                    ty,
                    init: None,
                };

                binding.apply_default_interpolation(&module.types[unsigned_ty].inner);

                let inner = Variable::Input(crate::FunctionArgument {
                    name: dec.name,
                    ty: unsigned_ty,
                    binding: Some(binding),
                });
                (inner, var)
            }
            ExtendedClass::Output => {
                // For output interface blocks, this would be a structure.
                let mut binding = dec.io_binding().ok();
                let init = match binding {
                    Some(crate::Binding::BuiltIn(built_in)) => {
                        match null::generate_default_built_in(
                            Some(built_in),
                            ty,
                            &module.types,
                            &mut module.constants,
                            span,
                        ) {
                            Ok(handle) => Some(handle),
                            Err(e) => {
                                log::warn!("Failed to initialize output built-in: {}", e);
                                None
                            }
                        }
                    }
                    Some(crate::Binding::Location { .. }) => None,
                    None => match module.types[ty].inner {
                        crate::TypeInner::Struct { ref members, .. } => {
                            // A temporary to avoid borrowing `module.types`
                            let pairs = members
                                .iter()
                                .map(|member| {
                                    let built_in = match member.binding {
                                        Some(crate::Binding::BuiltIn(built_in)) => Some(built_in),
                                        _ => None,
                                    };
                                    (built_in, member.ty)
                                })
                                .collect::<Vec<_>>();

                            let mut components = Vec::with_capacity(members.len());
                            for (built_in, member_ty) in pairs {
                                let handle = null::generate_default_built_in(
                                    built_in,
                                    member_ty,
                                    &module.types,
                                    &mut module.constants,
                                    span,
                                )?;
                                components.push(handle);
                            }
                            Some(module.constants.append(
                                crate::Constant {
                                    name: None,
                                    specialization: None,
                                    inner: crate::ConstantInner::Composite { ty, components },
                                },
                                span,
                            ))
                        }
                        _ => None,
                    },
                };

                let var = crate::GlobalVariable {
                    name: dec.name,
                    space: crate::AddressSpace::Private,
                    binding: None,
                    ty,
                    init,
                };
                if let Some(ref mut binding) = binding {
                    binding.apply_default_interpolation(&module.types[ty].inner);
                }
                let inner = Variable::Output(crate::FunctionResult { ty, binding });
                (inner, var)
            }
        };

        let handle = module.global_variables.append(var, span);

        if module.types[ty].inner.can_comparison_sample(module) {
            log::debug!("\t\ttracking {:?} for sampling properties", handle);

            self.handle_sampling
                .insert(handle, image::SamplingFlags::empty());
        }

        self.lookup_variable.insert(
            id,
            LookupVariable {
                inner,
                handle,
                type_id,
            },
        );
        Ok(())
    }
}

pub fn parse_u8_slice(data: &[u8], options: &Options) -> Result<crate::Module, Error> {
    if data.len() % 4 != 0 {
        return Err(Error::IncompleteData);
    }

    let words = data
        .chunks(4)
        .map(|c| u32::from_le_bytes(c.try_into().unwrap()));
    Parser::new(words, options).parse()
}

#[cfg(test)]
mod test {
    #[test]
    fn parse() {
        let bin = vec![
            // Magic number.           Version number: 1.0.
            0x03, 0x02, 0x23, 0x07, 0x00, 0x00, 0x01, 0x00,
            // Generator number: 0.    Bound: 0.
            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // Reserved word: 0.
            0x00, 0x00, 0x00, 0x00, // OpMemoryModel.          Logical.
            0x0e, 0x00, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, // GLSL450.
            0x01, 0x00, 0x00, 0x00,
        ];
        let _ = super::parse_u8_slice(&bin, &Default::default()).unwrap();
    }
}

/// Helper function to check if `child` is in the scope of `parent`
fn is_parent(mut child: usize, parent: usize, block_ctx: &BlockContext) -> bool {
    loop {
        if child == parent {
            // The child is in the scope parent
            break true;
        } else if child == 0 {
            // Searched finished at the root the child isn't in the parent's body
            break false;
        }

        child = block_ctx.bodies[child].parent;
    }
}