walrus 0.26.0

A library for performing WebAssembly transformations
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267

//! Handling wasm constant values

use crate::emit::EmitContext;
use crate::ir::Value;
use crate::parse::IndicesToIds;
use crate::ty::TypeId;
use crate::{FunctionId, GlobalId, Result};
use crate::{HeapType, RefType};
use anyhow::bail;

/// A constant which is produced in WebAssembly, typically used in global
/// initializers or element/data offsets.
#[derive(Debug, Clone)]
pub enum ConstExpr {
    /// An immediate constant value
    Value(Value),
    /// A constant value referenced by the global specified
    Global(GlobalId),
    /// A null reference
    RefNull(RefType),
    /// A function initializer
    RefFunc(FunctionId),
    /// Extended constant expression (sequence of instructions)
    Extended(Vec<ConstOp>),
}

/// Operations allowed in extended constant expressions
#[derive(Debug, Copy, Clone)]
pub enum ConstOp {
    /// An i32 constant value
    I32Const(i32),
    /// An i64 constant value
    I64Const(i64),
    /// An f32 constant value
    F32Const(f32),
    /// An f64 constant value
    F64Const(f64),
    /// A v128 constant value
    V128Const(u128),
    /// Get the value of a global
    GlobalGet(GlobalId),
    /// A null reference
    RefNull(RefType),
    /// A function reference
    RefFunc(FunctionId),
    /// i32 addition
    I32Add,
    /// i32 subtraction
    I32Sub,
    /// i32 multiplication
    I32Mul,
    /// i64 addition
    I64Add,
    /// i64 subtraction
    I64Sub,
    /// i64 multiplication
    I64Mul,
    /// Create i31ref from i32
    RefI31,
    /// Create a new struct instance
    StructNew(TypeId),
    /// Create a new struct instance with default field values
    StructNewDefault(TypeId),
    /// Create a new array instance
    ArrayNew(TypeId),
    /// Create a new array instance with default element value
    ArrayNewDefault(TypeId),
    /// Create a new fixed-size array instance from inline operands
    ArrayNewFixed {
        /// The array type
        ty: TypeId,
        /// Number of elements
        len: u32,
    },
    /// Convert an externref to anyref
    AnyConvertExtern,
    /// Convert an anyref to externref
    ExternConvertAny,
}

impl ConstExpr {
    pub(crate) fn eval(init: &wasmparser::ConstExpr, ids: &IndicesToIds) -> Result<ConstExpr> {
        use wasmparser::Operator::*;
        let mut reader = init.get_operators_reader();
        let mut ops = Vec::new();

        loop {
            let op = reader.read()?;
            match op {
                End => break,
                I32Const { value } => ops.push(ConstOp::I32Const(value)),
                I64Const { value } => ops.push(ConstOp::I64Const(value)),
                F32Const { value } => ops.push(ConstOp::F32Const(f32::from_bits(value.bits()))),
                F64Const { value } => ops.push(ConstOp::F64Const(f64::from_bits(value.bits()))),
                V128Const { value } => ops.push(ConstOp::V128Const(v128_to_u128(&value))),
                GlobalGet { global_index } => {
                    ops.push(ConstOp::GlobalGet(ids.get_global(global_index)?))
                }
                RefNull { hty } => {
                    let heap_type = HeapType::from_wasmparser(hty, ids, 0)?;
                    let ref_type = RefType {
                        nullable: true,
                        heap_type,
                    };
                    ops.push(ConstOp::RefNull(ref_type));
                }
                RefFunc { function_index } => {
                    ops.push(ConstOp::RefFunc(ids.get_func(function_index)?))
                }
                I32Add => ops.push(ConstOp::I32Add),
                I32Sub => ops.push(ConstOp::I32Sub),
                I32Mul => ops.push(ConstOp::I32Mul),
                I64Add => ops.push(ConstOp::I64Add),
                I64Sub => ops.push(ConstOp::I64Sub),
                I64Mul => ops.push(ConstOp::I64Mul),
                RefI31 => ops.push(ConstOp::RefI31),
                StructNew { struct_type_index } => {
                    ops.push(ConstOp::StructNew(ids.get_type(struct_type_index)?))
                }
                StructNewDefault { struct_type_index } => {
                    ops.push(ConstOp::StructNewDefault(ids.get_type(struct_type_index)?))
                }
                ArrayNew { array_type_index } => {
                    ops.push(ConstOp::ArrayNew(ids.get_type(array_type_index)?))
                }
                ArrayNewDefault { array_type_index } => {
                    ops.push(ConstOp::ArrayNewDefault(ids.get_type(array_type_index)?))
                }
                ArrayNewFixed {
                    array_type_index,
                    array_size,
                } => ops.push(ConstOp::ArrayNewFixed {
                    ty: ids.get_type(array_type_index)?,
                    len: array_size,
                }),
                AnyConvertExtern => ops.push(ConstOp::AnyConvertExtern),
                ExternConvertAny => ops.push(ConstOp::ExternConvertAny),
                _ => bail!("unsupported operation in constant expression: {:?}", op),
            }
        }

        reader.finish()?;

        // Optimize: if there's only one simple operation, use the simple form
        if ops.len() == 1 {
            match &ops[0] {
                ConstOp::I32Const(v) => return Ok(ConstExpr::Value(Value::I32(*v))),
                ConstOp::I64Const(v) => return Ok(ConstExpr::Value(Value::I64(*v))),
                ConstOp::F32Const(v) => return Ok(ConstExpr::Value(Value::F32(*v))),
                ConstOp::F64Const(v) => return Ok(ConstExpr::Value(Value::F64(*v))),
                ConstOp::V128Const(v) => return Ok(ConstExpr::Value(Value::V128(*v))),
                ConstOp::GlobalGet(g) => return Ok(ConstExpr::Global(*g)),
                ConstOp::RefNull(ty) => return Ok(ConstExpr::RefNull(*ty)),
                ConstOp::RefFunc(f) => return Ok(ConstExpr::RefFunc(*f)),
                _ => {}
            }
        }

        Ok(ConstExpr::Extended(ops))
    }

    pub(crate) fn to_wasmencoder_type(&self, cx: &EmitContext) -> wasm_encoder::ConstExpr {
        use wasm_encoder::{Encode, Instruction};
        match self {
            ConstExpr::Value(v) => match v {
                Value::I32(v) => wasm_encoder::ConstExpr::i32_const(*v),
                Value::I64(v) => wasm_encoder::ConstExpr::i64_const(*v),
                Value::F32(v) => wasm_encoder::ConstExpr::f32_const((*v).into()),
                Value::F64(v) => wasm_encoder::ConstExpr::f64_const((*v).into()),
                Value::V128(v) => wasm_encoder::ConstExpr::v128_const(*v as i128),
            },
            ConstExpr::Global(g) => {
                wasm_encoder::ConstExpr::global_get(cx.indices.get_global_index(*g))
            }
            ConstExpr::RefNull(ty) => {
                wasm_encoder::ConstExpr::ref_null(ty.heap_type.to_wasmencoder_heap_type(cx.indices))
            }
            ConstExpr::RefFunc(f) => {
                wasm_encoder::ConstExpr::ref_func(cx.indices.get_func_index(*f))
            }
            ConstExpr::Extended(ops) => {
                let mut bytes = Vec::new();
                for op in ops {
                    match op {
                        ConstOp::I32Const(v) => Instruction::I32Const(*v).encode(&mut bytes),
                        ConstOp::I64Const(v) => Instruction::I64Const(*v).encode(&mut bytes),
                        ConstOp::F32Const(v) => {
                            Instruction::F32Const((*v).into()).encode(&mut bytes)
                        }
                        ConstOp::F64Const(v) => {
                            Instruction::F64Const((*v).into()).encode(&mut bytes)
                        }
                        ConstOp::V128Const(v) => {
                            Instruction::V128Const(*v as i128).encode(&mut bytes)
                        }
                        ConstOp::GlobalGet(g) => {
                            Instruction::GlobalGet(cx.indices.get_global_index(*g))
                                .encode(&mut bytes)
                        }
                        ConstOp::RefNull(ty) => {
                            Instruction::RefNull(ty.heap_type.to_wasmencoder_heap_type(cx.indices))
                                .encode(&mut bytes)
                        }
                        ConstOp::RefFunc(f) => {
                            Instruction::RefFunc(cx.indices.get_func_index(*f)).encode(&mut bytes)
                        }
                        ConstOp::I32Add => Instruction::I32Add.encode(&mut bytes),
                        ConstOp::I32Sub => Instruction::I32Sub.encode(&mut bytes),
                        ConstOp::I32Mul => Instruction::I32Mul.encode(&mut bytes),
                        ConstOp::I64Add => Instruction::I64Add.encode(&mut bytes),
                        ConstOp::I64Sub => Instruction::I64Sub.encode(&mut bytes),
                        ConstOp::I64Mul => Instruction::I64Mul.encode(&mut bytes),
                        ConstOp::RefI31 => Instruction::RefI31.encode(&mut bytes),
                        ConstOp::StructNew(ty) => {
                            Instruction::StructNew(cx.indices.get_type_index(*ty))
                                .encode(&mut bytes)
                        }
                        ConstOp::StructNewDefault(ty) => {
                            Instruction::StructNewDefault(cx.indices.get_type_index(*ty))
                                .encode(&mut bytes)
                        }
                        ConstOp::ArrayNew(ty) => {
                            Instruction::ArrayNew(cx.indices.get_type_index(*ty)).encode(&mut bytes)
                        }
                        ConstOp::ArrayNewDefault(ty) => {
                            Instruction::ArrayNewDefault(cx.indices.get_type_index(*ty))
                                .encode(&mut bytes)
                        }
                        ConstOp::ArrayNewFixed { ty, len } => Instruction::ArrayNewFixed {
                            array_type_index: cx.indices.get_type_index(*ty),
                            array_size: *len,
                        }
                        .encode(&mut bytes),
                        ConstOp::AnyConvertExtern => {
                            Instruction::AnyConvertExtern.encode(&mut bytes)
                        }
                        ConstOp::ExternConvertAny => {
                            Instruction::ExternConvertAny.encode(&mut bytes)
                        }
                    }
                }
                // Don't add End instruction - wasm_encoder::ConstExpr::raw adds it automatically
                wasm_encoder::ConstExpr::raw(bytes)
            }
        }
    }
}

pub(crate) fn v128_to_u128(value: &wasmparser::V128) -> u128 {
    let n = value.bytes();
    (n[0] as u128)
        | ((n[1] as u128) << 8)
        | ((n[2] as u128) << 16)
        | ((n[3] as u128) << 24)
        | ((n[4] as u128) << 32)
        | ((n[5] as u128) << 40)
        | ((n[6] as u128) << 48)
        | ((n[7] as u128) << 56)
        | ((n[8] as u128) << 64)
        | ((n[9] as u128) << 72)
        | ((n[10] as u128) << 80)
        | ((n[11] as u128) << 88)
        | ((n[12] as u128) << 96)
        | ((n[13] as u128) << 104)
        | ((n[14] as u128) << 112)
        | ((n[15] as u128) << 120)
}