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// Copyright (c) The Diem Core Contributors
// Copyright (c) The Move Contributors
// SPDX-License-Identifier: Apache-2.0
use move_binary_format::{
binary_views::FunctionView,
control_flow_graph::{BlockId, ControlFlowGraph},
file_format::{Bytecode, CodeOffset},
};
use std::collections::BTreeMap;
/// Trait for finite-height abstract domains. Infinite height domains would require a more complex
/// trait with widening and a partial order.
pub trait AbstractDomain: Clone + Sized {
fn join(&mut self, other: &Self) -> JoinResult;
}
#[derive(Debug)]
pub enum JoinResult {
Changed,
Unchanged,
}
#[derive(Clone)]
pub enum BlockPostcondition<AnalysisError> {
/// Block not yet analyzed
Unprocessed,
/// Analyzing block was successful
/// TODO might carry post state at some point
Success,
/// Analyzing block resulted in an error
Error(AnalysisError),
}
#[allow(dead_code)]
#[derive(Clone)]
pub struct BlockInvariant<State, AnalysisError> {
/// Precondition of the block
pub pre: State,
/// Postcondition of the block
pub post: BlockPostcondition<AnalysisError>,
}
/// A map from block id's to the pre/post of each block after a fixed point is reached.
#[allow(dead_code)]
pub type InvariantMap<State, AnalysisError> =
BTreeMap<BlockId, BlockInvariant<State, AnalysisError>>;
/// Take a pre-state + instruction and mutate it to produce a post-state
/// Auxiliary data can be stored in self.
pub trait TransferFunctions {
type State: AbstractDomain;
type AnalysisError;
/// Execute local@instr found at index local@index in the current basic block from pre-state
/// local@pre.
/// Should return an AnalysisError if executing the instruction is unsuccessful, and () if
/// the effects of successfully executing local@instr have been reflected by mutatating
/// local@pre.
/// Auxilary data from the analysis that is not part of the abstract state can be collected by
/// mutating local@self.
/// The last instruction index in the current block is local@last_index. Knowing this
/// information allows clients to detect the end of a basic block and special-case appropriately
/// (e.g., normalizing the abstract state before a join).
fn execute(
&mut self,
pre: &mut Self::State,
instr: &Bytecode,
index: CodeOffset,
last_index: CodeOffset,
) -> Result<(), Self::AnalysisError>;
}
pub trait AbstractInterpreter: TransferFunctions {
/// Analyze procedure local@function_view starting from pre-state local@initial_state.
fn analyze_function(
&mut self,
initial_state: Self::State,
function_view: &FunctionView,
) -> InvariantMap<Self::State, Self::AnalysisError> {
let mut inv_map: InvariantMap<Self::State, Self::AnalysisError> = InvariantMap::new();
let entry_block_id = function_view.cfg().entry_block_id();
let mut next_block = Some(entry_block_id);
inv_map.insert(
entry_block_id,
BlockInvariant {
pre: initial_state,
post: BlockPostcondition::Unprocessed,
},
);
while let Some(block_id) = next_block {
let block_invariant = match inv_map.get_mut(&block_id) {
Some(invariant) => invariant,
None => {
// This can only happen when all predecessors have errors,
// so skip the block and move on to the next one
next_block = function_view.cfg().next_block(block_id);
continue;
}
};
let pre_state = &block_invariant.pre;
let post_state = match self.execute_block(block_id, pre_state, function_view) {
Err(e) => {
block_invariant.post = BlockPostcondition::Error(e);
next_block = function_view.cfg().next_block(block_id);
continue;
}
Ok(s) => {
block_invariant.post = BlockPostcondition::Success;
s
}
};
let mut next_block_candidate = function_view.cfg().next_block(block_id);
// propagate postcondition of this block to successor blocks
for successor_block_id in function_view.cfg().successors(block_id) {
match inv_map.get_mut(successor_block_id) {
Some(next_block_invariant) => {
let join_result = {
let old_pre = &mut next_block_invariant.pre;
old_pre.join(&post_state)
};
match join_result {
JoinResult::Unchanged => {
// Pre is the same after join. Reanalyzing this block would produce
// the same post
}
JoinResult::Changed => {
// If the cur->successor is a back edge, jump back to the beginning
// of the loop, instead of the normal next block
if function_view
.cfg()
.is_back_edge(block_id, *successor_block_id)
{
next_block_candidate = Some(*successor_block_id);
}
// Pre has changed, the post condition is now unknown for the block
next_block_invariant.post = BlockPostcondition::Unprocessed
}
}
}
None => {
// Haven't visited the next block yet. Use the post of the current block as
// its pre
inv_map.insert(
*successor_block_id,
BlockInvariant {
pre: post_state.clone(),
post: BlockPostcondition::Success,
},
);
}
}
}
next_block = next_block_candidate;
}
inv_map
}
fn execute_block(
&mut self,
block_id: BlockId,
pre_state: &Self::State,
function_view: &FunctionView,
) -> Result<Self::State, Self::AnalysisError> {
let mut state_acc = pre_state.clone();
let block_end = function_view.cfg().block_end(block_id);
for offset in function_view.cfg().instr_indexes(block_id) {
let instr = &function_view.code().code[offset as usize];
self.execute(&mut state_acc, instr, offset, block_end)?
}
Ok(state_acc)
}
}