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chore(refactor): Array set optimization context struct for analysis (n…
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…oir-lang#6204)

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## Summary\*

The `analyze_last_uses` method was starting to have multiple different
state variables. This PR just creates a separate context struct for
analyze the mutable array sets across a block in hopes of making it
simpler to add future additions.

## Additional Context



## Documentation\*

Check one:
- [X] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [X] I have tested the changes locally.
- [X] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.
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@vezenovm
vezenovm authored Oct 2, 2024
1 parent 268f2a0 commit 2eb4a2c
Showing 1 changed file with 85 additions and 72 deletions.
157 changes: 85 additions & 72 deletions compiler/noirc_evaluator/src/ssa/opt/array_set.rs
View file
Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
use std::mem;

use crate::ssa::{
ir::{
basic_block::BasicBlockId,
Expand Down Expand Up @@ -31,102 +33,113 @@ impl Function {
if !self.runtime().is_entry_point() {
assert_eq!(reachable_blocks.len(), 1, "Expected there to be 1 block remaining in Acir function for array_set optimization");
}
let mut array_to_last_use = HashMap::default();
let mut instructions_to_update = HashSet::default();
let mut arrays_from_load = HashSet::default();
let mut inner_nested_arrays = HashMap::default();

let mut context = Context::new(&self.dfg, matches!(self.runtime(), RuntimeType::Brillig));

for block in reachable_blocks.iter() {
analyze_last_uses(
&self.dfg,
*block,
matches!(self.runtime(), RuntimeType::Brillig),
&mut array_to_last_use,
&mut instructions_to_update,
&mut arrays_from_load,
&mut inner_nested_arrays,
);
context.analyze_last_uses(*block);
}

let instructions_to_update = mem::take(&mut context.instructions_that_can_be_made_mutable);
for block in reachable_blocks {
make_mutable(&mut self.dfg, block, &instructions_to_update);
}
}
}

/// Builds the set of ArraySet instructions that can be made mutable
/// because their input value is unused elsewhere afterward.
fn analyze_last_uses(
dfg: &DataFlowGraph,
block_id: BasicBlockId,
is_brillig_func: bool,
array_to_last_use: &mut HashMap<ValueId, InstructionId>,
instructions_that_can_be_made_mutable: &mut HashSet<InstructionId>,
arrays_from_load: &mut HashSet<ValueId>,
inner_nested_arrays: &mut HashMap<ValueId, InstructionId>,
) {
let block = &dfg[block_id];
struct Context<'f> {
dfg: &'f DataFlowGraph,
is_brillig_runtime: bool,
array_to_last_use: HashMap<ValueId, InstructionId>,
instructions_that_can_be_made_mutable: HashSet<InstructionId>,
arrays_from_load: HashSet<ValueId>,
inner_nested_arrays: HashMap<ValueId, InstructionId>,
}

for instruction_id in block.instructions() {
match &dfg[*instruction_id] {
Instruction::ArrayGet { array, .. } => {
let array = dfg.resolve(*array);
impl<'f> Context<'f> {
fn new(dfg: &'f DataFlowGraph, is_brillig_runtime: bool) -> Self {
Context {
dfg,
is_brillig_runtime,
array_to_last_use: HashMap::default(),
instructions_that_can_be_made_mutable: HashSet::default(),
arrays_from_load: HashSet::default(),
inner_nested_arrays: HashMap::default(),
}
}

if let Some(existing) = array_to_last_use.insert(array, *instruction_id) {
instructions_that_can_be_made_mutable.remove(&existing);
}
}
Instruction::ArraySet { array, value, .. } => {
let array = dfg.resolve(*array);
/// Builds the set of ArraySet instructions that can be made mutable
/// because their input value is unused elsewhere afterward.
fn analyze_last_uses(&mut self, block_id: BasicBlockId) {
let block = &self.dfg[block_id];

if let Some(existing) = array_to_last_use.insert(array, *instruction_id) {
instructions_that_can_be_made_mutable.remove(&existing);
}
if is_brillig_func {
let value = dfg.resolve(*value);
for instruction_id in block.instructions() {
match &self.dfg[*instruction_id] {
Instruction::ArrayGet { array, .. } => {
let array = self.dfg.resolve(*array);

if let Some(existing) = inner_nested_arrays.get(&value) {
instructions_that_can_be_made_mutable.remove(existing);
if let Some(existing) = self.array_to_last_use.insert(array, *instruction_id) {
self.instructions_that_can_be_made_mutable.remove(&existing);
}
let result = dfg.instruction_results(*instruction_id)[0];
inner_nested_arrays.insert(result, *instruction_id);
}
Instruction::ArraySet { array, value, .. } => {
let array = self.dfg.resolve(*array);

// If the array we are setting does not come from a load we can safely mark it mutable.
// If the array comes from a load we may potentially being mutating an array at a reference
// that is loaded from by other values.
let terminator = dfg[block_id].unwrap_terminator();
// If we are in a return block we are not concerned about the array potentially being mutated again.
let is_return_block = matches!(terminator, TerminatorInstruction::Return { .. });
// We also want to check that the array is not part of the terminator arguments, as this means it is used again.
let mut array_in_terminator = false;
terminator.for_each_value(|value| {
if value == array {
array_in_terminator = true;
if let Some(existing) = self.array_to_last_use.insert(array, *instruction_id) {
self.instructions_that_can_be_made_mutable.remove(&existing);
}
if self.is_brillig_runtime {
let value = self.dfg.resolve(*value);

if let Some(existing) = self.inner_nested_arrays.get(&value) {
self.instructions_that_can_be_made_mutable.remove(existing);
}
let result = self.dfg.instruction_results(*instruction_id)[0];
self.inner_nested_arrays.insert(result, *instruction_id);
}
});
if (!arrays_from_load.contains(&array) || is_return_block) && !array_in_terminator {
instructions_that_can_be_made_mutable.insert(*instruction_id);
}
}
Instruction::Call { arguments, .. } => {
for argument in arguments {
if matches!(dfg.type_of_value(*argument), Array { .. } | Slice { .. }) {
let argument = dfg.resolve(*argument);

if let Some(existing) = array_to_last_use.insert(argument, *instruction_id)
// If the array we are setting does not come from a load we can safely mark it mutable.
// If the array comes from a load we may potentially being mutating an array at a reference
// that is loaded from by other values.
let terminator = self.dfg[block_id].unwrap_terminator();
// If we are in a return block we are not concerned about the array potentially being mutated again.
let is_return_block =
matches!(terminator, TerminatorInstruction::Return { .. });
// We also want to check that the array is not part of the terminator arguments, as this means it is used again.
let mut array_in_terminator = false;
terminator.for_each_value(|value| {
if value == array {
array_in_terminator = true;
}
});
if (!self.arrays_from_load.contains(&array) || is_return_block)
&& !array_in_terminator
{
self.instructions_that_can_be_made_mutable.insert(*instruction_id);
}
}
Instruction::Call { arguments, .. } => {
for argument in arguments {
if matches!(self.dfg.type_of_value(*argument), Array { .. } | Slice { .. })
{
instructions_that_can_be_made_mutable.remove(&existing);
let argument = self.dfg.resolve(*argument);

if let Some(existing) =
self.array_to_last_use.insert(argument, *instruction_id)
{
self.instructions_that_can_be_made_mutable.remove(&existing);
}
}
}
}
}
Instruction::Load { .. } => {
let result = dfg.instruction_results(*instruction_id)[0];
if matches!(dfg.type_of_value(result), Array { .. } | Slice { .. }) {
arrays_from_load.insert(result);
Instruction::Load { .. } => {
let result = self.dfg.instruction_results(*instruction_id)[0];
if matches!(self.dfg.type_of_value(result), Array { .. } | Slice { .. }) {
self.arrays_from_load.insert(result);
}
}
_ => (),
}
_ => (),
}
}
}
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