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⚡ Bolt: Optimize liveness dataflow iteration order and reduce allocations #283

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github-actions merged 1 commit into from
Oct 11, 2026
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⚡ Bolt: Optimize liveness dataflow iteration order and reduce allocations #283

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10 changes: 7 additions & 3 deletions compiler/optimizer/src/analysis/liveness.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -66,7 +66,9 @@ impl LivenessAnalysis {

while changed {
changed = false;
for block in &func.blocks {
// OPTIMIZATION: Liveness is a backward dataflow analysis. Iterating
// through blocks in reverse order speeds up convergence significantly.
for block in func.blocks.iter().rev() {
let block_id = block.id;

// LiveOut = union of LiveIn(succs)
Expand All @@ -89,14 +91,16 @@ impl LivenessAnalysis {

if let Some(old_in) = live_in.get_mut(&block_id) {
if old_in.len() != new_in.len() {
*old_in = new_in.clone();
// OPTIMIZATION: Reuse existing HashSet capacity to avoid allocations in hot loop.
old_in.clone_from(&new_in);
changed = true;
}
}

if let Some(old_out) = live_out.get_mut(&block_id) {
if old_out.len() != new_out.len() {
*old_out = new_out.clone();
// OPTIMIZATION: Reuse existing HashSet capacity to avoid allocations in hot loop.
old_out.clone_from(&new_out);
changed = true;
}
}
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