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chore(mem2reg): Only add to per function last_loads if load is not removed #9647

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Merged
asterite merged 2 commits into from
Aug 26, 2025
Merged

chore(mem2reg): Only add to per function last_loads if load is not removed #9647

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5b24a2a
clarity surrounding when we add to PerFunctionContext::last_loads
vezenovm Aug 26, 2025
5fb715d
merge conflicts w/ master
vezenovm Aug 26, 2025
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19 changes: 9 additions & 10 deletions compiler/noirc_evaluator/src/ssa/opt/mem2reg.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -444,19 +444,10 @@ impl<'f> PerFunctionContext<'f> {
let result = self.inserter.function.dfg.instruction_results(instruction)[0];
self.inserter.map_value(result, value);
self.instructions_to_remove.insert(instruction);
} else {
// We don't know the exact value of the address, so we must keep the stores to it.
references.mark_value_used(address, self.inserter.function);

// Remember that this address has been loaded, so stores to it should not be removed.
self.last_loads.insert(address);
// Stores to any of its aliases should also be considered loaded.
self.last_loads.extend(references.get_aliases_for_value(address).iter());
}

// Check whether the block has a repeat load from the same address (w/ no calls or stores in between the loads).
// If we do have a repeat load, we can remove the current load and map its result to the previous load's result.
if let Some(last_load) = references.last_loads.get(&address) {
else if let Some(last_load) = references.last_loads.get(&address) {
let Instruction::Load { address: previous_address } =
&self.inserter.function.dfg[*last_load]
else {
Expand All @@ -469,7 +460,15 @@ impl<'f> PerFunctionContext<'f> {
self.inserter.map_value(result, previous_result);
self.instructions_to_remove.insert(instruction);
}
} else {
// We don't know the exact value of the address, so we must keep the stores to it.
references.mark_value_used(address, self.inserter.function);
// Remember that this address has been loaded, so stores to it should not be removed.
self.last_loads.insert(address);
// Stores to any of its aliases should also be considered loaded.
self.last_loads.extend(references.get_aliases_for_value(address).iter());
}

// We want to set the load for every load even if the address has a known value
// and the previous load instruction was removed.
// We are safe to still remove a repeat load in this case as we are mapping from the current load's
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