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[SCEV] Avoid redundant stack push/pop in createSCEVIter (#199352)

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This patch simplifies the iterative worklist handling in createSCEVIter.

In the previous implementation, a `Value` that could not be materialized
immediately would typically be pushed onto the stack twice and popped
twice: first in the initial unvisited state, and then again after being
re-queued in the visited state once its operands had to be processed
first.

This change avoids that redundant re-queue step by updating the existing
stack entry in place before pushing unresolved operands. Use
`setInt(true)` to update the existing `Stack` entry in place instead of
pushing a separate `(V, true)` entry. This saves one
`emplace_back`/`pop_back` pair for each `Value`, and reduces memory
consumption of the `Stack` worklist.
This commit is contained in:
Daemon 2026-06-12 02:32:30 +08:00 committed by GitHub
parent a296bdef76
commit 024f39cbef
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1 changed files with 7 additions and 6 deletions
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13
llvm/lib/Analysis/ScalarEvolution.cpp
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@ -7729,14 +7729,15 @@ const SCEV *ScalarEvolution::createSCEVIter(Value *V) {
using PointerTy = PointerIntPair<Value *, 1, bool>;
SmallVector<PointerTy> Stack;
Stack.emplace_back(V, true);
Stack.emplace_back(V, false);
while (!Stack.empty()) {
auto E = Stack.pop_back_val();
auto E = Stack.back();
Value *CurV = E.getPointer();
if (getExistingSCEV(CurV))
if (getExistingSCEV(CurV)) {
Stack.pop_back();
continue;
}
SmallVector<Value *> Ops;
const SCEV *CreatedSCEV = nullptr;
@ -7752,10 +7753,10 @@ const SCEV *ScalarEvolution::createSCEVIter(Value *V) {
if (CreatedSCEV) {
insertValueToMap(CurV, CreatedSCEV);
Stack.pop_back();
} else {
// Queue CurV for SCEV creation, followed by its's operands which need to
// be constructed first.
Stack.emplace_back(CurV, true);
Stack.back().setInt(true);
// Queue its operands which need to be constructed.
for (Value *Op : Ops)
Stack.emplace_back(Op, false);
}