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[NaryReassociate] Check to avoid introducing poison when reusing SCEVs #98156

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Merged
merged 2 commits into from
Jul 9, 2024
Merged

[NaryReassociate] Check to avoid introducing poison when reusing SCEVs #98156

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619aa12
[NaryReassociate] Check to avoid introducing poison when reusing SCEVs
d0k Jul 9, 2024
bd5c200
Check CandidateExpr instead of Dominatee
d0k Jul 9, 2024
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22 changes: 16 additions & 6 deletions llvm/lib/Transforms/Scalar/NaryReassociate.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -565,14 +565,24 @@ NaryReassociatePass::findClosestMatchingDominator(const SCEV *CandidateExpr,
// optimization makes the algorithm O(n).
while (!Candidates.empty()) {
// Candidates stores WeakTrackingVHs, so a candidate can be nullptr if it's
// removed
// during rewriting.
if (Value *Candidate = Candidates.back()) {
// removed during rewriting.
if (Value *Candidate = Candidates.pop_back_val()) {
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This change seems problematic. Previously, we returned a candidate without pop_back the stack. With this change, the stack popped before returning the candidate. I have seen some problems.

Instruction *CandidateInstruction = cast<Instruction>(Candidate);
if (DT->dominates(CandidateInstruction, Dominatee))
return CandidateInstruction;
if (!DT->dominates(CandidateInstruction, Dominatee))
continue;

// Make sure that the instruction is safe to reuse without introducing
// poison.
SmallVector<Instruction *> DropPoisonGeneratingInsts;
if (!SE->canReuseInstruction(CandidateExpr, CandidateInstruction,
DropPoisonGeneratingInsts))
continue;

for (Instruction *I : DropPoisonGeneratingInsts)
I->dropPoisonGeneratingAnnotations();

return CandidateInstruction;
}
Candidates.pop_back();
}
return nullptr;
}
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40 changes: 40 additions & 0 deletions llvm/test/Transforms/NaryReassociate/nary-gep.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -21,4 +21,44 @@ define void @no_sext_fat_pointer(ptr addrspace(2) %a, i32 %i, i32 %j) {
ret void
}

define void @or_disjoint(ptr addrspace(2) %a, i32 %i, i32 %j, i32 %k) {
; CHECK-LABEL: @or_disjoint(
; CHECK-NEXT: [[OR:%.*]] = or disjoint i32 [[I:%.*]], [[J:%.*]]
; CHECK-NEXT: [[V2:%.*]] = getelementptr float, ptr addrspace(2) [[A:%.*]], i32 [[OR]]
; CHECK-NEXT: call void @foo(ptr addrspace(2) [[V2]])
; CHECK-NEXT: [[ADD1:%.*]] = add nuw nsw i32 [[I]], [[J]]
; CHECK-NEXT: [[ADD2:%.*]] = add nuw nsw i32 [[ADD1]], [[K:%.*]]
; CHECK-NEXT: [[V3:%.*]] = getelementptr float, ptr addrspace(2) [[A]], i32 [[ADD2]]
; CHECK-NEXT: call void @foo(ptr addrspace(2) [[V3]])
; CHECK-NEXT: ret void
;
%or = or disjoint i32 %i, %j
%v2 = getelementptr float, ptr addrspace(2) %a, i32 %or
call void @foo(ptr addrspace(2) %v2)
%add1 = add nuw nsw i32 %i, %j
%add2 = add nuw nsw i32 %add1, %k
%v3 = getelementptr float, ptr addrspace(2) %a, i32 %add2
call void @foo(ptr addrspace(2) %v3)
ret void
}

define void @drop_nuw_nsw(ptr addrspace(2) %a, i32 %i, i32 %j, i32 %k) {
; CHECK-LABEL: @drop_nuw_nsw(
; CHECK-NEXT: [[ADD0:%.*]] = add i32 [[I:%.*]], [[J:%.*]]
; CHECK-NEXT: [[V2:%.*]] = getelementptr float, ptr addrspace(2) [[A:%.*]], i32 [[ADD0]]
; CHECK-NEXT: call void @foo(ptr addrspace(2) [[V2]])
; CHECK-NEXT: [[V3:%.*]] = getelementptr float, ptr addrspace(2) [[V2]], i32 [[K:%.*]]
; CHECK-NEXT: call void @foo(ptr addrspace(2) [[V3]])
; CHECK-NEXT: ret void
;
%add0 = add nuw nsw i32 %i, %j
%v2 = getelementptr float, ptr addrspace(2) %a, i32 %add0
call void @foo(ptr addrspace(2) %v2)
%add1 = add i32 %i, %j
%add2 = add nuw nsw i32 %add1, %k
%v3 = getelementptr float, ptr addrspace(2) %a, i32 %add2
call void @foo(ptr addrspace(2) %v3)
ret void
}

declare void @foo(ptr addrspace(2))
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