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[InstCombine] Fix use after free

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Make sure we only access cached nowrap flags.
This commit is contained in:
Nikita Popov 2024-12-04 17:20:04 +01:00
parent b79007d8a6
commit 66ed8fb973
1 changed files with 7 additions and 6 deletions
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13
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@ -2092,18 +2092,18 @@ Value *InstCombinerImpl::OptimizePointerDifference(Value *LHS, Value *RHS,
// To avoid duplicating the offset arithmetic, rewrite the GEP to use the
// computed offset. This may erase the original GEP, so be sure to cache the
// inbounds flag before emitting the offset.
// nowrap flags before emitting the offset.
// TODO: We should probably do this even if there is only one GEP.
bool RewriteGEPs = GEP2 != nullptr;
// Emit the offset of the GEP and an intptr_t.
bool GEP1IsInBounds = GEP1->isInBounds();
GEPNoWrapFlags GEP1NW = GEP1->getNoWrapFlags();
Value *Result = EmitGEPOffset(GEP1, RewriteGEPs);
// If this is a single inbounds GEP and the original sub was nuw,
// then the final multiplication is also nuw.
if (auto *I = dyn_cast<Instruction>(Result))
if (IsNUW && !GEP2 && !Swapped && GEP1IsInBounds &&
if (IsNUW && !GEP2 && !Swapped && GEP1NW.isInBounds() &&
I->getOpcode() == Instruction::Mul)
I->setHasNoUnsignedWrap();
@ -2111,11 +2111,12 @@ Value *InstCombinerImpl::OptimizePointerDifference(Value *LHS, Value *RHS,
// If both GEPs are inbounds, then the subtract does not have signed overflow.
// If both GEPs are nuw and the original sub is nuw, the new sub is also nuw.
if (GEP2) {
GEPNoWrapFlags GEP2NW = GEP2->getNoWrapFlags();
Value *Offset = EmitGEPOffset(GEP2, RewriteGEPs);
Result = Builder.CreateSub(Result, Offset, "gepdiff",
IsNUW && GEP1->hasNoUnsignedWrap() &&
GEP2->hasNoUnsignedWrap(),
GEP1IsInBounds && GEP2->isInBounds());
IsNUW && GEP1NW.hasNoUnsignedWrap() &&
GEP2NW.hasNoUnsignedWrap(),
GEP1NW.isInBounds() && GEP2NW.isInBounds());
}
// If we have p - gep(p, ...) then we have to negate the result.