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[MemCpyOpt] Check MDep aliases to avoid infinite loops (NFC) #140376

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Merged
merged 1 commit into from
May 27, 2025
+6 −9
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[MemCpyOpt] Check MDep aliases to avoid infinite loops (NFC) #140376

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15 changes: 6 additions & 9 deletions llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1104,16 +1104,17 @@ bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpyLoad,
bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
MemCpyInst *MDep,
BatchAAResults &BAA) {
// We can only optimize non-volatile memcpy's.
if (MDep->isVolatile())
return false;

// If dep instruction is reading from our current input, then it is a noop
// transfer and substituting the input won't change this instruction. Just
// ignore the input and let someone else zap MDep. This handles cases like:
// memcpy(a <- a)
// memcpy(b <- a)
if (M->getSource() == MDep->getSource())
return false;

// We can only optimize non-volatile memcpy's.
if (MDep->isVolatile())
// This also avoids infinite loops.
if (BAA.isMustAlias(MDep->getDest(), MDep->getSource()))
return false;

int64_t MForwardOffset = 0;
Expand Down Expand Up @@ -1177,10 +1178,6 @@ bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
CopySourceAlign = commonAlignment(*CopySourceAlign, MForwardOffset);
}

// Avoid infinite loops
if (BAA.isMustAlias(M->getSource(), CopySource))
return false;

// Verify that the copied-from memory doesn't change in between the two
// transfers. For example, in:
// memcpy(a <- b)
Expand Down