[llvm] [MemCpyOpt] Check `MDep` aliases to avoid infinite loops (NFC) (PR #140376)
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Sat May 17 05:24:06 PDT 2025
https://github.com/dianqk created https://github.com/llvm/llvm-project/pull/140376
cc #103218.
>From aa1c9bc06db868e64516c845ec46b5867c1d8d23 Mon Sep 17 00:00:00 2001
From: dianqk <dianqk at dianqk.net>
Date: Sat, 17 May 2025 20:00:16 +0800
Subject: [PATCH] [MemCpyOpt] Check `MDep` aliases to avoid infinite loops
(NFC)
---
llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 9c8cd53d56b56..a78e3770384ae 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -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;
@@ -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)
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