[llvm] [InstCombine] Support offsets in `memset` to load forwarding (PR #151924)

[Pedro Lobo via llvm-commits]

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@@ -645,7 +650,11 @@ static Value *getAvailableLoadStore(Instruction *Inst, const Value *Ptr,
 
     // Make sure the read bytes are contained in the memset.
     uint64_t LoadSize = LoadTypeSize.getFixedValue();
-    if ((Len->getValue() * 8).ult(LoadSize))
+    if ((Len->getValue() * 8).ult(LoadSize + Offset * 8))
+      return nullptr;
+
+    // If there is an offset, make sure the load size is a multiple of 8.
+    if (Offset && LoadSize % 8 != 0)
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pedroclobo wrote:

Right. I forgot loads with those types raise UB (https://alive2.llvm.org/ce/z/2Ws4Xd).

https://github.com/llvm/llvm-project/pull/151924