[llvm] [DirectX] Legalize memcpy (PR #139173)

[Farzon Lotfi via llvm-commits]

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@@ -246,6 +246,61 @@ downcastI64toI32InsertExtractElements(Instruction &I,
   }
 }
 
+static void emitMemcpyExpansion(IRBuilder<> &Builder, Value *Dst, Value *Src,
+                                ConstantInt *Length) {
+
+  uint64_t ByteLength = Length->getZExtValue();
+  if (ByteLength == 0)
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farzonl wrote:

should we error here?  Returning here lets the memcpy  live on past legalization. Feels weird that we would just let a memcpy live on if its malformed.

https://github.com/llvm/llvm-project/pull/139173