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

[Greg Roth via llvm-commits]

================
@@ -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)
----------------
pow2clk wrote:

```suggestion
  // If length to copy is zero, no memcpy is needed.
  if (ByteLength == 0)
```

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