Fix memcpy size calculation in ScalarReplAggregatesHLSL::ReplaceMemcpy (#2298)

Multiplying by the alignment made no sense, and fixed a case where the alignment also made no sense.

lib/Transforms/Scalar/ScalarReplAggregatesHLSL.cpp

@@ -1506,7 +1506,7 @@ static void EltMemCpy(Type *Ty, Value *Dest, Value *Src,
   Value *DestGEP = CreateMergedGEP(Dest, idxList, Builder);
   Value *SrcGEP = CreateMergedGEP(Src, idxList, Builder);
   unsigned size = DL.getTypeAllocSize(Ty);
-  Builder.CreateMemCpy(DestGEP, SrcGEP, size, size);
+  Builder.CreateMemCpy(DestGEP, SrcGEP, size, /* Align */ 1);
 }
 
 static bool IsMemCpyTy(Type *Ty, DxilTypeSystem &typeSys) {
@@ -3346,9 +3346,7 @@ static void ReplaceMemcpy(Value *V, Value *Src, MemCpyInst *MC,
         const DataLayout &DL = SrcBCI->getModule()->getDataLayout();
         unsigned SrcSize = DL.getTypeAllocSize(
             SrcBCI->getOperand(0)->getType()->getPointerElementType());
-        unsigned MemcpySize =
-            cast<ConstantInt>(MC->getLength())->getZExtValue() *
-            MC->getAlignment();
+        unsigned MemcpySize = cast<ConstantInt>(MC->getLength())->getZExtValue();
         if (SrcSize != MemcpySize) {
           DXASSERT(0, "Cannot handle partial memcpy");
           return;