[clang] [HLSL] Implement HLSL splatting (PR #118992)

[Ashley Coleman via cfe-commits]

================
@@ -491,6 +491,31 @@ static bool isTrivialFiller(Expr *E) {
   return false;
 }
 
+static void EmitHLSLSplatCast(CodeGenFunction &CGF, Address DestVal,
+                              QualType DestTy, llvm::Value *SrcVal,
+                              QualType SrcTy, SourceLocation Loc) {
+  // Flatten our destination
+  SmallVector<QualType> DestTypes; // Flattened type
+  SmallVector<std::pair<Address, llvm::Value *>, 16> StoreGEPList;
+  // ^^ Flattened accesses to DestVal we want to store into
+  CGF.FlattenAccessAndType(DestVal, DestTy, StoreGEPList, DestTypes);
+
+  assert(SrcTy->isScalarType() && "Invalid HLSL splat cast.");
+  for (unsigned I = 0, Size = StoreGEPList.size(); I < Size; I++) {
----------------
V-FEXrt wrote:

```suggestion
  for (unsigned I = 0, Size = StoreGEPList.size(); I < Size; ++I) {
```

Very small nit but the style guide says to prefer pre-increment https://llvm.org/docs/CodingStandards.html#prefer-preincrement

https://github.com/llvm/llvm-project/pull/118992