[clang] [HLSL] Implement HLSL Flat casting (excluding splat cases) (PR #118842)

[Justin Bogner via cfe-commits]

================
@@ -6358,3 +6359,81 @@ RValue CodeGenFunction::EmitPseudoObjectRValue(const PseudoObjectExpr *E,
 LValue CodeGenFunction::EmitPseudoObjectLValue(const PseudoObjectExpr *E) {
   return emitPseudoObjectExpr(*this, E, true, AggValueSlot::ignored()).LV;
 }
+
+void CodeGenFunction::FlattenAccessAndType(
+    Address Addr, QualType AddrType,
+    SmallVectorImpl<std::pair<Address, llvm::Value *>> &AccessList,
+    SmallVectorImpl<QualType> &FlatTypes) {
+  // WorkList is list of type we are processing + the Index List to access
+  // the field of that type in Addr for use in a GEP
+  llvm::SmallVector<std::pair<QualType, llvm::SmallVector<llvm::Value *, 4>>,
+                    16>
+      WorkList;
+  llvm::IntegerType *IdxTy = llvm::IntegerType::get(getLLVMContext(), 32);
+  WorkList.push_back(
+      {AddrType,
+       {llvm::ConstantInt::get(
+           IdxTy,
+           0)}}); // Addr should be a pointer so we need to 'dereference' it
----------------
bogner wrote:

nit: clang-format struggles with comments at the end of a line like this, I'd probably write this like:
```suggestion
  // Addr should be a pointer so we need to 'dereference' it
  WorkList.push_back({AddrType, {llvm::ConstantInt::get(IdxTy, 0)}});
```

https://github.com/llvm/llvm-project/pull/118842