[clang] [Clang] Track alloca element types to avoid getAllocatedType() calls (PR #181740)

[Oliver Hunt via cfe-commits]

================
@@ -992,12 +993,13 @@ void CGHLSLRuntime::emitEntryFunction(const FunctionDecl *FD,
   CI->setCallingConv(Fn->getCallingConv());
 
   if (Fn->getReturnType() != CGM.VoidTy)
-    OutputSemantic.try_emplace(FD, CI);
+    OutputSemantic.try_emplace(FD, std::make_pair(CI, /*unused*/ nullptr));
----------------
ojhunt wrote:

yes, but this is the tuple constructor for what is semantically (ha!) this:
```cpp
struct OutputSemantic { // I recognize this conflicts with the semantic set name, but I think that should be plural :D
Value *Source;
Type *ElementType;
  OutputSemantic(Value *Source, Type *ElementType) ///
}
```

In which case the style would be `OutputSemantic(CI, /*ElementType=*/nullptr)`

it wouldn't be `/*unused*/`

https://github.com/llvm/llvm-project/pull/181740