[clang] [HLSL] Rewrite semantics parsing (PR #152537)

[Chris B via cfe-commits]

================
@@ -232,6 +232,41 @@ class HLSLAnnotationAttr : public InheritableAttr {
   }
 };
 
+class HLSLSemanticAttr : public HLSLAnnotationAttr {
+  unsigned SemanticIndex : 30;
----------------
llvm-beanz wrote:

I was trying to figure out if we had any documentation on the valid ranges for this. It looks like DXC does allow a 32-bit integer, and while I hope to god that nobody is actually doing this it seems to work up to UINT32_MAX:

https://godbolt.org/z/eEazEbfrM

It probably won't hurt us to give a full 32-bit integer for the semantic index and have the bools be an extra bitfield.

https://github.com/llvm/llvm-project/pull/152537