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

[Chris B via cfe-commits]

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@@ -172,6 +193,9 @@ class CGHLSLRuntime {
   llvm::Triple::ArchType getArch();
 
   llvm::DenseMap<const clang::RecordType *, llvm::TargetExtType *> LayoutTypes;
+
+  std::unordered_set<std::string> ActiveInputSemantics;
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llvm-beanz wrote:

> We never use containers like unordered_set because they are generally very expensive (each insertion requires a malloc).

(source: https://www.llvm.org/docs/ProgrammersManual.html#other-set-like-container-options)

This can probably instead be an `llvm::StringSet`, although I also don't see where these are used, so maybe we don't need them?

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