[clang] [HLSL] Implement output parameter (PR #101083)

[Chris B via cfe-commits]

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@@ -4057,6 +4057,10 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, NamedDecl *&OldD, Scope *S,
                                                          NewQType))
       return MergeCompatibleFunctionDecls(New, Old, S, MergeTypeWithOld);
 
+    if (getLangOpts().HLSL && Context.hasSameFunctionTypeIgnoringParamABI(
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llvm-beanz wrote:

That's correct. We detect and diagnose the mismatch through `mergeParamDeclAttributes`, which gets called by `MergeCompatabileFunctionDecls`, so we need to allow the merge call to proceed even for cases here that might be invalid.

Alternatively we could move that diagnostic out somewhere earlier.

https://github.com/llvm/llvm-project/pull/101083