[clang] [HLSL][RootSignature] Define and integrate rootsig clang attr and decl (PR #137690)

[Chris B via cfe-commits]

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@@ -949,6 +950,23 @@ void SemaHLSL::emitLogicalOperatorFixIt(Expr *LHS, Expr *RHS,
       << NewFnName << FixItHint::CreateReplacement(FullRange, OS.str());
 }
 
+void SemaHLSL::handleRootSignatureAttr(Decl *D, const ParsedAttr &AL) {
+  if (AL.getNumArgs() != 1) {
+    Diag(AL.getLoc(), diag::err_attribute_wrong_number_arguments) << AL << 1;
+    return;
+  }
+
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llvm-beanz wrote:

We should only allow the attribute to appear more than once if it is the same root signature. Mismatching root signature attributes should be an error (err_disallowed_duplicate_attribute), and duplicate but identical attributes a warning (warn_duplicate_attribute_exact).

https://github.com/llvm/llvm-project/pull/137690