[clang] [HLSL] Allow input semantics on structs (PR #159047)

[Nathan Gauër via cfe-commits]

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@@ -3078,6 +3078,17 @@ static void emitAttributes(const RecordKeeper &Records, raw_ostream &OS,
 
       OS << "  {\n";
 
+      // The generator puts the arguments for each attribute in the child class,
+      // even if those are set in the inherited attribute class (in the TD
+      // file). This means I cannot access those from the parent class, and have
+      // to do this weirdness. Maybe the generator should be changed to
+      // arguments are put in the class they are declared in inside the TD file?
+      if (HLSLSemantic) {
+        OS << "  if (SemanticExplicitIndex)\n";
+        OS << "    setSemanticIndex(SemanticIndex);\n";
+        OS << "  setTargetDecl(Target);\n";
+      }
+
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Keenuts wrote:

Those are already added to the parent class (see `Attr.h`). This is to add the proper parent class field initialization in the ctor this generates.
(Otherwise, if I declared them in the TD file, those wouldn't be added to the parent class, but to each children, meaning I wouldn't be able to access those from the parent class `HLSLSemanticAttr` which defeats the point of inheriting).

note: this comment assumes we move ahead with the inherited attribute semantic bit this PR has. This is something we'll have to design if we decide to go with a different model like "textual semantic attr with no semantic" and then a "shader I/O attr" once sema gave semantic a meaning.

https://github.com/llvm/llvm-project/pull/159047