[HLSL] Disallow virtual inheritance and functions (#127346)

This PR disallows virtual inheritance and virtual functions in HLSL.

Author: llvm-beanz

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -1817,5 +1817,9 @@ def ext_hlsl_access_specifiers : ExtWarn<
   InGroup<HLSLExtension>;
 def err_hlsl_unsupported_component : Error<"invalid component '%0' used; expected 'x', 'y', 'z', or 'w'">;
 def err_hlsl_packoffset_invalid_reg : Error<"invalid resource class specifier '%0' for packoffset, expected 'c'">;
+def err_hlsl_virtual_function
+    : Error<"virtual functions are unsupported in HLSL">;
+def err_hlsl_virtual_inheritance
+    : Error<"virtual inheritance is unsupported in HLSL">;
 
 } // end of Parser diagnostics

clang/lib/Parse/ParseDecl.cpp

@@ -4411,6 +4411,10 @@ void Parser::ParseDeclarationSpecifiers(
         DiagID = diag::err_openclcxx_virtual_function;
         PrevSpec = Tok.getIdentifierInfo()->getNameStart();
         isInvalid = true;
+      } else if (getLangOpts().HLSL) {
+        DiagID = diag::err_hlsl_virtual_function;
+        PrevSpec = Tok.getIdentifierInfo()->getNameStart();
+        isInvalid = true;
       } else {
         isInvalid = DS.setFunctionSpecVirtual(Loc, PrevSpec, DiagID);
       }

clang/lib/Parse/ParseDeclCXX.cpp

@@ -2492,6 +2492,9 @@ BaseResult Parser::ParseBaseSpecifier(Decl *ClassDecl) {
     IsVirtual = true;
   }
 
+  if (getLangOpts().HLSL && IsVirtual)
+    Diag(Tok.getLocation(), diag::err_hlsl_virtual_inheritance);
+
   CheckMisplacedCXX11Attribute(Attributes, StartLoc);
 
   // Parse the class-name.

clang/test/SemaHLSL/Language/NoVirtual.hlsl

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.0-compute -verify %s
+
+struct Base {
+  int X;
+  void MemberFunction();  // valid
+  virtual void MemberFunction2(); // expected-error{{virtual functions are unsupported in HLSL}}
+};
+
+struct Derived : virtual Base { // expected-error{{virtual inheritance is unsupported in HLSL}}
+  int Y;
+
+  void MemberFunction2() override; // expected-error{{only virtual member functions can be marked 'override'}}
+};
+