[Sema] Fix reporting of invalid shader attribute on HLSL entry function

If the HLSL entry function had a shader attribute that conflicted
with the pipeline stage specified in the target triple, Clang
would emit:

   error: (null) attribute parameters do not match the previous declaration
   conflicting attribute is here

(where the second line doesn't reference an attribute).

This was because the code constructed a dummy attribute that had
only a source location, but no kind or syntax.

Noticed while doing some changes to the attribute handling.

Differential Revision: https://reviews.llvm.org/D147657

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -11752,6 +11752,8 @@ def err_hlsl_attr_invalid_type : Error<
    "attribute %0 only applies to a field or parameter of type '%1'">;
 def err_hlsl_attr_invalid_ast_node : Error<
    "attribute %0 only applies to %1">;
+def err_hlsl_entry_shader_attr_mismatch : Error<
+   "%0 attribute on entry function does not match the pipeline stage">;
 def err_hlsl_numthreads_argument_oor : Error<"argument '%select{X|Y|Z}0' to numthreads attribute cannot exceed %1">;
 def err_hlsl_numthreads_invalid : Error<"total number of threads cannot exceed %0">;
 def err_hlsl_missing_numthreads : Error<"missing numthreads attribute for %0 shader entry">;

clang/lib/Sema/SemaDecl.cpp

@@ -10205,14 +10205,19 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
       CheckHLSLEntryPoint(NewFD);
       if (!NewFD->isInvalidDecl()) {
         auto Env = TargetInfo.getTriple().getEnvironment();
-        AttributeCommonInfo AL(NewFD->getBeginLoc());
         HLSLShaderAttr::ShaderType ShaderType =
             static_cast<HLSLShaderAttr::ShaderType>(
                 hlsl::getStageFromEnvironment(Env));
         // To share code with HLSLShaderAttr, add HLSLShaderAttr to entry
         // function.
-        if (HLSLShaderAttr *Attr = mergeHLSLShaderAttr(NewFD, AL, ShaderType))
-          NewFD->addAttr(Attr);
+        if (HLSLShaderAttr *NT = NewFD->getAttr<HLSLShaderAttr>()) {
+          if (NT->getType() != ShaderType)
+            Diag(NT->getLocation(), diag::err_hlsl_entry_shader_attr_mismatch)
+                << NT;
+        } else {
+          NewFD->addAttr(HLSLShaderAttr::Create(Context, ShaderType,
+                                                NewFD->getBeginLoc()));
+        }
       }
     }
     // HLSL does not support specifying an address space on a function return

clang/test/SemaHLSL/entry_shader.hlsl

@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-compute -x hlsl -hlsl-entry foo  -o - %s -DSHADER='"anyHit"' -verify
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-compute -x hlsl -hlsl-entry foo  -o - %s -DSHADER='"compute"'
+
+// expected-error@+1 {{'shader' attribute on entry function does not match the pipeline stage}}
+[numthreads(1,1,1), shader(SHADER)]
+void foo() {
+
+}