[Clang][Sema] Fix a SemaType/VisitTagTypeLoc assertion

[yonghong-song]

Summary

Patch [1] added btf_type_tag attribute support. In particular,
in class TypeSpecLocFiller, it permitted to visit pointee's
of a PointerTypeLoc. This caused a behavior change outside
of the btf_type_tag area. Saleem Abdulrasool reported that
assertion would happen for the following code:

struct dispatch_object_s;
void *_dispatch_queue_get_head(struct dispatch_object_s * volatile dq_items_head) {

return (void *)(_Atomic __typeof__(dq_items_head) *)dq_items_head;

}

The following is what happened:

...   
1. In Parse/ParseDecl.cpp, ParseTypeofSpecifier() is called to handle typeof
   specifier. DeclSpec is set to TST_typeofExpr.
2. Later, in Sema/SemaType.cpp,
   TypeSpecLocFiller(S, S.Context, State, D.getDeclSpec()).Visit(CurrTL)
   is called.
3. The specific types visited in the following order:
   VisitAtomicTypeLoc()
   VisitPointerTypeLoc()
   VisitElaboratedTypeLo()c
   VisitTagTypeLoc()

During VisitTagTypeLoc(), since DeclSpec is TST_typeofExpr, this will cause
assertion error in DS.getTypeSpecTypeNameLoc().

clang: /home/yhs/work/llvm-project/clang/include/clang/Sema/DeclSpec.h:519:
  clang::SourceLocation clang::DeclSpec::getTypeSpecTypeNameLoc() const:
  Assertion `isDeclRep((TST) TypeSpecType) || TypeSpecType == TST_typename' failed.

If we remove the _Atomic in the above code like

struct dispatch_object_s;
void *_dispatch_queue_get_head(struct dispatch_object_s * volatile dq_items_head) {

return (void *)(_Atomic __typeof__(dq_items_head) *)dq_items_head;

}

The above step 3 will have VisitTypeOfExprTypeLoc() and no assertion happens.

To fix the issue, in VisitTagTypeLoc(), let us not do DS.getTypeSpecTypeNameLoc()
if the DeclSpec is TST_typeofExpr.

[1] https://reviews.llvm.org/D111199

[yonghong-song]

@compnerd provided a better fix https://reviews.llvm.org/D126093, so I am going to close this one.

clang/lib/Sema/SemaType.cpp

void VisitAutoTypeLoc(AutoTypeLoc TL) {
       TemplateArgumentListInfo TemplateArgsInfo;
       ASTTemplateArgsPtr TemplateArgsPtr(TemplateId->getTemplateArgs(),
                                          TemplateId->NumArgs);
       SemaRef.translateTemplateArguments(TemplateArgsPtr, TemplateArgsInfo);
       for (unsigned I = 0; I < TemplateId->NumArgs; ++I)
         TL.setArgLocInfo(I, TemplateArgsInfo.arguments()[I].getLocInfo());
     }
     void VisitTagTypeLoc(TagTypeLoc TL) {
+      if (DS.getTypeSpecType() != DeclSpec::TST_typeofExpr)
         TL.setNameLoc(DS.getTypeSpecTypeNameLoc());
     }
     void VisitAtomicTypeLoc(AtomicTypeLoc TL) {
       // An AtomicTypeLoc can come from either an _Atomic(...) type specifier
       // or an _Atomic qualifier.
       if (DS.getTypeSpecType() == DeclSpec::TST_atomic) {
         TL.setKWLoc(DS.getTypeSpecTypeLoc());
         TL.setParensRange(DS.getTypeofParensRange());
 

clang/test/Sema/atomic-typeof.c

+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c11 -x c %s
+
+struct dispatch_object_s;
+void _dispatch_queue_get_head(struct dispatch_object_s * volatile dq_items_head) {
+  (_Atomic __typeof__(dq_items_head) *)dq_items_head;
+}