[clang][Sema] Fix a clang crash with btf_type_tag

For the following program,
  $ cat t.c
  struct t {
   int (__attribute__((btf_type_tag("rcu"))) *f)();
   int a;
  };
  int foo(struct t *arg) {
    return arg->a;
  }
Compiling with 'clang -g -O2 -S t.c' will cause a failure like below:
  clang: /home/yhs/work/llvm-project/clang/lib/Sema/SemaType.cpp:6391: void {anonymous}::DeclaratorLocFiller::VisitParenTypeLoc(clang::ParenTypeLoc):
         Assertion `Chunk.Kind == DeclaratorChunk::Paren' failed.
  PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
  Stack dump:
  ......
  rust-lang#5 0x00007f89e4280ea5 abort (/lib64/libc.so.6+0x21ea5)
  rust-lang#6 0x00007f89e4280d79 _nl_load_domain.cold.0 (/lib64/libc.so.6+0x21d79)
  rust-lang#7 0x00007f89e42a6456 (/lib64/libc.so.6+0x47456)
  rust-lang#8 0x00000000045c2596 GetTypeSourceInfoForDeclarator((anonymous namespace)::TypeProcessingState&, clang::QualType, clang::TypeSourceInfo*) SemaType.cpp:0:0
  rust-lang#9 0x00000000045ccfa5 GetFullTypeForDeclarator((anonymous namespace)::TypeProcessingState&, clang::QualType, clang::TypeSourceInfo*) SemaType.cpp:0:0
  ......

The reason of the failure is due to the mismatch of TypeLoc and D.getTypeObject().Kind. For example,
the TypeLoc is
  BTFTagAttributedType 0x88614e0 'int  btf_type_tag(rcu)()' sugar
  |-ParenType 0x8861480 'int ()' sugar
  | `-FunctionNoProtoType 0x8861450 'int ()' cdecl
  |   `-BuiltinType 0x87fd500 'int'
while corresponding D.getTypeObject().Kind points to DeclaratorChunk::Paren, and
this will cause later assertion.

To fix the issue, similar to AttributedTypeLoc, let us skip BTFTagAttributedTypeLoc in
GetTypeSourceInfoForDeclarator().

Differential Revision: https://reviews.llvm.org/D136807

clang/docs/ReleaseNotes.rst

@@ -268,6 +268,8 @@ Bug Fixes
   functions. `Issue 56154 <https://github.com/llvm/llvm-project/issues/56154>`_
 - Fix handling of unexpanded packs in template argument expressions.
   `Issue 58679 <https://github.com/llvm/llvm-project/issues/58679>`_
+- Fix a crash when a ``btf_type_tag`` attribute is applied to the pointee of
+  a function pointer.
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaType.cpp

@@ -6515,6 +6515,9 @@ GetTypeSourceInfoForDeclarator(TypeProcessingState &State,
       CurrTL = TL.getNextTypeLoc().getUnqualifiedLoc();
     }
 
+    while (BTFTagAttributedTypeLoc TL = CurrTL.getAs<BTFTagAttributedTypeLoc>())
+      CurrTL = TL.getNextTypeLoc().getUnqualifiedLoc();
+
     while (DependentAddressSpaceTypeLoc TL =
                CurrTL.getAs<DependentAddressSpaceTypeLoc>()) {
       fillDependentAddressSpaceTypeLoc(TL, D.getTypeObject(i).getAttrs());

clang/test/CodeGen/attr-btf_type_tag-func-ptr.c

@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -triple %itanium_abi_triple -debug-info-kind=limited -S -emit-llvm -o - %s | FileCheck %s
+
+struct t {
+ int (__attribute__((btf_type_tag("rcu"))) *f)();
+ int a;
+};
+int foo(struct t *arg) {
+  return arg->a;
+}
+
+// CHECK:      !DIDerivedType(tag: DW_TAG_member, name: "f"
+// CHECK-SAME: baseType: ![[L18:[0-9]+]]
+// CHECK:      ![[L18]] = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: ![[#]], size: [[#]], annotations: ![[L21:[0-9]+]])
+// CHECK:      ![[L21]] = !{![[L22:[0-9]+]]}
+// CHECK:      ![[L22]] = !{!"btf_type_tag", !"rcu"}