[clang] Crash in release mode and assertion fail in build with asserts when compiling for Windows with -std=c++17

[Fznamznon]

Code

struct a { int j; };
template<int a::* i> void g_() { }
void bar() {
  g_< (int a::*)0 >();
}

Additional options required: -target x86_64-windows -std=c++17

godbolt demo https://godbolt.org/z/GcMGcW4PE

Seems like clang 21 regression.

Triage notes:

1. The assertion message is:

clang++: /root/llvm-project/llvm/tools/clang/lib/AST/MicrosoftCXXABI.cpp:234: clang::MSInheritanceModel clang::CXXRecordDecl::getMSInheritanceModel() const: Assertion `IA && "Expected MSInheritanceAttr on the CXXRecordDecl!"' failed.

Seems MSInheritanceAttr is missing.

2. The attribute is added in assignInheritanceModel function defined in SemaType.cpp if the sample is compiled in C++14 mode. We never enter it when compiling in C++17 mode. The codepath to assignInheritanceModel leads through Sema::CheckTemplateArgument and then CheckTemplateArgumentPointerToMember. In C++17 mode we exit from Sema::CheckTemplateArgument earlier and never call assignInheritanceModel

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Mariya Podchishchaeva (Fznamznon)

Code

struct a { int j; };
template<int a::* i> void g_() { }
void bar() {
  g_< (int a::*)0 >();
}

Additional options required: -target x86_64-windows -std=c++17

godbolt demo https://godbolt.org/z/GcMGcW4PE

Seems like clang 21 regression.

Triage notes:

1. The assertion message is:

clang++: /root/llvm-project/llvm/tools/clang/lib/AST/MicrosoftCXXABI.cpp:234: clang::MSInheritanceModel clang::CXXRecordDecl::getMSInheritanceModel() const: Assertion `IA && "Expected MSInheritanceAttr on the CXXRecordDecl!"' failed.

Seems MSInheritanceAttr is missing.

2. The attribute is added in assignInheritanceModel function defined in SemaType.cpp if the sample is compiled in C++14 mode. We never enter it when compiling in C++17 mode. The codepath to assignInheritanceModel leads though Sema::CheckTemplateArgument and then CheckTemplateArgumentPointerToMember. In C++17 mode we exit from Sema::CheckTemplateArgument earlier and never call assignInheritanceModel

[shafik]

@mizvekov this bisect down to 6003c30