Clang frontend C++ crash on invalid code when using some built-in type traits

[brutalsavage]

To quickly reproduce: https://gcc.godbolt.org/z/K1sTM53s7

#include <type_traits>
#include <cstddef>

enum Day {
    sunday, monday, tuesday, wednesday,
    thursday, friday, saturday
};

class A {};

int main() {
   std::__add_rvalue_reference<A>::type ptr; // swap __add_rvalue_reference for (__add_pointer or __add_rvalue_reference) also leads to same crash
}

Compiling the above invalid code crashes clang clang++ -x c++ -std=c++23, crashes locally using clang-17.0 (a10019a), also on trunk (see godbolt link)

Note: Also tested with other built-in type traits like __add_pointer and __add_rvalue_reference and also leads to the same crash. Not sure if there could be more.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[shafik]

Confirmed: https://gcc.godbolt.org/z/acjqT9dEv

Potentially related to: #48673

Assertion:

clang++: /root/llvm-project/llvm/include/llvm/Support/Casting.h:578:
decltype(auto) llvm::cast(From*) [with To = clang::FunctionTemplateDecl; From = clang::NamedDecl]:
Assertion `isa<To>(Val) && "cast<Ty>() argument of incompatible type!"' failed.

Backtrace:

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:
0.	Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics <source>
1.	<source>:12:34: current parser token '::'
2.	<source>:11:12: parsing function body 'main'
3.	<source>:11:12: in compound statement ('{}')
 #0 0x00005587f6cf424f llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3c2824f)
 #1 0x00005587f6cf1fbc llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3c25fbc)
 #2 0x00005587f6c3b3b8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f29ff9d0420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00007f29ff49d00b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #5 0x00007f29ff47c859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #6 0x00007f29ff47c729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #7 0x00007f29ff48dfd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #8 0x00005587f9d49f66 clang::Sema::ResolveSingleFunctionTemplateSpecialization(clang::OverloadExpr*, bool, clang::DeclAccessPair*, clang::TemplateSpecCandidateSet*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c7df66)
 #9 0x00005587f9d4a056 clang::Sema::ResolveAndFixSingleFunctionTemplateSpecialization(clang::ActionResult<clang::Expr*, true>&, bool, bool, clang::SourceRange, clang::QualType, unsigned int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c7e056)
#10 0x00005587f99a8f8e clang::Sema::CheckPlaceholderExpr(clang::Expr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68dcf8e)
#11 0x00005587f9b09f33 clang::Sema::ActOnFinishFullExpr(clang::Expr*, clang::SourceLocation, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a3df33)
#12 0x00005587f9d8f22e clang::Sema::ActOnExprStmt(clang::ActionResult<clang::Expr*, true>, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6cc322e)
#13 0x00005587f95337e1 clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x64677e1)
#14 0x00005587f9529ab3 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x645dab3)
#15 0x00005587f952a9b1 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x645e9b1)
#16 0x00005587f952b9a9 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x645f9a9)
#17 0x00005587f952d35a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x646135a)
#18 0x00005587f9457e81 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x638be81)
#19 0x00005587f947ed90 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x63b2d90)
#20 0x00005587f944b721 clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x637f721)
#21 0x00005587f944bfdf clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (.part.0) Parser.cpp:0:0
#22 0x00005587f9452981 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6386981)
#23 0x00005587f94532f6 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x63872f6)
#24 0x00005587f94470ba clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x637b0ba)
#25 0x00005587f7f47598 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4e7b598)
#26 0x00005587f7797c79 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x46cbc79)
#27 0x00005587f771c316 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4650316)
#28 0x00005587f787a0b6 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47ae0b6)
#29 0x00005587f419d16d cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x10d116d)
#30 0x00005587f4198e6a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#31 0x00005587f7584c1d void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#32 0x00005587f6c3b8c0 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b6f8c0)
#33 0x00005587f758523f clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#34 0x00005587f754ca1c clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4480a1c)
#35 0x00005587f754d4ad clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44814ad)
#36 0x00005587f755558d clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x448958d)
#37 0x00005587f419b3ca clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x10cf3ca)
#38 0x00005587f40a22b5 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xfd62b5)
#39 0x00007f29ff47e083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#40 0x00005587f4193c4e _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x10c7c4e)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

[shafik]

A couple of tips. If it does not require a specific standard version to crash then it is better to report without referring to a specific standard.

It is often helpful to check using assertions trunk since the backtrace can look very different with assertions and often this gives us a better clue to what is going on and can help to track down duplicates.

Including he assertion and backtrace as I did above can be very helpful as well.

[brutalsavage]

Noted, thanks for the tips!