Clang frontend C++ crash with variadic templates in function args

[brutalsavage]

To quickly reproduce: https://gcc.godbolt.org/z/E6ceGq5eP (assertion-trunk)

#include <concepts>

template <typename... T>
void f1(bool B = (std::integral<T> ||...)) {
}

Compiling the above valid code crashes clang clang++ -x c++ --std=c++20 , crashes locally using clang-17.0 (a10019a), also on trunk with assertion (see godbolt link). Furthermore, GCC compiles the above code without any issue (see godbolt link)

[brutalsavage]

Assertion

clang++: /root/llvm-project/llvm/include/llvm/Support/Casting.h:662: 
decltype(auto) llvm::dyn_cast(From*) [with To = clang::BinaryOperator; From = const clang::Stmt]: 
Assertion `detail::isPresent(Val) && "dyn_cast on a non-existent value"' 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 --std=c++20 <source>
1.	<source>:4:42: current parser token ')'
 #0 0x00000000037000b8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x37000b8)
 #1 0x00000000036fdd7c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x36fdd7c)
 #2 0x0000000003646908 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007fc9941d0420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00007fc993c9300b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #5 0x00007fc993c72859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #6 0x00007fc993c72729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #7 0x00007fc993c83fd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #8 0x00000000062679f1 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::CheckDefaultArgumentVisitor, bool>::Visit(clang::Stmt const*) SemaDeclCXX.cpp:0:0
 #9 0x0000000006267f94 (anonymous namespace)::CheckDefaultArgumentVisitor::VisitExpr(clang::Expr const*) SemaDeclCXX.cpp:0:0
#10 0x00000000062675f1 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::CheckDefaultArgumentVisitor, bool>::Visit(clang::Stmt const*) SemaDeclCXX.cpp:0:0
#11 0x0000000006267d64 clang::Sema::ActOnParamDefaultArgument(clang::Decl*, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6267d64)
#12 0x0000000005ea345d clang::Parser::ParseParameterDeclarationClause(clang::DeclaratorContext, clang::ParsedAttributes&, llvm::SmallVectorImpl<clang::DeclaratorChunk::ParamInfo>&, clang::SourceLocation&, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ea345d)
#13 0x0000000005ea3f78 clang::Parser::ParseFunctionDeclarator(clang::Declarator&, clang::ParsedAttributes&, clang::BalancedDelimiterTracker&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ea3f78)
#14 0x0000000005ea7c5f clang::Parser::ParseDirectDeclarator(clang::Declarator&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ea7c5f)
#15 0x0000000005e96e50 clang::Parser::ParseDeclaratorInternal(clang::Declarator&, void (clang::Parser::*)(clang::Declarator&)) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e96e50)
#16 0x0000000005fb5111 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5fb5111)
#17 0x0000000005e8690f clang::Parser::ParseDeclarator(clang::Declarator&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e8690f)
#18 0x0000000005f5e822 clang::Parser::ParseSingleDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo const&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f5e822)
#19 0x0000000005f648c8 clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#20 0x0000000005f64b83 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f64b83)
#21 0x0000000005ea28bb clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ea28bb)
#22 0x0000000005e6d6c4 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6d6c4)
#23 0x0000000005e6e5cd clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6e5cd)
#24 0x0000000005e6290a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6290a)
#25 0x0000000004966c88 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4966c88)
#26 0x00000000041cd289 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41cd289)
#27 0x000000000414dfde clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x414dfde)
#28 0x00000000042ac50e clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42ac50e)
#29 0x0000000000bdc4b6 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbdc4b6)
#30 0x0000000000bd3d7a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#31 0x0000000003fabcc9 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 0x0000000003646db4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3646db4)
#33 0x0000000003fac2bf 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 0x0000000003f74605 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f74605)
#35 0x0000000003f7506d 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+++0x3f7506d)
#36 0x0000000003f7cf95 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f7cf95)
#37 0x0000000000bd995c clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd995c)
#38 0x0000000000ad4821 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xad4821)
#39 0x00007fc993c74083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#40 0x0000000000bd385e _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd385e)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

[llvmbot]

@llvm/issue-subscribers-clang-frontend

To quickly reproduce: https://gcc.godbolt.org/z/E6ceGq5eP (assertion-trunk)

#include <concepts>

template <typename... T>
void f1(bool B = (std::integral<T> ||...)) {
}

Compiling the above valid code crashes clang clang++ -x c++ --std=c++20 , crashes locally using clang-17.0 (a10019a), also on trunk with assertion (see godbolt link). Furthermore, GCC compiles the above code without any issue (see godbolt link)

[shafik]

Removed need for header: https://gcc.godbolt.org/z/oGnvae7KK

template <typename T>
concept C = true;

template <typename... T>
void f1(bool B = (C<T> || ...)) {
}

[shafik]

When I dump the CXXFoldExpr, we have this:

CXXFoldExpr 0x10f873d08 '<dependent type>'
|-<<<NULL>>>
|-ConceptSpecializationExpr 0x10f873ce0 '_Bool' Concept 0x10f873a78 'C'
| |-ImplicitConceptSpecializationDecl 0x10f873c28 
| | `-TemplateArgument type 'type-parameter-0-0'
| |   `-TemplateTypeParmType 0x10f873b20 'type-parameter-0-0' dependent contains_unexpanded_pack depth 0 index 0 pack
| `-TemplateArgument type 'T'
|   `-TemplateTypeParmType 0x10f873b50 'T' dependent contains_unexpanded_pack depth 0 index 0 pack
|     `-TemplateTypeParm 0x10f873ac8 'T'
`-<<<NULL>>>

but here:

llvm-project/clang/lib/Sema/SemaDeclCXX.cpp

Lines 86 to 89 in ebfea26

	bool CheckDefaultArgumentVisitor::VisitExpr(const Expr *Node) {
	bool IsInvalid = false;
	for (const Stmt *SubStmt : Node->children())
	IsInvalid |= Visit(SubStmt);

we iterate over the children as if they can not be NULL which from what it looks like looking at other visitors that is not a correct assumption.

[shafik]

Simplified to not require concepts:

template <typename>
bool f();

template <typename... T>
void g(bool = (f<T>() || ...));