Clang frontend C++ crash with atomic constraints

[brutalsavage]

To quickly reproduce: https://gcc.godbolt.org/z/Gc1Y17PKf (assertion-trunk)

#include <concepts>
#include <iostream>

template <typename T>
concept Iterator = requires(T a) {
  { a } -> std::same_as<T>;
};

template <typename T>
concept Container = requires(T a) {
  { std::end } -> Iterator;
};

Compiling the above code crashes clang clang++ -x c++ --std=c++20 , crashes locally using clang-17.0 (a10019a), also on trunk with assertion (see godbolt link)

[brutalsavage]

Assertion

clang++: /root/llvm-project/clang/lib/AST/ASTContext.cpp:3442: 
clang::QualType clang::ASTContext::getLValueReferenceType(clang::QualType, bool) const: 
Assertion `(!T->isPlaceholderType() || T->isSpecificPlaceholderType(BuiltinType::UnknownAny)) && "Unresolved placeholder 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 --std=c++20 <source>
1.	<source>:11:19: at annotation token
 #0 0x00000000036be0a8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x36be0a8)
 #1 0x00000000036bbd6c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x36bbd6c)
 #2 0x0000000003605128 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f0782c58420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00007f078271b00b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #5 0x00007f07826fa859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #6 0x00007f07826fa729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #7 0x00007f078270bfd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #8 0x0000000006cafa23 clang::ASTContext::getLValueReferenceType(clang::QualType, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6cafa23)
 #9 0x000000000647bddc clang::Sema::BuildExprRequirement(clang::Expr*, bool, clang::SourceLocation, clang::concepts::ExprRequirement::ReturnTypeRequirement) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x647bddc)
#10 0x000000000647c739 clang::Sema::ActOnCompoundRequirement(clang::Expr*, clang::SourceLocation, clang::CXXScopeSpec&, clang::TemplateIdAnnotation*, unsigned int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x647c739)
#11 0x0000000005e90b7d clang::Parser::ParseRequiresExpression() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e90b7d)
#12 0x0000000005e7d5d7 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e7d5d7)
#13 0x0000000005e8ba76 clang::Parser::ParseConstraintExpression() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e8ba76)
#14 0x0000000005f0f18c clang::Parser::ParseConceptDefinition(clang::Parser::ParsedTemplateInfo const&, clang::SourceLocation&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f0f18c)
#15 0x0000000005f18959 clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#16 0x0000000005f18b63 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f18b63)
#17 0x0000000005e56830 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e56830)
#18 0x0000000005e21694 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e21694)
#19 0x0000000005e2257d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e2257d)
#20 0x0000000005e168da clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e168da)
#21 0x000000000491e758 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x491e758)
#22 0x00000000041862e9 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41862e9)
#23 0x00000000041070ee clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41070ee)
#24 0x000000000426562e clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x426562e)
#25 0x0000000000bd9f7e cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd9f7e)
#26 0x0000000000bd1b0a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#27 0x0000000003f685a9 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
#28 0x00000000036055d4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x36055d4)
#29 0x0000000003f68b9f 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
#30 0x0000000003f30ee5 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f30ee5)
#31 0x0000000003f3194d 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+++0x3f3194d)
#32 0x0000000003f39875 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f39875)
#33 0x0000000000bd76ec clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd76ec)
#34 0x0000000000ad3ad1 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xad3ad1)
#35 0x00007f07826fc083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#36 0x0000000000bd15ee _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd15ee)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

[cor3ntin]

@erichkeane

[llvmbot]

@llvm/issue-subscribers-clang-frontend

To quickly reproduce: https://gcc.godbolt.org/z/Gc1Y17PKf (assertion-trunk)

#include <concepts>
#include <iostream>

template <typename T>
concept Iterator = requires(T a) {
  { a } -> std::same_as<T>;
};

template <typename T>
concept Container = requires(T a) {
  { std::end } -> Iterator;
};

Compiling the above code crashes clang clang++ -x c++ --std=c++20 , crashes locally using clang-17.0 (a10019a), also on trunk with assertion (see godbolt link)

[erichkeane]

Reduced to not require the STL: https://gcc.godbolt.org/z/1qa5nbhMd

template<typename C>
auto end(C& c) ->decltype(c.end());

template <typename T>
concept Iterator = requires(T a) {
  { a };
};
template <typename CT>
concept Container = requires(CT b) {
  { end } -> Iterator;
};

[erichkeane]

Further simplified to: https://gcc.godbolt.org/z/s1x3bqdbb (plus added a static-assert).

I changed the BuildExprRequirement function to consider the placeholder type as a dependent expression, which produces the same error as above. I've put a commit up for review here: #66683