Clang crashed on compiling some constexpr templated code

[AirFig]

Crash is reproduced here: https://godbolt.org/z/vfbjEEq7d

[llvmbot]

@llvm/issue-subscribers-clang-codegen

[llvmbot]

@llvm/issue-subscribers-c-20

[inclyc]

See assertion trunk: https://godbolt.org/z/1qqneG51Y

Assertion `!isDependentType() && "This doesn't make sense for dependent types"' failed.

[shafik]

Much reduced reproducer, see godbolt: https://godbolt.org/z/vod14q9nP

template<auto>
class F {};

template<typename D=int>
F<[](){}> E() {
    return {};
}

int main() {
    static auto f = E();
}

[shafik]

If we remove the static from the declaration in main we obtain a different assertion, see godbolt: https://godbolt.org/z/P944993dE

template<auto>
class F {};

template<typename D=int>
F<[](){}> E() {
    return {};
}

int main() {
     auto f = E();
}

Backtrace:

clang++: /root/llvm-project/clang/lib/AST/ASTContext.cpp:2354: clang::TypeInfo clang::ASTContext::getTypeInfoImpl(const clang::Type*) const: Assertion `!A->getDeducedType().isNull() && "cannot request the size of an undeduced or dependent auto type"' 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:
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.	<eof> parser at end of file
2.	<source>:9:5: LLVM IR generation of declaration 'main'
3.	<source>:9:5: Generating code for declaration 'main'
 #0 0x000055b82e5cd684 PrintStackTraceSignalHandler(void*) Signals.cpp:0:0
 #1 0x000055b82e5cb42c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f6d42c)
 #2 0x000055b82e5023b8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007feca177e420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00007feca124b00b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #5 0x00007feca122a859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #6 0x00007feca122a729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #7 0x00007feca123bfd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #8 0x000055b831904a2d clang::ASTContext::getTypeInfoImpl(clang::Type const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x72a6a2d)
 #9 0x000055b83190447f clang::ASTContext::getTypeInfo(clang::Type const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x72a647f)
#10 0x000055b831914473 clang::ASTContext::getPreferredTypeAlign(clang::Type const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x72b6473)
#11 0x000055b831914d4b clang::ASTContext::getDeclAlign(clang::Decl const*, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x72b6d4b)
#12 0x000055b82ed99f6b clang::CodeGen::CodeGenFunction::EmitAutoVarAlloca(clang::VarDecl const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x473bf6b)
#13 0x000055b82ed9b007 clang::CodeGen::CodeGenFunction::EmitVarDecl(clang::VarDecl const&) (.part.0) CGDecl.cpp:0:0
#14 0x000055b82ed9b2d0 clang::CodeGen::CodeGenFunction::EmitDecl(clang::Decl const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x473d2d0)
#15 0x000055b82ea348e7 clang::CodeGen::CodeGenFunction::EmitDeclStmt(clang::DeclStmt const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43d68e7)
#16 0x000055b82ea486a7 clang::CodeGen::CodeGenFunction::EmitSimpleStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43ea6a7)
#17 0x000055b82ea41c6c clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43e3c6c)
#18 0x000055b82ea47fa4 clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43e9fa4)
#19 0x000055b82eaa60ee clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44480ee)
#20 0x000055b82eab8614 clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x445a614)
#21 0x000055b82eb16c94 clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44b8c94)
#22 0x000055b82eb11f55 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44b3f55)
#23 0x000055b82eb125f3 clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44b45f3)
#24 0x000055b82eb1bcf2 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#25 0x000055b82f8e9409 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#26 0x000055b82f8db530 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x527d530)
#27 0x000055b830b421c4 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x64e41c4)
#28 0x000055b82f8e6328 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5288328)
#29 0x000055b82f17fe69 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4b21e69)
#30 0x000055b82f10762e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4aa962e)
#31 0x000055b82f265413 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c07413)
#32 0x000055b82ba82df4 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x1424df4)
#33 0x000055b82ba7bed8 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) driver.cpp:0:0
#34 0x000055b82ef76779 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#35 0x000055b82e502b5a llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ea4b5a)
#36 0x000055b82ef76fcf clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#37 0x000055b82ef41909 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48e3909)
#38 0x000055b82ef4238d 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+++0x48e438d)
#39 0x000055b82ef4be2c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48ede2c)
#40 0x000055b82ba811d3 clang_main(int, char**) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x14231d3)
#41 0x00007feca122c083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#42 0x000055b82ba7bace _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x141dace)
clang-16: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

and this assert looks like: #53510

but at this point it looks like two bugs since they are failing in different places.

[shafik]

I think both of these are failing b/c we don't fully implement Lambdas in unevaluated contexts see the clang status page: https://clang.llvm.org/cxx_status.html

I believe we should be issuing a diagnostic rather than attempting to codegen this code.

[cor3ntin]

@shafik There are multiple issues, with unevaluated lambdas, the partial implementation and the fact that the implementation is junky.

The core problem i was never able to resolve is that the type of a lambda isn't just a transform, it creates a new type. Which afaik is fairly unique, other records are just transformed.

That newly created type is being created in the wrong context, and end up being (incorrectly) dependant as a result, leading to these asserts down the line.
But the correct context doesn't yet exist at this point, so there is a chicken and egg problem.

That's the gist of it, but I would have to looked into it again to give you more details.
Looking up and down the call stack from TransformLambdaExpr should give you a starting point.

I think someone said they would look into it a couple of months ago.

The partial implementation is completely unrelated, we compile ill-formed code https://godbolt.org/z/dj1344f37

[shafik]

Related to #57170 and #57155