clang++ crashes with constexpr address of label stuff

clang++ 23.1.0 https://mirrors.edge.kernel.org/pub/tools/llvm/files/llvm-23.1.0-x86_64.tar.xz

1. save as /tmp/a.c++:

   static auto foo() {
   
   label1:
   
   	constexpr void * label1addr = &&label1;
   
   	struct dummy {
   
   		constexpr static void * getlabel1addr() {
   
   			return label1addr;
   
   		}
   
   	};
   
   	return dummy{};
   
   }
   
   
   void * a = decltype(foo())::getlabel1addr();

2. run clang++ /tmp/a.c++

and it crashes:

/tmp/a.c++:6:11: warning: returning address of label, which is local [-Wreturn-stack-address]

    6 |                         return label1addr;

      |                                ^~~~~~~~~~

/tmp/a.c++:3:19: note: via initialization of variable 'label1addr' here

    3 |         constexpr void * label1addr = &&label1;

      |                          ^            ~~~~~~~~

PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and dumped files.

Stack dump:

0.	Program arguments: /tmp/llvm-23.1.0-x86_64/bin/llvm clang++ -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -dumpdir a- -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name a.c++ -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=all -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -fdebug-compilation-dir=/ -fcoverage-compilation-dir=/ -resource-dir /tmp/llvm-23.1.0-x86_64/lib/clang/23 -internal-isystem /usr/lib64/gcc/x86_64-suse-linux/16/../../../../include/c++/16 -internal-isystem /usr/lib64/gcc/x86_64-suse-linux/16/../../../../include/c++/16/x86_64-suse-linux -internal-isystem /usr/lib64/gcc/x86_64-suse-linux/16/../../../../include/c++/16/backward -internal-isystem /tmp/llvm-23.1.0-x86_64/lib/clang/23/include -internal-isystem /usr/local/include -internal-isystem /usr/lib64/gcc/x86_64-suse-linux/16/../../../../x86_64-suse-linux/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -ferror-limit 19 -fmessage-length=251 -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -faddrsig -fdwarf2-cfi-asm -o /tmp/a-34e002.o -x c++ /tmp/a.c++

1.	<eof> parser at end of file

2.	/tmp/a.c++:12:8: LLVM IR generation of declaration 'a'

3.	/tmp/a.c++:12:8: Generating code for declaration 'a'

 #0 0x0000564a81e625da llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) Signals.cpp:0:0

 #1 0x0000564a81e62fef SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0

 #2 0x00007fa3e4443190 __restore_rt (/lib64/libc.so.6+0x43190)

 #3 0x0000564a82a09f1d clang::CodeGen::CodeGenFunction::GetAddrOfLabel(clang::LabelDecl const*) (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x8609f1d)

 #4 0x0000564a82fc21c2 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::ConstantLValueEmitter, (anonymous namespace)::ConstantLValue>::Visit(clang::Stmt const*) (.cold.0) CGExprConstant.cpp:0:0

 #5 0x0000564a8254bba9 clang::CodeGen::ConstantEmitter::tryEmitPrivate(clang::APValue const&, clang::QualType, bool) CGExprConstant.cpp:0:0

 #6 0x0000564a8254bf4c clang::CodeGen::ConstantEmitter::tryEmitPrivateForMemory(clang::APValue const&, clang::QualType) CGExprConstant.cpp:0:0

 #7 0x0000564a8254bd95 clang::CodeGen::ConstantEmitter::tryEmitForInitializer(clang::VarDecl const&) (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x814bd95)

 #8 0x0000564a82478c49 clang::CodeGen::CodeGenModule::EmitGlobalVarDefinition(clang::VarDecl const*, bool) CodeGenModule.cpp:0:0

 #9 0x0000564a82479cf5 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) CodeGenModule.cpp:0:0

#10 0x0000564a8247aefb clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x807aefb)

#11 0x0000564a8224195a clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x7e4195a)

#12 0x0000564a82204354 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0

#13 0x0000564a82204275 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) CodeGenAction.cpp:0:0

#14 0x0000564a82228e19 clang::ParseAST(clang::Sema&, bool, bool) (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x7e28e19)

#15 0x0000564a827b2179 clang::FrontendAction::Execute() (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x83b2179)

#16 0x0000564a827b20d9 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x83b20d9)

#17 0x0000564a827b1627 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x83b1627)

#18 0x0000564a827b14ba cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x83b14ba)

#19 0x0000564a827b0a73 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>) driver.cpp:0:0

#20 0x0000564a828f4b74 clang_main(int, char**, llvm::ToolContext const&) (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x84f4b74)

#21 0x0000564a828f2335 findTool(int, char**, char const*) llvm-driver.cpp:0:0

#22 0x0000564a8320fb4d findTool(int, char**, char const*) (.cold.0) llvm-driver.cpp:0:0

#23 0x0000564a82871dc3 main (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x8471dc3)

#24 0x00007fa3e442b4fe __libc_start_call_main /usr/src/debug/glibc-2.43/csu/../sysdeps/nptl/libc_start_call_main.h:83:3

#25 0x00007fa3e442b62b call_init /usr/src/debug/glibc-2.43/csu/../csu/libc-start.c:128:20

#26 0x00007fa3e442b62b __libc_start_main@GLIBC_2.2.5 /usr/src/debug/glibc-2.43/csu/../csu/libc-start.c:347:5

#27 0x0000564a8258ba6a _start (/tmp/llvm-23.1.0-x86_64/bin/llvm+0x818ba6a)

clang++: error: unable to execute command: Segmentation fault (core dumped)

clang++: error: clang frontend command failed with exit code -2 (use -v to see invocation)

ClangBuiltLinux clang version 23.1.0 (https://github.com/llvm/llvm-project.git ea7d852a70e8bdfaf601d6626a760f9771b2c4b4)

Target: x86_64-unknown-linux-gnu

Thread model: posix

InstalledDir: /tmp/llvm-23.1.0-x86_64/bin

clang++: note: diagnostic msg: 

********************


PLEASE ATTACH THE FOLLOWING CRASH REPRODUCER FILES TO THE BUG REPORT:

clang++: note: diagnostic msg: /tmp/a-1e24ad.cpp

clang++: note: diagnostic msg: /tmp/a-1e24ad.sh

clang++: note: diagnostic msg: 

********************

Aborted                    (core dumped) clang++ /tmp/a.c++

---

question: Is there a simpler than returning dummy struct way to expose address of label to outside scope for other functions to use?

First reproduce the crash with clang++ /tmp/a.c++ and the supplied compiler build. Trace the stack from CodeGenFunction::GetAddrOfLabel into CGExprConstant.cpp, particularly ConstantLValueEmitter, and use the reported global initializer as the boundary for investigation. Done means this reproducer no longer causes a frontend segmentation fault, with the resulting compiler behavior captured in a regression test.

Written by the indexing model from the issue text.