[Clang] ICE on `void{}`

[MagentaTreehouse]

Reproducer:

int main() { void{}; }

This expression void{} causes an ICE in clang trunk. In clang 19.1, it gets rejected.
See compiler Explorer: https://godbolt.org/z/e85YYTaTx

[MagentaTreehouse]

Assertion:

clang++: /root/llvm-project/clang/lib/CodeGen/CGExprScalar.cpp:2077: llvm::Value* {anonymous}::ScalarExprEmitter::VisitInitListExpr(clang::InitListExpr*): Assertion `Ignore == false && "init list ignored"' failed.

Stacktrace:

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 -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics <source>
1.	<eof> parser at end of file
2.	<source>:1:5: LLVM IR generation of declaration 'main'
3.	<source>:1:5: Generating code for declaration 'main'
 #0 0x0000000003c25588 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3c25588)
 #1 0x0000000003c2328c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3c2328c)
 #2 0x0000000003b70978 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007b58a8642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007b58a86969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007b58a8642476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007b58a86287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x00007b58a862871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x00007b58a8639e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x000000000447734a (anonymous namespace)::ScalarExprEmitter::VisitInitListExpr(clang::InitListExpr*) CGExprScalar.cpp:0:0
#10 0x0000000004472006 clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(clang::Stmt*) CGExprScalar.cpp:0:0
#11 0x00000000044775ec clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44775ec)
#12 0x000000000440086e clang::CodeGen::CodeGenFunction::EmitAnyExpr(clang::Expr const*, clang::CodeGen::AggValueSlot, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x440086e)
#13 0x00000000044246f5 clang::CodeGen::CodeGenFunction::EmitIgnoredExpr(clang::Expr const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44246f5)
#14 0x000000000447b84f (anonymous namespace)::ScalarExprEmitter::VisitCastExpr(clang::CastExpr*) CGExprScalar.cpp:0:0
#15 0x0000000004471943 clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(clang::Stmt*) CGExprScalar.cpp:0:0
#16 0x00000000044775ec clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44775ec)
#17 0x000000000440086e clang::CodeGen::CodeGenFunction::EmitAnyExpr(clang::Expr const*, clang::CodeGen::AggValueSlot, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x440086e)
#18 0x00000000044246f5 clang::CodeGen::CodeGenFunction::EmitIgnoredExpr(clang::Expr const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44246f5)
#19 0x0000000003f8b5e5 clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f8b5e5)
#20 0x0000000003f93324 clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f93324)
#21 0x0000000003ffc694 clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ffc694)
#22 0x000000000400e538 clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x400e538)
#23 0x000000000407743a clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x407743a)
#24 0x0000000004072685 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4072685)
#25 0x0000000004072a6b clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4072a6b)
#26 0x000000000407cc53 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#27 0x00000000045a58d6 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#28 0x0000000004596608 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4596608)
#29 0x0000000006769324 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6769324)
#30 0x00000000045a3488 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x45a3488)
#31 0x000000000485dc89 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x485dc89)
#32 0x00000000047ddc6e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47ddc6e)
#33 0x0000000004948a3e clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4948a3e)
#34 0x0000000000ce3657 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xce3657)
#35 0x0000000000cdb21a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#36 0x00000000045e6689 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
#37 0x0000000003b70e24 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b70e24)
#38 0x00000000045e6c7f 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
#39 0x00000000045acf6d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x45acf6d)
#40 0x00000000045ae05d 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+++0x45ae05d)
#41 0x00000000045b5415 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x45b5415)
#42 0x0000000000ce04c3 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xce04c3)
#43 0x0000000000bb7164 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbb7164)
#44 0x00007b58a8629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#45 0x00007b58a8629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#46 0x0000000000cdacce _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcdacce)

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: None (MagentaTreehouse)

This expression `void{}` causes an ICE in clang trunk. In clang 19.1, it gets rejected. See compiler Explorer: https://godbolt.org/z/e85YYTaTx

[DimitryAndric]

Looks like this regressed with llvmorg-20-init-3126-g9d739e5 ("[Clang] Implement CWG2351 void{} (#78060)") by @MitalAshok.

cc @Endilll @shafik @AaronBallman @cor3ntin @zygoloid