Clang 18 regression on C++20 mode: Unexpected placeholder builtin type! crash

[egorpugin]

clang++ -v
clang version 20.0.0git (https://github.com/llvm/llvm-project c047a5b3f6e2295dd74f1e8f17f1a023150b246c)
Target: x86_64-pc-windows-msvc
Thread model: posix

clang++ main.cpp -std=c++20

struct A {
    void f() {
        l(r);
    }
    static void r() {}
    static auto l(auto &&f) {}    // error
  //static void l(auto &&f) {}    // ok
};

int main() {
    A k;
    k.f();
}

[Endilll]

Confirmed on trunk. Regression since Clang 18 in C++20 mode (https://godbolt.org/z/a5sdrf77P):

<source>:3:9: error: cannot compile this l-value expression yet
    3 |         l(r);
      |         ^

Unexpected placeholder builtin type!
UNREACHABLE executed at /root/llvm-project/clang/lib/CodeGen/CodeGenTypes.cpp:581!

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 -fno-verbose-asm -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.	Per-file LLVM IR generation
3.	<source>:2:10: Generating code for declaration 'A::f'
 #0 0x0000000003ca32d8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ca32d8)
 #1 0x0000000003ca0fe4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ca0fe4)
 #2 0x0000000003bed168 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007e7f41e42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007e7f41e969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007e7f41e42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007e7f41e287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x0000000003bf8aca (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bf8aca)
 #8 0x000000000427967b clang::CodeGen::CodeGenTypes::ConvertType(clang::QualType) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x427967b)
 #9 0x0000000003fd98b0 clang::CodeGen::CodeGenFunction::EmitUnsupportedLValue(clang::Expr const*, char const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fd98b0)
#10 0x000000000400b285 clang::CodeGen::CodeGenFunction::EmitLValueHelper(clang::Expr const*, clang::CodeGen::KnownNonNull_t) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x400b285)
#11 0x000000000400bde7 void llvm::function_ref<void ()>::callback_fn<clang::CodeGen::CodeGenFunction::EmitLValue(clang::Expr const*, clang::CodeGen::KnownNonNull_t)::'lambda'()>(long) CGExpr.cpp:0:0
#12 0x0000000007dfea01 clang::StackExhaustionHandler::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7dfea01)
#13 0x0000000003fd9bea clang::CodeGen::CodeGenFunction::EmitLValue(clang::Expr const*, clang::CodeGen::KnownNonNull_t) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fd9bea)
#14 0x00000000040054d8 clang::CodeGen::CodeGenFunction::EmitCallee(clang::Expr const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x40054d8)
#15 0x0000000004006bd3 clang::CodeGen::CodeGenFunction::EmitCallExpr(clang::CallExpr const*, clang::CodeGen::ReturnValueSlot, llvm::CallBase**) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4006bd3)
#16 0x0000000004075134 (anonymous namespace)::ScalarExprEmitter::VisitCallExpr(clang::CallExpr const*) CGExprScalar.cpp:0:0
#17 0x0000000004068ff0 clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(clang::Stmt*) CGExprScalar.cpp:0:0
#18 0x000000000406edac clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x406edac)
#19 0x0000000003fdfa6e clang::CodeGen::CodeGenFunction::EmitAnyExpr(clang::Expr const*, clang::CodeGen::AggValueSlot, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fdfa6e)
#20 0x000000000400511d clang::CodeGen::CodeGenFunction::EmitIgnoredExpr(clang::Expr const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x400511d)
#21 0x000000000414356e clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x414356e)
#22 0x000000000414b30c clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x414b30c)
#23 0x00000000041b039c clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41b039c)
#24 0x00000000041c341e clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41c341e)
#25 0x000000000422befa clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x422befa)
#26 0x0000000004227195 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4227195)
#27 0x0000000004232f8d clang::CodeGen::CodeGenModule::EmitDeferred() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4232f8d)
#28 0x0000000004235273 clang::CodeGen::CodeGenModule::Release() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4235273)
#29 0x00000000046329be (anonymous namespace)::CodeGeneratorImpl::HandleTranslationUnit(clang::ASTContext&) ModuleBuilder.cpp:0:0
#30 0x0000000004630745 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4630745)
#31 0x000000000664fd1c clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x664fd1c)
#32 0x0000000004630eb8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4630eb8)
#33 0x00000000048f1c75 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48f1c75)
#34 0x00000000048745ee clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48745ee)
#35 0x00000000049df0ae clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x49df0ae)
#36 0x0000000000cf134f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcf134f)
#37 0x0000000000ce8e2a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#38 0x0000000004676f39 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
#39 0x0000000003bed614 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bed614)
#40 0x000000000467752f 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
#41 0x000000000463abed clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x463abed)
#42 0x000000000463bc6e 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+++0x463bc6e)
#43 0x0000000004643795 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4643795)
#44 0x0000000000cee183 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcee183)
#45 0x0000000000bb9724 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbb9724)
#46 0x00007e7f41e29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#47 0x00007e7f41e29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#48 0x0000000000ce88d5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xce88d5)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

[llvmbot]

@llvm/issue-subscribers-c-20

Author: Egor Pugin (egorpugin)

``` clang++ -v clang version 20.0.0git (https://github.com/llvm/llvm-project c047a5b) Target: x86_64-pc-windows-msvc Thread model: posix ```

clang++ main.cpp -std=c++20

struct A {
    void f() {
        l(r);
    }
    static void r() {}
    static auto l(auto &&f) {}    // error
  //static void l(auto &&f) {}    // ok
};

int main() {
    A k;
    k.f();
}

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Egor Pugin (egorpugin)

``` clang++ -v clang version 20.0.0git (https://github.com/llvm/llvm-project c047a5b) Target: x86_64-pc-windows-msvc Thread model: posix ```

clang++ main.cpp -std=c++20

struct A {
    void f() {
        l(r);
    }
    static void r() {}
    static auto l(auto &&f) {}    // error
  //static void l(auto &&f) {}    // ok
};

int main() {
    A k;
    k.f();
}

[shafik]

@Fznamznon git bisect points to this commit at the cause of the regression: 20a0567