Unreachable with __unknown_anytype in CodeGen: "Unexpected placeholder builtin type!"

[gburgessiv]

Bugzilla Link	32900
Version	trunk
OS	All

Extended Description

Repro on trunk:

$ echo '__unknown_anytype foo; __unknown_anytype bar = foo;' | $clang -cc1 -x c++ -o - -S -emit-llvm - -funknown-anytype

Unexpected placeholder builtin type!
UNREACHABLE executed at ../../tools/clang/lib/CodeGen/CodeGenTypes.cpp:484!
#0 0x0000000001cd5a44 PrintStackTraceSignalHandler(void*) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x1cd5a44)
#1 0x0000000001cd5d56 SignalHandler(int) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x1cd5d56)
#2 0x00007f0216e6a330 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x10330)
#3 0x00007f0215a5ac37 gsignal /build/eglibc-MjiXCM/eglibc-2.19/signal/../nptl/sysdeps/unix/sysv/linux/raise.c:56:0
#4 0x00007f0215a5e028 abort /build/eglibc-MjiXCM/eglibc-2.19/stdlib/abort.c:91:0
#5 0x0000000001c8d0cd llvm::llvm_unreachable_internal(char const*, char const*, unsigned int) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x1c8d0cd)
#6 0x0000000001f4725f clang::CodeGen::CodeGenTypes::ConvertType(clang::QualType) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x1f4725f)
#7 0x0000000001f466e0 clang::CodeGen::CodeGenTypes::ConvertTypeForMem(clang::QualType) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x1f466e0)
#8 0x0000000001e8beb7 clang::CodeGen::CodeGenModule::EmitNullConstant(clang::QualType) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x1e8beb7)
#9 0x0000000001efb7bc clang::CodeGen::CodeGenModule::EmitGlobalVarDefinition(clang::VarDecl const*, bool) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x1efb7bc)
#10 0x0000000001ef69e0 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x1ef69e0)
#11 0x0000000001efdb31 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x1efdb31)
#12 0x000000000256ef10 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x256ef10)
#13 0x000000000256c42c clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x256c42c)
#14 0x0000000002a140a4 clang::ParseAST(clang::Sema&, bool, bool) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x2a140a4)
#15 0x0000000002221898 clang::FrontendAction::Execute() (/path/to/clang/llvm/llvm/build/release/bin/clang+0x2221898)
#16 0x00000000021e5d51 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x21e5d51)
#17 0x00000000022ab1f5 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x22ab1f5)
#18 0x000000000083c299 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/path/to/clang/llvm/llvm/build/release/bin/clang+0x83c299)
#19 0x000000000083a742 main (/path/to/clang/llvm/llvm/build/release/bin/clang+0x83a742)
#20 0x00007f0215a45f45 __libc_start_main /build/eglibc-MjiXCM/eglibc-2.19/csu/libc-start.c:321:0
#21 0x0000000000837439 _start (/path/to/clang/llvm/llvm/build/release/bin/clang+0x837439)
Stack dump:
0.      Program arguments: /path/to/clang/llvm/llvm/build/release/bin/clang -cc1 -x c++ -o - -S -emit-llvm - -funknown-anytype
1.      <stdin>:1:24: current parser token '__unknown_anytype'
2.      <stdin>:1:19: LLVM IR generation of declaration 'foo'
3.      <stdin>:1:19: Generating code for declaration 'foo'

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[Quuxplusone]

I've marked this [clang:frontend] because I believe the placeholder type is not supposed to be making it all the way into the codegen stage. Yesterday I discovered a similar problem with an UnknownAny placeholder making it further than it should. My test case won't reproduce on trunk; you have to edit getLValueReferenceType to include assert(!T->isPlaceholderType() && "Unresolved placeholder type") as its first line. But I claim (and @rjmccall in D118552 seemed to agree) that this should never happen.

extern __unknown_anytype var;
double *d = (double*)&var;

Clang says:

$ bin/clang++ -c -Xclang -funknown-anytype x.cpp
Assertion failed: (!T->isPlaceholderType() && "Unresolved placeholder type"), function getLValueReferenceType, file /tmp/llvm-project/clang/lib/AST/ASTContext.cpp, line 3375.
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: bin/clang++ -c -Xclang -funknown-anytype x.cpp
1.  x.cpp:2:26: current parser token ';'
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  clang++                  0x000000010d9564cd llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 61
1  clang++                  0x000000010d956a4b PrintStackTraceSignalHandler(void*) + 27
2  clang++                  0x000000010d95496a llvm::sys::RunSignalHandlers() + 138
3  clang++                  0x000000010d955d4e llvm::sys::CleanupOnSignal(unsigned long) + 110
4  clang++                  0x000000010d7e1b50 (anonymous namespace)::CrashRecoveryContextImpl::HandleCrash(int, unsigned long) + 192
5  clang++                  0x000000010d7e1f43 CrashRecoverySignalHandler(int) + 195
6  libsystem_platform.dylib 0x00007fff677255fd _sigtramp + 29
7  libsystem_platform.dylib 0x00007ffee629e940 _sigtramp + 18446744071540544352
8  libsystem_c.dylib        0x00007fff675fb808 abort + 120
9  libsystem_c.dylib        0x00007fff675faac6 err + 0
10 clang++                  0x0000000112cbf78f clang::ASTContext::getLValueReferenceType(clang::QualType, bool) const + 127
11 clang++                  0x00000001131ae04f (anonymous namespace)::getStorageType(clang::ASTContext const&, clang::Expr const*) + 95
12 clang++                  0x00000001131ad8aa clang::Expr::EvaluateAsConstantExpr(clang::Expr::EvalResult&, clang::ASTContext const&, clang::Expr::ConstantExprKind) const + 634
13 clang++                  0x0000000113023d03 clang::computeDependence(clang::UnaryOperator*, clang::ASTContext const&) + 275
14 clang++                  0x000000011319361b clang::UnaryOperator::UnaryOperator(clang::ASTContext const&, clang::Expr*, clang::UnaryOperatorKind, clang::QualType, clang::ExprValueKind, clang::ExprObjectKind, clang::SourceLocation, bool, clang::FPOptionsOverride) + 251
15 clang++                  0x000000011319370d clang::UnaryOperator::UnaryOperator(clang::ASTContext const&, clang::Expr*, clang::UnaryOperatorKind, clang::QualType, clang::ExprValueKind, clang::ExprObjectKind, clang::SourceLocation, bool, clang::FPOptionsOverride) + 125
16 clang++                  0x000000011319380e clang::UnaryOperator::Create(clang::ASTContext const&, clang::Expr*, clang::UnaryOperatorKind, clang::QualType, clang::ExprValueKind, clang::ExprObjectKind, clang::SourceLocation, bool, clang::FPOptionsOverride) + 238
17 clang++                  0x0000000111d95806 clang::Sema::CreateBuiltinUnaryOp(clang::SourceLocation, clang::UnaryOperatorKind, clang::Expr*) + 5062
18 clang++                  0x0000000111d8b622 clang::Sema::BuildUnaryOp(clang::Scope*, clang::SourceLocation, clang::UnaryOperatorKind, clang::Expr*) + 434
19 clang++                  0x0000000111dbf573 clang::Sema::ActOnUnaryOp(clang::Scope*, clang::SourceLocation, clang::tok::TokenKind, clang::Expr*) + 83
20 clang++                  0x000000011151f560 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) + 12784
21 clang++                  0x0000000111518cc9 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) + 89
22 clang++                  0x0000000111522d7a clang::Parser::ParseParenExpression(clang::Parser::ParenParseOption&, bool, bool, clang::OpaquePtr<clang::QualType>&, clang::SourceLocation&) + 5354
23 clang++                  0x000000011151c52c clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) + 444
24 clang++                  0x0000000111518cc9 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) + 89
25 clang++                  0x0000000111517158 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) + 280
26 clang++                  0x000000011150296a clang::Parser::ParseInitializer() + 58

[rjmccall]

Hmm. In this case, I think it would probably be difficult to refactor the constant evaluator to avoid building a reference type, and it might be easier to just relax the assertion to allow this specific placeholder type. I don't love that because of the possibilities it creates for "escapes", but it's probably a more resilient approach than trying to chase down all the places in C++ type-checking that try to build reference types from expression types. But thank you for chasing this down; the example and stack trace was instrumentally helpful.

[llvmbot]

@llvm/issue-subscribers-clang-codegen

[AaronBallman]

The issue still reproduces as of Clang 16.0.0: https://godbolt.org/z/v8McTGdjY