Compiler crash while using variants.

[bogado]

The following program caused the crash:

#include <variant>
#include <utility>
#include <concepts>
#include <cstdint>
#include <array>

template<typename NUMERICAL>
concept is_numeric = requires(const NUMERICAL val) {
    { val + val } -> std::convertible_to<NUMERICAL>;
    { val *val } -> std::convertible_to<NUMERICAL>;
    { 1 * val } -> std::convertible_to<NUMERICAL>;
    { 1.0 * val } -> std::convertible_to<NUMERICAL>;
} && std::three_way_comparable_with<NUMERICAL, NUMERICAL>;

template<is_numeric... NUMERICs>
struct numeric_union
{
    using value_type = std::variant<NUMERICs...>;

    value_type value;

    static constexpr auto type_count = sizeof...(NUMERICs);

    template <std::integral auto I>
    requires(I >= 0 && I < type_count)
    using type = std::variant_alternative_t<I, value_type>;

    template <std::integral auto I>
    constexpr static auto prototype = type<I>{};

    constexpr static auto sizes = []<std::size_t... INDEX>(std::index_sequence<INDEX...>) {
        return std::array{ sizeof(prototype<INDEX>)... };
    }(std::make_index_sequence<type_count-1>{});
};
using int_value = numeric_union<std::int8_t,
                                    std::int16_t,
                                    std::int32_t,
                                    std::int64_t>;

using unsigned_value = numeric_union<std::uint8_t,
                                    std::uint16_t,
                                    std::uint32_t,
                                    std::uint64_t>;

//using integral_value = numeric_union<int_value, unsigned_value>;

using float_value = numeric_union<float, double>;

static_assert(sizeof(float_value)==sizeof(float_value::value_type));

tested on trunk from compiler-explorer and latest fedora.

https://compiler-explorer.com/z/96q5d9vj5

Assertion:

clang++: /root/llvm-project/clang/lib/AST/ASTContext.cpp:2415:
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.

Stack dump:

0.	Program arguments: /opt/compiler-explorer/clang-19.1.0/bin/clang++ -gdwarf-4 -g -o /app/output.s -fno-verbose-asm -c --gcc-toolchain=/opt/compiler-explorer/gcc-14.2.0 -fcolor-diagnostics -fno-crash-diagnostics --std=c++23 -O2 <source>
1.	<source>:49:34: current parser token '=='
2.	<source>:16:8: instantiating class definition 'numeric_union<float, double>'
 #0 0x00000000036fdb08 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x36fdb08)
 #1 0x00000000036fbc74 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x36fbc74)
 #2 0x0000000003647be8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x000077a56a642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x0000000006ff2330 clang::ASTContext::getTypeInfoImpl(clang::Type const*) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6ff2330)
 #5 0x0000000006fdc9db clang::ASTContext::getTypeInfo(clang::Type const*) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6fdc9db)
 #6 0x0000000006ff405b clang::ASTContext::getTypeInfoInChars(clang::Type const*) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6ff405b)
 #7 0x0000000006ff48f9 clang::ASTContext::getTypeSizeInChars(clang::QualType) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6ff48f9)
 #8 0x000000000721b8a3 HandleSizeof((anonymous namespace)::EvalInfo&, clang::SourceLocation, clang::QualType, clang::CharUnits&, SizeOfType) ExprConstant.cpp:0:0
 #9 0x0000000007282f6f clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::IntExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#10 0x000000000724bbfe Evaluate(clang::APValue&, (anonymous namespace)::EvalInfo&, clang::Expr const*) ExprConstant.cpp:0:0
#11 0x0000000007262bee EvaluateInPlace(clang::APValue&, (anonymous namespace)::EvalInfo&, (anonymous namespace)::LValue const&, clang::Expr const*, bool) ExprConstant.cpp:0:0
#12 0x0000000007264544 (anonymous namespace)::ArrayExprEvaluator::VisitCXXParenListOrInitListExpr(clang::Expr const*, llvm::ArrayRef<clang::Expr*>, clang::Expr const*, clang::QualType) ExprConstant.cpp:0:0
#13 0x00000000072a0191 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::ArrayExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#14 0x0000000007262bb5 EvaluateInPlace(clang::APValue&, (anonymous namespace)::EvalInfo&, (anonymous namespace)::LValue const&, clang::Expr const*, bool) ExprConstant.cpp:0:0
#15 0x00000000072652e0 (anonymous namespace)::RecordExprEvaluator::VisitCXXParenListOrInitListExpr(clang::Expr const*, llvm::ArrayRef<clang::Expr*>) ExprConstant.cpp:0:0
#16 0x000000000729e6a6 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#17 0x00000000072a2ad4 (anonymous namespace)::ExprEvaluatorBase<(anonymous namespace)::RecordExprEvaluator>::VisitCastExpr(clang::CastExpr const*) ExprConstant.cpp:0:0
#18 0x00000000072a2d37 (anonymous namespace)::RecordExprEvaluator::VisitCastExpr(clang::CastExpr const*) ExprConstant.cpp:0:0
#19 0x000000000729db52 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#20 0x0000000007262d31 EvaluateInPlace(clang::APValue&, (anonymous namespace)::EvalInfo&, (anonymous namespace)::LValue const&, clang::Expr const*, bool) ExprConstant.cpp:0:0
#21 0x000000000725c268 EvaluateStmt((anonymous namespace)::StmtResult&, (anonymous namespace)::EvalInfo&, clang::Stmt const*, clang::SwitchCase const*) (.part.0) ExprConstant.cpp:0:0
#22 0x000000000725c438 EvaluateStmt((anonymous namespace)::StmtResult&, (anonymous namespace)::EvalInfo&, clang::Stmt const*, clang::SwitchCase const*) (.part.0) ExprConstant.cpp:0:0
#23 0x0000000007260f36 HandleFunctionCall(clang::SourceLocation, clang::FunctionDecl const*, (anonymous namespace)::LValue const*, clang::Expr const*, llvm::ArrayRef<clang::Expr const*>, (anonymous namespace)::CallRef, clang::Stmt const*, (anonymous namespace)::EvalInfo&, clang::APValue&, (anonymous namespace)::LValue const*) (.isra.0) ExprConstant.cpp:0:0
#24 0x0000000007286030 (anonymous namespace)::ExprEvaluatorBase<(anonymous namespace)::RecordExprEvaluator>::handleCallExpr(clang::CallExpr const*, clang::APValue&, (anonymous namespace)::LValue const*) ExprConstant.cpp:0:0
#25 0x000000000729dae3 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#26 0x00000000072a2ad4 (anonymous namespace)::ExprEvaluatorBase<(anonymous namespace)::RecordExprEvaluator>::VisitCastExpr(clang::CastExpr const*) ExprConstant.cpp:0:0
#27 0x00000000072a2d37 (anonymous namespace)::RecordExprEvaluator::VisitCastExpr(clang::CastExpr const*) ExprConstant.cpp:0:0
#28 0x000000000729d9e6 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#29 0x000000000729dd27 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#30 0x0000000007262d31 EvaluateInPlace(clang::APValue&, (anonymous namespace)::EvalInfo&, (anonymous namespace)::LValue const&, clang::Expr const*, bool) ExprConstant.cpp:0:0
#31 0x000000000726b72d clang::Expr::EvaluateAsInitializer(clang::APValue&, clang::ASTContext const&, clang::VarDecl const*, llvm::SmallVectorImpl<std::pair<clang::SourceLocation, clang::PartialDiagnostic>>&, bool) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x726b72d)
#32 0x0000000007184e66 clang::VarDecl::evaluateValueImpl(llvm::SmallVectorImpl<std::pair<clang::SourceLocation, clang::PartialDiagnostic>>&, bool) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x7184e66)
#33 0x000000000718517e clang::VarDecl::checkForConstantInitialization(llvm::SmallVectorImpl<std::pair<clang::SourceLocation, clang::PartialDiagnostic>>&) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x718517e)
#34 0x00000000062d509b clang::Sema::CheckCompleteVariableDeclaration(clang::VarDecl*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x62d509b)
#35 0x00000000062d9f62 clang::Sema::AddInitializerToDecl(clang::Decl*, clang::Expr*, bool) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x62d9f62)
#36 0x0000000006be08f8 clang::Sema::InstantiateVariableInitializer(clang::VarDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6be08f8)
#37 0x0000000006c23ae2 clang::Sema::BuildVariableInstantiation(clang::VarDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&, llvm::SmallVector<clang::Sema::LateInstantiatedAttribute, 16u>*, clang::DeclContext*, clang::LocalInstantiationScope*, bool, clang::VarTemplateSpecializationDecl*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6c23ae2)
#38 0x0000000006c2f623 clang::TemplateDeclInstantiator::VisitVarDecl(clang::VarDecl*, bool, llvm::ArrayRef<clang::BindingDecl*>*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6c2f623)
#39 0x0000000006b9dcf5 clang::Sema::InstantiateClass(clang::SourceLocation, clang::CXXRecordDecl*, clang::CXXRecordDecl*, clang::MultiLevelTemplateArgumentList const&, clang::TemplateSpecializationKind, bool) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6b9dcf5)
#40 0x0000000006bbdc5a clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6bbdc5a)
#41 0x0000000006c6043f void llvm::function_ref<void ()>::callback_fn<clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*)::'lambda'()>(long) SemaType.cpp:0:0
#42 0x0000000006097151 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6097151)
#43 0x0000000006c648f5 clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6c648f5)
#44 0x0000000006c64975 clang::Sema::RequireCompleteType(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6c64975)
#45 0x00000000064968cc clang::Sema::CheckUnaryExprOrTypeTraitOperand(clang::QualType, clang::SourceLocation, clang::SourceRange, clang::UnaryExprOrTypeTrait, llvm::StringRef) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x64968cc)
#46 0x000000000652a3d8 clang::Sema::CreateUnaryExprOrTypeTraitExpr(clang::TypeSourceInfo*, clang::SourceLocation, clang::UnaryExprOrTypeTrait, clang::SourceRange) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x652a3d8)
#47 0x0000000006550aee clang::Sema::ActOnUnaryExprOrTypeTraitExpr(clang::SourceLocation, clang::UnaryExprOrTypeTrait, bool, void*, clang::SourceRange) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6550aee)
#48 0x0000000005fab121 clang::Parser::ParseUnaryExprOrTypeTraitExpression() (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5fab121)
#49 0x0000000005f9d36a clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f9d36a)
#50 0x0000000005fabac9 clang::Parser::ParseConstantExpressionInExprEvalContext(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5fabac9)
#51 0x0000000005f81cbf clang::Parser::ParseStaticAssertDeclaration(clang::SourceLocation&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f81cbf)
#52 0x0000000005f71028 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f71028)
#53 0x0000000005f27cfa clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f27cfa)
#54 0x0000000005f29ac8 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f29ac8)
#55 0x0000000005f1877a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f1877a)
#56 0x0000000003fce825 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3fce825)
#57 0x0000000004274201 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x4274201)
#58 0x00000000041f699b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x41f699b)
#59 0x000000000435a843 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x435a843)
#60 0x0000000000c874dc cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0xc874dc)
#61 0x0000000000c8146d ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#62 0x0000000004017309 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
#63 0x0000000003648013 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3648013)
#64 0x0000000004017529 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
#65 0x0000000003fdd947 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3fdd947)
#66 0x0000000003fde2fd clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3fde2fd)
#67 0x0000000003fe7d4c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3fe7d4c)
#68 0x0000000000c847f1 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0xc847f1)
#69 0x0000000000b5c2d4 main (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0xb5c2d4)
#70 0x000077a56a629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#71 0x000077a56a629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#72 0x0000000000c80f0e _start (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0xc80f0e)
clang++: error: clang frontend command failed with exit code 139 (use -v to see invocation)
Compiler returned: 139

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Victor Bogado da Silva Lins (bogado)

The following program caused the crash:

#include <variant>
#include <utility>
#include <concepts>
#include <cstdint>
#include <array>

template<typename NUMERICAL>
concept is_numeric = requires(const NUMERICAL val) {
    { val + val } -> std::convertible_to<NUMERICAL>;
    { val *val } -> std::convertible_to<NUMERICAL>;
    { 1 * val } -> std::convertible_to<NUMERICAL>;
    { 1.0 * val } -> std::convertible_to<NUMERICAL>;
} && std::three_way_comparable_with<NUMERICAL, NUMERICAL>;

template<is_numeric... NUMERICs>
struct numeric_union
{
    using value_type = std::variant<NUMERICs...>;

    value_type value;

    static constexpr auto type_count = sizeof...(NUMERICs);

    template <std::integral auto I>
    requires(I >= 0 && I < type_count)
    using type = std::variant_alternative_t<I, value_type>;

    template <std::integral auto I>
    constexpr static auto prototype = type<I>{};

    constexpr static auto sizes = []<std::size_t... INDEX>(std::index_sequence<INDEX...>) {
        return std::array{ sizeof(prototype<INDEX>)... };
    }(std::make_index_sequence<type_count-1>{});
};
using int_value = numeric_union<std::int8_t,
                                    std::int16_t,
                                    std::int32_t,
                                    std::int64_t>;

using unsigned_value = numeric_union<std::uint8_t,
                                    std::uint16_t,
                                    std::uint32_t,
                                    std::uint64_t>;

//using integral_value = numeric_union<int_value, unsigned_value>;

using float_value = numeric_union<float, double>;

static_assert(sizeof(float_value)==sizeof(float_value::value_type));

tested on trunk from compiler-explorer and latest fedora.

https://compiler-explorer.com/z/96q5d9vj5

Stack dump:
0. Program arguments: /opt/compiler-explorer/clang-19.1.0/bin/clang++ -gdwarf-4 -g -o /app/output.s -fno-verbose-asm -c --gcc-toolchain=/opt/compiler-explorer/gcc-14.2.0 -fcolor-diagnostics -fno-crash-diagnostics --std=c++23 -O2 <source>

1. <source>:49:34: current parser token '=='
2. <source>:16:8: instantiating class definition 'numeric_union<float, double>'
   #0 0x00000000036fdb08 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x36fdb08)
   #1 0x00000000036fbc74 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x36fbc74)
   #2 0x0000000003647be8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
   #3 0x000077a56a642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
   #4 0x0000000006ff2330 clang::ASTContext::getTypeInfoImpl(clang::Type const*) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6ff2330)
   #5 0x0000000006fdc9db clang::ASTContext::getTypeInfo(clang::Type const*) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6fdc9db)
   #6 0x0000000006ff405b clang::ASTContext::getTypeInfoInChars(clang::Type const*) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6ff405b)
   #7 0x0000000006ff48f9 clang::ASTContext::getTypeSizeInChars(clang::QualType) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6ff48f9)
   #8 0x000000000721b8a3 HandleSizeof((anonymous namespace)::EvalInfo&, clang::SourceLocation, clang::QualType, clang::CharUnits&, SizeOfType) ExprConstant.cpp:0:0
   #9 0x0000000007282f6f clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::IntExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
   #10 0x000000000724bbfe Evaluate(clang::APValue&, (anonymous namespace)::EvalInfo&, clang::Expr const*) ExprConstant.cpp:0:0
   #11 0x0000000007262bee EvaluateInPlace(clang::APValue&, (anonymous namespace)::EvalInfo&, (anonymous namespace)::LValue const&, clang::Expr const*, bool) ExprConstant.cpp:0:0
   #12 0x0000000007264544 (anonymous namespace)::ArrayExprEvaluator::VisitCXXParenListOrInitListExpr(clang::Expr const*, llvm::ArrayRef<clang::Expr*>, clang::Expr const*, clang::QualType) ExprConstant.cpp:0:0
   #13 0x00000000072a0191 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::ArrayExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
   #14 0x0000000007262bb5 EvaluateInPlace(clang::APValue&, (anonymous namespace)::EvalInfo&, (anonymous namespace)::LValue const&, clang::Expr const*, bool) ExprConstant.cpp:0:0
   #15 0x00000000072652e0 (anonymous namespace)::RecordExprEvaluator::VisitCXXParenListOrInitListExpr(clang::Expr const*, llvm::ArrayRef<clang::Expr*>) ExprConstant.cpp:0:0
   #16 0x000000000729e6a6 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
   #17 0x00000000072a2ad4 (anonymous namespace)::ExprEvaluatorBase<(anonymous namespace)::RecordExprEvaluator>::VisitCastExpr(clang::CastExpr const*) ExprConstant.cpp:0:0
   #18 0x00000000072a2d37 (anonymous namespace)::RecordExprEvaluator::VisitCastExpr(clang::CastExpr const*) ExprConstant.cpp:0:0
   #19 0x000000000729db52 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
   #20 0x0000000007262d31 EvaluateInPlace(clang::APValue&, (anonymous namespace)::EvalInfo&, (anonymous namespace)::LValue const&, clang::Expr const*, bool) ExprConstant.cpp:0:0
   #21 0x000000000725c268 EvaluateStmt((anonymous namespace)::StmtResult&, (anonymous namespace)::EvalInfo&, clang::Stmt const*, clang::SwitchCase const*) (.part.0) ExprConstant.cpp:0:0
   #22 0x000000000725c438 EvaluateStmt((anonymous namespace)::StmtResult&, (anonymous namespace)::EvalInfo&, clang::Stmt const*, clang::SwitchCase const*) (.part.0) ExprConstant.cpp:0:0
   #23 0x0000000007260f36 HandleFunctionCall(clang::SourceLocation, clang::FunctionDecl const*, (anonymous namespace)::LValue const*, clang::Expr const*, llvm::ArrayRef<clang::Expr const*>, (anonymous namespace)::CallRef, clang::Stmt const*, (anonymous namespace)::EvalInfo&, clang::APValue&, (anonymous namespace)::LValue const*) (.isra.0) ExprConstant.cpp:0:0
   #24 0x0000000007286030 (anonymous namespace)::ExprEvaluatorBase<(anonymous namespace)::RecordExprEvaluator>::handleCallExpr(clang::CallExpr const*, clang::APValue&, (anonymous namespace)::LValue const*) ExprConstant.cpp:0:0
   #25 0x000000000729dae3 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
   #26 0x00000000072a2ad4 (anonymous namespace)::ExprEvaluatorBase<(anonymous namespace)::RecordExprEvaluator>::VisitCastExpr(clang::CastExpr const*) ExprConstant.cpp:0:0
   #27 0x00000000072a2d37 (anonymous namespace)::RecordExprEvaluator::VisitCastExpr(clang::CastExpr const*) ExprConstant.cpp:0:0
   #28 0x000000000729d9e6 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
   #29 0x000000000729dd27 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::RecordExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
   #30 0x0000000007262d31 EvaluateInPlace(clang::APValue&, (anonymous namespace)::EvalInfo&, (anonymous namespace)::LValue const&, clang::Expr const*, bool) ExprConstant.cpp:0:0
   #31 0x000000000726b72d clang::Expr::EvaluateAsInitializer(clang::APValue&, clang::ASTContext const&, clang::VarDecl const*, llvm::SmallVectorImpl<std::pair<clang::SourceLocation, clang::PartialDiagnostic>>&, bool) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x726b72d)
   #32 0x0000000007184e66 clang::VarDecl::evaluateValueImpl(llvm::SmallVectorImpl<std::pair<clang::SourceLocation, clang::PartialDiagnostic>>&, bool) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x7184e66)
   #33 0x000000000718517e clang::VarDecl::checkForConstantInitialization(llvm::SmallVectorImpl<std::pair<clang::SourceLocation, clang::PartialDiagnostic>>&) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x718517e)
   #34 0x00000000062d509b clang::Sema::CheckCompleteVariableDeclaration(clang::VarDecl*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x62d509b)
   #35 0x00000000062d9f62 clang::Sema::AddInitializerToDecl(clang::Decl*, clang::Expr*, bool) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x62d9f62)
   #36 0x0000000006be08f8 clang::Sema::InstantiateVariableInitializer(clang::VarDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6be08f8)
   #37 0x0000000006c23ae2 clang::Sema::BuildVariableInstantiation(clang::VarDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&, llvm::SmallVector<clang::Sema::LateInstantiatedAttribute, 16u>, clang::DeclContext, clang::LocalInstantiationScope*, bool, clang::VarTemplateSpecializationDecl*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6c23ae2)
   #38 0x0000000006c2f623 clang::TemplateDeclInstantiator::VisitVarDecl(clang::VarDecl*, bool, llvm::ArrayRef<clang::BindingDecl*>) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6c2f623)
   #39 0x0000000006b9dcf5 clang::Sema::InstantiateClass(clang::SourceLocation, clang::CXXRecordDecl, clang::CXXRecordDecl*, clang::MultiLevelTemplateArgumentList const&, clang::TemplateSpecializationKind, bool) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6b9dcf5)
   #40 0x0000000006bbdc5a clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6bbdc5a)
   #41 0x0000000006c6043f void llvm::function_ref<void ()>::callback_fn<clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*)::'lambda'()>(long) SemaType.cpp:0:0
   #42 0x0000000006097151 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6097151)
   #43 0x0000000006c648f5 clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6c648f5)
   #44 0x0000000006c64975 clang::Sema::RequireCompleteType(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6c64975)
   #45 0x00000000064968cc clang::Sema::CheckUnaryExprOrTypeTraitOperand(clang::QualType, clang::SourceLocation, clang::SourceRange, clang::UnaryExprOrTypeTrait, llvm::StringRef) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x64968cc)
   #46 0x000000000652a3d8 clang::Sema::CreateUnaryExprOrTypeTraitExpr(clang::TypeSourceInfo*, clang::SourceLocation, clang::UnaryExprOrTypeTrait, clang::SourceRange) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x652a3d8)
   #47 0x0000000006550aee clang::Sema::ActOnUnaryExprOrTypeTraitExpr(clang::SourceLocation, clang::UnaryExprOrTypeTrait, bool, void*, clang::SourceRange) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x6550aee)
   #48 0x0000000005fab121 clang::Parser::ParseUnaryExprOrTypeTraitExpression() (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5fab121)
   #49 0x0000000005f9d36a clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f9d36a)
   #50 0x0000000005fabac9 clang::Parser::ParseConstantExpressionInExprEvalContext(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5fabac9)
   #51 0x0000000005f81cbf clang::Parser::ParseStaticAssertDeclaration(clang::SourceLocation&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f81cbf)
   #52 0x0000000005f71028 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f71028)
   #53 0x0000000005f27cfa clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f27cfa)
   #54 0x0000000005f29ac8 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f29ac8)
   #55 0x0000000005f1877a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x5f1877a)
   #56 0x0000000003fce825 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3fce825)
   #57 0x0000000004274201 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x4274201)
   #58 0x00000000041f699b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x41f699b)
   #59 0x000000000435a843 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x435a843)
   #60 0x0000000000c874dc cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0xc874dc)
   #61 0x0000000000c8146d ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
   #62 0x0000000004017309 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
   #63 0x0000000003648013 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3648013)
   #64 0x0000000004017529 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
   #65 0x0000000003fdd947 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3fdd947)
   #66 0x0000000003fde2fd clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3fde2fd)
   #67 0x0000000003fe7d4c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0x3fe7d4c)
   #68 0x0000000000c847f1 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0xc847f1)
   #69 0x0000000000b5c2d4 main (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0xb5c2d4)
   #70 0x000077a56a629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
   #71 0x000077a56a629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
   #72 0x0000000000c80f0e _start (/opt/compiler-explorer/clang-19.1.0/bin/clang+++0xc80f0e)
   clang++: error: clang frontend command failed with exit code 139 (use -v to see invocation)
   Compiler returned: 139

[shafik]

You can use ```console to quote any sort of console output such as stack dumps.

[shafik]

The last reproducer here: #75847

has the same backtrace. This could be a duplicate but we need a reduction in order to know for sure.

[shafik]

CC @Endilll

[bogado]

This version works: https://compiler-explorer.com/z/a4zz1PGr3

[bogado]

Smaller version showing the issue :

#include <variant>
#include <concepts>
#include <array>

template<typename... NUMERICs>
struct numeric_union
{
    using value_type = std::variant<NUMERICs...>;

    template <std::integral auto I>
    static constexpr auto prototype = std::variant_alternative_t<I, value_type>{};

    constexpr static auto sizes = []<std::size_t... INDEX>(std::index_sequence<INDEX...>) {
        return std::array{ sizeof(prototype<INDEX>)... };
    }(std::make_index_sequence<std::variant_size_v<value_type>-1>{});
};

using float_value = numeric_union<float, double>;

static_assert(sizeof(float_value)==sizeof(float_value::value_type));

while this version seems to work fine:

#include <variant>
#include <array>

template<typename... NUMERICs>
struct numeric_union
{
    using value_type = std::variant<NUMERICs...>;

    template <int I>
    using prototype = std::variant_alternative_t<I, value_type>;

    constexpr static auto sizes = []<std::size_t... INDEX>(std::index_sequence<INDEX...>) {
        return std::array{ sizeof(prototype<INDEX>)... };
    }(std::make_index_sequence<std::variant_size_v<value_type>-1>{});
};

static_assert(sizeof(numeric_union<float, double>)==1);

Using sizeof(«value») triggers the issue, while sizeof(«type») does not.

[MagentaTreehouse]

Reduced: https://compiler-explorer.com/z/eG7eGjMrb

template<typename...>
struct numeric_union
{
    template <int>
    static constexpr auto prototype = 0;

    constexpr static auto sizes = sizeof(prototype<0>);
};

numeric_union<int> a;

The difference from #75847 is that the problematic sizeof in this issue is inside the class template. They could have the same underlying cause.

[shafik]

Reduced: https://compiler-explorer.com/z/eG7eGjMrb

template<typename...>
struct numeric_union
{
template
static constexpr auto prototype = 0;

constexpr static auto sizes = sizeof(prototype<0>);

};

numeric_union a;
The difference from #75847 is that the problematic sizeof in this issue is inside the class template. They could have the same underlying cause.

They could be the same but it is not conclusive at this point. Once we have a proposed fix it should become more obvious.