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JoniSt opened this issue Nov 15, 2023 · 5 comments
Closed

C++ frontend crash when expanding parameter packs in a fold over a requires expression #72418

JoniSt opened this issue Nov 15, 2023 · 5 comments
Labels
c++20 clang:frontend Language frontend issues, e.g. anything involving "Sema" confirmed Verified by a second party crash Prefer [crash-on-valid] or [crash-on-invalid]

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@JoniSt
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JoniSt commented Nov 15, 2023 •
edited by tbaederr
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Dear Clang maintainers,

I've hit a crash in the C++ front-end when compiling the following C++20 code, which I believe to be valid:

using size_t = unsigned long long;

template<typename... Ts>
struct fake_tuple;

template<size_t I, typename First, typename... Rest>
struct fake_tuple_element {
    using type = fake_tuple_element<I - 1, Rest...>::type;
};

template<typename First, typename... Rest>
struct fake_tuple_element<0, First, Rest...> {
    using type = First;
};

namespace std {
    template<class T, T... Ints>
    class integer_sequence {
        static constexpr size_t size() noexcept { return sizeof...(Ints); }
    };

    template<size_t... Ints>
    using index_sequence = integer_sequence<size_t, Ints...>;

    template<bool cond, typename T, typename F>
    struct conditional;

    template<typename T, typename F>
    struct conditional<true, T, F> {
        using type = T;
    };

    template<typename T, typename F>
    struct conditional<false, T, F> {
        using type = F;
    };

    template<class T, bool keep_going, T first, T... rest>
    struct make_integer_sequence_helper2;

    template<class T, T first, T... rest>
    struct make_integer_sequence_helper {
        using type = typename make_integer_sequence_helper2<T, first != 0, first, rest...>::type;
    };

    template<class T, T first, T... rest>
    struct make_integer_sequence_helper2<T, true, first, rest...> {
        using type = typename make_integer_sequence_helper<T, first - T{1}, first, rest...>::type;
    };

    template<class T, T first, T... rest>
    struct make_integer_sequence_helper2<T, false, first, rest...> {
        using type = integer_sequence<T, first, rest...>;
    };

    template<class T, T N>
    using make_integer_sequence = typename make_integer_sequence_helper<T, N - 1>::type;

    template<size_t N>
    using make_index_sequence = make_integer_sequence<size_t, N>;

    template<class T>
    struct tuple_size;

    template<typename... Ts>
    struct tuple_size<fake_tuple<Ts...>> {
        static constexpr size_t value = sizeof...(Ts);
    };

    template<size_t I, class T>
    struct tuple_element;

    template<size_t I, typename... Ts>
    struct tuple_element<I, fake_tuple<Ts...>> {
        using type = typename fake_tuple_element<I, Ts...>::type;
    };

    template<size_t I, typename... Ts>
    const typename fake_tuple_element<I, Ts...>::type& get(const fake_tuple<Ts...>&);

    template<class From, class To>
    concept convertible_to = requires (From f) {
        { To{f} };
    };
}


// This crashes both Clang and GCC
template<typename T>
constexpr bool is_tuplelike_v = requires {
    std::tuple_size<T>{};
    { std::tuple_size<T>::value } -> std::convertible_to<size_t>;

    requires [] <size_t... Is> (std::index_sequence<Is...>) {
        return ((requires (T t) {
            std::tuple_element<Is, T>{};
            typename std::tuple_element<Is, T>::type;
            { std::get<Is>(t) } -> std::convertible_to<typename std::tuple_element<Is, T>::type>;
        }) && ...);
    }(std::make_index_sequence<std::tuple_size<T>::value>{});
};

static_assert(is_tuplelike_v<fake_tuple<int, float>>);

The crash occurs both with the regular STL, as well as with the minimal std templates I've included in the reproducer in order to minify it a bit.

It appears that expanding a parameter pack within a requires expression trips the frontend up.

Compiler versions tested: 17.0.1, trunk

Godbolt (minified std templates): https://godbolt.org/z/baxqv6vra
Godbolt (regular STL): https://godbolt.org/z/eKjW99qoE

Crash output:

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-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++20 <source>
1.	<source>:103:53: current parser token ')'
2.	<source>:90:16: instantiating variable definition 'is_tuplelike_v<fake_tuple<int, float>>'
3.	<source>:94:14: instantiating function definition '(anonymous class)::operator()<0ULL, 1ULL>'
 #0 0x00000000034e5cd8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x34e5cd8)
 #1 0x00000000034e3e24 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x34e3e24)
 #2 0x0000000003431fc8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007fce9657e420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00000000064bb433 clang::Sema::CheckTemplateArgument(clang::TypeSourceInfo*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64bb433)
 #5 0x00000000064c9ec9 clang::Sema::CheckTemplateTypeArgument(clang::TemplateTypeParmDecl*, clang::TemplateArgumentLoc&, llvm::SmallVectorImpl<clang::TemplateArgument>&, llvm::SmallVectorImpl<clang::TemplateArgument>&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64c9ec9)
 #6 0x00000000064d01dd clang::Sema::CheckTemplateArgument(clang::NamedDecl*, clang::TemplateArgumentLoc&, clang::NamedDecl*, clang::SourceLocation, clang::SourceLocation, unsigned int, llvm::SmallVectorImpl<clang::TemplateArgument>&, llvm::SmallVectorImpl<clang::TemplateArgument>&, clang::Sema::CheckTemplateArgumentKind) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64d01dd)
 #7 0x00000000064d1acc clang::Sema::CheckTemplateArgumentList(clang::TemplateDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo&, bool, llvm::SmallVectorImpl<clang::TemplateArgument>&, llvm::SmallVectorImpl<clang::TemplateArgument>&, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64d1acc)
 #8 0x00000000064dc0e9 clang::Sema::CheckTemplateIdType(clang::TemplateName, clang::SourceLocation, clang::TemplateArgumentListInfo&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64dc0e9)
 #9 0x000000000661ec55 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformTemplateSpecializationType(clang::TypeLocBuilder&, clang::TemplateSpecializationTypeLoc, clang::TemplateName) SemaTemplateInstantiate.cpp:0:0
#10 0x0000000006619597 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformTSIInObjectScope(clang::TypeLoc, clang::QualType, clang::NamedDecl*, clang::CXXScopeSpec&) SemaTemplateInstantiate.cpp:0:0
#11 0x0000000006619cc6 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformNestedNameSpecifierLoc(clang::NestedNameSpecifierLoc, clang::QualType, clang::NamedDecl*) SemaTemplateInstantiate.cpp:0:0
#12 0x000000000661fa4f clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformDependentNameType(clang::TypeLocBuilder&, clang::DependentNameTypeLoc, bool) SemaTemplateInstantiate.cpp:0:0
#13 0x0000000006613f89 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformType(clang::TypeLocBuilder&, clang::TypeLoc) SemaTemplateInstantiate.cpp:0:0
#14 0x000000000661789b clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformType(clang::TypeSourceInfo*) SemaTemplateInstantiate.cpp:0:0
#15 0x000000000661a618 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformTemplateArgument(clang::TemplateArgumentLoc const&, clang::TemplateArgumentLoc&, bool) SemaTemplateInstantiate.cpp:0:0
#16 0x000000000661c450 bool clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformTemplateArguments<clang::TemplateArgumentLoc const*>(clang::TemplateArgumentLoc const*, clang::TemplateArgumentLoc const*, clang::TemplateArgumentListInfo&, bool) (.constprop.0) SemaTemplateInstantiate.cpp:0:0
#17 0x000000000661d2f3 clang::Sema::SubstTypeConstraint(clang::TemplateTypeParmDecl*, clang::TypeConstraint const*, clang::MultiLevelTemplateArgumentList const&, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x661d2f3)
#18 0x0000000006641d10 clang::TemplateDeclInstantiator::VisitTemplateTypeParmDecl(clang::TemplateTypeParmDecl*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6641d10)
#19 0x00000000066911cb clang::TemplateDeclInstantiator::SubstTemplateParams(clang::TemplateParameterList*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x66911cb)
#20 0x000000000662dc0d clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformRequiresExpr(clang::RequiresExpr*) SemaTemplateInstantiate.cpp:0:0
#21 0x0000000006607aee clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#22 0x00000000066131f5 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformParenExpr(clang::ParenExpr*) SemaTemplateInstantiate.cpp:0:0
#23 0x0000000006607bea clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#24 0x000000000660fa78 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCXXFoldExpr(clang::CXXFoldExpr*) SemaTemplateInstantiate.cpp:0:0
#25 0x00000000066081d5 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#26 0x0000000006609045 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformInitializer(clang::Expr*, bool) SemaTemplateInstantiate.cpp:0:0
#27 0x000000000660a767 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformReturnStmt(clang::ReturnStmt*) SemaTemplateInstantiate.cpp:0:0
#28 0x00000000066385eb clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCompoundStmt(clang::CompoundStmt*, bool) SemaTemplateInstantiate.cpp:0:0
#29 0x000000000663ce91 clang::Sema::SubstStmt(clang::Stmt*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x663ce91)
#30 0x0000000006684818 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6684818)
#31 0x0000000005c64d01 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5c64d01)
#32 0x00000000065879c1 clang::Sema::DeduceReturnType(clang::FunctionDecl*, clang::SourceLocation, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x65879c1)
#33 0x000000000604f7f7 clang::Sema::DiagnoseUseOfDecl(clang::NamedDecl*, llvm::ArrayRef<clang::SourceLocation>, clang::ObjCInterfaceDecl const*, bool, bool, clang::ObjCInterfaceDecl*, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x604f7f7)
#34 0x00000000063c9057 CreateFunctionRefExpr(clang::Sema&, clang::FunctionDecl*, clang::NamedDecl*, clang::Expr const*, bool, clang::SourceLocation, clang::DeclarationNameLoc const&) SemaOverload.cpp:0:0
#35 0x00000000064122ba clang::Sema::BuildCallToObjectOfClassType(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64122ba)
#36 0x00000000060c0506 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60c0506)
#37 0x00000000060c5ebc clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60c5ebc)
#38 0x0000000006610fc7 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCallExpr(clang::CallExpr*) SemaTemplateInstantiate.cpp:0:0
#39 0x000000000660834d clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#40 0x0000000006636ecf clang::Sema::SubstConstraintExpr(clang::Expr*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6636ecf)
#41 0x0000000005dc82b1 calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)::operator()(clang::Expr const*) const SemaConcept.cpp:0:0
#42 0x0000000005dc98db clang::ActionResult<clang::Expr*, true> calculateConstraintSatisfaction<calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)>(clang::Sema&, clang::Expr const*, clang::ConstraintSatisfaction&, calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)&&) SemaConcept.cpp:0:0
#43 0x0000000005dca328 CheckConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::SmallVectorImpl<clang::Expr*>&, clang::MultiLevelTemplateArgumentList const&, clang::SourceRange, clang::ConstraintSatisfaction&) SemaConcept.cpp:0:0
#44 0x0000000005dcab9f clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::SmallVectorImpl<clang::Expr*>&, clang::MultiLevelTemplateArgumentList const&, clang::SourceRange, clang::ConstraintSatisfaction&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5dcab9f)
#45 0x000000000662e05f clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformRequiresExpr(clang::RequiresExpr*) SemaTemplateInstantiate.cpp:0:0
#46 0x0000000006607aee clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#47 0x0000000006609045 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformInitializer(clang::Expr*, bool) SemaTemplateInstantiate.cpp:0:0
#48 0x000000000660a8ea clang::Sema::SubstInitializer(clang::Expr*, clang::MultiLevelTemplateArgumentList const&, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x660a8ea)
#49 0x0000000006644c64 clang::Sema::InstantiateVariableInitializer(clang::VarDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6644c64)
#50 0x0000000006644f3d clang::Sema::CompleteVarTemplateSpecializationDecl(clang::VarTemplateSpecializationDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6644f3d)
#51 0x00000000066820c3 clang::Sema::InstantiateVariableDefinition(clang::SourceLocation, clang::VarDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x66820c3)
#52 0x0000000005c64d01 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5c64d01)
#53 0x00000000060740f8 DoMarkVarDeclReferenced(clang::Sema&, clang::SourceLocation, clang::VarDecl*, clang::Expr*, llvm::DenseMap<clang::VarDecl const*, int, llvm::DenseMapInfo<clang::VarDecl const*, void>, llvm::detail::DenseMapPair<clang::VarDecl const*, int>>&) SemaExpr.cpp:0:0
#54 0x000000000609bf94 MarkExprReferenced(clang::Sema&, clang::SourceLocation, clang::Decl*, clang::Expr*, bool, llvm::DenseMap<clang::VarDecl const*, int, llvm::DenseMapInfo<clang::VarDecl const*, void>, llvm::detail::DenseMapPair<clang::VarDecl const*, int>>&) SemaExpr.cpp:0:0
#55 0x000000000609c4e3 clang::Sema::BuildDeclRefExpr(clang::ValueDecl*, clang::QualType, clang::ExprValueKind, clang::DeclarationNameInfo const&, clang::NestedNameSpecifierLoc, clang::NamedDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x609c4e3)
#56 0x000000000609cafc clang::Sema::BuildDeclRefExpr(clang::ValueDecl*, clang::QualType, clang::ExprValueKind, clang::DeclarationNameInfo const&, clang::CXXScopeSpec const*, clang::NamedDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x609cafc)
#57 0x00000000060a1adc clang::Sema::BuildDeclarationNameExpr(clang::CXXScopeSpec const&, clang::DeclarationNameInfo const&, clang::NamedDecl*, clang::NamedDecl*, clang::TemplateArgumentListInfo const*, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60a1adc)
#58 0x00000000064e1e02 clang::Sema::BuildTemplateIdExpr(clang::CXXScopeSpec const&, clang::SourceLocation, clang::LookupResult&, bool, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64e1e02)
#59 0x00000000060a74b9 clang::Sema::ActOnIdExpression(clang::Scope*, clang::CXXScopeSpec&, clang::SourceLocation, clang::UnqualifiedId&, bool, bool, clang::CorrectionCandidateCallback*, bool, clang::Token*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60a74b9)
#60 0x0000000005b93778 clang::Parser::tryParseCXXIdExpression(clang::CXXScopeSpec&, bool, clang::Token&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b93778)
#61 0x0000000005b9396a clang::Parser::ParseCXXIdExpression(bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b9396a)
#62 0x0000000005b760e8 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b760e8)
#63 0x0000000005b76b0c clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b76b0c)
#64 0x0000000005b850d9 clang::Parser::ParseConstantExpressionInExprEvalContext(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b850d9)
#65 0x0000000005b5c112 clang::Parser::ParseStaticAssertDeclaration(clang::SourceLocation&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b5c112)
#66 0x0000000005b4bac0 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b4bac0)
#67 0x0000000005b197f7 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b197f7)
#68 0x0000000005b1b567 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b1b567)
#69 0x0000000005b0a8ca clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b0a8ca)
#70 0x0000000003d1e795 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d1e795)
#71 0x0000000003f9da91 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f9da91)
#72 0x0000000003f1b97b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f1b97b)
#73 0x000000000407cec3 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x407cec3)
#74 0x0000000000c051c6 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc051c6)
#75 0x0000000000bfdc1d ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#76 0x0000000003d65da9 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
#77 0x00000000034323f3 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x34323f3)
#78 0x0000000003d65fc9 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
#79 0x0000000003d2dfc7 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d2dfc7)
#80 0x0000000003d2e97d clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d2e97d)
#81 0x0000000003d386ec clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d386ec)
#82 0x0000000000c025c1 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc025c1)
#83 0x0000000000afd6f1 main (/opt/compiler-explorer/clang-trunk/bin/clang+++0xafd6f1)
#84 0x00007fce96022083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#85 0x0000000000bfd41e _start (/opt/compiler-explorer/clang-trunk/bin/clang+++0xbfd41e)
clang++: error: clang frontend command failed with exit code 139 (use -v to see invocation)
Compiler returned: 139

Thanks for your support!
@EugeneZelenko EugeneZelenko added c++20 clang:frontend Language frontend issues, e.g. anything involving "Sema" crash Prefer [crash-on-valid] or [crash-on-invalid] and removed new issue labels Nov 15, 2023
@llvmbot
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llvmbot commented Nov 15, 2023

@llvm/issue-subscribers-c-20

Author: None (JoniSt)

Dear Clang maintainers,

I've hit a crash in the C++ front-end when compiling the following C++20 code, which I believe to be valid:

using size_t = unsigned long long;

template&lt;typename... Ts&gt;
struct fake_tuple;

template&lt;size_t I, typename First, typename... Rest&gt;
struct fake_tuple_element {
    using type = fake_tuple_element&lt;I - 1, Rest...&gt;::type;
};

template&lt;typename First, typename... Rest&gt;
struct fake_tuple_element&lt;0, First, Rest...&gt; {
    using type = First;
};

namespace std {
    template&lt;class T, T... Ints&gt;
    class integer_sequence {
        static constexpr size_t size() noexcept { return sizeof...(Ints); }
    };

    template&lt;size_t... Ints&gt;
    using index_sequence = integer_sequence&lt;size_t, Ints...&gt;;

    template&lt;bool cond, typename T, typename F&gt;
    struct conditional;

    template&lt;typename T, typename F&gt;
    struct conditional&lt;true, T, F&gt; {
        using type = T;
    };

    template&lt;typename T, typename F&gt;
    struct conditional&lt;false, T, F&gt; {
        using type = F;
    };

    template&lt;class T, bool keep_going, T first, T... rest&gt;
    struct make_integer_sequence_helper2;

    template&lt;class T, T first, T... rest&gt;
    struct make_integer_sequence_helper {
        using type = typename make_integer_sequence_helper2&lt;T, first != 0, first, rest...&gt;::type;
    };

    template&lt;class T, T first, T... rest&gt;
    struct make_integer_sequence_helper2&lt;T, true, first, rest...&gt; {
        using type = typename make_integer_sequence_helper&lt;T, first - T{1}, first, rest...&gt;::type;
    };

    template&lt;class T, T first, T... rest&gt;
    struct make_integer_sequence_helper2&lt;T, false, first, rest...&gt; {
        using type = integer_sequence&lt;T, first, rest...&gt;;
    };

    template&lt;class T, T N&gt;
    using make_integer_sequence = typename make_integer_sequence_helper&lt;T, N - 1&gt;::type;

    template&lt;size_t N&gt;
    using make_index_sequence = make_integer_sequence&lt;size_t, N&gt;;

    template&lt;class T&gt;
    struct tuple_size;

    template&lt;typename... Ts&gt;
    struct tuple_size&lt;fake_tuple&lt;Ts...&gt;&gt; {
        static constexpr size_t value = sizeof...(Ts);
    };

    template&lt;size_t I, class T&gt;
    struct tuple_element;

    template&lt;size_t I, typename... Ts&gt;
    struct tuple_element&lt;I, fake_tuple&lt;Ts...&gt;&gt; {
        using type = typename fake_tuple_element&lt;I, Ts...&gt;::type;
    };

    template&lt;size_t I, typename... Ts&gt;
    const typename fake_tuple_element&lt;I, Ts...&gt;::type&amp; get(const fake_tuple&lt;Ts...&gt;&amp;);

    template&lt;class From, class To&gt;
    concept convertible_to = requires (From f) {
        { To{f} };
    };
}


// This crashes both Clang and GCC
template&lt;typename T&gt;
constexpr bool is_tuplelike_v = requires {
    std::tuple_size&lt;T&gt;{};
    { std::tuple_size&lt;T&gt;::value } -&gt; std::convertible_to&lt;size_t&gt;;

    requires [] &lt;size_t... Is&gt; (std::index_sequence&lt;Is...&gt;) {
        return ((requires (T t) {
            std::tuple_element&lt;Is, T&gt;{};
            typename std::tuple_element&lt;Is, T&gt;::type;
            { std::get&lt;Is&gt;(t) } -&gt; std::convertible_to&lt;typename std::tuple_element&lt;Is, T&gt;::type&gt;;
        }) &amp;&amp; ...);
    }(std::make_index_sequence&lt;std::tuple_size&lt;T&gt;::value&gt;{});
};

static_assert(is_tuplelike_v&lt;fake_tuple&lt;int, float&gt;&gt;);

The crash occurs both with the regular STL, as well as with the minimal std templates I've included in the reproducer in order to minify it a bit.

It appears that expanding a parameter pack within a requires expression trips the frontend up.

Compiler versions tested: 17.0.1, trunk

Godbolt (minified std templates): https://godbolt.org/z/baxqv6vra
Godbolt (regular STL): https://godbolt.org/z/eKjW99qoE

Crash output:

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-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++20 &lt;source&gt;
1.	&lt;source&gt;:103:53: current parser token ')'
2.	&lt;source&gt;:90:16: instantiating variable definition 'is_tuplelike_v&lt;fake_tuple&lt;int, float&gt;&gt;'
3.	&lt;source&gt;:94:14: instantiating function definition '(anonymous class)::operator()&lt;0ULL, 1ULL&gt;'
 #<!-- -->0 0x00000000034e5cd8 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x34e5cd8)
 #<!-- -->1 0x00000000034e3e24 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x34e3e24)
 #<!-- -->2 0x0000000003431fc8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x00007fce9657e420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #<!-- -->4 0x00000000064bb433 clang::Sema::CheckTemplateArgument(clang::TypeSourceInfo*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64bb433)
 #<!-- -->5 0x00000000064c9ec9 clang::Sema::CheckTemplateTypeArgument(clang::TemplateTypeParmDecl*, clang::TemplateArgumentLoc&amp;, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64c9ec9)
 #<!-- -->6 0x00000000064d01dd clang::Sema::CheckTemplateArgument(clang::NamedDecl*, clang::TemplateArgumentLoc&amp;, clang::NamedDecl*, clang::SourceLocation, clang::SourceLocation, unsigned int, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, clang::Sema::CheckTemplateArgumentKind) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64d01dd)
 #<!-- -->7 0x00000000064d1acc clang::Sema::CheckTemplateArgumentList(clang::TemplateDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo&amp;, bool, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64d1acc)
 #<!-- -->8 0x00000000064dc0e9 clang::Sema::CheckTemplateIdType(clang::TemplateName, clang::SourceLocation, clang::TemplateArgumentListInfo&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64dc0e9)
 #<!-- -->9 0x000000000661ec55 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformTemplateSpecializationType(clang::TypeLocBuilder&amp;, clang::TemplateSpecializationTypeLoc, clang::TemplateName) SemaTemplateInstantiate.cpp:0:0
#<!-- -->10 0x0000000006619597 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformTSIInObjectScope(clang::TypeLoc, clang::QualType, clang::NamedDecl*, clang::CXXScopeSpec&amp;) SemaTemplateInstantiate.cpp:0:0
#<!-- -->11 0x0000000006619cc6 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformNestedNameSpecifierLoc(clang::NestedNameSpecifierLoc, clang::QualType, clang::NamedDecl*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->12 0x000000000661fa4f clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformDependentNameType(clang::TypeLocBuilder&amp;, clang::DependentNameTypeLoc, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->13 0x0000000006613f89 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformType(clang::TypeLocBuilder&amp;, clang::TypeLoc) SemaTemplateInstantiate.cpp:0:0
#<!-- -->14 0x000000000661789b clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformType(clang::TypeSourceInfo*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->15 0x000000000661a618 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformTemplateArgument(clang::TemplateArgumentLoc const&amp;, clang::TemplateArgumentLoc&amp;, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->16 0x000000000661c450 bool clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformTemplateArguments&lt;clang::TemplateArgumentLoc const*&gt;(clang::TemplateArgumentLoc const*, clang::TemplateArgumentLoc const*, clang::TemplateArgumentListInfo&amp;, bool) (.constprop.0) SemaTemplateInstantiate.cpp:0:0
#<!-- -->17 0x000000000661d2f3 clang::Sema::SubstTypeConstraint(clang::TemplateTypeParmDecl*, clang::TypeConstraint const*, clang::MultiLevelTemplateArgumentList const&amp;, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x661d2f3)
#<!-- -->18 0x0000000006641d10 clang::TemplateDeclInstantiator::VisitTemplateTypeParmDecl(clang::TemplateTypeParmDecl*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6641d10)
#<!-- -->19 0x00000000066911cb clang::TemplateDeclInstantiator::SubstTemplateParams(clang::TemplateParameterList*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x66911cb)
#<!-- -->20 0x000000000662dc0d clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformRequiresExpr(clang::RequiresExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->21 0x0000000006607aee clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->22 0x00000000066131f5 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformParenExpr(clang::ParenExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->23 0x0000000006607bea clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->24 0x000000000660fa78 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCXXFoldExpr(clang::CXXFoldExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->25 0x00000000066081d5 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->26 0x0000000006609045 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformInitializer(clang::Expr*, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->27 0x000000000660a767 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformReturnStmt(clang::ReturnStmt*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->28 0x00000000066385eb clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCompoundStmt(clang::CompoundStmt*, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->29 0x000000000663ce91 clang::Sema::SubstStmt(clang::Stmt*, clang::MultiLevelTemplateArgumentList const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x663ce91)
#<!-- -->30 0x0000000006684818 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6684818)
#<!-- -->31 0x0000000005c64d01 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5c64d01)
#<!-- -->32 0x00000000065879c1 clang::Sema::DeduceReturnType(clang::FunctionDecl*, clang::SourceLocation, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x65879c1)
#<!-- -->33 0x000000000604f7f7 clang::Sema::DiagnoseUseOfDecl(clang::NamedDecl*, llvm::ArrayRef&lt;clang::SourceLocation&gt;, clang::ObjCInterfaceDecl const*, bool, bool, clang::ObjCInterfaceDecl*, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x604f7f7)
#<!-- -->34 0x00000000063c9057 CreateFunctionRefExpr(clang::Sema&amp;, clang::FunctionDecl*, clang::NamedDecl*, clang::Expr const*, bool, clang::SourceLocation, clang::DeclarationNameLoc const&amp;) SemaOverload.cpp:0:0
#<!-- -->35 0x00000000064122ba clang::Sema::BuildCallToObjectOfClassType(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64122ba)
#<!-- -->36 0x00000000060c0506 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60c0506)
#<!-- -->37 0x00000000060c5ebc clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60c5ebc)
#<!-- -->38 0x0000000006610fc7 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCallExpr(clang::CallExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->39 0x000000000660834d clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->40 0x0000000006636ecf clang::Sema::SubstConstraintExpr(clang::Expr*, clang::MultiLevelTemplateArgumentList const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6636ecf)
#<!-- -->41 0x0000000005dc82b1 calculateConstraintSatisfaction(clang::Sema&amp;, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&amp;, clang::Expr const*, clang::ConstraintSatisfaction&amp;)::'lambda'(clang::Expr const*)::operator()(clang::Expr const*) const SemaConcept.cpp:0:0
#<!-- -->42 0x0000000005dc98db clang::ActionResult&lt;clang::Expr*, true&gt; calculateConstraintSatisfaction&lt;calculateConstraintSatisfaction(clang::Sema&amp;, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&amp;, clang::Expr const*, clang::ConstraintSatisfaction&amp;)::'lambda'(clang::Expr const*)&gt;(clang::Sema&amp;, clang::Expr const*, clang::ConstraintSatisfaction&amp;, calculateConstraintSatisfaction(clang::Sema&amp;, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&amp;, clang::Expr const*, clang::ConstraintSatisfaction&amp;)::'lambda'(clang::Expr const*)&amp;&amp;) SemaConcept.cpp:0:0
#<!-- -->43 0x0000000005dca328 CheckConstraintSatisfaction(clang::Sema&amp;, clang::NamedDecl const*, llvm::ArrayRef&lt;clang::Expr const*&gt;, llvm::SmallVectorImpl&lt;clang::Expr*&gt;&amp;, clang::MultiLevelTemplateArgumentList const&amp;, clang::SourceRange, clang::ConstraintSatisfaction&amp;) SemaConcept.cpp:0:0
#<!-- -->44 0x0000000005dcab9f clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*, llvm::ArrayRef&lt;clang::Expr const*&gt;, llvm::SmallVectorImpl&lt;clang::Expr*&gt;&amp;, clang::MultiLevelTemplateArgumentList const&amp;, clang::SourceRange, clang::ConstraintSatisfaction&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5dcab9f)
#<!-- -->45 0x000000000662e05f clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformRequiresExpr(clang::RequiresExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->46 0x0000000006607aee clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->47 0x0000000006609045 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformInitializer(clang::Expr*, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->48 0x000000000660a8ea clang::Sema::SubstInitializer(clang::Expr*, clang::MultiLevelTemplateArgumentList const&amp;, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x660a8ea)
#<!-- -->49 0x0000000006644c64 clang::Sema::InstantiateVariableInitializer(clang::VarDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6644c64)
#<!-- -->50 0x0000000006644f3d clang::Sema::CompleteVarTemplateSpecializationDecl(clang::VarTemplateSpecializationDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6644f3d)
#<!-- -->51 0x00000000066820c3 clang::Sema::InstantiateVariableDefinition(clang::SourceLocation, clang::VarDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x66820c3)
#<!-- -->52 0x0000000005c64d01 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5c64d01)
#<!-- -->53 0x00000000060740f8 DoMarkVarDeclReferenced(clang::Sema&amp;, clang::SourceLocation, clang::VarDecl*, clang::Expr*, llvm::DenseMap&lt;clang::VarDecl const*, int, llvm::DenseMapInfo&lt;clang::VarDecl const*, void&gt;, llvm::detail::DenseMapPair&lt;clang::VarDecl const*, int&gt;&gt;&amp;) SemaExpr.cpp:0:0
#<!-- -->54 0x000000000609bf94 MarkExprReferenced(clang::Sema&amp;, clang::SourceLocation, clang::Decl*, clang::Expr*, bool, llvm::DenseMap&lt;clang::VarDecl const*, int, llvm::DenseMapInfo&lt;clang::VarDecl const*, void&gt;, llvm::detail::DenseMapPair&lt;clang::VarDecl const*, int&gt;&gt;&amp;) SemaExpr.cpp:0:0
#<!-- -->55 0x000000000609c4e3 clang::Sema::BuildDeclRefExpr(clang::ValueDecl*, clang::QualType, clang::ExprValueKind, clang::DeclarationNameInfo const&amp;, clang::NestedNameSpecifierLoc, clang::NamedDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x609c4e3)
#<!-- -->56 0x000000000609cafc clang::Sema::BuildDeclRefExpr(clang::ValueDecl*, clang::QualType, clang::ExprValueKind, clang::DeclarationNameInfo const&amp;, clang::CXXScopeSpec const*, clang::NamedDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x609cafc)
#<!-- -->57 0x00000000060a1adc clang::Sema::BuildDeclarationNameExpr(clang::CXXScopeSpec const&amp;, clang::DeclarationNameInfo const&amp;, clang::NamedDecl*, clang::NamedDecl*, clang::TemplateArgumentListInfo const*, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60a1adc)
#<!-- -->58 0x00000000064e1e02 clang::Sema::BuildTemplateIdExpr(clang::CXXScopeSpec const&amp;, clang::SourceLocation, clang::LookupResult&amp;, bool, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64e1e02)
#<!-- -->59 0x00000000060a74b9 clang::Sema::ActOnIdExpression(clang::Scope*, clang::CXXScopeSpec&amp;, clang::SourceLocation, clang::UnqualifiedId&amp;, bool, bool, clang::CorrectionCandidateCallback*, bool, clang::Token*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60a74b9)
#<!-- -->60 0x0000000005b93778 clang::Parser::tryParseCXXIdExpression(clang::CXXScopeSpec&amp;, bool, clang::Token&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b93778)
#<!-- -->61 0x0000000005b9396a clang::Parser::ParseCXXIdExpression(bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b9396a)
#<!-- -->62 0x0000000005b760e8 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&amp;, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b760e8)
#<!-- -->63 0x0000000005b76b0c clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&amp;, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b76b0c)
#<!-- -->64 0x0000000005b850d9 clang::Parser::ParseConstantExpressionInExprEvalContext(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b850d9)
#<!-- -->65 0x0000000005b5c112 clang::Parser::ParseStaticAssertDeclaration(clang::SourceLocation&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b5c112)
#<!-- -->66 0x0000000005b4bac0 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b4bac0)
#<!-- -->67 0x0000000005b197f7 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b197f7)
#<!-- -->68 0x0000000005b1b567 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b1b567)
#<!-- -->69 0x0000000005b0a8ca clang::ParseAST(clang::Sema&amp;, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b0a8ca)
#<!-- -->70 0x0000000003d1e795 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d1e795)
#<!-- -->71 0x0000000003f9da91 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f9da91)
#<!-- -->72 0x0000000003f1b97b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f1b97b)
#<!-- -->73 0x000000000407cec3 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x407cec3)
#<!-- -->74 0x0000000000c051c6 cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc051c6)
#<!-- -->75 0x0000000000bfdc1d ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->76 0x0000000003d65da9 void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const::'lambda'()&gt;(long) Job.cpp:0:0
#<!-- -->77 0x00000000034323f3 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x34323f3)
#<!-- -->78 0x0000000003d65fc9 clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const (.part.0) Job.cpp:0:0
#<!-- -->79 0x0000000003d2dfc7 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d2dfc7)
#<!-- -->80 0x0000000003d2e97d clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d2e97d)
#<!-- -->81 0x0000000003d386ec clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d386ec)
#<!-- -->82 0x0000000000c025c1 clang_main(int, char**, llvm::ToolContext const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc025c1)
#<!-- -->83 0x0000000000afd6f1 main (/opt/compiler-explorer/clang-trunk/bin/clang+++0xafd6f1)
#<!-- -->84 0x00007fce96022083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#<!-- -->85 0x0000000000bfd41e _start (/opt/compiler-explorer/clang-trunk/bin/clang+++0xbfd41e)
clang++: error: clang frontend command failed with exit code 139 (use -v to see invocation)
Compiler returned: 139

Thanks for your support!

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llvmbot commented Nov 15, 2023

@llvm/issue-subscribers-clang-frontend

Author: None (JoniSt)

Dear Clang maintainers,

I've hit a crash in the C++ front-end when compiling the following C++20 code, which I believe to be valid:

using size_t = unsigned long long;

template&lt;typename... Ts&gt;
struct fake_tuple;

template&lt;size_t I, typename First, typename... Rest&gt;
struct fake_tuple_element {
    using type = fake_tuple_element&lt;I - 1, Rest...&gt;::type;
};

template&lt;typename First, typename... Rest&gt;
struct fake_tuple_element&lt;0, First, Rest...&gt; {
    using type = First;
};

namespace std {
    template&lt;class T, T... Ints&gt;
    class integer_sequence {
        static constexpr size_t size() noexcept { return sizeof...(Ints); }
    };

    template&lt;size_t... Ints&gt;
    using index_sequence = integer_sequence&lt;size_t, Ints...&gt;;

    template&lt;bool cond, typename T, typename F&gt;
    struct conditional;

    template&lt;typename T, typename F&gt;
    struct conditional&lt;true, T, F&gt; {
        using type = T;
    };

    template&lt;typename T, typename F&gt;
    struct conditional&lt;false, T, F&gt; {
        using type = F;
    };

    template&lt;class T, bool keep_going, T first, T... rest&gt;
    struct make_integer_sequence_helper2;

    template&lt;class T, T first, T... rest&gt;
    struct make_integer_sequence_helper {
        using type = typename make_integer_sequence_helper2&lt;T, first != 0, first, rest...&gt;::type;
    };

    template&lt;class T, T first, T... rest&gt;
    struct make_integer_sequence_helper2&lt;T, true, first, rest...&gt; {
        using type = typename make_integer_sequence_helper&lt;T, first - T{1}, first, rest...&gt;::type;
    };

    template&lt;class T, T first, T... rest&gt;
    struct make_integer_sequence_helper2&lt;T, false, first, rest...&gt; {
        using type = integer_sequence&lt;T, first, rest...&gt;;
    };

    template&lt;class T, T N&gt;
    using make_integer_sequence = typename make_integer_sequence_helper&lt;T, N - 1&gt;::type;

    template&lt;size_t N&gt;
    using make_index_sequence = make_integer_sequence&lt;size_t, N&gt;;

    template&lt;class T&gt;
    struct tuple_size;

    template&lt;typename... Ts&gt;
    struct tuple_size&lt;fake_tuple&lt;Ts...&gt;&gt; {
        static constexpr size_t value = sizeof...(Ts);
    };

    template&lt;size_t I, class T&gt;
    struct tuple_element;

    template&lt;size_t I, typename... Ts&gt;
    struct tuple_element&lt;I, fake_tuple&lt;Ts...&gt;&gt; {
        using type = typename fake_tuple_element&lt;I, Ts...&gt;::type;
    };

    template&lt;size_t I, typename... Ts&gt;
    const typename fake_tuple_element&lt;I, Ts...&gt;::type&amp; get(const fake_tuple&lt;Ts...&gt;&amp;);

    template&lt;class From, class To&gt;
    concept convertible_to = requires (From f) {
        { To{f} };
    };
}


// This crashes both Clang and GCC
template&lt;typename T&gt;
constexpr bool is_tuplelike_v = requires {
    std::tuple_size&lt;T&gt;{};
    { std::tuple_size&lt;T&gt;::value } -&gt; std::convertible_to&lt;size_t&gt;;

    requires [] &lt;size_t... Is&gt; (std::index_sequence&lt;Is...&gt;) {
        return ((requires (T t) {
            std::tuple_element&lt;Is, T&gt;{};
            typename std::tuple_element&lt;Is, T&gt;::type;
            { std::get&lt;Is&gt;(t) } -&gt; std::convertible_to&lt;typename std::tuple_element&lt;Is, T&gt;::type&gt;;
        }) &amp;&amp; ...);
    }(std::make_index_sequence&lt;std::tuple_size&lt;T&gt;::value&gt;{});
};

static_assert(is_tuplelike_v&lt;fake_tuple&lt;int, float&gt;&gt;);

The crash occurs both with the regular STL, as well as with the minimal std templates I've included in the reproducer in order to minify it a bit.

It appears that expanding a parameter pack within a requires expression trips the frontend up.

Compiler versions tested: 17.0.1, trunk

Godbolt (minified std templates): https://godbolt.org/z/baxqv6vra
Godbolt (regular STL): https://godbolt.org/z/eKjW99qoE

Crash output:

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-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++20 &lt;source&gt;
1.	&lt;source&gt;:103:53: current parser token ')'
2.	&lt;source&gt;:90:16: instantiating variable definition 'is_tuplelike_v&lt;fake_tuple&lt;int, float&gt;&gt;'
3.	&lt;source&gt;:94:14: instantiating function definition '(anonymous class)::operator()&lt;0ULL, 1ULL&gt;'
 #<!-- -->0 0x00000000034e5cd8 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x34e5cd8)
 #<!-- -->1 0x00000000034e3e24 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x34e3e24)
 #<!-- -->2 0x0000000003431fc8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x00007fce9657e420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #<!-- -->4 0x00000000064bb433 clang::Sema::CheckTemplateArgument(clang::TypeSourceInfo*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64bb433)
 #<!-- -->5 0x00000000064c9ec9 clang::Sema::CheckTemplateTypeArgument(clang::TemplateTypeParmDecl*, clang::TemplateArgumentLoc&amp;, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64c9ec9)
 #<!-- -->6 0x00000000064d01dd clang::Sema::CheckTemplateArgument(clang::NamedDecl*, clang::TemplateArgumentLoc&amp;, clang::NamedDecl*, clang::SourceLocation, clang::SourceLocation, unsigned int, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, clang::Sema::CheckTemplateArgumentKind) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64d01dd)
 #<!-- -->7 0x00000000064d1acc clang::Sema::CheckTemplateArgumentList(clang::TemplateDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo&amp;, bool, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, llvm::SmallVectorImpl&lt;clang::TemplateArgument&gt;&amp;, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64d1acc)
 #<!-- -->8 0x00000000064dc0e9 clang::Sema::CheckTemplateIdType(clang::TemplateName, clang::SourceLocation, clang::TemplateArgumentListInfo&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64dc0e9)
 #<!-- -->9 0x000000000661ec55 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformTemplateSpecializationType(clang::TypeLocBuilder&amp;, clang::TemplateSpecializationTypeLoc, clang::TemplateName) SemaTemplateInstantiate.cpp:0:0
#<!-- -->10 0x0000000006619597 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformTSIInObjectScope(clang::TypeLoc, clang::QualType, clang::NamedDecl*, clang::CXXScopeSpec&amp;) SemaTemplateInstantiate.cpp:0:0
#<!-- -->11 0x0000000006619cc6 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformNestedNameSpecifierLoc(clang::NestedNameSpecifierLoc, clang::QualType, clang::NamedDecl*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->12 0x000000000661fa4f clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformDependentNameType(clang::TypeLocBuilder&amp;, clang::DependentNameTypeLoc, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->13 0x0000000006613f89 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformType(clang::TypeLocBuilder&amp;, clang::TypeLoc) SemaTemplateInstantiate.cpp:0:0
#<!-- -->14 0x000000000661789b clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformType(clang::TypeSourceInfo*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->15 0x000000000661a618 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformTemplateArgument(clang::TemplateArgumentLoc const&amp;, clang::TemplateArgumentLoc&amp;, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->16 0x000000000661c450 bool clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformTemplateArguments&lt;clang::TemplateArgumentLoc const*&gt;(clang::TemplateArgumentLoc const*, clang::TemplateArgumentLoc const*, clang::TemplateArgumentListInfo&amp;, bool) (.constprop.0) SemaTemplateInstantiate.cpp:0:0
#<!-- -->17 0x000000000661d2f3 clang::Sema::SubstTypeConstraint(clang::TemplateTypeParmDecl*, clang::TypeConstraint const*, clang::MultiLevelTemplateArgumentList const&amp;, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x661d2f3)
#<!-- -->18 0x0000000006641d10 clang::TemplateDeclInstantiator::VisitTemplateTypeParmDecl(clang::TemplateTypeParmDecl*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6641d10)
#<!-- -->19 0x00000000066911cb clang::TemplateDeclInstantiator::SubstTemplateParams(clang::TemplateParameterList*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x66911cb)
#<!-- -->20 0x000000000662dc0d clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformRequiresExpr(clang::RequiresExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->21 0x0000000006607aee clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->22 0x00000000066131f5 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformParenExpr(clang::ParenExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->23 0x0000000006607bea clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->24 0x000000000660fa78 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCXXFoldExpr(clang::CXXFoldExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->25 0x00000000066081d5 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->26 0x0000000006609045 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformInitializer(clang::Expr*, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->27 0x000000000660a767 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformReturnStmt(clang::ReturnStmt*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->28 0x00000000066385eb clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCompoundStmt(clang::CompoundStmt*, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->29 0x000000000663ce91 clang::Sema::SubstStmt(clang::Stmt*, clang::MultiLevelTemplateArgumentList const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x663ce91)
#<!-- -->30 0x0000000006684818 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6684818)
#<!-- -->31 0x0000000005c64d01 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5c64d01)
#<!-- -->32 0x00000000065879c1 clang::Sema::DeduceReturnType(clang::FunctionDecl*, clang::SourceLocation, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x65879c1)
#<!-- -->33 0x000000000604f7f7 clang::Sema::DiagnoseUseOfDecl(clang::NamedDecl*, llvm::ArrayRef&lt;clang::SourceLocation&gt;, clang::ObjCInterfaceDecl const*, bool, bool, clang::ObjCInterfaceDecl*, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x604f7f7)
#<!-- -->34 0x00000000063c9057 CreateFunctionRefExpr(clang::Sema&amp;, clang::FunctionDecl*, clang::NamedDecl*, clang::Expr const*, bool, clang::SourceLocation, clang::DeclarationNameLoc const&amp;) SemaOverload.cpp:0:0
#<!-- -->35 0x00000000064122ba clang::Sema::BuildCallToObjectOfClassType(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64122ba)
#<!-- -->36 0x00000000060c0506 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60c0506)
#<!-- -->37 0x00000000060c5ebc clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60c5ebc)
#<!-- -->38 0x0000000006610fc7 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCallExpr(clang::CallExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->39 0x000000000660834d clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->40 0x0000000006636ecf clang::Sema::SubstConstraintExpr(clang::Expr*, clang::MultiLevelTemplateArgumentList const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6636ecf)
#<!-- -->41 0x0000000005dc82b1 calculateConstraintSatisfaction(clang::Sema&amp;, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&amp;, clang::Expr const*, clang::ConstraintSatisfaction&amp;)::'lambda'(clang::Expr const*)::operator()(clang::Expr const*) const SemaConcept.cpp:0:0
#<!-- -->42 0x0000000005dc98db clang::ActionResult&lt;clang::Expr*, true&gt; calculateConstraintSatisfaction&lt;calculateConstraintSatisfaction(clang::Sema&amp;, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&amp;, clang::Expr const*, clang::ConstraintSatisfaction&amp;)::'lambda'(clang::Expr const*)&gt;(clang::Sema&amp;, clang::Expr const*, clang::ConstraintSatisfaction&amp;, calculateConstraintSatisfaction(clang::Sema&amp;, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&amp;, clang::Expr const*, clang::ConstraintSatisfaction&amp;)::'lambda'(clang::Expr const*)&amp;&amp;) SemaConcept.cpp:0:0
#<!-- -->43 0x0000000005dca328 CheckConstraintSatisfaction(clang::Sema&amp;, clang::NamedDecl const*, llvm::ArrayRef&lt;clang::Expr const*&gt;, llvm::SmallVectorImpl&lt;clang::Expr*&gt;&amp;, clang::MultiLevelTemplateArgumentList const&amp;, clang::SourceRange, clang::ConstraintSatisfaction&amp;) SemaConcept.cpp:0:0
#<!-- -->44 0x0000000005dcab9f clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*, llvm::ArrayRef&lt;clang::Expr const*&gt;, llvm::SmallVectorImpl&lt;clang::Expr*&gt;&amp;, clang::MultiLevelTemplateArgumentList const&amp;, clang::SourceRange, clang::ConstraintSatisfaction&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5dcab9f)
#<!-- -->45 0x000000000662e05f clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformRequiresExpr(clang::RequiresExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->46 0x0000000006607aee clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->47 0x0000000006609045 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformInitializer(clang::Expr*, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->48 0x000000000660a8ea clang::Sema::SubstInitializer(clang::Expr*, clang::MultiLevelTemplateArgumentList const&amp;, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x660a8ea)
#<!-- -->49 0x0000000006644c64 clang::Sema::InstantiateVariableInitializer(clang::VarDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6644c64)
#<!-- -->50 0x0000000006644f3d clang::Sema::CompleteVarTemplateSpecializationDecl(clang::VarTemplateSpecializationDecl*, clang::VarDecl*, clang::MultiLevelTemplateArgumentList const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6644f3d)
#<!-- -->51 0x00000000066820c3 clang::Sema::InstantiateVariableDefinition(clang::SourceLocation, clang::VarDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x66820c3)
#<!-- -->52 0x0000000005c64d01 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5c64d01)
#<!-- -->53 0x00000000060740f8 DoMarkVarDeclReferenced(clang::Sema&amp;, clang::SourceLocation, clang::VarDecl*, clang::Expr*, llvm::DenseMap&lt;clang::VarDecl const*, int, llvm::DenseMapInfo&lt;clang::VarDecl const*, void&gt;, llvm::detail::DenseMapPair&lt;clang::VarDecl const*, int&gt;&gt;&amp;) SemaExpr.cpp:0:0
#<!-- -->54 0x000000000609bf94 MarkExprReferenced(clang::Sema&amp;, clang::SourceLocation, clang::Decl*, clang::Expr*, bool, llvm::DenseMap&lt;clang::VarDecl const*, int, llvm::DenseMapInfo&lt;clang::VarDecl const*, void&gt;, llvm::detail::DenseMapPair&lt;clang::VarDecl const*, int&gt;&gt;&amp;) SemaExpr.cpp:0:0
#<!-- -->55 0x000000000609c4e3 clang::Sema::BuildDeclRefExpr(clang::ValueDecl*, clang::QualType, clang::ExprValueKind, clang::DeclarationNameInfo const&amp;, clang::NestedNameSpecifierLoc, clang::NamedDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x609c4e3)
#<!-- -->56 0x000000000609cafc clang::Sema::BuildDeclRefExpr(clang::ValueDecl*, clang::QualType, clang::ExprValueKind, clang::DeclarationNameInfo const&amp;, clang::CXXScopeSpec const*, clang::NamedDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x609cafc)
#<!-- -->57 0x00000000060a1adc clang::Sema::BuildDeclarationNameExpr(clang::CXXScopeSpec const&amp;, clang::DeclarationNameInfo const&amp;, clang::NamedDecl*, clang::NamedDecl*, clang::TemplateArgumentListInfo const*, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60a1adc)
#<!-- -->58 0x00000000064e1e02 clang::Sema::BuildTemplateIdExpr(clang::CXXScopeSpec const&amp;, clang::SourceLocation, clang::LookupResult&amp;, bool, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64e1e02)
#<!-- -->59 0x00000000060a74b9 clang::Sema::ActOnIdExpression(clang::Scope*, clang::CXXScopeSpec&amp;, clang::SourceLocation, clang::UnqualifiedId&amp;, bool, bool, clang::CorrectionCandidateCallback*, bool, clang::Token*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60a74b9)
#<!-- -->60 0x0000000005b93778 clang::Parser::tryParseCXXIdExpression(clang::CXXScopeSpec&amp;, bool, clang::Token&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b93778)
#<!-- -->61 0x0000000005b9396a clang::Parser::ParseCXXIdExpression(bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b9396a)
#<!-- -->62 0x0000000005b760e8 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&amp;, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b760e8)
#<!-- -->63 0x0000000005b76b0c clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&amp;, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b76b0c)
#<!-- -->64 0x0000000005b850d9 clang::Parser::ParseConstantExpressionInExprEvalContext(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b850d9)
#<!-- -->65 0x0000000005b5c112 clang::Parser::ParseStaticAssertDeclaration(clang::SourceLocation&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b5c112)
#<!-- -->66 0x0000000005b4bac0 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b4bac0)
#<!-- -->67 0x0000000005b197f7 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b197f7)
#<!-- -->68 0x0000000005b1b567 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b1b567)
#<!-- -->69 0x0000000005b0a8ca clang::ParseAST(clang::Sema&amp;, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5b0a8ca)
#<!-- -->70 0x0000000003d1e795 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d1e795)
#<!-- -->71 0x0000000003f9da91 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f9da91)
#<!-- -->72 0x0000000003f1b97b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f1b97b)
#<!-- -->73 0x000000000407cec3 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x407cec3)
#<!-- -->74 0x0000000000c051c6 cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc051c6)
#<!-- -->75 0x0000000000bfdc1d ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->76 0x0000000003d65da9 void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const::'lambda'()&gt;(long) Job.cpp:0:0
#<!-- -->77 0x00000000034323f3 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x34323f3)
#<!-- -->78 0x0000000003d65fc9 clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const (.part.0) Job.cpp:0:0
#<!-- -->79 0x0000000003d2dfc7 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d2dfc7)
#<!-- -->80 0x0000000003d2e97d clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d2e97d)
#<!-- -->81 0x0000000003d386ec clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d386ec)
#<!-- -->82 0x0000000000c025c1 clang_main(int, char**, llvm::ToolContext const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc025c1)
#<!-- -->83 0x0000000000afd6f1 main (/opt/compiler-explorer/clang-trunk/bin/clang+++0xafd6f1)
#<!-- -->84 0x00007fce96022083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#<!-- -->85 0x0000000000bfd41e _start (/opt/compiler-explorer/clang-trunk/bin/clang+++0xbfd41e)
clang++: error: clang frontend command failed with exit code 139 (use -v to see invocation)
Compiler returned: 139

Thanks for your support!

@shafik
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shafik commented Nov 18, 2023

Interesting clang-15 requires typename on this line but won't crash once we add it: https://godbolt.org/z/8T3of7bM5

using type = typename  fake_tuple_element<I - 1, Rest...>::type;

I think this looks like a regression.

Worth noting only MSVC accepts this: https://godbolt.org/z/3bYKWf5ob

CC @erichkeane @cor3ntin @royjacobson

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shafik commented Nov 18, 2023

Might be a duplicate of: #64607

@shafik shafik added the confirmed Verified by a second party label Nov 18, 2023
@zyn0217
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zyn0217 commented Feb 26, 2024

ISTM that this is working on trunk. Closing.
https://godbolt.org/z/6qvsh3GT6

@zyn0217 zyn0217 closed this as completed Feb 26, 2024
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