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[clang] [frontend] crash when instantiating a parameter pack in a lambda constraint #101754

Closed xtactis closed 4 weeks ago

xtactis commented 2 months ago

The following program causes the clang frontend to crash.

#include <concepts>

template <typename... Ts>
struct Overloaded : Ts... {
    using Ts::operator()...;
};

template <typename... Ts>
Overloaded(Ts...) -> Overloaded<Ts...>;

template <typename... Ts>
auto foo() {
    return Overloaded{
        [](std::same_as<Ts> auto) {} ...
    };
}

int main() {
    foo<int, double*>()(42);
    return 0;
}

This is likely a regression between clang++15 and clang++16, as 15 has the correct behavior, but all later versions crash. Happens when compiling with -std=c++20, c++23, c++2b and c++2c. I wasn't able to find a version of GCC that has the correct behavior, all of them seem to believe this is an ill-formed program.

Godbolt link: https://godbolt.org/z/7czh4ndcv

Backtrace:

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: clang++ -std=c++20 main.cpp -c
1.      main.cpp:19:27: current parser token ')'
2.      main.cpp:18:12: parsing function body 'main'
3.      main.cpp:18:12: in compound statement ('{}')
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  clang++   0x000055b65c67da28 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 40
1  clang++   0x000055b65c67b9ee llvm::sys::RunSignalHandlers() + 238
2  clang++   0x000055b65c5fbee9
3  libc.so.6 0x00007fe1ad93f520
4  clang++   0x000055b65f187d78
5  clang++   0x000055b65f1413cb
6  clang++   0x000055b65f13d876
7  clang++   0x000055b65f13d2ef clang::Expr::EvaluateAsConstantExpr(clang::Expr::EvalResult&, clang::ASTContext const&, clang::Expr::ConstantExprKind) const + 991
8  clang++   0x000055b65e6617b3
9  clang++   0x000055b65e65ba4f
10 clang++   0x000055b65e65b7e0 clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::SmallVectorImpl<clang::Expr*>&, clang::MultiLevelTemplateArgumentList const&, clang::SourceRange, clang::ConstraintSatisfaction&) + 624
11 clang++   0x000055b65e65e79f clang::Sema::CheckInstantiatedFunctionTemplateConstraints(clang::SourceLocation, clang::FunctionDecl*, llvm::ArrayRef<clang::TemplateArgument>, clang::ConstraintSatisfaction&) + 767
12 clang++   0x000055b65ec021c6 clang::Sema::FinishTemplateArgumentDeduction(clang::FunctionTemplateDecl*, llvm::SmallVectorImpl<clang::DeducedTemplateArgument>&, unsigned int, clang::FunctionDecl*&, clang::sema::TemplateDeductionInfo&, llvm::SmallVectorImpl<clang::Sema::OriginalCallArg> const*, bool, llvm::function_ref<bool ()>) + 3190
13 clang++   0x000055b65ec55029
14 clang++   0x000055b65e5801cf clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) + 47
15 clang++   0x000055b65ec03832 clang::Sema::DeduceTemplateArguments(clang::FunctionTemplateDecl*, clang::TemplateArgumentListInfo*, llvm::ArrayRef<clang::Expr*>, clang::FunctionDecl*&, clang::sema::TemplateDeductionInfo&, bool, bool, llvm::function_ref<bool (llvm::ArrayRef<clang::QualType>)>) + 2274
16 clang++   0x000055b65eadeb69 clang::Sema::AddMethodTemplateCandidate(clang::FunctionTemplateDecl*, clang::DeclAccessPair, clang::CXXRecordDecl*, clang::TemplateArgumentListInfo*, clang::QualType, clang::Expr::Classification, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool, bool, clang::OverloadCandidateParamOrder) + 633
17 clang++   0x000055b65eaf78bf clang::Sema::BuildCallToObjectOfClassType(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation) + 1183
18 clang++   0x000055b65e80499a clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) + 2938
19 clang++   0x000055b65e81bf4a clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*) + 58
20 clang++   0x000055b65e4c23b2 clang::Parser::ParsePostfixExpressionSuffix(clang::ActionResult<clang::Expr*, true>) + 5138
21 clang++   0x000055b65e4c39c2 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) + 2194
22 clang++   0x000055b65e4bf68f clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) + 223
23 clang++   0x000055b65e4bf599 clang::Parser::ParseExpression(clang::Parser::TypeCastState) + 9
24 clang++   0x000055b65e51d931 clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) + 49
25 clang++   0x000055b65e51bea7 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) + 1047
26 clang++   0x000055b65e51b85f clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) + 303
27 clang++   0x000055b65e523be1 clang::Parser::ParseCompoundStatementBody(bool) + 1905
28 clang++   0x000055b65e524b34 clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) + 164
29 clang++   0x000055b65e4778de clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) + 4094
30 clang++   0x000055b65e48ff1f clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) + 4863
31 clang++   0x000055b65e47653c clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) + 988
32 clang++   0x000055b65e475f81 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) + 417
33 clang++   0x000055b65e475281 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) + 1969
34 clang++   0x000055b65e4737b4 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) + 1476
35 clang++   0x000055b65e46f7ce clang::ParseAST(clang::Sema&, bool, bool) + 782
36 clang++   0x000055b65cedf847 clang::FrontendAction::Execute() + 87
37 clang++   0x000055b65ce53274 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 788
38 clang++   0x000055b65cf9688f clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 639
39 clang++   0x000055b65a89a2b6 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) + 2582
40 clang++   0x000055b65a897e81
41 clang++   0x000055b65ccbf139
42 clang++   0x000055b65c5fbccc llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) + 140
43 clang++   0x000055b65ccbeb76 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const + 326
44 clang++   0x000055b65cc81e7c clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const + 460
45 clang++   0x000055b65cc8231e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const + 142
46 clang++   0x000055b65cc9fab0 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) + 912
47 clang++   0x000055b65a8974bd clang_main(int, char**, llvm::ToolContext const&) + 11549
48 clang++   0x000055b65a8a4f11 main + 33
49 libc.so.6 0x00007fe1ad926d90
50 libc.so.6 0x00007fe1ad926e40 __libc_start_main + 128
51 clang++   0x000055b65a894495 _start + 37
clang++: error: clang frontend command failed with exit code 139 (use -v to see invocation)
clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/md/bin
clang++: note: diagnostic msg:
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++: note: diagnostic msg: /tmp/main-568d09.cpp
clang++: note: diagnostic msg: /tmp/main-568d09.sh
clang++: note: diagnostic msg:

main-568d09.zip.zip

llvmbot commented 2 months ago

@llvm/issue-subscribers-clang-frontend

Author: Matija Dizdar (xtactis)

The following program causes the clang frontend to crash. ```cpp #include <concepts> template <typename... Ts> struct Overloaded : Ts... { using Ts::operator()...; }; template <typename... Ts> Overloaded(Ts...) -> Overloaded<Ts...>; template <typename... Ts> auto foo() { return Overloaded{ [](std::same_as<Ts> auto) {} ... }; } int main() { foo<int, double*>()(42); return 0; } ``` This is likely a regression between clang++15 and clang++16, as 15 has the correct behavior, but all later versions crash. Happens when compiling with -std=c++20, c++23, c++2b and c++2c. I wasn't able to find a version of GCC that has the correct behavior, all of them seem to believe this is an ill-formed program. Godbolt link: https://godbolt.org/z/7czh4ndcv Backtrace: ``` 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: clang++ -std=c++20 main.cpp -c 1. main.cpp:19:27: current parser token ')' 2. main.cpp:18:12: parsing function body 'main' 3. main.cpp:18:12: in compound statement ('{}') Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it): 0 clang++ 0x000055b65c67da28 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 40 1 clang++ 0x000055b65c67b9ee llvm::sys::RunSignalHandlers() + 238 2 clang++ 0x000055b65c5fbee9 3 libc.so.6 0x00007fe1ad93f520 4 clang++ 0x000055b65f187d78 5 clang++ 0x000055b65f1413cb 6 clang++ 0x000055b65f13d876 7 clang++ 0x000055b65f13d2ef clang::Expr::EvaluateAsConstantExpr(clang::Expr::EvalResult&, clang::ASTContext const&, clang::Expr::ConstantExprKind) const + 991 8 clang++ 0x000055b65e6617b3 9 clang++ 0x000055b65e65ba4f 10 clang++ 0x000055b65e65b7e0 clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::SmallVectorImpl<clang::Expr*>&, clang::MultiLevelTemplateArgumentList const&, clang::SourceRange, clang::ConstraintSatisfaction&) + 624 11 clang++ 0x000055b65e65e79f clang::Sema::CheckInstantiatedFunctionTemplateConstraints(clang::SourceLocation, clang::FunctionDecl*, llvm::ArrayRef<clang::TemplateArgument>, clang::ConstraintSatisfaction&) + 767 12 clang++ 0x000055b65ec021c6 clang::Sema::FinishTemplateArgumentDeduction(clang::FunctionTemplateDecl*, llvm::SmallVectorImpl<clang::DeducedTemplateArgument>&, unsigned int, clang::FunctionDecl*&, clang::sema::TemplateDeductionInfo&, llvm::SmallVectorImpl<clang::Sema::OriginalCallArg> const*, bool, llvm::function_ref<bool ()>) + 3190 13 clang++ 0x000055b65ec55029 14 clang++ 0x000055b65e5801cf clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) + 47 15 clang++ 0x000055b65ec03832 clang::Sema::DeduceTemplateArguments(clang::FunctionTemplateDecl*, clang::TemplateArgumentListInfo*, llvm::ArrayRef<clang::Expr*>, clang::FunctionDecl*&, clang::sema::TemplateDeductionInfo&, bool, bool, llvm::function_ref<bool (llvm::ArrayRef<clang::QualType>)>) + 2274 16 clang++ 0x000055b65eadeb69 clang::Sema::AddMethodTemplateCandidate(clang::FunctionTemplateDecl*, clang::DeclAccessPair, clang::CXXRecordDecl*, clang::TemplateArgumentListInfo*, clang::QualType, clang::Expr::Classification, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool, bool, clang::OverloadCandidateParamOrder) + 633 17 clang++ 0x000055b65eaf78bf clang::Sema::BuildCallToObjectOfClassType(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation) + 1183 18 clang++ 0x000055b65e80499a clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) + 2938 19 clang++ 0x000055b65e81bf4a clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*) + 58 20 clang++ 0x000055b65e4c23b2 clang::Parser::ParsePostfixExpressionSuffix(clang::ActionResult<clang::Expr*, true>) + 5138 21 clang++ 0x000055b65e4c39c2 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) + 2194 22 clang++ 0x000055b65e4bf68f clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) + 223 23 clang++ 0x000055b65e4bf599 clang::Parser::ParseExpression(clang::Parser::TypeCastState) + 9 24 clang++ 0x000055b65e51d931 clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) + 49 25 clang++ 0x000055b65e51bea7 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) + 1047 26 clang++ 0x000055b65e51b85f clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) + 303 27 clang++ 0x000055b65e523be1 clang::Parser::ParseCompoundStatementBody(bool) + 1905 28 clang++ 0x000055b65e524b34 clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) + 164 29 clang++ 0x000055b65e4778de clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) + 4094 30 clang++ 0x000055b65e48ff1f clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) + 4863 31 clang++ 0x000055b65e47653c clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) + 988 32 clang++ 0x000055b65e475f81 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) + 417 33 clang++ 0x000055b65e475281 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) + 1969 34 clang++ 0x000055b65e4737b4 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) + 1476 35 clang++ 0x000055b65e46f7ce clang::ParseAST(clang::Sema&, bool, bool) + 782 36 clang++ 0x000055b65cedf847 clang::FrontendAction::Execute() + 87 37 clang++ 0x000055b65ce53274 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 788 38 clang++ 0x000055b65cf9688f clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 639 39 clang++ 0x000055b65a89a2b6 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) + 2582 40 clang++ 0x000055b65a897e81 41 clang++ 0x000055b65ccbf139 42 clang++ 0x000055b65c5fbccc llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) + 140 43 clang++ 0x000055b65ccbeb76 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const + 326 44 clang++ 0x000055b65cc81e7c clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const + 460 45 clang++ 0x000055b65cc8231e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const + 142 46 clang++ 0x000055b65cc9fab0 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) + 912 47 clang++ 0x000055b65a8974bd clang_main(int, char**, llvm::ToolContext const&) + 11549 48 clang++ 0x000055b65a8a4f11 main + 33 49 libc.so.6 0x00007fe1ad926d90 50 libc.so.6 0x00007fe1ad926e40 __libc_start_main + 128 51 clang++ 0x000055b65a894495 _start + 37 clang++: error: clang frontend command failed with exit code 139 (use -v to see invocation) clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18) Target: x86_64-unknown-linux-gnu Thread model: posix InstalledDir: /home/md/bin clang++: note: diagnostic msg: ******************** PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT: Preprocessed source(s) and associated run script(s) are located at: clang++: note: diagnostic msg: /tmp/main-568d09.cpp clang++: note: diagnostic msg: /tmp/main-568d09.sh clang++: note: diagnostic msg: ``` [main-568d09.zip.zip](https://github.com/user-attachments/files/16475445/main-568d09.zip.zip)
xtactis commented 2 months ago

a smaller example with the same behavior

#include <tuple>

template <class, class>
concept C = false;

template <class... Ts>
auto f(Ts...) {
    return std::tuple{
        [](std::same_as<Ts> auto){} ...
    };
}

int main() {
    auto [a, b] = f(42, "arst");
    a(43);
}

Note that the crash happens when evaluating a(43);, and that the following program compiles fine

#include <tuple>

template <class... Ts>
auto f(Ts...) {
    return std::tuple{
        [](Ts){} ...
    };
}

int main() {
    auto [a, b] = f(42, "arst");
    a(43);
}
zyn0217 commented 2 months ago

I guess this is another case where the constraints are not properly expanded in a fold expression. It's similar to the symptoms in https://github.com/llvm/llvm-project/pull/86265, but I have dropped the fix for constraints (hopefully to speed up the review process) in that patch.