Clang-20 Crash: not a non-type template argument UNREACHABLE executed at /root/llvm-project/clang/lib/Sema/SemaTemplate.cpp:7688!

[iamanonymouscs]

Description

I encountered a crash in Clang-20 when compiling the following code snippet:

#include <iostream>

template <bool compare>
struct outer
{
  template <bool compare_with,bool second>
  struct inner           // unspecialized compare != compare_with
  {
    static inline void test()
    {
      std::cout << "invert" << std::endl;
      // call version with inverted template value
      inner<! compare_with, ! second>::test();
    }
  };
  template <bool second> // specialization compare == compare_with
  struct inner<compare,second>
  {
    static inline void test()
    {
      std::cout << "second: " << second << std::endl;
    }
  };
};

int main(int argc,char* argv[],char** envp)
{
  // expected output:
  //  invert
  //  second: true
  outer<false>::inner<true,false>::test();

  // expected output:
  //  second: false
  outer<true>::inner<true,false>::test();

  return 0;
}

template <bool B1> struct outer { 
    template <bool B2, bool B3> 
    struct inner { 
        static int f() { return inner<!B2,!B3>::N; }; 
    }; 
 
    template <bool B3> 
    struct inner<B1,B3> { 
        static const int N = 1; 
    }; 
};

int i = outer<false>::inner<true,false>::f(); 

template <bool B1> struct outer { 
    template <bool B2> 
    struct inner { 
        static int f() { return inner<!B2>::N; }; 
    }; 
 
    template <> 
    struct inner<B1> { 
        static const int N = 1; 
    }; 
};

int i = outer<false>::inner<true>::f(); 

template <typename T> struct outer { 
    template <typename T2, typename U> 
    struct inner { 
        static int f() { return inner<T,int>::N; }; 
    }; 
 
    template <typename U> 
    struct inner<T,U> { 
        static const int N = 1; 
    }; 
};

int i = outer<int>::inner<double,int>::f();

Command

The compilation command used was:

clang++  -fno-rtlib-add-rpath  -fno-ident -std=c++23  -Wall -Wextra -fno-strict-aliasing -fwrapv -g -fsanitize=address  test.cpp 

Error Message

<source>:26:14: warning: unused parameter 'argc' [-Wunused-parameter]
   26 | int main(int argc,char* argv[],char** envp)
      |              ^
<source>:26:25: warning: unused parameter 'argv' [-Wunused-parameter]
   26 | int main(int argc,char* argv[],char** envp)
      |                         ^
<source>:26:39: warning: unused parameter 'envp' [-Wunused-parameter]
   26 | int main(int argc,char* argv[],char** envp)
      |                                       ^
<source>:40:27: error: redefinition of 'outer'
   40 | template <bool B1> struct outer { 
      |                           ^
<source>:4:8: note: previous definition is here
    4 | struct outer
      |        ^
<source>:52:42: error: no member named 'f' in 'outer<false>::inner<true, false>'
   52 | int i = outer<false>::inner<true,false>::f(); 
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
<source>:54:27: error: redefinition of 'outer'
   54 | template <bool B1> struct outer { 
      |                           ^
<source>:4:8: note: previous definition is here
    4 | struct outer
      |        ^
<source>:66:5: error: redefinition of 'i'
   66 | int i = outer<false>::inner<true>::f(); 
      |     ^
<source>:52:5: note: previous definition is here
   52 | int i = outer<false>::inner<true,false>::f(); 
      |     ^
<source>:66:23: error: too few template arguments for class template 'inner'
   66 | int i = outer<false>::inner<true>::f(); 
      |                       ^
<source>:7:10: note: template is declared here
    6 |   template <bool compare_with,bool second>
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    7 |   struct inner           // unspecialized compare != compare_with
      |          ^
<source>:68:20: error: template parameter has a different kind in template redeclaration
   68 | template <typename T> struct outer { 
      |                    ^
<source>:3:16: note: previous template declaration is here
    3 | template <bool compare>
      |                ^
<source>:80:5: error: redefinition of 'i'
   80 | int i = outer<int>::inner<double,int>::f();
      |     ^
<source>:52:5: note: previous definition is here
   52 | int i = outer<false>::inner<true,false>::f(); 
      |     ^
not a non-type template argument
UNREACHABLE executed at /root/llvm-project/clang/lib/Sema/SemaTemplate.cpp:7688!
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -fno-rtlib-add-rpath -fno-ident -std=c++23 -Wall -Wextra -fno-strict-aliasing -fwrapv -g -fsanitize=address <source>
1.	<source>:80:21: current parser token 'inner'
2.	<source>:4:8: instantiating class definition 'outer<int>'
 #0 0x0000000003be87b8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3be87b8)
 #1 0x0000000003be64bc llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3be64bc)
 #2 0x0000000003b33df8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f77ff642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007f77ff6969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007f77ff642476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007f77ff6287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x0000000003b3f71a (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b3f71a)
 #8 0x0000000007244d04 clang::Sema::BuildExpressionFromNonTypeTemplateArgument(clang::TemplateArgument const&, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7244d04)
 #9 0x000000000747c1c3 (anonymous namespace)::TemplateInstantiator::transformNonTypeTemplateParmRef(clang::Decl*, clang::NonTypeTemplateParmDecl const*, clang::SourceLocation, clang::TemplateArgument, std::optional<unsigned int>) SemaTemplateInstantiate.cpp:0:0
#10 0x000000000748df0d (anonymous namespace)::TemplateInstantiator::TransformDeclRefExpr(clang::DeclRefExpr*) SemaTemplateInstantiate.cpp:0:0
#11 0x000000000746252d clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#12 0x0000000007481983 (anonymous namespace)::TemplateInstantiator::TransformTemplateArgument(clang::TemplateArgumentLoc const&, clang::TemplateArgumentLoc&, bool) SemaTemplateInstantiate.cpp:0:0
#13 0x0000000007485065 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
#14 0x0000000007485507 clang::Sema::SubstTemplateArguments(llvm::ArrayRef<clang::TemplateArgumentLoc>, clang::MultiLevelTemplateArgumentList const&, clang::TemplateArgumentListInfo&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7485507)
#15 0x000000000751cabb clang::TemplateDeclInstantiator::InstantiateClassTemplatePartialSpecialization(clang::ClassTemplateDecl*, clang::ClassTemplatePartialSpecializationDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x751cabb)
#16 0x000000000748717b clang::Sema::InstantiateClass(clang::SourceLocation, clang::CXXRecordDecl*, clang::CXXRecordDecl*, clang::MultiLevelTemplateArgumentList const&, clang::TemplateSpecializationKind, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x748717b)
#17 0x0000000007488e6e clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7488e6e)
#18 0x000000000754af0f 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
#19 0x00000000081be4d1 clang::StackExhaustionHandler::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x81be4d1)
#20 0x00000000075543b7 clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x75543b7)
#21 0x0000000007554705 clang::Sema::RequireCompleteType(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7554705)
#22 0x00000000068e9f6c clang::Sema::RequireCompleteDeclContext(clang::CXXScopeSpec&, clang::DeclContext*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68e9f6c)
#23 0x0000000007251146 clang::Sema::LookupTemplateName(clang::LookupResult&, clang::Scope*, clang::CXXScopeSpec&, clang::QualType, bool, clang::Sema::RequiredTemplateKind, clang::Sema::AssumedTemplateKind*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7251146)
#24 0x0000000007252709 clang::Sema::isTemplateName(clang::Scope*, clang::CXXScopeSpec&, bool, clang::UnqualifiedId const&, clang::OpaquePtr<clang::QualType>, bool, clang::OpaquePtr<clang::TemplateName>&, bool&, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7252709)
#25 0x0000000006776d3e clang::Parser::ParseOptionalCXXScopeSpecifier(clang::CXXScopeSpec&, clang::OpaquePtr<clang::QualType>, bool, bool, bool*, bool, clang::IdentifierInfo const**, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6776d3e)
#26 0x00000000066e8603 clang::Parser::TryAnnotateTypeOrScopeToken(clang::ImplicitTypenameContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66e8603)
#27 0x000000000675c63e clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x675c63e)
#28 0x000000000675e567 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x675e567)
#29 0x000000000675e5f9 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x675e5f9)
#30 0x0000000006717f28 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6717f28)
#31 0x0000000006726f89 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6726f89)
#32 0x00000000066e6fae clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66e6fae)
#33 0x00000000066e776e clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66e776e)
#34 0x00000000066eef03 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66eef03)
#35 0x00000000066efded clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66efded)
#36 0x00000000066e230a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66e230a)
#37 0x0000000004560df8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4560df8)
#38 0x000000000481b949 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x481b949)
#39 0x000000000479abbe clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x479abbe)
#40 0x00000000049016de clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x49016de)
#41 0x0000000000ce5b8f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xce5b8f)
#42 0x0000000000cdd84a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#43 0x00000000045a3f79 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
#44 0x0000000003b342a4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b342a4)
#45 0x00000000045a456f 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
#46 0x000000000456a8dd clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x456a8dd)
#47 0x000000000456b9cd clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x456b9cd)
#48 0x0000000004572d85 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4572d85)
#49 0x0000000000ce2a29 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xce2a29)
#50 0x0000000000bafbc4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbafbc4)
#51 0x00007f77ff629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#52 0x00007f77ff629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#53 0x0000000000cdd2fe _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcdd2fe)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

The issue can also be reproduced on Compiler Explorer:https://godbolt.org/z/91cMa4abK
Please let me know if you need any more details.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Anonymous (iamanonymouscs)

### Description I encountered a crash in Clang-20 when compiling the following code snippet:

#include <iostream>

template <bool compare>
struct outer
{
  template <bool compare_with,bool second>
  struct inner           // unspecialized compare != compare_with
  {
    static inline void test()
    {
      std::cout << "invert" << std::endl;
      // call version with inverted template value
      inner<! compare_with, ! second>::test();
    }
  };
  template <bool second> // specialization compare == compare_with
  struct inner<compare,second>
  {
    static inline void test()
    {
      std::cout << "second: " << second << std::endl;
    }
  };
};

int main(int argc,char* argv[],char** envp)
{
  // expected output:
  //  invert
  //  second: true
  outer<false>::inner<true,false>::test();

  // expected output:
  //  second: false
  outer<true>::inner<true,false>::test();

  return 0;
}

template <bool B1> struct outer { 
    template <bool B2, bool B3> 
    struct inner { 
        static int f() { return inner<!B2,!B3>::N; }; 
    }; 
 
    template <bool B3> 
    struct inner<B1,B3> { 
        static const int N = 1; 
    }; 
};

int i = outer<false>::inner<true,false>::f(); 

template <bool B1> struct outer { 
    template <bool B2> 
    struct inner { 
        static int f() { return inner<!B2>::N; }; 
    }; 
 
    template <> 
    struct inner<B1> { 
        static const int N = 1; 
    }; 
};

int i = outer<false>::inner<true>::f(); 

template <typename T> struct outer { 
    template <typename T2, typename U> 
    struct inner { 
        static int f() { return inner<T,int>::N; }; 
    }; 
 
    template <typename U> 
    struct inner<T,U> { 
        static const int N = 1; 
    }; 
};

int i = outer<int>::inner<double,int>::f();

Command

The compilation command used was:

clang++  -fno-rtlib-add-rpath  -fno-ident -std=c++23  -Wall -Wextra -fno-strict-aliasing -fwrapv -g -fsanitize=address  test.cpp 

Error Message

<source>:26:14: warning: unused parameter 'argc' [-Wunused-parameter]
   26 | int main(int argc,char* argv[],char** envp)
      |              ^
<source>:26:25: warning: unused parameter 'argv' [-Wunused-parameter]
   26 | int main(int argc,char* argv[],char** envp)
      |                         ^
<source>:26:39: warning: unused parameter 'envp' [-Wunused-parameter]
   26 | int main(int argc,char* argv[],char** envp)
      |                                       ^
<source>:40:27: error: redefinition of 'outer'
   40 | template <bool B1> struct outer { 
      |                           ^
<source>:4:8: note: previous definition is here
    4 | struct outer
      |        ^
<source>:52:42: error: no member named 'f' in 'outer<false>::inner<true, false>'
   52 | int i = outer<false>::inner<true,false>::f(); 
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
<source>:54:27: error: redefinition of 'outer'
   54 | template <bool B1> struct outer { 
      |                           ^
<source>:4:8: note: previous definition is here
    4 | struct outer
      |        ^
<source>:66:5: error: redefinition of 'i'
   66 | int i = outer<false>::inner<true>::f(); 
      |     ^
<source>:52:5: note: previous definition is here
   52 | int i = outer<false>::inner<true,false>::f(); 
      |     ^
<source>:66:23: error: too few template arguments for class template 'inner'
   66 | int i = outer<false>::inner<true>::f(); 
      |                       ^
<source>:7:10: note: template is declared here
    6 |   template <bool compare_with,bool second>
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    7 |   struct inner           // unspecialized compare != compare_with
      |          ^
<source>:68:20: error: template parameter has a different kind in template redeclaration
   68 | template <typename T> struct outer { 
      |                    ^
<source>:3:16: note: previous template declaration is here
    3 | template <bool compare>
      |                ^
<source>:80:5: error: redefinition of 'i'
   80 | int i = outer<int>::inner<double,int>::f();
      |     ^
<source>:52:5: note: previous definition is here
   52 | int i = outer<false>::inner<true,false>::f(); 
      |     ^
not a non-type template argument
UNREACHABLE executed at /root/llvm-project/clang/lib/Sema/SemaTemplate.cpp:7688!
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -fno-rtlib-add-rpath -fno-ident -std=c++23 -Wall -Wextra -fno-strict-aliasing -fwrapv -g -fsanitize=address <source>
1.	<source>:80:21: current parser token 'inner'
2.	<source>:4:8: instantiating class definition 'outer<int>'
 #<!-- -->0 0x0000000003be87b8 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3be87b8)
 #<!-- -->1 0x0000000003be64bc llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3be64bc)
 #<!-- -->2 0x0000000003b33df8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x00007f77ff642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #<!-- -->4 0x00007f77ff6969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #<!-- -->5 0x00007f77ff642476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #<!-- -->6 0x00007f77ff6287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #<!-- -->7 0x0000000003b3f71a (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b3f71a)
 #<!-- -->8 0x0000000007244d04 clang::Sema::BuildExpressionFromNonTypeTemplateArgument(clang::TemplateArgument const&amp;, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7244d04)
 #<!-- -->9 0x000000000747c1c3 (anonymous namespace)::TemplateInstantiator::transformNonTypeTemplateParmRef(clang::Decl*, clang::NonTypeTemplateParmDecl const*, clang::SourceLocation, clang::TemplateArgument, std::optional&lt;unsigned int&gt;) SemaTemplateInstantiate.cpp:0:0
#<!-- -->10 0x000000000748df0d (anonymous namespace)::TemplateInstantiator::TransformDeclRefExpr(clang::DeclRefExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->11 0x000000000746252d clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->12 0x0000000007481983 (anonymous namespace)::TemplateInstantiator::TransformTemplateArgument(clang::TemplateArgumentLoc const&amp;, clang::TemplateArgumentLoc&amp;, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->13 0x0000000007485065 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
#<!-- -->14 0x0000000007485507 clang::Sema::SubstTemplateArguments(llvm::ArrayRef&lt;clang::TemplateArgumentLoc&gt;, clang::MultiLevelTemplateArgumentList const&amp;, clang::TemplateArgumentListInfo&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7485507)
#<!-- -->15 0x000000000751cabb clang::TemplateDeclInstantiator::InstantiateClassTemplatePartialSpecialization(clang::ClassTemplateDecl*, clang::ClassTemplatePartialSpecializationDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x751cabb)
#<!-- -->16 0x000000000748717b clang::Sema::InstantiateClass(clang::SourceLocation, clang::CXXRecordDecl*, clang::CXXRecordDecl*, clang::MultiLevelTemplateArgumentList const&amp;, clang::TemplateSpecializationKind, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x748717b)
#<!-- -->17 0x0000000007488e6e clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7488e6e)
#<!-- -->18 0x000000000754af0f void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*)::'lambda'()&gt;(long) SemaType.cpp:0:0
#<!-- -->19 0x00000000081be4d1 clang::StackExhaustionHandler::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x81be4d1)
#<!-- -->20 0x00000000075543b7 clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x75543b7)
#<!-- -->21 0x0000000007554705 clang::Sema::RequireCompleteType(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7554705)
#<!-- -->22 0x00000000068e9f6c clang::Sema::RequireCompleteDeclContext(clang::CXXScopeSpec&amp;, clang::DeclContext*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68e9f6c)
#<!-- -->23 0x0000000007251146 clang::Sema::LookupTemplateName(clang::LookupResult&amp;, clang::Scope*, clang::CXXScopeSpec&amp;, clang::QualType, bool, clang::Sema::RequiredTemplateKind, clang::Sema::AssumedTemplateKind*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7251146)
#<!-- -->24 0x0000000007252709 clang::Sema::isTemplateName(clang::Scope*, clang::CXXScopeSpec&amp;, bool, clang::UnqualifiedId const&amp;, clang::OpaquePtr&lt;clang::QualType&gt;, bool, clang::OpaquePtr&lt;clang::TemplateName&gt;&amp;, bool&amp;, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7252709)
#<!-- -->25 0x0000000006776d3e clang::Parser::ParseOptionalCXXScopeSpecifier(clang::CXXScopeSpec&amp;, clang::OpaquePtr&lt;clang::QualType&gt;, bool, bool, bool*, bool, clang::IdentifierInfo const**, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6776d3e)
#<!-- -->26 0x00000000066e8603 clang::Parser::TryAnnotateTypeOrScopeToken(clang::ImplicitTypenameContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66e8603)
#<!-- -->27 0x000000000675c63e clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&amp;, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x675c63e)
#<!-- -->28 0x000000000675e567 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x675e567)
#<!-- -->29 0x000000000675e5f9 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x675e5f9)
#<!-- -->30 0x0000000006717f28 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6717f28)
#<!-- -->31 0x0000000006726f89 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&amp;, clang::DeclaratorContext, clang::ParsedAttributes&amp;, clang::Parser::ParsedTemplateInfo&amp;, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6726f89)
#<!-- -->32 0x00000000066e6fae clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec&amp;, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66e6fae)
#<!-- -->33 0x00000000066e776e clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66e776e)
#<!-- -->34 0x00000000066eef03 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66eef03)
#<!-- -->35 0x00000000066efded clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66efded)
#<!-- -->36 0x00000000066e230a clang::ParseAST(clang::Sema&amp;, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66e230a)
#<!-- -->37 0x0000000004560df8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4560df8)
#<!-- -->38 0x000000000481b949 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x481b949)
#<!-- -->39 0x000000000479abbe clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x479abbe)
#<!-- -->40 0x00000000049016de clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x49016de)
#<!-- -->41 0x0000000000ce5b8f cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xce5b8f)
#<!-- -->42 0x0000000000cdd84a ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->43 0x00000000045a3f79 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
#<!-- -->44 0x0000000003b342a4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b342a4)
#<!-- -->45 0x00000000045a456f 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
#<!-- -->46 0x000000000456a8dd clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x456a8dd)
#<!-- -->47 0x000000000456b9cd 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-assertions-trunk/bin/clang+++0x456b9cd)
#<!-- -->48 0x0000000004572d85 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-assertions-trunk/bin/clang+++0x4572d85)
#<!-- -->49 0x0000000000ce2a29 clang_main(int, char**, llvm::ToolContext const&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xce2a29)
#<!-- -->50 0x0000000000bafbc4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbafbc4)
#<!-- -->51 0x00007f77ff629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#<!-- -->52 0x00007f77ff629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#<!-- -->53 0x0000000000cdd2fe _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcdd2fe)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

The issue can also be reproduced on Compiler Explorer:https://godbolt.org/z/91cMa4abK
Please let me know if you need any more details.

[jiixyj]

I've minimized the original example with cvise:

template <bool B1> struct outer {
  template <B2> struct inner
  struct inner<B1>
}template < typename > struct outer;
  outer<int>::

I could bisect it to 2bb3d3a (PR).

Here is another reproducer in valid C++ (which is the reason I stumbled upon this bug):

import std;

int main()
{
    std::tuple<int> t{};
    std::get<0>(t);
}

Modules are involved here, so the underlying bug may be a different one... The assert being hit is the same, though.

[shafik]

CC @sdkrystian