<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/138820>138820</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang  crashes with ICE when concept constraint uses incomplete requires block with ellipsis since version 20 with -std=c++20
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          mariete1223
      </td>
    </tr>
</table>

<pre>
    Using a concept with a requires clause that includes an incomplete expression using ellipsis (...) results in an internal compiler error (ICE)

## Assertion 

No assertion arises

## Program

```
int a;
template<typename T>
concept atomicish = requires() {
  {
    a
   ...
 };
};
atomicish<int> f();
```

## Stack dump

```
Stack dump:
0.      Program arguments: /opt/compiler-explorer/clang-20.1.0/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-14.2.0 -fcolor-diagnostics -fno-crash-diagnostics -x c++ -std=c++20 <source>
1.      <source>:9:16: current parser token 'f'
 #0 0x0000000003a59568 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x3a59568)
 #1 0x0000000003a576ac llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x3a576ac)
 #2 0x00000000039a69e8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x000070092b642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x000000000742ef29 clang::Expr::IgnoreParenImpCasts() (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x742ef29)
 #5 0x00000000065c1b26 clang::ActionResult<clang::Expr*, true> calculateConstraintSatisfaction<calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&, clang::Expr const*, clang::ConstraintSatisfaction&)::ConstraintEvaluator>(clang::Sema&, clang::Expr const*, clang::ConstraintSatisfaction&, calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, clang::SourceLocation, clang::MultiLevelTemplateArgumentList const&, clang::Expr const*, clang::ConstraintSatisfaction&)::ConstraintEvaluator const&) SemaConcept.cpp:0:0
 #6 0x00000000065c484a 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
 #7 0x00000000065c4d97 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-20.1.0/bin/clang+++0x65c4d97)
 #8 0x0000000006ced338 clang::Sema::CheckConceptTemplateId(clang::CXXScopeSpec const&, clang::SourceLocation, clang::DeclarationNameInfo const&, clang::NamedDecl*, clang::ConceptDecl*, clang::TemplateArgumentListInfo const*) (.constprop.0) SemaTemplate.cpp:0:0
 #9 0x0000000006ceeb06 clang::Sema::BuildTemplateIdExpr(clang::CXXScopeSpec const&, clang::SourceLocation, clang::LookupResult&, bool, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x6ceeb06)
#10 0x00000000067f9e35 clang::Sema::ActOnIdExpression(clang::Scope*, clang::CXXScopeSpec&, clang::SourceLocation, clang::UnqualifiedId&, bool, bool, clang::CorrectionCandidateCallback*, bool, clang::Token*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x67f9e35)
#11 0x000000000636ab85 clang::Parser::tryParseCXXIdExpression(clang::CXXScopeSpec&, bool, clang::Token&) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x636ab85)
#12 0x000000000636ae10 clang::Parser::ParseCXXIdExpression(bool) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x636ae10)
#13 0x000000000634ae63 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x634ae63)
#14 0x000000000634bf45 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x634bf45)
#15 0x000000000634c46a clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x634c46a)
#16 0x000000000634c639 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x634c639)
#17 0x00000000063518d9 clang::Parser::ParseExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x63518d9)
#18 0x00000000063625f0 clang::Parser::ParseRequiresExpression() (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x63625f0)
#19 0x000000000634b3ee clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x634b3ee)
#20 0x0000000006359b86 clang::Parser::ParseConstraintExpression() (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x6359b86)
#21 0x00000000063ee95b clang::Parser::ParseConceptDefinition(clang::Parser::ParsedTemplateInfo const&, clang::SourceLocation&) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x63ee95b)
#22 0x00000000063f6cf1 clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x63f6cf1)
#23 0x00000000063f6e4f clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x63f6e4f)
#24 0x000000000631dd02 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x631dd02)
#25 0x00000000062d39fa clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x62d39fa)
#26 0x00000000062d5268 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x62d5268)
#27 0x00000000062c38ca clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x62c38ca)
#28 0x00000000043aa295 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x43aa295)
#29 0x0000000004682ca1 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x4682ca1)
#30 0x000000000460260b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x460260b)
#31 0x000000000476e173 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x476e173)
#32 0x0000000000d116c1 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0xd116c1)
#33 0x0000000000d09eed ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#34 0x00000000043f5b49 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
#35 0x00000000039a6e13 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x39a6e13)
#36 0x00000000043f5d69 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
#37 0x00000000043b9ebd clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x43b9ebd)
#38 0x00000000043bae51 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x43bae51)
#39 0x00000000043c51ec clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0x43c51ec)
#40 0x0000000000d0e391 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0xd0e391)
#41 0x0000000000bd3bc4 main (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0xbd3bc4)
#42 0x000070092b629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#43 0x000070092b629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#44 0x0000000000d09985 _start (/opt/compiler-explorer/clang-20.1.0/bin/clang+++0xd09985)
```

## To quickly reproduce

It only happens in version 20 and current with -std=c++20 flag 

https://gcc.godbolt.org/z/x47naqv91

</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzkmltz27gVxz8N_YKRhgQvIh_8wMj21tvsJhNn27xpQPBIQk0BDAA68n76DgBKvOiSZMvddpqMM5JIXP7ndw4OQBBEKbbhALde_MaL725Io7dC3u6IZKAhwDi8KUT5evubYnyDCKKCU6g1-sL0FhEk4XPDJChEK9IoQHpLNGKcVk0JChFuvotdXYEGBPtaglJMcNTY1qCqWK2YQh5O5_O5hzMkQTWVVohxV1mD5KRCpg1WgUQgpZCm_OPy3sOZ5-fmD4ceDlGuFEhtmneXfxWIHC8RyRSoQfn3Umwk2bXXEr_983PGNSJe-Mbzcw27uiIavHCpX2vgZAfooxfee35-IEG02DHK1BZ54d0RiIdTY4-3MK2g4ydCxH0ae_0ceYs719Hxy7E5L1wyrr3wHq1dY23BntDOlidN6DMqm119ak7vXmju-XPPz1rjEZGbZgdcKy_MkYcfRK09_HDgPYN9XQkJ0lyrCN_MsD8P5r6HHwrGDxc9_MbDb9BsU34hcj2L0GyDZsK0RuratNnoutFzhWa7qnrZodlsnyYzonYz9co12XvhnfF0hWZrLmYvIAuhwNxHsyc0m20onWkhKroljHvh3VWVpnAQzfHcR7M1FZWQs5KRDRdKM6pcD1QStR1e3iN6sELp0gvv2p_YR164VKKRFJzbA0NvcC3MMy_Mg8QQpI2UwDWqiVQgkRbPwJGHF2sPL6y_cegjf-8f_oUkzuIkRYaL8U6Yq1flvryXjGvru4-SUPBw2hWS5MtKKC2B7DyceHhphoqNNxMp_4ETPfzG37ei3PgykoOR5EVC6DnJywoIb-p3_IltOKk8nDbcppcSVcJ0MZ1AI6ETiAcCM5JkkKKlcfMHoOIF5KtT9DfCy8r0k7a8BmWWgmvY6zmtzUjx7X_Xfti2v_D9DBdJhGMTGNaUihUeftinySqJZhXjzX624Y27QedKzBMr2VbpBEd9wYsIwxpnyJlpSd7va-m-PW64kPCeSOCPu3pJlD7mlilQtn13yuK-siSmQYGTvrKcmnz6weZpL1yONePcRKOWjRkaiJKKNiZ_LgVXWhIT0UQztSa2FVP_KyVw2uvhCXakjffe1V_JDso7oGaa4Eq3EvrV7FB9KyhxTQ5u_tJUmr2FF6g-trk-b1PiW6b0oclxn8bWS91dsiSxOXxY4v6FVA3RQppE8g22_sF-l1_1xI_CuddRhoydSzeNnxn0yWgkRGlE0HIL9Hlqhl0qzaUkrx9gfTqyugomUvp1nnakqv4BVAv5uKur84PSVBqL-WMucV7-QPgGvsMhX2G9GLMuswUa03SdfKsDflzUk0wMrRO6iSEduIhCGYbpdRcZXx_MfSyH3ll--vRERQ1PNdDr5l_IJ8azRNo7xtOPfC0utXOMhLM5xKg8f_Ocq_r95C3suf1dS1Ebni7UD3XPxHo2AgmFn5wH-aZhVdkRdAE2KcW3Qjw3dTubu6qFENUfBDFB1Dkc7aMdDoPBajlZrDMI4_OwcqrfcQfJPWWO8rHhdCYAegS_k91v_HNDKrZmUJroHsA7A3EppAQ7TJeEl6w0czGpqoLQ51bWOfLmAWJSwA5hB3iwtk_ChBTpAPB7-yTjvmv5an8uP326DPoM0cuGTZivnPTOMDw2DAL_kmEXrHK6JxQIgd8JDIcCIwJJeF0gUfoS9X5hU87-_jvj5WlUjoO8X_Xja227edJEw2nVCePQ2dvRiEY0inV0MQ7_H2kYezsa8YgGjRLy59L4H0BgjOwQJGMESZhdRZDbrUwzP30LiJFhE1qRhFlnxXBhG8ZBWl634r-p3arrtKejDIrj9fUM-qHd_BzYMGUCNQo6fdk4ZYQAP1TKCAGONLA_irSsSJPrNLqn4z_JX1ZDp3C01ADI4uJrCt3qfM04O33COynfrZWvPA2M13RTLkGsSZ3BoyXIOqHr4KrBB_29h5t30iykGKnY7-QUwaGgkO3m5deNPQ3dMtdasqLRoE5L5JSCUlbDmhkWk8GyODpY4RgWROursHqQnjSRmvHNP5neHhj-BaAmRAHRukMxWgsFZenjb0XxV8fH10uM-5gyB1o0HbjhsgmXYba-vmy637s3jBcBTgHAlGB8Y_pwD0UTEnA2dgSSEYEYJ-n1lCNquy_ltkD6pr-ryecG3ms53OYyBX-Soqnt3tmZva7ukfwXUTYVPO5qIQ8T4oSjxhnXmT5camEapvTU-fnTx4v7tMOpejKZVkgnc7CqikJCcBYP9wlK-Al43r4hcTuLQBsN-WGXczJxbfeduMGSKkpSTMlgxnqQJo3w8oy6SXW5no-6hi9No8THiV8MobmeHrnShFM4z-2yIRPGZauu0z5Y9kSLBIJFOHzHYVV2JrwcU2V6zcQJ00irqtM8WLn4ZRAkNECUBqsdMQ2k57fRt-Rk73x4DS_Ri2DllNKdtk55OFTuZwAlOiBeBh_t2E6vbumfmJEM3wKYNtrpdPA6qZTsBeRox9doioZDfh0XUWZB9BpdN9yG4kpalvbu4dzHvStC2-3C1ZoPU7LruA2TZbAUux3h5Xh0nvWZPe1grona9E4MgB4cLRnftIneOfRYYbWi-30QuB8FUYyulC3eIhwUNhdW5mFDq8PtUXOkqkzYC9m7b4rko4cnB9xW8fCiIruiJB5edKhwejhr8LMozjgjHp8VgCDs-eHciQB350PDn8gaqtcBy-t-m-zEg9PZhXkyDqkyGewr_HAhYV_E1ERq9w7mvO8XQ2pFBkV5kZr1FTmZ5w4oB8l5VNEUuPT8eaVoPliI9AybYqa3xnYBNFqGFATi4HtR_CwKdZnDz6I4ebl5Le8e_V4TJtvTb9-Brg2OPxGgQdQBHC6VQhoHQC-Jvet9H0z3Z-b5S-D_QoCTrS4tlCOyyB_NzRBmbcwd1hUHyTZZ5Cfv7C_NvNOsJKyeTu1g3eYXZVjQCBmd03TnGuy6w8MzZjgrs-88Y2ardA2G4wYh8tFqZeqslCZSr3rGfHMXEPW6iMaLrSyNkWt8Kp-YJtsOz558_SjQ54bR5-oVSailKBsKrsCjRoJXr2hL6hq4PVP8AtKeP8Y-sqHfnta0h5lPDn6uK7JpjxJvta7tGUf84M6YzjeiLESl50JuPPzwu2EXLTj5_JIFnp_flLdhmYUZuYHbYBEliR8vfHyzvSV-ibFflAEpcRpnUUyyRVKaZUgZQpIFN-wW-zj2Y3_hp0Hs47m_CIIgSfwFZIs0CxIv8mFHWDU3o8J0f8OUauA2CNMU-zcVKaBS9jQ3xi1N7MV3N_LWVJgVzUZ5kV8xpVXXhGa6gtulKY6QPR4LylF5XN6jL1vgx4Pf9LhrjBoFqn_A-3gYvKgEfXb1j2e8FeMU-g44C_2mkdXtiDbT26aYU7Ez0WhSgfuY1VL8C6gJL0tAefihhfByi_8dAAD__7w7LmQ">