<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/118423>118423</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Clang] Crash involving lambda in unevaluated context referring to a template type parameter
        </td>
    </tr>

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

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

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

<pre>
    ```c++
template <int>
struct A {
  template <class F, class G = decltype([] { return F{}; })>
  static auto foo(F, G g = {}) { g(); }
};

int main() {
 A<0>::foo(0.);
}
```

Unreachable:
```console
undeduced type in IR-generation
UNREACHABLE executed at /root/llvm-project/clang/lib/CodeGen/CodeGenFunction.cpp:266!
```

Stack dump:
```console
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 -std=c++20 <source>
1.      <eof> parser at end of file
2.      Per-file LLVM IR generation
3.      <source>:4:15: Generating code for declaration 'A<0>::foo'
 #0 0x0000000003bf8558 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bf8558)
 #1 0x0000000003bf625c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bf625c)
 #2 0x0000000003b43708 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x000075fca9042520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x000075fca90969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x000075fca9042476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x000075fca90287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x0000000003b4f06a (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b4f06a)
 #8 0x0000000003fceaca clang::CodeGen::CodeGenFunction::getEvaluationKind(clang::QualType) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fceaca)
 #9 0x00000000043d9955 clang::CodeGen::CodeGenFunction::EmitAnyExpr(clang::Expr const*, clang::CodeGen::AggValueSlot, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43d9955)
#10 0x00000000043fd765 clang::CodeGen::CodeGenFunction::EmitIgnoredExpr(clang::Expr const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43fd765)
#11 0x0000000003f5f395 clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f5f395)
#12 0x0000000003f670d4 clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f670d4)
#13 0x0000000003fd0124 clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fd0124)
#14 0x0000000003fe30ec clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fe30ec)
#15 0x000000000404abfa clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x404abfa)
#16 0x0000000004045e95 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4045e95)
#17 0x000000000405203d clang::CodeGen::CodeGenModule::EmitDeferred() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x405203d)
#18 0x0000000004054323 clang::CodeGen::CodeGenModule::Release() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4054323)
#19 0x000000000457e28e (anonymous namespace)::CodeGeneratorImpl::HandleTranslationUnit(clang::ASTContext&) ModuleBuilder.cpp:0:0
#20 0x000000000457bf35 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x457bf35)
#21 0x00000000065215ec clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65215ec)
#22 0x000000000457c6e8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x457c6e8)
#23 0x0000000004837619 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4837619)
#24 0x00000000047b74de clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47b74de)
#25 0x000000000492252e clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x492252e)
#26 0x0000000000cae8af cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcae8af)
#27 0x0000000000ca644a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#28 0x00000000045bf939 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
#29 0x0000000003b43bb4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b43bb4)
#30 0x00000000045bff2f 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
#31 0x00000000045861cd clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x45861cd)
#32 0x00000000045872bd 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+++0x45872bd)
#33 0x000000000458e675 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x458e675)
#34 0x0000000000cab6f3 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcab6f3)
#35 0x0000000000b7ffc4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xb7ffc4)
#36 0x000075fca9029d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#37 0x000075fca9029e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#38 0x0000000000ca5efe _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xca5efe)
```

Compiler Explorer: https://godbolt.org/z/5W6WTcnWd
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzkWl9z4yj2_TTKCyWXDPpjPeRBceJM5tfz294k0_3oQgjJ2kagApRx9tNvAXJkFKe70xVPbdV2uSsSgss5h8vlgoSVahtO6WWQXAXJ9QUe9E7Iyz9wQ7nGj5LSnRgUvShF9XwZpJH7kQBemV9UaNr1DGsKArRuuQ7QTRAVSsuBaFCAIDN1ADiuRRhWCmwCuAbu8hYE6BpUlDD93NMArhwU0xhIqgfJwcYYyq4DdAXMH5i7fgBQGuuWADxoAWohAriyhm9BY42OzWBujTXGtmnrrESFM2kuoqLlGnS45a7OAXkRoHVkOkNFgArXQ7RwRkYDUfEii7P0J5cUkx0uGTXNjp4TwZVgNIiKgVe0GgitgOEMWg7u7sOGciqxbgU3Vv7__qZY_1ZcfboBdE_JoGkFsAYB3EghdAA3jD11YS_Fvygxt4Rh3pjitgzgZi0qekv5dLUZODGmF6TvA1TANA3g8jX4B43JN1ANXf8m9mgRRPlnKRqJO4BlM3SUaxWgwmATvcUiur5lVIZ03zMhqTzgC7FSVBocKtRy4N8CuCmN6Af4xq1A2FR_YVmHMQgbEApjF_e9sT7oftALBcLOsAdhuF-lIVZdqJ65xvsAXbdcUwbCmovwicpSKGqeg_ABhGFDSKiFYGRnBhpdfxevqaw47tVOaBDWRDAhw6rFDRdKt0S5PojEaucXK10F6HqcIjAyPq_EIAl1Trs08gVoTUUdoBvQY6moNCNLeQVEDerWqgytylSG5h58-vTlD3B3DzwXQaOlyToq4gAVy8QMxu1YlTeAiIqCWkg7ybBrDwKYnfDuzHh9AFEEon10-IfKepUkK2A0d3XVs3IXn2XLtXWaR4mJmb1TJYn_2gqlJcVdAFMzL02EMJPLzLEPcZUAXkX7EZ6ZlQ78cgY-hQk5BX7NKOZD_w_-0DYcswCuBm7DYQWYMF2cA6oBM0GFPtQYZdEKrI1T3VMinqh8dth-w7xipsfVqKFXZy24pns9zu3I_nf20Wg_S2qC8yiGifFIS8oFiv0q3aZxyFo-7MOGD-4BWSixSC1k22QCHPsG8zSvCej1TlJcbb-1jL3Pum0_WU_mcOMsBY2yErwXdpylk-HUNwxXWY0ALoXU7zNrG05ms9nw1VGKP95nrNmp05XXaU0oJhi4Vs6tx9h_fHMI_66wofrmCbPBRoL_a3kVwNWRgX8OmD3atfjjJ4CDO5HJj8nEqMrzJHkfmZuu1QV_vtn30qdhSoBZt3QAizHfOGm2aJovmA30gZmFdQ1KIdgZuI_sHHcTpiKfe11l6S9wv2u4kLT6If8z8LGIJz5-3K2TGuW_wOdBd9onYkq8gZxieSElfr6ntUssDw0KrY-Yo5uzOLKlN5H3I3mdZlEVv5_8WnS9GHhlKH9t9U4M-oEImxZ7tqZaB57p5Lk_6-lnEMXSnkRBvihVtIS_IMqh5EpUz9_1jDMQspAnQrFPiKKIkvcRGvMyah76ZG6ZKDG7poT5Pv7S_vtRbH17qHjHa3HkFmdQxfKeVEm8QBbFuKx_uCL9IarB7ZDcIDv2BwrXtG5561j_jEau3Pr2mYKdYzVxTmecE_rjYHea838jV8Nm4pr5XBMYoeq9XK9pTaWk1WGD_dGQLagJ8moGOUYQvQfyPWUUK3o2tAbPhNbPgpKMwhU1nWIu-HMnBgU47qjq7RYr90CbYCLkXdczV-x2Co8Sc8Vsfvcnb2frafHwOO4YxvjgiF8NLauonO0izCYlmsEra-T5-hUm3yiv1oKroaPy14F8tM4O6ovO0MtQ0gQuEz98fza78eLhcbbK0A7PFtgzpYgjpAkwnClPUro64cbF8YrpTovGovP4rwMywfTW-XiFsnSZH8PcSDPMvDqB80wIHYYJobdwx1mZxRUFs5TK9HnHlcac0NNavk3pPP7rcE4s_IU2hzCBHosR70TmSRD8GvsrsudZRhy-Cb23ZEYE0xWuASHL7Xjwejqt3-FZLr8GfhlcgyfRVuch4VBOHLIZhzSOMTjIvl4-2rhwxOShw4x9oeQlRp8glPrru7ExhkUvi6tk-3QyPPtrXVLWOcqtJEdG6zGx2kqrqn16OA8fDwAJZqzE5Nu25v52ynU8us56uRZdh3k1n8UnR88ehpoy0ZvesRHgSBwtW97Ymjfj0L402G7Jfr9cupsSq5Zsla0-SuhVNgVbLXGr1eHxzBxmzEwFIY-emyrFFM2t-zjBbZMAZgx3ZYUDmE1SwdXhbPB3UZ4YjHx-oleW8dE4nDq3GzOOgT_gmrJnT8vvj9s5Tigt4heHR9HcuWpYg_9l5zCKL3os9SJ60wv8I-g4WaVLUr2pmh01_GplPEjphe5ZQ1PBOwH4uaqFl84cEfvYLMHSnlxplsysMli-W5TfRaneVuR3UX5qlX8m8r1Y_OIBPW7l-ArzHSKObvK3SGnEmqREMylpmiVvwb4-uvYShBOZwVtD8DdKeYZs1coziRfP1vAyrce94SETOYC3oaR4der41gr94bmHQTbh9rK_qMzqmsT2pfVHd-xMTx3P357kVf7Ot0i2yWQwmxukcQS2W9NmqzSWentE66e7oPFRF6vZICe0psAZ__hxMsbHrv336YdMG9wcrKMC7LTu7StIuAngphFVKZheCNkEcPPvAG6Sr-nXR8K_VhfVJapylOMLernMEIJRhPL8YneJqwpFSb2sl3mWlSmOk7LMk2VZ57iOl3F-0V7CCMZLGKEoRmiZL2ANaZ6uKhzFJCGoDOKIdrhlC-PVpu-LVqmBXi6XqxiiC4ZLytThqxB5aT82KIdGBXHEWqXV1E63mtnvR9ZWluTavZsELX8S7KnlDXBZFGg5GDh1752onfp2Akl7MGTqaQHw9K2I_TKixxJ3VFN5MUh2OROu1buhXBDRjV9DvP4ownJSAdyMtJ4u4X8CAAD__5sfp0I">