<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/149759>149759</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [analyzer] UNREACHABLE executed after saying "Support for this Decl not implemented."
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang:static analyzer,
            crash
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          k-arrows
      </td>
    </tr>
</table>

<pre>
    Reproducer:
https://godbolt.org/z/7T5eq5WPo
```cpp
template<int I, typename... Ts>
using Type = Ts...[I];

template<int I, auto... Ts>
constexpr auto Var = Ts...[I];
template <int I, auto...Ts>
int foo()
{
  return Ts...[I];
}

void bar()
{
  int r = foo<2, 0, 1, 42>();
}
```

Backtrace:
```console
Support for this Decl not implemented.
UNREACHABLE executed at /root/llvm-project/llvm/tools/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp:3337!
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 --analyze <source>
1.      <eof> parser at end of file
2.      While analyzing stack: 
        #0 Calling foo() at line 14
        #1 Calling bar()
3.      <source>:9:10: Error evaluating statement
4.      <source>:9:10: Error evaluating statement
 #0 0x0000000003fc1498 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fc1498)
 #1 0x0000000003fbe8c4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fbe8c4)
 #2 0x0000000003f03098 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007ded82e42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007ded82e969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007ded82e42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007ded82e287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x0000000003f0e85a (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f0e85a)
 #8 0x0000000006523dc1 clang::ento::ExprEngine::VisitCommonDeclRefExpr(clang::Expr const*, clang::NamedDecl const*, clang::ento::ExplodedNode*, clang::ento::ExplodedNodeSet&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6523dc1)
 #9 0x0000000006529801 clang::ento::ExprEngine::Visit(clang::Stmt const*, clang::ento::ExplodedNode*, clang::ento::ExplodedNodeSet&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6529801)
#10 0x000000000652bdcd clang::ento::ExprEngine::ProcessStmt(clang::Stmt const*, clang::ento::ExplodedNode*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x652bdcd)
#11 0x00000000064e0d0a clang::ento::CoreEngine::HandleBlockEntrance(clang::BlockEntrance const&, clang::ento::ExplodedNode*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x64e0d0a)
#12 0x00000000064e1282 clang::ento::CoreEngine::dispatchWorkItem(clang::ento::ExplodedNode*, clang::ProgramPoint, clang::ento::WorkListUnit const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x64e1282)
#13 0x00000000064e1611 clang::ento::CoreEngine::ExecuteWorkList(clang::LocationContext const*, unsigned int, llvm::IntrusiveRefCntPtr<clang::ento::ProgramState const>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x64e1611)
#14 0x00000000060a8727 (anonymous namespace)::AnalysisConsumer::HandleCode(clang::Decl*, unsigned int, clang::ento::ExprEngine::InliningModes, llvm::DenseSet<clang::Decl const*, llvm::DenseMapInfo<clang::Decl const*, void>>*) AnalysisConsumer.cpp:0:0
#15 0x00000000060aa35e (anonymous namespace)::AnalysisConsumer::HandleDeclsCallGraph(unsigned int) AnalysisConsumer.cpp:0:0
#16 0x00000000060abd63 (anonymous namespace)::AnalysisConsumer::HandleTranslationUnit(clang::ASTContext&) AnalysisConsumer.cpp:0:0
#17 0x000000000666650c clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x666650c)
#18 0x0000000004c64025 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c64025)
#19 0x0000000004be0e6e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4be0e6e)
#20 0x0000000004d57b01 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4d57b01)
#21 0x0000000000d9ec4f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd9ec4f)
#22 0x0000000000d9582a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#23 0x00000000049d7709 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
#24 0x0000000003f03534 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f03534)
#25 0x00000000049d7d1f 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
#26 0x0000000004999d6d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4999d6d)
#27 0x000000000499adfe 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+++0x499adfe)
#28 0x00000000049a3945 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x49a3945)
#29 0x0000000000d9b0ff clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd9b0ff)
#30 0x0000000000c4f5b4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc4f5b4)
#31 0x00007ded82e29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#32 0x00007ded82e29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#33 0x0000000000d952d5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd952d5)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134
```
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzkWl1z4yjW_jXkhpJLRl_WRS4Ux34nUz3zppLM9KULAbLZINACSjvz67dAcvTRTm8yk8zW1nZ1p20B5zzn4Xwhgo3he8nYJUiuQHJ9gVt7UPryMcBaq2_molT0-fKONVrRljANogKExcHaxriPaAvQdq9oqYRdKL0HaPsHQNvsIWH_TL7eKhAWIA27v6RpQFhYVjcCWwaiNZcW3gC0hva5YRLXbLFYwAcDog0Ii9ZwuYcPzw2DILqGD2axWIDk6gYk1yC6cnLPy8KtVWM5RElj2bHRfgT-jvUr8k7C4BlpJ2HueaUUQCuAcochcysh1My2Wp4DmV13UJ8Up7DE-rulTmQHyQmO1sipDd2PpfsRI6e5WzSWeCK1k36FyaPVmLBuewbKlTRKMBAW923TKO3Qa2gP3MBrRgSUykJeN4LVTFpGFyAsfvv1blOsfyquvmwgOzLSWkYhthCgrVbKArQV4qkOGq3-wcjpK0Bbq5QwAG2JwNK5geAlQNt7iy0nhcTi-Q-mAdqulWYAbTfHRm_knku2cG4RFVEUZQAtQVjcftkU9xto2rLmFmJYtnuomQdvFZx5HreHtlwQVQ9AZvC4MS1zwCCWFHJJREsZtAcGicbmAMsX6tAaNto5OmHGMAqNanX32K3ExijCsWNDtxIaonljHWH3FpNHSNu66cgPFyDMb7Xaa1xDrPet49ZBdhSqxmEiqm64YDpgx0Yo7YnxvAXYGKYtV9IEVrfyEaBtyeVA6xVAVzDY029YV0EMgz0MlJOLm8ZJb23T2oWBQe1YgEFwXKUBNnVgnqXFRxBdc2mZgEElVfDEdKkMc-MwuIdBsCckcNtIDphLEF3_EK-bbCRuzEFZGFRECaUDyvFeKmM5MZ0Oz_H0cYA7b3Bx1lPsY2vpeAPRmqkKRBvYYG2Ydp7HJIWqghX3jozctK8HLhjsBLk0YdweeIpdOOQARSFcYyHc2Eu8OlmCSwaX8cu05cu0cWxGPZQBXlTkICqWodOx0VppyJ6waLHttVsfQSAs4j-_FHrY4TE8_YkqsozzFfSOHRUgKsyz6T7cai6t97yHzndXwySNv-2UsZrhGqDU-S-X1tnv7fsQFwToKjz28DrKoCdzAr5kKxKfA78WDMu2-X95z_cSC4BWrfRFiEKhnIpPgOrBDFDRFGoYhfkKrp2z3jGinph-7rD9hCUVTuOq53AyZ62kZUfbp7DQ_-vkR738jDK6QixGCQp7o7rEeFyluzQOBJftMdjLthsgC6MWqYfslwyA46nAPM0rAht70AzT3SMX4n3S_fpBejKHG2cp3BtPwXthx1k6CE6ngtEqqyKIS5fM3yXWLxzEZrPtY6sEf7zPeLGD0tVYaZqgiJIl7FZ5t2bSqu7TUN26779zw-1a1bWSruzescrNAGg1Wu2eQN-sAFS4oB2N_YprRn3BfmXCRLVQlNFfFWVvnXfPrE8UHx52PUkDhfmMwnwVvofCKWP3trb_fYQ4k_sOEEXLcEZISQl9GyG3XZ_iSPgQWj7DVmfNYOukPKQxC2mIz4NzTeLY1i4LXwlFHjfSaix9xRstnQydjE__k8Z35g3Go5nxS7RCbzOectNgSw5flX68sayeWv5WR-8b0lvl69grvDgVX7ixv0luRyx-BjvO_oGdaM5OunwlL8zZ2XRHlBPyKTlfFMEOT1-nJ1Hx0nL0hAx9yo20ujX8id2xai3trdUgWp8F05PqDjknr3OHtU_hK12O0kY84SvEqwxlTimWSj7XqjXQHadN41vDvAPrD2GGm7WSpq27k_wptNbeZ8bUuWrzClNvSk83UnDJ5f4XRd3pa8zvNZPGp9gJq9-Vt9mCX3BzIyv1bxa5Y7Zvujd9XM-tnvVqjsxkRiaOEvZXyHSgjDtW_J_GzWHc3fY95BswpTNMJU2jv4LpQWNphA8GF9zTvS7uH_oI6cP9DQAnHViapmkSkkm-cce34v5hVptYjfvEXColhv8_PmQ6SEPITLq3mKRxiJIx4K12FEhaECd-klz64-MHI-wxDAgnzVFcspClbIxw3eu8kcb6EjjG2MOesD0z6VNSeY_zxQo06WhimmTltMXr8Q7GPPVJeor9O2M_pUz3-Ab0kx4lpDkjcQUJWe5q7ASMTtmF1vj5jlUuIR3wqHV3qWcNp89OmelTjOhQDjagmQ3JCmF4on29fPABN7LkvsZC_M6IVfqmbsRZg9JpRnYyZkXVOxfV_OlcukCTAh_nNMvC3FMyElq10jvqTntW_ejpzeemm0KwECUmj7tKTgtBp7h3nfXSnbWwpPMoPrt7xvbzVOO0Y0fAiByrudz7mZt-a18W7HbkeFwuuy8lNpzsjJ_eUziZ7B7srMbcmtPwTBwWwoWC0qPxvo6d0qR3n77RKPxb0EzguqQYoGygCq1Or1F-VuWZzYjnLz-SaPye5twrjm7krpX3uGLiecLlj_ftM17meMSDwydz56LLCv4vO4djfNFgbRfh616QTlnLc5rSV1nzu4a_q4wnKiepe7bQTXjtSPaDqcWkTxgZ9qH5vzN7cKVsRgqmFXsvKT-r0rzOyM-qdAeVCSM_ysUvHtBgrrurqfeQ2LvJ30KlI2ugctpw5TjK4-Q12Nejz5MG4Uxn8NoW_I1Ufnwf0tEzkJfPangZVn1KO3UiJ_A-lRTfnZleq9Af3ns4ZC-4p_cXIYmrpIyhQ_zRijvRg-Ll7EVzTvN3vnD3SwaBaC6QxSHc7dyanbFY293IrDerYPFIRTRv1BBNYCf84_fJCe9Uj8eiAjKtXVUpOveCVX9ogKT3_wpzwSj8xu0BsqN_MUQZXEaxw9gaBoMnaBU0jEE-auadplMT39-PMxd-buX4ivqCXkY0j3J8wS6XWRKFaYbQ8uJwyUpEEEki195GYRpWcRjjkOYZZVlFcXjBL1GIkjBDyzAKs3C5KAmJWU4yglBEKUEgDlmNuVi4sFgovb_wl8GXyzjPkvxC4JIJ43_vAaFTEjD-wrq_WnRMI4DWbtw1Re5bcn2hL_0dc9nuDYhDwY01gwrLrfC_TPEiIrmG5y_VK8s0NPiZyz0ECL3xih6hi1aLyz9_Ed6b_3SJ_hUAAP__tkdtRg">