<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/62054>62054</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            llvm_unreachable when processing comment & line continuation
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang,
            clang:frontend,
            crash
      </td>
    </tr>

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

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

<pre>
    Crash when processing an "almost trailing comment" line:

https://godbolt.org/z/ehPM8f1ob

```
/*<*\
/
```

->

```
<source>:1:5: warning: escaped newline between */ characters at block comment end [-Wcomment]
/*<*\
    ^
if this is an almost Doxygen comment, it should be ordinary
UNREACHABLE executed at /root/llvm-project/clang/lib/Sema/Sema.cpp:2405!
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 -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics <source>
1.      <unknown> parser at unknown location
 #0 0x0000562be67b783f llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3c6283f)
 #1 0x0000562be67b557c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3c6057c)
 #2 0x0000562be67028c8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f668966b420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00007f668913800b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #5 0x00007f6689117859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #6 0x0000562be670dbae (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bb8bae)
 #7 0x0000562be900ed4e clang::Sema::ActOnComment(clang::SourceRange) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x64b9d4e)
 #8 0x0000562be8eaf494 (anonymous namespace)::ActionCommentHandler::HandleComment(clang::Preprocessor&, clang::SourceRange) Parser.cpp:0:0
 #9 0x0000562bea9ba487 clang::Preprocessor::HandleComment(clang::Token&, clang::SourceRange) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7e65487)
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJy0Vktv2zAS_jX0ZSCDoh6WDj44Toweutug6WKPwYgaS9xQpEBSjbO_fkFZebhNH1i0QCKL1Gi-b74ZDQe9V50h2rLiihXXK5xCb93WTePoSPZh1dj2abt36Ht47MnA6Kwk75XpAA0wIVAP1gcIDpWOu9IOA5nAhACtDLFsx_g148u1D2H0cU8cmDh0tm2sDmvrOiYO_2XiQP3tP6pjapu3L7GSL3_nZXx3x7J9vBb71813jedrwrKbn3nM9t5OTlI0y3Ypy3YFy3bwiM4o08Vb8hJHasHQYwwLGgqPRFGBCA2yR4cykPOAARpt5cOzEkCmBVZcJf9-lqa4_kkgAACsWNiqI4ReeVA-qr1IfW1PTx2ZV6X3oAL43k66hYbAulYZdE9nF__65-eb3f7D7urjDdCJ5BSojRyZODhrAxMHrb8Oyejsf0jGpdRoYjq0apg43NGAy89ajiPLdiLnBRPp2fvtx5vd3Q34qRlUAIRm6sDRaF2AYOGbbKvQT81a2mEB_R5beT-Rj4KiaUEZqaeWIPQEci7BBuVDcCgpBj06WqqRWljyJ_bzm-i9lQpjqG4y4KVTY1ifKd8FlA_QTsP4Upt8zXh962zncAB03RR1jcSjSnacVbHDqDS5hE6jto7cs1IJek8uKGt8EtxkHpg4NMq8CnnFxBUkXfuI7pjkkHSQ2OgXxzF6n8I4hbWHZIhaQJKcqjJBPyT-yQQ8sexamUAakjtIkk7KJFirZY_KsOz6p_SisTc4-t4GSI7SauuSVmFnrA9KekiOxiazsBfbF1_DrE8a9WHZfjIPxj4alt3AiM6Ti4W0bIK2EqMMSxkzkXHgJ845L0rRULlpNlV2hDnx2Y5lO__kzze3Tpkwp-XLObfVq5HDx3vrgyMcmCjnWo8lXwMT1R9KDhNX_JTJUlTZkYn6lX_6Df-i2Mj3-O81oZnGT-ZOdQY1E9Vk5rbagrYR5W-w5cVGXrAVl2y5qGQFc-f-TNJ-Jfd0pvcBTasjaLUoeWGztybQKSzfOp__XyCyBWJzLMuqLssmFxzu7x35YB3du7DEeW4dp6q8L_NEKzOdks5M5wdj6B1hu_Z2zedY0jwX_CKS_AImzSrOG3CoPP2Gfxk9l7PnPOO8ufBcXHpON1VRAzb2t5i_8SxEVdQXnstv1G8bpD-e9aapGqQL3M1b3JpzanOC84tzbc79e77byfDJ7J_PjOqtzfy1f0bT0V-o1TJv6ja_ZF29ZV0RHvM6j7horHka7OTB4EB-nLtB_cJf2ecAnot4fnJevBva7csZYd3SP34c-O3c094v_fotY6wbzKsN_AjoV6y-2Acyv6Tzh_OwobLIq81LHl5moFW7zdo6q3FF27Ss0nSTp2W56rdphjylY53TpuBIqcyrqqzoKLis6qKSK7UVXGQ8T1PO81qUazrWpaiFwE3DJZZHlnMaUOl17JpxzFvNJ_y2FLzIVxob0n4ePYVY6Aom9i-rbHd0sR-Z9vVBbFZxVVyv3HYeH5qp8yznWvngX4GCCppmg_vJOELZY6PpuyH2eUhjopznVZDWBGWm-ShbTU5v__8hZo7yfwEAAP__MduDbQ">