<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/140934>140934</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            trunk regression
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          scarf005
      </td>
    </tr>
</table>

<pre>
    ## Reproduction

[20.1.0 (works)](<https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:c%2B%2B,selection:(endColumn:13,endLineNumber:11,positionColumn:13,positionLineNumber:11,selectionStartColumn:13,selectionStartLineNumber:11,startColumn:13,startLineNumber:11),source:'%23include+%3Cvector%3E%0A%23include+%3Cranges%3E%0A%23include+%3Ciostream%3E%0A%0A///+@remark+poor+person!'s+flatmap%0Ainline+constexpr+auto+flat_map+%3D+%5B%5D(+auto+%26%26func+)%0A%7B%0A++++return+std::views::transform(+std::forward%3Cdecltype(+func+)%3E(+func+)+)+%7C+std::views::join%3B%0A%7D%3B%0A%0Aint+main()+%7B%0A++++auto+res+%3D+std::vector%7B+1,+2,+3+%7D%0A+++++++++++++++++++%7C+flat_map(+%5B%5D(+const+int+i+)+-%3E+auto+%7B+return+std::vector%7Bi,+i+*+2+%7D%3B+%7D+)%0A+++++++++++++++++++%7C+std::ranges::to%3Cstd::vector%3E()%3B%0A+++++++++++++++++++%0A++++for+(int+i+:+res)+%7B%0A++++++++std::cout+%3C%3C+i+%3C%3C+!'+!'%3B%0A++++%7D%0A++++return+0%3B%0A%7D%0A'),l:'5',n:'0',o:'C%2B%2B+source+%231',t:'0')),header:(),k:51.06906906906907,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:compiler,i:(compiler:clang2010,filters:(b:'0',binary:'1',binaryObject:'1',commentOnly:'0',debugCalls:'1',demangle:'0',directives:'0',execute:'0',intel:'0',libraryCode:'1',trim:'1',verboseDemangling:'0'),flagsViewOpen:'1',fontScale:14,fontUsePx:'0',j:1,lang:c%2B%2B,libs:!(),options:'-std%3Dc%2B%2B23',overrides:!(),selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:'5',n:'0',o:'+x86-64+clang+20.1.0+(Editor+%231)',t:'0'),(h:output,i:(compilerName:'x86-64+gcc+14.2',editorid:1,fontScale:14,fontUsePx:'0',j:1,wrap:'1'),l:'5',n:'0',o:'Output+of+x86-64+clang+20.1.0+(Compiler+%231)',t:'0')),header:(),k:48.93093093093094,l:'4',n:'0',o:'',s:0,t:'0')),l:'2',n:'0',o:'',t:'0')),version:4>)
[trunk (fails)](<https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:c%2B%2B,selection:(endColumn:24,endLineNumber:16,positionColumn:24,positionLineNumber:16,selectionStartColumn:24,selectionStartLineNumber:16,startColumn:24,startLineNumber:16),source:'%23include+%3Cvector%3E%0A%23include+%3Cranges%3E%0A%23include+%3Ciostream%3E%0A%0A///+@remark+poor+person!'s+flatmap%0Ainline+constexpr+auto+flat_map+%3D+%5B%5D(+auto+%26%26func+)%0A%7B%0A++++return+std::views::transform(+std::forward%3Cdecltype(+func+)%3E(+func+)+)+%7C+std::views::join%3B%0A%7D%3B%0A%0Aint+main()+%7B%0A++++auto+res+%3D+std::vector%7B+1,+2,+3+%7D%0A+++++++++++++++++++%7C+flat_map(+%5B%5D(+const+int+i+)+-%3E+auto+%7B+return+std::vector%7Bi,+i+*+2+%7D%3B+%7D+)%0A+++++++++++++++++++%7C+std::ranges::to%3Cstd::vector%3E()%3B%0A+++++++++++++++++++%0A++++for+(int+i+:+res)+%7B%0A++++++++std::cout+%3C%3C+i+%3C%3C+!'+!'%3B%0A++++%7D%0A++++return+0%3B%0A%7D%0A'),l:'5',n:'0',o:'C%2B%2B+source+%231',t:'0')),header:(),k:51.06906906906907,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:compiler,i:(compiler:clang_trunk,filters:(b:'0',binary:'1',binaryObject:'1',commentOnly:'0',debugCalls:'1',demangle:'0',directives:'0',execute:'0',intel:'0',libraryCode:'1',trim:'1',verboseDemangling:'0'),flagsViewOpen:'1',fontScale:14,fontUsePx:'0',j:1,lang:c%2B%2B,libs:!(),options:'-std%3Dc%2B%2B23',overrides:!(),selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:'5',n:'0',o:'+x86-64+clang+(trunk)+(Editor+%231)',t:'0'),(h:output,i:(compilerName:'x86-64+gcc+14.2',editorid:1,fontScale:14,fontUsePx:'0',j:1,wrap:'1'),l:'5',n:'0',o:'Output+of+x86-64+clang+(trunk)+(Compiler+%231)',t:'0')),header:(),k:48.93093093093094,l:'4',n:'0',o:'',s:0,t:'0')),l:'2',n:'0',o:'',t:'0')),version:4>)

also fails to build on ubuntu clang++ 20.1.6

## Error log

```
In file included from <source>:2:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/ranges:45:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/iterator:68:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/streambuf_iterator.h:37:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/streambuf:45:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/ios_base.h:43:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/locale_classes.h:42:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/string:57:
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.tcc:633:12: error: variable has incomplete type 'void'
  633 |       auto __r = std::move(__op)(__p + 0, __n + 0);
      | ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.tcc:607:7: note: in instantiation of function template specialization 'std::basic_string<wchar_t>::resize_and_overwrite<(lambda at /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.h:4832:9) &>' requested here
  607 |     { resize_and_overwrite<_Operation&>(__n, __op); }
      | ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.h:4831:7: note: in instantiation of function template specialization 'std::basic_string<wchar_t>::__resize_and_overwrite<(lambda at /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.h:4832:9)>' requested here
 4831 |         __ws.__resize_and_overwrite(__s.size(),
 |              ^
1 error generated.
ASM generation compiler returned: 1
In file included from <source>:2:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/ranges:45:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/iterator:68:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/streambuf_iterator.h:37:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/streambuf:45:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/ios_base.h:43:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/locale_classes.h:42:
In file included from /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/string:57:
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.tcc:633:12: error: variable has incomplete type 'void'
  633 |       auto __r = std::move(__op)(__p + 0, __n + 0);
      | ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.tcc:607:7: note: in instantiation of function template specialization 'std::basic_string<wchar_t>::resize_and_overwrite<(lambda at /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.h:4832:9) &>' requested here
  607 |     { resize_and_overwrite<_Operation&>(__n, __op); }
      | ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.h:4831:7: note: in instantiation of function template specialization 'std::basic_string<wchar_t>::__resize_and_overwrite<(lambda at /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/basic_string.h:4832:9)>' requested here
 4831 |         __ws.__resize_and_overwrite(__s.size(),
 |              ^
1 error generated.
Execution build compiler returned: 1
Build failed
```
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzsW1-Po7oV_zTOizURGAjwkIeQmUiV2rtVV-0rMmAS7xqb2iYzez99dWxCkhkye297Vc3uzYglwT62z__zO0mWGsP3krE1SgqUPC7oYA9Kr01NdRsEyaJSzbc1IhEiEf4H67VqhtpyJVGwgSspSLAMlwFGJHtW-qtBJEfJIyIZirYHa3uDog0iO0R2e9VUStil0ns3EO3dVAi0JLv9cEDRplYNe2q4VRqRLXezWcsFk7Rj7ikNEUkR2bZK2s81FTAaxuPAPw37-4snCzzZF5hGZCuohLNqRBJSjLetYYJ5Gd05TDZbJYYOHsMIkS2TzV-5ZL8MXcU0DMJOvTIc1lyTnkbf0k-HfLZU2-tV13Mza2eWzFLmMKMGXY9KAgkjLmsxNAw5gaPtkdVOrUn0hEgSbOZoNJV7Zt6n4cpYzWh3RRWMtndXgeJAs47qr4gUvYJDi55po6SzdWoQKVpBbUd7t5RLwSXsXytpLHvpYQEdrBrpSkfoTn_0r4m7Oe-bKIHXlbu1g6zdQH5iLy3Gd8V0aWYHLREpjG1AadHmyNmz8W-tptK0Snf-hImkVfqZ6sbpoWG1sN965kmuzgS9vB6c7km6vXHqF8UlrC4mth-vHkFTFpGio0CXnTd8K92oEw3GnBR3PvPkCrCyAE9DpCD-JRr3fHyz5--8vJxn-2UzpnMGR6TwcvFJSw-jEi9sm94w2lkU7gXwu2y8RMWlFk8PF57xP0o3sTEGjnce5fzjLYujW-SXRv3vGbhe3booQyS7UCWkAu8Ctx3l8po4rtVgT-E-3ka1Xgz4WL54My_UnCdNZgzeunvg8xdkNOGTWeJTubxK7Mo_bS8TejGmQD8QjZXCXq7L_c4HRhuXPE8G2X5F0SYJl8EqP1_pmYf4HR78Axg_mDluO1_mup4LdlHkppFoU0OxIkEIu7VcWKZ9bc2qq9MrLqn-dlUU_dCn6gur7dVErbqOSftJim9XezSsGvZbKoS5Im9YR-VesGtarqFYHZm5GmYvrB7sNSmXlomrEcErTfW3rWquy7jVvLsaODJdKcMePQdc7l-rsxV0b_7F2fOnnsk_HBIIXpkLY8GBqocKPQr9ADEC6fRiGWAm5w5HpjVv2OsN3oMZcyhjFmTcxBjvQIzvIIy3AGMeX7yCF-FvDk5Eipds9bCKIdM7dZMRRfpUdQJ6U7jm8xG7HaNGDbaHxPQ6Zn6ZwOF03L6GwhvGSzJ6qTuKN6OUv9NVnjXtL13tN8r_aeS3UO33VLGdEsL3lHE7fcXZMo-C8xX_EenrQlTy3U3mFh-ZNt73YwQFMPfdhNWD_ArNREu5-MmbCRLPhflqLs4d6Xygr25Hulv1Xqiv3sS6XzJLeW8m7s3EvZm4NxP3ZuJnaSZKV23v7cS9nfjZ2glEstG383tPMaePP1ljEWyoMAq7pgJbhauBiwYriYdqkHbAZz0V2PVfq_H7Df_Fx5PWSmOh9uPoKhivYPMXiaF3wCOAbXCrVYdRNHnyE6Bq4PMmLdmp3iKyO_nYA3vphdJgnN2-rh-MpL05KCARvPKDiOxeslW5ih8El8PLw14OiOzC1TKA1nG3XL69TRB7V5-K5HnBhC3i5MPzyi3TFKI52qyyD89txa1BZOf7mWpoyxP7S8gzUfrhBZg4_zG8Y9Q3V6asqGFOy3H0o7AtFJSKshbUGGY88x8_exirPYZKRnf-EFyNKq2o4XXpWVzauoa0EYFDhKBYzCC3w5sj1ZxWguEDNaBk1fWCWYah_8aIpEfFGyg0wQbjVRRhlG6x_4MGEpelxih6xFOD06kj9O1lqXpXmbKy7DEUGCh7uCzl6SFHUeF2hT_YFSVPP4AOA7A1_MNSOWSOucRcGkul5RTQIFYtbgfpkCG2rOsFtQybntWcCv6rp0EknVR2eQyKts_1gerS-hoKDTAz_FdWUtmUgIKfNYdzAbIJ2lUNxdR-jHiY05oL5SwCnwOkghFZOXySYs3-PTBjWYMPTDPvX0E6-RdKC3xD8vJTD7UE4M64W1aW0ruX97qowCh9_JG8a9RT-P92rrL8mdzrpmuBai9SF8Zl-WyWN4QHdzJLmJiAP-xxudy7lXOp0OdSvGcSvJI1SxRsNp__dhoAg5zUhv3HMwxsg8M7jr7j6DuO_ljs3nH0HUffcfQdR380rd1x9B1H_wlx9JP7Agxs4T-7vgmkCzfdUi5Yc_lZ9aJZR00e5XTB1mEap1mc5mm8OKyTOKponidNTesmW60Slgd51eYRrcKqrVYLviYBSYKEhGEa5lG8zFqW1k3QNkmV1mFWozhgHeViKcSxWyq9X3BjBrYO4yCP4oWgFRPG_QcDQiR7xm4WEYKSx4Vew6KHatgbFAeCG2vO21huBVv73wRpttfMGK7kYtBi_ernQNwehmpZqw78RRxPLw-9Vu5rSrJzh4K5R66Oa_KfAAAA__9AgdGe">