<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/131488>131488</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang-21 crashed with ifunc attribute at O2 and above. Assertion `!Callees.empty() && "Expecting successful collection of versions"' failed.
        </td>
    </tr>

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

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

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

<pre>
    clang-21 crashed with `ifunc` attribute at `O2` and above.

Compiler explorer: https://godbolt.org/z/hbh1odEE6

```
$cat mutant.c
void a() __attribute__((ifunc("resolve_do_it_right_at_runtime")));
void *resolve_do_it_right_at_runtime() {
  for (;;)
 a();
}
```

```
$clang-21 -O2 mutant.c
clang: /root/llvm-project/llvm/lib/Transforms/IPO/GlobalOpt.cpp:2722: bool OptimizeNonTrivialIFuncs(llvm::Module&, llvm::function_ref<llvm::TargetTransformInfo&(llvm::Function&)>): Assertion `!Callees.empty() && "Expecting successful collection of versions"' failed.
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 -O2 <source>
1.      <eof> parser at end of file
2.      Optimizer
3.      Running pass "globalopt" on module "<source>"
 #0 0x0000000003e828c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3e828c8)
 #1 0x0000000003e80554 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3e80554)
 #2 0x0000000003dc53e8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x000071370b642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x000071370b6969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x000071370b642476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x000071370b6287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x000071370b62871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x000071370b639e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x00000000057199d2 OptimizeNonTrivialIFuncs(llvm::Module&, llvm::function_ref<llvm::TargetTransformInfo& (llvm::Function&)>) (.constprop.0) GlobalOpt.cpp:0:0
#10 0x000000000572109e optimizeGlobalsInModule(llvm::Module&, llvm::DataLayout const&, llvm::function_ref<llvm::TargetLibraryInfo& (llvm::Function&)>, llvm::function_ref<llvm::TargetTransformInfo& (llvm::Function&)>, llvm::function_ref<llvm::BlockFrequencyInfo& (llvm::Function&)>, llvm::function_ref<llvm::DominatorTree& (llvm::Function&)>, llvm::function_ref<void (llvm::Function&)>, llvm::function_ref<void (llvm::Function&)>) (.constprop.0) GlobalOpt.cpp:0:0
#11 0x0000000005721d5f llvm::GlobalOptPass::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x5721d5f)
#12 0x0000000005554c6e llvm::detail::PassModel<llvm::Module, llvm::GlobalOptPass, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x5554c6e)
#13 0x0000000003821f90 llvm::PassManager<llvm::Module, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3821f90)
#14 0x0000000004134d24 (anonymous namespace)::EmitAssemblyHelper::RunOptimizationPipeline(clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream>>&, std::unique_ptr<llvm::ToolOutputFile, std::default_delete<llvm::ToolOutputFile>>&, clang::BackendConsumer*) BackendUtil.cpp:0:0
#15 0x000000000413856b clang::emitBackendOutput(clang::CompilerInstance&, clang::CodeGenOptions&, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream>>, clang::BackendConsumer*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x413856b)
#16 0x000000000483dd90 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x483dd90)
#17 0x000000000649d5ec clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x649d5ec)
#18 0x000000000483e198 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x483e198)
#19 0x0000000004b0dc75 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4b0dc75)
#20 0x0000000004a8fdbe clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4a8fdbe)
#21 0x0000000004bfd99e clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4bfd99e)
#22 0x0000000000d4f95f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xd4f95f)
#23 0x0000000000d4711a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#24 0x00000000048866f9 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
#25 0x0000000003dc5884 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3dc5884)
#26 0x0000000004886d0f 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
#27 0x000000000484977d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x484977d)
#28 0x000000000484a80e 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+0x484a80e)
#29 0x0000000004851ee5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4851ee5)
#30 0x0000000000d4c758 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xd4c758)
#31 0x0000000000c13f14 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xc13f14)
#32 0x000071370b629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#33 0x000071370b629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#34 0x0000000000d46bc5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xd46bc5)
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/eJzkWt9T47iT_2vEiyopW_79wIMnkF22Zg9qYO81JUtyokOWvJKcgf3rryQ7sR1ggN3s1NV9pzIQZHfr05_uVrdsYWP4VjJ2CZIvILm6wJ3dKX3JcYOlks-N6gwxF5Wiz5dEYLldoBASjc2OUfid2x0EacDrThKQBhBbq3nVWQaxdRdukR-VFOJK7dkSBCUIypVqWi6YhuypFUozDaIS7qxtDYhKgNYArbeKVkrYpdJbgNZ_AbTeVbtQ0evrtNcB0mD4BCVAMcEWNp3F0i4JCMq94hRigHKACrjZHGFtNn4s7wG7r0gzo8SebajacLvRfLuzG2w3upOWNwwgBFAxfKIvB9UAle_J-alB5kQgrJWGbij64j6ocIMDvF4ryK5OjXpp44H-xS2aGuvHHYUArbVSFqC1EPtm0Wr1P4wc_nS_eAXQ-kFjaWqlGwPQ-ubuFqD1L0JVWNy2dknaFkQlyhByCiulBLxtLW_4X-y_lHzQfM-xuFl3khiAcq83KkFU_q5oJxhAKUArOA47mi1XcqNZDaLVeOEB6y2zRyg3slZeeKJyPcj68QJE1_5nCUtjmHYXXIABFK6wEIyZJWta-3zg3cmkECB0_dQyYrncQtMRwoypOwGJEoJ55VDVcM-04Uoa7-sM1pgLRl2o3n29Lu-voemqhluIYdVtoWat0hZadRqw3O66aklUM-F77gVuTMcc6T4huCSiowzaHevzCVaYPFqNCXMctpq1WjnAjEKjOt0P-1QyRhGOLaNQdxIaonlrHd57i8kjpF3jfAiCMliCoLjTaqtxA7Hedg2T1gyRolqHiQypuDimIlr3cYYPNJuF1Z18BGhdcXm4DBdb-h3rehHDxRYulNOI29bp7Wzb2aWBi8bZDxeLpzxdYNMszLO0-AlEV1xaJuCilmqxZ7pShrnrcHEPF4stIQurlCA7zCWIrn6I1N1sJG7NTlm4qIkSSi8ox1upjOXE9HN4dufDtwiCaDXQGl2DoAwdVyBaMVWD6Bq2WBum3SrGJHVBUnPBQFAid9shIzQIysgNfOukdCHWYmNc0G19PnncCCoJG58d7spsVoTcOgBQFMDgKTj8i1iOcpJPssg8m_7LnebSei8_9HEySReNv2-UsZrhZkhDLm2fC_k_djdAX4KnAdiwfAEUhSewgySJX4O9EgzLrr2V93wrsQAo76QvOhQK5ZSfF6SDMYJEM5CUJBHL4cqFxDdG1J7p5x7Vr1hS4ebKB95m96yUtOzpsD4G_n-vPxr0Z2GUBVUaowQFgzn9evuUp5s0Xgguu6fFVnb9BbI0apl6yF5kBBzPFRZpURPY2p1mmG4euRCf0-7lR-3JKdw4S-HWeAo-CzvO0lFxOleM8qyOXNXX9nNqveCoNnuhNqw-rTCsRoX5XGFUsCL9nEIvMiospgGWZGFRUPQziyZ8t2q6O5ZESWNbrdqlizV4WvIPIe3SOphbhMKgYFANFvWC5kYe0L9v0BW2-Ct-Vp2FHsVnLf7KK43180ft_Te5_JDuL0KRx7Vmf3ZMkvPCvlINl9gq_aAZ-4dah07235X_dPCFp8FHk3qC4Sh6h81QXnQnPxKFpcTi2XDzO5Z46_YcqxciDnB61nI0GNCvFs68WTlKkiQmKZuApMxiLoZqj435XVEmXoM6M21Oyt-w2n3-z1PZkzVSGc0qe47CuggmID19bwP8f8rSwMPIUjxlKQ6jmKLYTXfc3UOJG2Za308WPbrrhlu3zWoq8fwrE63foYOo_NbJobBhh-KOt0xw6WrAYQ_qVj9MHpmk5bASrKCxtL_SSf5nxzatnXPhOtf2u-aWbQ7960SIshp3wm4oE8yydwR7J_WOeG_aB6XErd-srHkfDx-Z80RqOuFLDlZKmq5xDiydk4fRPywXryx8yYmj8iStpjpZw-2goQcwp_3wUOVGGoslYS9BrRRlvzDvQb_bPQnXe6u53H5j9Xz4ENzl6yaObh5FbqTVneF79o3VK2nvTojf18PC7Ri8fzaWNUOp-fmR8gGvnS01B5-OqZnOPJ5HlBbBj_D4wX6f4hsX4bPwD8lPQqG8fxj2K-deXQaQownZ1IQ0LmjCyNSEO7ePLu8f5gDvWYOH-KuUEuPvM0IdwIxQ8xO2WVjkr6THEND9OvjESGfZIcbzc3PpIIwAZxuJuAooyZIpwLV2Tj2m3BTh2bH1sx-xodmWIMZ5TSsGf7T6vMrf28acO057hCP-cM5tTYtihn9AOpqxVwS_RP1ykT3zEtEjG3HP2sWAxnWR1JCQcNNgPm9CSq3x8zffmJMd1oedVnlY5mZjaAVd935u-D2-EX10gj4LQwwPVK_CB5_zExvuGyzEfzNilb5pWvGqKSdVy-kYFrvJ5rKAVPM90y_LLJr3Q3mepnXhyXh_ozPsafwtBAtRYfK4qaWDOYZIP_EQLqtwpZoGS3qara_67VjJlC_ReN74j_X5WLuOApsNeXoKw_6PChtOXJ3jDpOncHazG9hYjbk1h8sn6rAQLvyVnlx3t5TjSu0DpyfciwCUCdxUFAOUjVSh_PCA7zdVveKM5PThXJ5PnyC-9gju2Ine45qJ5xmXP_bbWdvsHusY6ulpWNGghv_JYeH3_S3Wtt_yv-7_bM5aXGQZfZM17y_8ovYdqJwt1CeC7obZs6eP3VrOmpSJYefqALzBYxCdtCgxzgP2WTp-U5V5m4vfVPWVm7eew71cf4--bzF3bvfPxj9O33R79O-R6GgaSZy3UXkSMpa8Bfhq8n3WArxS-98i_yeSeNbu0xNzpG3-DiqgMcmSoT0-9BoH2H7hKIe0f78Sn7G7cJhGxLOeLiBhVIcxdFjPN2WvdJwSnbyNKNyO7XNvI4rp_un07REqWBzAzcbJbIzF2m4mBn14ChZPpohPHJtWJIG98nP6xqntJz2eR2BaK3-2o39lXA8tPyRDhPdv2vtTJOyJu7ChDIaRfz7VGQYXe2gVNIxBPmnIi-kREs1spyVzCeYkp6cmLuhlRIuowBfsMsxiFBQpStKL3WWUZXVUFyFNKA3TNKasSAoWZiRIsqpKyQW_RAFKgihMgyjKonRZBTnKMpZgmlGKEwTigDWYi6UL_6XS2wv_cv8yjMI4zy8Erpgw_kQNQpJ9h_4qQAgkVxf60p8LqLqtAXEguLFmVGO5FeyNgzb-0Mr8iM0tmhyu-VknIy46LS7__umHgaP9JfrfAAAA__8eOEfp">