<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/151659>151659</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang crashes at -O{s,2,3} on x86_64-linux-gnu running pass 'Register Coalescer'
        </td>
    </tr>

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

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

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

<pre>
    It appears to be a recent regression as the latest build on Compiller Explorer doesn't crash. 

```
[507] % clangtk -v
clang version 22.0.0git (https://github.com/llvm/llvm-project.git 3e2fadf3beff93433f125eb1ea1abe470db5aa12)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /local/home/suz/software/local/clang-trunk/bin
Build config: +assertions
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/13
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/14
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/14
Candidate multilib: .;@m64
Selected multilib: .;@m64
Found CUDA installation: /usr/local/cuda, version 12.9
[508] % 
[508] % clangtk -O3 small.c
clang-22: /local/suz-local/software/clangbuild/llvm-project/llvm/lib/CodeGen/RegisterCoalescer.cpp:1500: bool {anonymous}::RegisterCoalescer::reMaterializeTrivialDef(const llvm::CoalescerPair&, llvm::MachineInstr*, bool&): Assertion `MO.isImplicit() && MO.getReg().isPhysical() && (MO.isDead() || (DefSubIdx && ((TRI->getSubReg(MO.getReg(), DefSubIdx) == MCRegister((unsigned)NewMI.getOperand(0).getReg())) || TRI->isSubRegisterEq(NewMI.getOperand(0).getReg(), MO.getReg()))))' 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: /local/home/suz/software/local/clang-trunk/bin/clang-22 -cc1 -triple x86_64-unknown-linux-gnu -O3 -emit-obj -dumpdir a- -disable-free -clear-ast-before-backend -main-file-name small.c -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=none -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -fdebug-compilation-dir=/home/suz/20250801-clangtk-m64-O3-build-003550/delta -fcoverage-compilation-dir=/home/suz/20250801-clangtk-m64-O3-build-003550/delta -resource-dir /local/home/suz/software/local/clang-trunk/lib/clang/22 -I /usr/local/include -I /local/suz-local/software/local/include -internal-isystem /local/home/suz/software/local/clang-trunk/lib/clang/22/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/14/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -ferror-limit 19 -fmessage-length=100 -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcolor-diagnostics -vectorize-loops -vectorize-slp -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/small-c8a24d.o -x c small.c
1.      <eof> parser at end of file
2.      Code generation
3.      Running pass 'Function Pass Manager' on module 'small.c'.
4.      Running pass 'Register Coalescer' on function '@main'
 #0 0x00005b8b26ed93e2 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x42ab3e2)
 #1 0x00005b8b26ed60df llvm::sys::RunSignalHandlers() (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x42a80df)
 #2 0x00005b8b26ed622c SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0x00007144aa445330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
 #4 0x00007144aa49eb2c __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #5 0x00007144aa49eb2c __pthread_kill_internal ./nptl/pthread_kill.c:78:10
 #6 0x00007144aa49eb2c pthread_kill ./nptl/pthread_kill.c:89:10
 #7 0x00007144aa44527e raise ./signal/../sysdeps/posix/raise.c:27:6
 #8 0x00007144aa4288ff abort ./stdlib/abort.c:81:7
 #9 0x00007144aa42881b _nl_load_domain ./intl/loadmsgcat.c:1177:9
#10 0x00007144aa43b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#11 0x00005b8b2636b86f (anonymous namespace)::RegisterCoalescer::reMaterializeTrivialDef(llvm::CoalescerPair const&, llvm::MachineInstr*, bool&) RegisterCoalescer.cpp:0:0
#12 0x00005b8b2636c9a7 (anonymous namespace)::RegisterCoalescer::joinCopy(llvm::MachineInstr*, bool&, llvm::SmallPtrSetImpl<llvm::MachineInstr*>&) RegisterCoalescer.cpp:0:0
#13 0x00005b8b2636eab2 (anonymous namespace)::RegisterCoalescer::copyCoalesceWorkList(llvm::MutableArrayRef<llvm::MachineInstr*>) RegisterCoalescer.cpp:0:0
#14 0x00005b8b26372369 (anonymous namespace)::RegisterCoalescer::run(llvm::MachineFunction&) RegisterCoalescer.cpp:0:0
#15 0x00005b8b263734cb (anonymous namespace)::RegisterCoalescerLegacy::runOnMachineFunction(llvm::MachineFunction&) RegisterCoalescer.cpp:0:0
#16 0x00005b8b26135623 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0
#17 0x00005b8b267bd281 llvm::FPPassManager::runOnFunction(llvm::Function&) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x3b8f281)
#18 0x00005b8b267bd6d1 llvm::FPPassManager::runOnModule(llvm::Module&) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x3b8f6d1)
#19 0x00005b8b267be024 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x3b90024)
#20 0x00005b8b2719181c (anonymous namespace)::EmitAssemblyHelper::emitAssembly(clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream>>, clang::BackendConsumer*) BackendUtil.cpp:0:0
#21 0x00005b8b271924ec 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*) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x45644ec)
#22 0x00005b8b2788920e clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x4c5b20e)
#23 0x00005b8b293354ac clang::ParseAST(clang::Sema&, bool, bool) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x67074ac)
#24 0x00005b8b27bb6617 clang::FrontendAction::Execute() (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x4f88617)
#25 0x00005b8b27b3776d clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x4f0976d)
#26 0x00005b8b27ca7b7b clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0x5079b7b)
#27 0x00005b8b23af6f1b cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0xec8f1b)
#28 0x00005b8b23aec687 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#29 0x00005b8b23af10da clang_main(int, char**, llvm::ToolContext const&) (/local/home/suz/software/local/clang-trunk/bin/clang-22+0xec30da)
#30 0x00005b8b2398c4fa main (/local/home/suz/software/local/clang-trunk/bin/clang-22+0xd5e4fa)
#31 0x00007144aa42a1ca __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#32 0x00007144aa42a28b call_init ./csu/../csu/libc-start.c:128:20
#33 0x00007144aa42a28b __libc_start_main ./csu/../csu/libc-start.c:347:5
#34 0x00005b8b23aebc05 _start (/local/home/suz/software/local/clang-trunk/bin/clang-22+0xebdc05)
clangtk: error: unable to execute command: Aborted
clangtk: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 22.0.0git (https://github.com/llvm/llvm-project.git 3e2fadf3beff93433f125eb1ea1abe470db5aa12)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /local/home/suz/software/local/clang-trunk/bin
Build config: +assertions
clangtk: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clangtk: note: diagnostic msg: /tmp/small-f29223.c
clangtk: note: diagnostic msg: /tmp/small-f29223.sh
clangtk: note: diagnostic msg: 

********************
[509] % 
[509] % cat small.c
int printf(const char *, ...);
int a, b;
short c = 1, f;
long d, e;
int main() {
  long g = 0, h = 1 % c;
  short i = 0;
  if (b && !(d < f || h < e))
  j:
    i = c;
  long k = d & g;
  short l = i + k;
  if (l - 1)
    while (b) {
 printf("0\n");
      if (a)
        goto j;
      g = b;
 }
}
```
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzsektz2zrv96dhNhh6JEq25EUWih23mWmfZJKc5yw9FAXJPJFJPSSVJv3075CS40vS60ln3sW_kyY2BIA_QCAAXri1slGI52R6QabLM967jTbnXzeoKq0a25-Vuno-v3LAuw65seA0lAgcDApUDgw2Bq2VWgG34DYILXdoHZS9bCvQChZ628m2RQOXT12rDRqoNFpFWOZAGG43EyBR4X9m0fgTFWR6MY0yMl0CYVMQLVeNewD6SKIifIFHNGFUxibRJGqkA8LyjXOdJUlB2IqwVSPdpi8nQm8JW7Xt4-4P7Yz-B4WbeKkEWc2rOimxrudJmiR1zKZYxshjXmKaRVU55TxmhM1JVNxz06AjSQFP-Ww9S2mvHpT-omgrVf9EG9V7po1BXsFWV9h61k5b-USi4kpZx9sWq6U0nu7haMFbwlYbvUXCVrb_6n_r2n3hBg-eB5upM716IGxVSkWi4iJ4WGhVy2ZQd8GtReOkVpZExUr3qgLBVSUr7hA-LBYgBwjc84wQemv8QLL0HhOCsNVo2t4ktoqT91aYkqi4wxaFw-rfa1q8gNr2rZNeJClgQpILkkbb2dFg3-QY7Fv8tSy-A2b3QvqKE7Z4CcOYTea7sM13YfuK8BLH1wnYLW_bidgFNGXsJCZs_5W-fN6HROAOs-sknA-CPHhsoSv8gIqw1S020jo0C81btALNRHQdSYp4GkV-0FLrFkh2wZVWz1vdW5It_SxKileSA9ngZ-7QSN7Kr3hv5KPk7RJrwnKhlXUQcATOF8EbLg1hM--z_dPPXGykQj8xDGGFf-ixBL65R1bsAhrILPp8PZH2atu1UkhHWE7YHALrDD5fTxp0t9gM5Im0N5tnK4PzDvkIy4OWJfJq9yRbkGzhnyyxvuvLq-rpgJuw_P72ipLkskF315fDECfDedwvwkFnsiTJEj4vdv4bNPUqZNuKsPl_8MvnK6_kukPDlQcTeeDHaucHAEcY0g4ogtrL_xGW_5yqxamPjn8yqLlssZqQqLj5dFncXYLty610wKHsGzDYaeN89v-1HEvYSlrboyVsBVxVIJVo-wpDqQjZH0ouHpzhAj3IzmBntEBrsQKrezOQvSS3VgvJ_RQ2vQIrjOycx3vnuHiAqt_6mCZREU1INL8xujF8C9w0_RaVs_864-5ojAEVIgbqjOxa_GYlCLOc4lY6qst_gHqAlTTAKdBKWl62SGuDCFS0yA3l1tESa22QepegqoBuuVS0li1Sxbe4yxlAtwY9UD8zaKgz0EkBtJOCtviILbDhi7S0kwh0Wxu-RdppqXw0JkulFQKtt9xtKBqjNNC67qjQyr8KR5KlVkBrpanxWVGqhnpeoNsww00vnDaUt5JbtEDrXn2RqqLOW2VJsmRAXaiVVHS9dxGdpUBdrzAQGlRoPOIKy75p0PhHUjUkWTZVCbQOdCpC7zCYWfmiuTx9cyxi0yiPYjqmVrqdpfQ6oSFB0ihKptOIsFWFreNAa6Ef0fAG312zwSFYvbLfD7MhcQeaR8CAXr0uPbsZNDz7QbV4JRQCQPGWSvtsHW7fD-yPRvmGFd9h_WHhZ6vJ5PWvN3hfj4ZP_oN4PerI-oae70v_-hBAazRGG9pKn2jjuZ-QaK2PzxZV4zYkWcZRBLRuVC_o2GuQZJlO2CQGWtsH2VFdGSo2KB6oVLTZ1iHMW21oJXmjtHVSWKCP6Ges_Iq01bo7Iti2A1rzqjJWNkCX6_WHxWL9sfjv5Xr5d3G7YuvF6mpd3H32cIBqb4jbdj5GfD6iIucsrSYa6BOIg74m9nmYJAvUNUkuoePGogHuwKc2XYPPayQqmGfzzcqQFYaeKyoST77tlU8L0HFrgbBs1SsR2oEbT_jMFW98cc38QmOrq75Fz7WDwDJfHtK3FO0qKOw7m0FLvRuBsMx3htxn_oxEvngkEURPURRF0zIv2QyreYLsoJ2xz3b4cGOkcqEs3Q-FLd8zGf5lra0zyLdjPySVG1qU_J3qE2EX0VPKeJnguG7x4OMT8LOoqt8Cf9urO9ko3n7kqmrR2JcW6r3x5VFV7_GxU3yMCThCQlgefLUAKxupar12Y9f4qGUVPs5HCTu2uFH4PwyQjANkcZpynqbTJIl2VoVU80biaGUpJlZPZgNmL7JHnB4rnGPJBKzXnQsLwPWDbNu13HYt-gYkxDX4_KQ65z10yDYRJCnSlCRFNhuVT39G-Zhqvqs2y32rv3PC7C21hzLf1ZXPD3Vlpw5lGYLh0mJQYsOb2GVl-2wr7HwfOKyH2SpwBrUsI0mxMzw_1sryvK6Bl779DHpcNbytQBpQxd7MUXz-SjwuYa3adat5ta60n9FBkVTBRk_e2kbwQVccZx5MWMyxJI6OtSXlNM5-LWaCyBAzXuHxLExmZT6rvcKXtRf4Ts92IW3Mf3MV9o31F4Te7ddWYfCtxeNuZnmj2IlRYs6z3zTqHy3VQnfPR1Z8D-GhJXc-8d84c4fOrxNJsvi2juTyFwxMTgxEXrLfNFDo7nlH-lubh0_Sv5JDY_vQRRfG8OdbrH9oxM9ZkB5bkLFkNv_duOvVW29nV5t_wa3TE1BJKspfBvUJGy6eX6Bdq1d43gXr7AhrnExnLHk9iXaKfX9yAOlNLCcgCMsnHTdu4isMvKHvDVDZEaisrFgeH4Ba3Xi5XZv0y3Des9wnZV6zPN4nwvwU-qz6GeifQ5d3_E5H0p-CPasOYM9PYGPE0gPY7UEwHhgwZKM3J88fBT-PIpa-gGdH_WsWz-M8Fj-ab5db6QprcVu2zx-x7XZvAw_ohOXDOjA8uRh2L4oxmhZgXTU86ZX8X4_rzpmjrOZb4u6LkQ7Xu8b4QKjCmvetW1fYosMfCCaXIScu4DWehVa236IZ-8SR-peT7euJxeITT7EUxaFOb_2o4bp3Xe-OXTAceqAJW_5K4FipjjjC7ux1N2zXv6pkzkjV-PR_XKrHaCneNnHv8r3IlXKmt_IRb7FeKHdz4vvHesxTK9niXViojh78__KtvfciZDpLUxT7GXLUyWR5PmcRfg9VIA7Lk3vDlR22lP5S8iQgirv7hVYOn9yfmeqpmJYswr0hRx3LPEmmKT8K4Bu_Gi_u7o9h3uGWj7E4NFi7v-8OeJZFWcoPPH_UoGRlOZvF2SHglfH-e4nxITc9oegd_qEFap3ns4PWnU2PESZZNqvge5P-EONuaubfNunPBEYdzbNZtbfiqI_JBM_KrDy0YsS7N-Zx3Gj-UYb7E_NzGmXzMiv36I8anoTXszouQYh4PWzUHBTWg_5ZbPjL2qfYZZoj2vEWwjsbgSKv4wMb8mMbUMzyDHZuX8T3YcLlJ6ua_4btunFV89qgk_LhdYz55mDRN4fKyMe3uls2P_FrHFV8iIqdZ8edFz90cFPxcyO-uy-TqOIvvjzekUvmuUhrDmGJ_84DV1NM64OB45NtBh4LDuu1X_uvrePGrQVv2_XLboOw_eudkHGb5S2hyYYkRZaSpEjGEdnpiCwvIfBLJd3pIMNHr5kGzcPmBstJUrDxpZ9uiA0aj2x4C_6bmpM0I0kxHRWnJxFeimgKg8p3D4iyEtF0eC_jSQ1JCggb6_5Dr_xiGpwGHGYYCL3dclWF4-VSG4fVN0SHiyb1mKR3cuNBKVR90DpscnmreotAHwMNEeRB3pz_362Vn761cvAilPaNYwH7cwzY2kEoKnY56Ld-wnWj8Zi7uL8vFh_h_uMlrK4_fbr---o_H2B19enyDu6vA_nirw9we3lzfXs_nC_fvHVGnVuf7b55Tv3CYBDCyS1WwN2g7-dMPj5zqdmcsWR_feT3xO3mVzz-750-vZhG89PbMS8Ewd3B6ZFUDjojldtfKwllb6w8E5-L5iS5GFnDbZxy-G432jgQQJIlxJ5eD_RWqwYqT8C94FjehpsWnggQ-JogHnnuzaBpADlIAgyDyJFrJMqwl1vuL5DEhOUVkGQB9e4ixyZ8xfHmhZf6Z4gDABj1vQwSkDwEWuWVQnM8fBseST-L4OEYRAsU4t0IAF82MhyO5eWBpS_-JYxFZLpQhLEXr0L4Nyjje0X-X6Od9qj3bIO3Rv8DyZb-7Q6_d7f6zqrzpJonc36G53E2TaOEpfnsbHOeZEmNIsayjBlGaZrW8bzO5mkkypinAs_k-e4wPpSq2WQWVwyjMirjskyiLCdphFsu24lPlBNtmrNw6eQ8nsaz6fys5SW2NtxxZGw8sGZkujwz5yGzln1jSRq10jq7V-Gka_F8yNvhpgpa4A7oNckuLGELRtgiIdkStIJXR8XmZ84bz3rTnv_-fZrRusdz9v8CAAD__4UH5d0">