<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/69220>69220</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang: crash at clang::CodeGen::CodeGenFunction::EmitAtomicExpr
        </td>
    </tr>

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

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

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

<pre>
    Compiler explorer: https://godbolt.org/z/oa181PGWW.

The following program `small.c` triggers a crash in clang-18:

``` sh
% cat small.c
char x[], y[], z[];

void foo () {
  __atomic_exchange (&x, &y, &z, 0);
}

% clang -O0 small.c
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-9.2.0 -fcolor-diagnostics -fno-crash-diagnostics -O0 <source>
1.  <eof> parser at end of file
2. <source>:3:6: LLVM IR generation of declaration 'foo'
3.  <source>:3:6: Generating code for declaration 'foo'
 #0 0x000000000372f498 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x372f498)
 #1 0x000000000372d15c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x372d15c)
 #2 0x0000000003675a78 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f4735471420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x0000000003c16172 clang::CodeGen::CodeGenFunction::EmitAtomicExpr(clang::AtomicExpr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3c16172)
 #5 0x0000000003e845be clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(clang::Stmt*) CGExprScalar.cpp:0:0
 #6 0x0000000003e8a21c clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3e8a21c)
 #7 0x0000000003e22016 clang::CodeGen::CodeGenFunction::EmitAnyExpr(clang::Expr const*, clang::CodeGen::AggValueSlot, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3e22016)
 #8 0x0000000003e435bb clang::CodeGen::CodeGenFunction::EmitIgnoredExpr(clang::Expr const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3e435bb)
 #9 0x0000000003a49ba2 clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3a49ba2)
#10 0x0000000003a5003c clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3a5003c)
#11 0x0000000003aaf5a6 clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3aaf5a6)
#12 0x0000000003ac264a clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3ac264a)
#13 0x0000000003b234a3 clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3b234a3)
#14 0x0000000003b1e675 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3b1e675)
#15 0x0000000003b1ec3b clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3b1ec3b)
#16 0x0000000003b27fa3 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#17 0x000000000499dc46 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#18 0x000000000498ed08 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x498ed08)
#19 0x0000000005ea1304 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x5ea1304)
#20 0x000000000499b538 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x499b538)
#21 0x00000000041fefa9 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x41fefa9)
#22 0x000000000418044e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x418044e)
#23 0x00000000042de12e clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x42de12e)
#24 0x0000000000befa56 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xbefa56)
#25 0x0000000000be731a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#26 0x0000000003fdc649 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
#27 0x0000000003675f24 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3675f24)
#28 0x0000000003fdcc3f 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
#29 0x0000000003fa4e05 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3fa4e05)
#30 0x0000000003fa586d 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+0x3fa586d)
#31 0x0000000003fad795 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3fad795)
#32 0x0000000000becefc clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xbecefc)
#33 0x0000000000ae7091 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xae7091)
#34 0x00007f4734f15083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#35 0x0000000000be6dfe _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xbe6dfe)
clang: error: clang frontend command failed with exit code 136 (use -v to see invocation)
```

Clang version:

```
clang version 18.0.0 (https://github.com/llvm/llvm-project.git ab737a86993bc7bf92cbb9d51f47f8825a717333)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/compiler-explorer/clang-assertions-trunk/bin
Compiler returned: 0
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzkWt9v2zgS_muUF8KGRP1-yIPjxLkuutiiKbqPxoiiZF4pUiCp1Nm__kBRdkTXSZus93DAFW1tU9Tw-74ZckYUQWvWCkqvg_QmSG-vYDA7qa6JFKLlnF1Vsn66XsuuZ5wqRPc9l4qqIF6hnTG9DuJVgDcB3rSyriQ3S6naAG_-CvBGQlREn-7__HMZhLdBuHL_f9lR1EjO5XcmWtQr2SroUJCFugPOlyTIQmQUa1uqNAJEFOgdYgIRDqJdRIUdcGYuyEL3F-nd1IJTRMCgg72xkexAob2jGOA1enr--tf0Nb6Z232UrEaNlCjARYBLFOTTZYS2WzCyY2RL92QHoqWuT7a31gKcPU2ff9nPMMDls-n81sNukVpaaPFH6OP99PFu9XCH9FB1zCBA1dAiRXupDDLyVHlmdkO1JLIL8Ibzx8PHolfy35SYAG-Y1gPVAd4gEDVigvChpsjs6KRvBeSbUUCohdwr2itJqNa0RloOyjXbO0FrSRgYWiM1CKSJYr2Z3PtggHxD9dD1RxeFS4Q-TR4G1Q4dFcbiRjY6eguMTIG1OAYW3jhPg9ZUGSaFXhg1iG8B3lRMHC6jRVt_B9UsErRo0cK6aQN9b-0Oph_MUqNFZ0VAi8W-yBagu4V-Egb2QXzLhKEcLR7QYtESsjBScrIDJoL49lVgtnO5xMsQLRoiuVSLmkErpDaMaLRohFyMcvrNf4QoiNeTjvGdUyZaIttKZRPEd6gHpalCYBAVNZINahinriNe-nfHqziIV5kV8ePHr7-jD59RSwVVYKWyt9aUcJh-BjhvpAxw7mzFbtCzxu4nI6JFRNZ2iqrXTKEAxyEK9-HhT5zjJikLNMZfvArilX7S7ssnxYQZo-OLC7HiuZOC71upjaLQBTizYcaEGeebnVJ_M0gCfBPuJ2B2Gh6RRyfI6ygl55CvOQUx9H-IB9YK4AEuBjGuljXi0tq_LE4Lw8OJPZxZnkJeoLUNsc-UyEeqnhywf4GouR2umNTz-qylMHRvlqS3MzMc_x2HiKch8ibJ4zTJowSHaLtVVBup6FaZiSFnVYA3-yLbZsmCMzHsF60Y3IXe7BSFeqnlMhy5REmCQ49J4jEhURbl2K19k9KypvdUeD82gyBWM9d41zGzGtfdu31vqc7unrevLusVB9XjknpcaJGkFZ1zeTCd-co0M1LdgKZ2xpnaXYK63vbSrj_KJYkChBRPnRw0EtBR3Y8TpJwMEeCgLC1LfrrnOUy_Ah-oJTzOZNtgB_WVsVgmTdb31pKzeT4WshNigCPydic9o_ah2BZEpNAO0BpVUvLLOstB9pyV-5wwDqPsHYEnnn6B0EtmV207-uqBS_MPER95ecQLn3gSp1X1duIfWiEVrX9K_qJkRqwemdIjA0lZwTuWDzcZTqeH58Ln2bVSCp4-0yaI195KY2a047vLMnfEjsxtpvKTLKR29Xw7c1u_y0HUlu-fzOzkYB6I7KmvxrzXgWT2HLC_GuAXVWQk7CniJ2-AJoV3zOhDy42sn16NiYuyGcF6bPwUDwRnCbyNzVS5UXvRZ3LPZQX8lhLuh_bx_teXrfX9oeMH0chZQFxUkpGxJ0nsSVLhOIH4Z5L8LuuB02f3OuoH_Le0YYI5yr8ikGs_5teLEnZ8PMJ-cVRFNMvT9xH-nyI68vCIpqdESfzTnHSe6Mv0LkyBxJVHITsJzrx5e3B-kf1H-kgnwHMiruXgiGUPytiSukSepR-rN4vMq3SSsqxJkv2swpzM2vVDqg9dz12ze554Hea9kkNv8yMukYN1MzBe0zO1pUVX-OgKWofFXLcbIN-oqNdS6KEb95fegeNinp8Aep73apCUQhSHyZzBJ_sQv3r4cpJNaAcnWfTi5d8EZo4WhyfRUKVxcSZOV_O0uKdkMHRqmra9LqfoCMHD6GXyJGpoA-Uc40bZJ1dRnwF5cXhudA8e9uEVYZJQdFIu2QE_CG1AEHpexZf5XDiVTgg9Cl4qTXBNI-xRmMA-M3mUBH4E_gPTC-eKCZkH3UuKYUUbSDNESLTtwN5dnK_Ud3BSnq-R34bX6FGy-tIMHD6PQHpCII8jQAfB19GXcRWY0XjogPOvlBxX4jNsMj99WxvT7o5XntWKPb6wEGM_gTU1yZJylGRmt5nqpq0aVR2vuhl33GsgwHkF5Nu2Ef4Tkht7ipt1tJZdB6I-nbxnvXfcJpG9HR2sBjN9jGKiHXveTa493rDdkv0-ityPCjQjWz12n1T0OtuGrVHAjD5cPjEHnNt5INXsuu0y27YYw8dpPt4S4JxDV9UQ4PxZKlwc9gl_k9V5f-Sne3wNTmauOLeT5658HsQDNJQ_eXK-7rqLVkcOqxfzxWlwkbhB_8_BcVLGvRgF_gZHAwkN0xeFG70GP-TEg5re0n1yo-3gPdr_WteVV8LMuF0olBzheSidvF1oIC2y-q2K_CYr_bIcv8nqI9P-Tsdry_ExAnpg1vnjXvuvKziFyT-so5XJ0zE60bHOyxcj63b23SsNztQEL-n_X9TxkouZE8ZTDp8kcEKbaevtUIMckI-LyOqHLcSX0vMFqw6LyQPtVXwh0DwsI2ThXm5UZ9QbNZm_RUqaKA2LGG23nFV2rQVltjMIr71KIkstl9k4DE7CwtsniU8rqqxuKHL2L6mpNXsc9xCViColx2MP7v1zM9XyiEzx2QDjtEbfmdkhumfGvUaN4vEZfNAULR6RkUhTitiszC5PjjHMzwesx5EeqdLTwnbu3MMM5qEriopluAztwG87KbBsmUFQ5XEORVaWcUXyqikxqaqyTqMmyZuiwCnkUR7Hz675AqqltihBk08H8U3I72Lm2-nkh6JQo07WlNvevdRs7y6NDxac0_qWqb93PsAJdziuoqgZlKB2vUHhiXBX9XVcl3EJV_Q6yso8yQpcJle76zysmzyKS5ySqIpIioukolGMM4qjAmpyxa5xiOMojLIoSYsoXpIszPIkpWUcQpNUECQh7YDxpRV3KVV7NR7AuM5KjMMrDhXlejxvg_EUeDhIb6_U9eiMamh1kIScaaOfLRhmOL0-hqM7twHm77xEvRoUv37_WZKRzX8CAAD__1WkJJs">