<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/137860>137860</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang 21 crash (stack dump) when using _Atomic anonymous struct field access with atomic_fetch_add
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          mariete1223
      </td>
    </tr>
</table>

<pre>
    ## Summary

Clang 21 crashes with a stack dump when trying to compile C code that uses _Atomic struct containing an anonymous struct, and accessing a subfield with atomic_fetch_add.
Instead of reporting a normal diagnostic, Clang crashes during semantic analysis (Sema::RefersToMemberWithReducedAlignment).

## Stack Trace

```
Stack dump:
0.      Program arguments: /usr/local/bin/clang-21 -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -dumpdir a- -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name prueba.cpp -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=all -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=/root -fcoverage-compilation-dir=/root -resource-dir /usr/local/lib/clang/21 -internal-isystem /usr/local/lib/clang/21/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/9/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=c2x -ferror-limit 19 -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcolor-diagnostics -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/prueba-d1672b.o -x c prueba.cpp
1.      prueba.cpp:17:1: current parser token '}'
2.      prueba.cpp:15:1: parsing function body 'add'
3. prueba.cpp:15:1: in compound statement ('{}')
 #0 0x000055bf6ccfb18f llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/usr/local/bin/clang-21+0x3c4a18f)
 #1 0x000055bf6ccf8bd4 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #2 0x00007fcb90f86420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #3 0x000055bf704f588b getInterestingTagDecl(clang::TagDecl*) Type.cpp:0:0
 #4 0x000055bf6f170b2b clang::Sema::RefersToMemberWithReducedAlignment(clang::Expr*, llvm::function_ref<void (clang::Expr*, clang::RecordDecl*, clang::FieldDecl*, clang::CharUnits)>) (/usr/local/bin/clang-21+0x60bfb2b)
 #5 0x000055bf6f171180 clang::Sema::CheckAddressOfPackedMember(clang::Expr*) (/usr/local/bin/clang-21+0x60c0180)
 #6 0x000055bf6f43e823 clang::Sema::CheckAddressOfOperand(clang::ActionResult<clang::Expr*, true>&, clang::SourceLocation) (/usr/local/bin/clang-21+0x638d823)
 #7 0x000055bf6f462710 clang::Sema::CreateBuiltinUnaryOp(clang::SourceLocation, clang::UnaryOperatorKind, clang::Expr*, bool) (/usr/local/bin/clang-21+0x63b1710)
 #8 0x000055bf6f462f85 clang::Sema::BuildUnaryOp(clang::Scope*, clang::SourceLocation, clang::UnaryOperatorKind, clang::Expr*, bool) (/usr/local/bin/clang-21+0x63b1f85)
 #9 0x000055bf6f541845 clang::TreeTransform<(anonymous namespace)::TransformTypos>::TransformInitializer(clang::Expr*, bool) SemaExprCXX.cpp:0:0
#10 0x000055bf6f5415c2 clang::TreeTransform<(anonymous namespace)::TransformTypos>::TransformExprs(clang::Expr* const*, unsigned int, bool, llvm::SmallVectorImpl<clang::Expr*>&, bool*) SemaExprCXX.cpp:0:0
#11 0x000055bf6f54851d clang::TreeTransform<(anonymous namespace)::TransformTypos>::TransformCallExpr(clang::CallExpr*) SemaExprCXX.cpp:0:0
#12 0x000055bf6f55fd4e (anonymous namespace)::TransformTypos::RecursiveTransformLoop(clang::Expr*, bool&) SemaExprCXX.cpp:0:0
#13 0x000055bf6f53d14a clang::Sema::CorrectDelayedTyposInExpr(clang::Expr*, clang::VarDecl*, bool, llvm::function_ref<clang::ActionResult<clang::Expr*, true> (clang::Expr*)>) (/usr/local/bin/clang-21+0x648c14a)
#14 0x000055bf6f53f45d clang::Sema::ActOnFinishFullExpr(clang::Expr*, clang::SourceLocation, bool, bool, bool) (/usr/local/bin/clang-21+0x648e45d)
#15 0x000055bf6f87b09e clang::Sema::ActOnExprStmt(clang::ActionResult<clang::Expr*, true>, bool) (/usr/local/bin/clang-21+0x67ca09e)
#16 0x000055bf6f02fdcc clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) (/usr/local/bin/clang-21+0x5f7edcc)
#17 0x000055bf6f0236b2 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) (/usr/local/bin/clang-21+0x5f726b2)
#18 0x000055bf6f024104 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/usr/local/bin/clang-21+0x5f73104)
#19 0x000055bf6f02546c clang::Parser::ParseCompoundStatementBody(bool) (/usr/local/bin/clang-21+0x5f7446c)
#20 0x000055bf6f0277e2 clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/usr/local/bin/clang-21+0x5f767e2)
#21 0x000055bf6ef1ee83 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/usr/local/bin/clang-21+0x5e6de83)
#22 0x000055bf6ef68f05 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/usr/local/bin/clang-21+0x5eb7f05)
#23 0x000055bf6ef1762d clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/usr/local/bin/clang-21+0x5e6662d)
#24 0x000055bf6ef1816e clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/usr/local/bin/clang-21+0x5e6716e)
#25 0x000055bf6ef21d73 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/usr/local/bin/clang-21+0x5e70d73)
#26 0x000055bf6ef236a8 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/usr/local/bin/clang-21+0x5e726a8)
#27 0x000055bf6ef1162a clang::ParseAST(clang::Sema&, bool, bool) (/usr/local/bin/clang-21+0x5e6062a)
#28 0x000055bf6d67fe45 clang::CodeGenAction::ExecuteAction() (/usr/local/bin/clang-21+0x45cee45)
#29 0x000055bf6d9649b8 clang::FrontendAction::Execute() (/usr/local/bin/clang-21+0x48b39b8)
#30 0x000055bf6d8e2d3b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/usr/local/bin/clang-21+0x4831d3b)
#31 0x000055bf6da56c7b clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/usr/local/bin/clang-21+0x49a5c7b)
#32 0x000055bf69f53f51 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/usr/local/bin/clang-21+0xea2f51)
#33 0x000055bf69f4c5fd ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#34 0x000055bf69f4f99f clang_main(int, char**, llvm::ToolContext const&) (/usr/local/bin/clang-21+0xe9e99f)
#35 0x000055bf69e2230b main (/usr/local/bin/clang-21+0xd7130b)
```

## Program

```
#include <stdint.h>
#include <stdatomic.h>
struct S {

 struct {
        uint8_t h;
        uint8_t f;
    };

};
_Atomic struct S s = {
                     .h = UINT8_MIN,};
void add(void)
{
 atomic_fetch_add(&s.f, UINT8_MIN);
}
```

## To reproduce quickly 

https://gcc.godbolt.org/z/ojzzEevv7

</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzMWltz2ziW_jX0CwoqErw_-EGRoh7Xpiep2N0zbyoQOJDQIQEOADp2__otkJQpSvJFM9u760psCcTl-z4cnHMAglordwrgNkg_Ben6hnZur81tQ40EBxEh8U2l-fNtQOKAxOi-axpqnoNwGYTLVU3VDpEIMUPtHiz6Kd0eUWQdZT8Q75oW_dyDQs48S7VDTiOmm1bWgFaIaQ7I7alDnQWLtkunG8mQdaZjDjGtHJXKt6IKUaXVc6M7Oz4OyApRxRFlDKztKyHbVUJCzUcMfW9bAY7tt5TzRRAu75R1QDnSAhlotXFDQ6VNQ2vEJd0pbZ1kvveB2YEW74yva6GhykmGqKL1s5UWBaS4h4YG8TKIl99BgLEP-ldoKjD_kG7_HXjHgC9ruVMNKBeQcjEod1CzF-rBUAZjeRaO_8Ll_YuKvv9wGS5Q__PN6J2hDaJm1_lebRAvUUA2nTUB2dSa0Togm0qqgGyY54FJhDBjEcLOyLYG9FRk2yzBnfqh9E-Fa6m6J7xTHcLQSId19QfCflwuDaIYYS4trWrAwgAgzGqgBlPrcAVCG8AVZT9A8aleXT82-BGMFBJMX8yo4fiR1h1gRRuwCDdUKixkPRSg1nRQ0QVrW4QbA56Fk1rhRnOoUSsZwq1kuIZHqBEZvkiLWwkIN8LQBnCrpXJggnhN6xph0VC3x2CM0ggL0WJvU4YyF8RrrRAWSmOjO8Wl2mFfF-GGaTVYmDaY1pJ6y8SiUz-l4th5bjaI1wRhR80OHGZt58XEWYKw6xT0BTtQYDxgDlW324Hxj6TaBfF6xyuERV-Oh6UwsOTSww7IxmjtEBZMP4KhO3irkgGrO8PAl59Pfy2rw_QHZOMNoBdH0RpL-2wdNO-3CchGKlZ3HD7S-iNV-wF2jAVkM9rgi-0FZFMGZLNYnP-6UPV8MHjyH9j5oGPVC_283fr6IRC2jgfxmpEnhAUYow2uZSMdikqExU51zK8KK7UK4nWyIIsIYWF_yBZrbjDbA_uBpcK7RvQ2UGuDJ7fkLZFybqzcIbzebn9ZrbZ_W_7-ebv-x_L7hmxXm7vt8v7XIF5HCGsPzjVtQDbDysI8ynJSLTTCT4gdLbcgXEajYzkqjJdR7n9518I6Y0A51FJjwSCnf4BCAcmDfO1_h0tysX16aO_befcpOsW8ISMfT3wHlPOhg3jxWlup-pDhl6mPKg68w_Nutx__0wiBlEHoXWAcovApDMMwTSuRMSaqqBDIe6PBQ9tnO3z4ZqRyvX8dfC8ppkqG_txq6wzQJiCZDway99zDqG962YB8Cp9iltCoEBOo6ARUUfEE3cudovXfqOI1mIAU_RgrZOVOKqG3LiBL__1RS95_LMcWdpQo7P8PA5BxgFywqgxFkSUkRNutAeu0ga0ZBRuX34XVVMuqdXsDlC-sXoQ9jShJSDiRiI9I5GEi0qKo0A7cnV8cYH0sfaC7NbA6IMXgQno1Xwp7Dg_PLVwgkBwrJKI8rEiFjjq5LsYeD__5qTWjlNMMHwxxa0AE8cprjF5tdlT6HZg2_IXO7NnG5x6XH6321PympLNezfjzFaaUhZWoSDXNQnoiVBQV4WWhVt6ZLDk3YO1X8c1HaD6I9grTK0CxMCqOTCObgUpiKEj8EVBfWzBU8TmeZT8z38F2tQvi1eU5caaDXsnsROr7PiJ-GZOHa0jFBS98TnYglc9JZSSPXlPaAHXwqZO1k-o3Rc3z13bO6RTVDPLYAgx12vyX9HrMnh_RrrSur-JURXl0NFHFKSdRpJc5eTb8MhemWzi38f9DiqJIJ4rljGKaREUyo_hgAB4MVVZo0wTxKiDFtLnoM9O2jwflofpY9eG51dab3Lz4TkknaS3_fHVZTZS8ur549c9_nrhAHyPCU-ApI38hcA_EXoSM-hx4xN6pfnPI0RieBi7HvvS-oXX9O_iM-a5p68tL9mWpDu2X78sRnchRpBH_C-VY0boewB4rMpV-ADGZI04FTwBdCWsMMp2x8nGi90Xr9h3ryt7HF8_xxTxK6CsOTRsDzK2hps_Ae2h36lydyzHyd2qOouC5vZzE3n_T878Wrq-Nr0nBooQO7sOLlJyIJJKUXxZpydxXtZFK2v2mu2Q8l-U595MHieZ_r6EASconCvMUocirsIQ3KHiY965x_0kUvh50zmhYwgR6nkKERHDGjkF_67ceR58H2ON-YI79rC73_FZaOXi6Jo9PRQ7cb1UPIPMTkHFWkTdBvgD82q8JavpJXwoHZumckVXnwM72HkfedC77MEW97DHpLuY-7_B-0wxPzXRofwzy4minNa7RlmQVmbQtTrRNojD5N7T9_yLmNULEUZhMQpQnQqRJ9vZKWI3b4xdBPmn-HJDiyiWZijxJssnaSXgCJM_hbWvfjJ79FMhRm8v7o_O5HXLMKw0qy2EyKDJLIEBEAEX8IfhrENJndb0xnTSQancwNm0-YjQP0LQ1dXCnhD4kVm-1-kIdTCvrixwTsY_LABmHIp5kIHMZskKE6ZuQPb9fjO7aV9nft8DOWUy6XF4kH_Qor6r3_l7vLbPaaPOdqh34fP1aRatchOmkaHxiWHlG-LuKfjVH5nU3nideCFvXu9yzGm_O0rJ_YeKf9Ufz11lWlpEpzyDJiQ5FlMG7OoxueibHq6vtf1yNUwv5j9TIo2xKYEg6V4NEPH_b3Xx-GoxgHrz-FxS4gmMe8vzIl2QnHOOMFm9yfNDtF3iE-vxU8GtL_9XBN3cSmF-cz3e_Obh0vvOSvP6qeVfDXdNq4_qIc2W8gJxktJjI5SfmHGWEnpFb3j-cnIZ4PMdb26tT4RSyMCPTFoTMMiGe5QLmJxgrzeEXUEOGfsjJgXUOxiI_7oeHT1IGkBy5t1n-wcssKavZJG-Md--KXxj_ypGLKi6raQbmZ_e8AMLjak68f3Vs7pR1VDG4zP11qFfZR1LEEY-rCd0sn-A0zVhezc-wehwTyMeXwFS8ReKqJZmUNGX5EapZeC_9hjWNEGPRtqFyngwvjaHP34c9956a6ZRn2MDNy-YvHj4IDigRaTRhi-fYEpYKjg4yraKHfp1cTtcPJ0lnQLP5YYLvY0w3jrKrEnEjH8GcH4LMXzSUIhFlKYZZPCg2HnT5oXv6y4-N-FGNSihLMWk0CxslEBKHFfJIPtohz6M4PBjE0d2B6YrBeFvg_HpBQOLDe8sgXlnHpXKLvZf5wrPhPsXh8XhJ4x4F-aeh48O9jaEAjT-dVK7YOrQP4kvFYioO8vXwxf87fD65E3KPLAri9ckYs5_Fvq_x293fH4rtr3d_D8jqpbf-NU__yrEYjLvXbOjr9LpIr35mF8LP_lFv5QgyX7-q94NGBlqjeccA_auT7Ef9jIYae-fa_pSPbIbX4Iud5pWu3UKbXUA2fwZko__488_P8PiYB-Hyht_GvIxLegO3UZ6kZUqSjNzsb0USCy4EKymPQyAFoZUoBIlKEhZlltEbeUtCkoYJKaMiyROyCLOqqkoWRmEGAGEWJCE0VNYLb9p--BtpbQe3UZwXWXhT0wpq218JImS8EECCdH1jbvu7HVW3s0ES1tI6O3XhpKvhdn4pyBvydB3IL5X-RlDXvxE-TPDp_R403OQZrvdcvtBz05n69kRQ6fZdtWC68WvGL9nhD26N_gOYC8imJ2kDshl5Pt6S_w4AAP__Pn5VHw">