<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/133404>133404</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang][IR] Missing assignment in loop, which may comes from wrong TBAA.
        </td>
    </tr>

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

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

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

<pre>
    While testing real code during work, I found a potential bug, here is my code:


https://godbolt.org/z/fzd71aPcx


It can be observed that the assignment to `cmd.regOp` inside the loop actually affects subsequent logic. However, in assembly, this assignment operation is removed. In fact, it has already been eliminated at the IR generation stage.

I suspect this is related to an incorrect analysis of TBAA upon memcpy.  Below are the memcpy instruction and the current TBAA. 

```
call void @llvm.memcpy.p0.p0.i32(ptr noundef nonnull align 4 dereferenceable(56) %astEntry.i, ptr noundef nonnull readonly align 8 dereferenceable(56) %stRegCmd, i32 56, i1 false), !tbaa.struct !11

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 1, !"target-abi", !"ilp32"}
!2 = !{i32 6, !"riscv-isa", !3}
!3 = !{!"rv32i2p1_m2p0_a2p1_c2p0_zmmul1p0"}
!4 = !{i32 8, !"SmallDataLimit", i32 8}
!5 = !{!"clang version 19.0.0git"}
!6 = !{!7, !7, i64 0}
!7 = !{!"omnipotent char", !8, i64 0}
!8 = !{!"Simple C/C++ TBAA"}
!9 = !{!10, !7, i64 16}
!10 = !{!"", !7, i64 0, !7, i64 4, !7, i64 5, !7, i64 6, !7, i64 7, !7, i64 8, !7, i64 16, !7, i64 17,!7, i64 18, !7, i64 19, !7, i64 20}
!11 = distinct !{!11, !12}
!12 = !{!"llvm.loop.mustprogress"}
!13 = !{!14, !7, i64 0}
!14 = !{!"", !7, i64 0, !7, i64 4}
!15 = !{i64 0, i64 56, !6}
!16 = !{!"branch_weights", !"expected", i32 1, i32 2000}
!17 = !{i64 0, i64 1, !6, i64 4, i64 0, !6}
!18 = distinct !{!18, !12}
```

</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJycVl-Pq7YT_TTOy2iRMX8SHvKw2fyiu9KvanVvpT6ujBnArbGpbZKb_fSVgU1Ycm8fKiFhxj4zc84MtrlzstGIe5IdSHbc8MG3xu6vZtDNl5dNaarr_o9WKgSPzkvdgEWuQJgKoRpsMFyM_YuwF3iF2gy6Ag698ai95ArKoQlTLVoE6aC7jkiSPBM6P633vQsGdiLs1JiqNMpHxjaEnd4JO9Xv1Tbmv4nvN8SrB8E1lAimdGjPWIFvuQffIkx0OtQevAGSU9FVkcXm157kFKR2ssJxoTKmBy78wJW6Aq9rFN6BG0qHfw8BrkwjRQRfzAXPaAMJqYN77Ep1DZ--lW4Zz_RouZdGB6IWO3PGKoJXDTUXfsR7aLkDrizy6gologZUspOae6xgZvD6FRrUH66c5w1GM29wg-tR-Cn0GEWNUG-Aa5BaGGvDPNdcXZ10YGr4_fD8DENvNHTYif4aARxQmQtwOykxmYM23g5ijMp1NU6JwdpALfiIYC5ATueHPguuFJyNrICkVKlzF80xehoemTDCdr23oENjYA3aaD0oBVzJRkMKFVqs0aIWyEuFhO2ynLACCMu48__T3l4jGbT7kZMgo9GheqO33b95c_4rNi9dNdYhYRAmXkDGUHPlkLAifBIW-5LzaBIifMbxTJrFFEhyDDayPQQP8YwgjF1Ey-2bk-9IGPuIkJLtcULGP0d6bhv0T7yUM3IyS9UH6djNBVu5yO9rrXTi_CQdv3tIbrhkgZuXnxMmWR-_daynbzyMRBi9d92g4p4uo6arqLt71G8dV-rIPf-_7KRf0N7d0NlDbKG4buCM1oUmi4uIRrSZ0B-g_DNoO0cc3zJPgd5Wbh_cm07LaeeBUJC7HrtH9O4B_U12vUJ4Iez0QtiBsMPY9svkis-gmK6zi_N70elDhHtCCzorQ7o2ZGtDvjY8aLT7QVprSxh9MjyCirWF3eWbe7qS4UiYfpVZk4_mju-yfereSYpxrwhbcNQNzvfWNBadW2q9bt34QZlFNul_1PrmYNmrt7Wj_B_SLSqbP0QrLdeifbugbFrvPv3K-D3s2FgtfpH4Y8AoXZDY_iyH-JbCskmWlBbJ7X5WmN26MIt9fFPtk6pICr7BfbxNkzjLkm2xafd1mvO8oHXJsjoVmPMyL2iS7Mosx6zM843cM8oymrAdLdIiKSLBsjyJt2WaMZqyqiApxY5LFY0lN7bZSOcG3MdJktJ0o3iJyo2Xj3l_CEJlx43dB8BTOTQunC3SeXd34aVX441lQmRHkh1ev5LsCL9I58KdZHEuSz0e9oH-pZWihY6HW0iHDmprOrhYo5vpiNsMVu1XFxLp26GMhOkIO4UE5tdTb82fGA7200jIEXaaOZ337J8AAAD__7ghj5Y">