<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/75708>75708</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [SystemZ] Problem with i128 induction variable
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          JonPsson1
      </td>
    </tr>
</table>

<pre>
    Reduced test case:

```
__int128 a;
char *b;
void c() {
  for (;; a++)
    if (b[a])
      break;
}
```

cat tc.ll
```
@b = dso_local local_unnamed_addr global ptr null, align 8
@a = dso_local local_unnamed_addr global i128 0, align 8

define dso_local void @c() local_unnamed_addr {
entry:
  %0 = load ptr, ptr @b, align 8
  %a.promoted = load i128, ptr @a, align 8
  %idxprom2 = trunc i128 %a.promoted to i64
  %arrayidx3 = getelementptr inbounds i8, ptr %0, i64 %idxprom2
  %1 = load i8, ptr %arrayidx3, align 1
 %tobool.not4 = icmp eq i8 %1, 0
  br i1 %tobool.not4, label %for.inc, label %for.end

for.inc:
  %inc15 = phi i128 [ %inc, %for.inc ], [ %a.promoted, %entry ]
  %inc = add nsw i128 %inc15, 1
  store i128 %inc, ptr @a, align 8
  %idxprom = trunc i128 %inc to i64
  %arrayidx = getelementptr inbounds i8, ptr %0, i64 %idxprom
  %2 = load i8, ptr %arrayidx, align 1
  %tobool.not = icmp eq i8 %2, 0
  br i1 %tobool.not, label %for.inc, label %for.end

for.end: ; preds = %for.inc, %entry
  ret void
}
```

```
llc -mcpu=z13 tc.ll -o -

Impossible reg-to-reg copy
UNREACHABLE executed at /home/ijonpan/llvm-project/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp:863!
```

`renamable $r3d = COPY killed renamable $v0`

It looks like the i128 induction variable is truncated to i64, which is selected as '%11:addr64bit = COPY %2:vr128bit', which then results later in the above COPY.

</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJykVk1v4zYQ_TX0ZWBDoiRbOfhgx2s0RdEutu2hvQQUOZa4oUiVpJykv74gLdly4u0GLSDI1ny8eZw3Gog5J2uNuCbFllDaP6OsmRaEUlLsZqz3jbHrH43-7JzR6awy4nX9BUXPUYBH54EzhyTbkGRHkvG-TIYrPj4-Su1TWgIj2fZk4g2zQOimOluORgrghJaE3gFZDVaAgwmBZYjLtsAI3cbrbvQDyEMIqEixZaTYXbkAKovs6VyErHY3GQ6kmAfPF0rdjsmTCki2A-HMozKcKYj3x15r1qJ4ZEJYqJWpmILOW9C9UoTeA1Oy1lCeUdiHUWRoWvIeI94FHqTGCU7sIMmTsYk3cM99Re3t61k1AEKLJNJShonAPhQNhwinfkcgxrNFZ01rPIpLYiA8yWS3M6V4Cak05nnba3466TWoNyCX-bSgtexVipcs5tXoUWGL2odiUlem18KBvNSnRWydXObTohPAdEJ8mnYudKGfDmmEFt5UxqiFNj6P-ZK3HeBfIOMB0pCTjEUqCzJ9kxQCFKtQBfvB2IXU_J0NtZhqPYZdCSY1T4tIoWvk0MFiO3gC4gUf4otxP_ovXR7C4jjEoCv4CM6EAO2ezxLFsiFv7Ak4byxO_R8egRsTEMp-U_r_o_wEjn5H-Pe6X2t4Q3f6Pd3_q-zBlG0gLL_OonCx9jXEKOBY3aKPy-AjO--NUSkO85Z3Pcl2f6fZaR3C3MB8mvTQdsY5WSkEi_Xcm7nFGrjpBgq___zl0-b-h832p0-AL8j78D4zD4TuG9MioXv51eiOaUL3Sh3beWfNV-R-eAw_siJ0_xuzNQbrr6_OY_vn5d-Ddt4-6INZ8K4j2aZcZoSm_35Oi5q1LJAmNLfZaW3d__L5D3iSSqGAq4DjW4QHD8qYJwdKPiH4Zph4qUXPvTQajszKmC3daabZZI3Re3huJG-C06FCHlvigNBV2BopyTZhQy_zSvoLsThY2eZoU1pW0sfgEcg3qMGi65V3oJjH8C5EXqwyR4wAixP1mVhn4i67YzNcp6uErgpa0mLWrNOiyCk_FDxlebrEFV2KoqpwdSjZXZ4IOpNrmtAspekyLYssLxZZulomh1QceML4sqQkT7BlUi2CcAtj65l0rsf1qlgl5SwOtxs-LTQ-Q3QO3xZ2HbWv-tqRPFHSeXdB8dKr-E0ySl_s4LM1lcIWnqVvvtX8WW_VuvG-c2FZ0j2h-1r6pq8W3LST-bqeukjLEbqPtP8JAAD__0-9ohI">