<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/63112>63112</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            update_mir_test_checks.py doesn't separate different prefix checks
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            good first issue,
            llvm-tools
      </td>
    </tr>

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

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

<pre>
    Other update scripts put an empty ';' line between checks for different prefixes (e.g. update_llc_test_checks.py):
```
; SSE-LABEL: test1:
; SSE:       # %bb.0:
; SSE-NEXT:    xorps %xmm1, %xmm1
; SSE-NEXT:    blendps {{.*#+}} xmm0 = xmm0[0],xmm1[1,2,3]
; SSE-NEXT:    retq
;
; AVX-LABEL: test1:
; AVX:       # %bb.0:
; AVX-NEXT:    vxorps %xmm1, %xmm1, %xmm1
; AVX-NEXT:    vblendps {{.*#+}} xmm0 = xmm0[0],xmm1[1,2,3]
; AVX-NEXT:    retq
```
But update_mir_test_checks.py fails to do this, making quick visual separation of the checks a lot harder:
```
    ; X64-LABEL: name: test_add_i1
 ; X64: [[COPY:%[0-9]+]]:_(s32) = COPY $edx
    ; X64-NEXT: [[TRUNC:%[0-9]+]]:_(s8) = G_TRUNC [[COPY]](s32)
    ; X64-NEXT: [[TRUNC1:%[0-9]+]]:_(s8) = G_TRUNC [[COPY]](s32)
    ; X64-NEXT: [[ADD:%[0-9]+]]:_(s8) = G_ADD [[TRUNC]], [[TRUNC1]]
    ; X64-NEXT: [[ANYEXT:%[0-9]+]]:_(s32) = G_ANYEXT [[ADD]](s8)
    ; X64-NEXT: $eax = COPY [[ANYEXT]](s32)
    ; X64-NEXT: RET 0
    ; X32-LABEL: name: test_add_i1
    ; X32: [[COPY:%[0-9]+]]:_(s32) = COPY $edx
    ; X32-NEXT: [[TRUNC:%[0-9]+]]:_(s8) = G_TRUNC [[COPY]](s32)
    ; X32-NEXT: [[TRUNC1:%[0-9]+]]:_(s8) = G_TRUNC [[COPY]](s32)
    ; X32-NEXT: [[ADD:%[0-9]+]]:_(s8) = G_ADD [[TRUNC]], [[TRUNC1]]
    ; X32-NEXT: [[ANYEXT:%[0-9]+]]:_(s32) = G_ANYEXT [[ADD]](s8)
    ; X32-NEXT: $eax = COPY [[ANYEXT]](s32)
    ; X32-NEXT: RET 0
```
</pre>
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