[llvm] [GlobalISel] Combine away G_UNMERGE(G_IMPLICITDEF). (PR #119183)

[Thorsten Schütt via llvm-commits]

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@@ -220,10 +220,8 @@ body:             |
     ; CHECK-NEXT: [[ICMP:%[0-9]+]]:_(s32) = G_ICMP intpred(ne), [[UADDE]](s32), [[SEXT_INREG2]]
     ; CHECK-NEXT: [[UV4:%[0-9]+]]:_(s8), [[UV5:%[0-9]+]]:_(s8), [[UV6:%[0-9]+]]:_(s8), [[UV7:%[0-9]+]]:_(s8) = G_UNMERGE_VALUES [[UADDE]](s32)
     ; CHECK-NEXT: [[DEF:%[0-9]+]]:_(s8) = G_IMPLICIT_DEF
-    ; CHECK-NEXT: [[DEF1:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
-    ; CHECK-NEXT: [[UV8:%[0-9]+]]:_(s8), [[UV9:%[0-9]+]]:_(s8), [[UV10:%[0-9]+]]:_(s8), [[UV11:%[0-9]+]]:_(s8) = G_UNMERGE_VALUES [[DEF1]](s32)
     ; CHECK-NEXT: [[MV:%[0-9]+]]:_(s32) = G_MERGE_VALUES [[UV4]](s8), [[UV5]](s8), [[UV6]](s8), [[DEF]](s8)
-    ; CHECK-NEXT: [[MV1:%[0-9]+]]:_(s32) = G_MERGE_VALUES [[UV8]](s8), [[UV9]](s8), [[UV10]](s8), [[UV8]](s8)
+    ; CHECK-NEXT: [[MV1:%[0-9]+]]:_(s32) = G_MERGE_VALUES [[DEF]](s8), [[DEF]](s8), [[DEF]](s8), [[DEF]](s8)
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tschuett wrote:

It is. I was wondering whether the placement of the combine influences other combines (order matters).

https://github.com/llvm/llvm-project/pull/119183