[llvm] PeepholeOpt: Fix looking for def of current copy to coalesce (PR #125533)

[Lei Huang via llvm-commits]

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@@ -26,14 +26,18 @@ define void @testMultiply(ptr nocapture noundef readonly %a, ptr nocapture nound
 ; CHECK-NEXT:    std r29, -24(r30) # 8-byte Folded Spill
 ; CHECK-NEXT:    mr r29, r5
 ; CHECK-NEXT:    bl _Z15buildVectorPairPu13__vector_pairDv16_hS0_ at notoc
-; CHECK-NEXT:    xxsetaccz acc0
-; CHECK-NEXT:    xvf32gerpp acc0, v31, v30
+; CHECK-NEXT:    xxsetaccz acc1
+; CHECK-NEXT:    xvf32gerpp acc1, v31, v30
 ; CHECK-NEXT:    lxv v3, 32(r1)
-; CHECK-NEXT:    lxv v2, 48(r1)
-; CHECK-NEXT:    xvf32gerpp acc0, v3, v2
+; CHECK-NEXT:    lxv vs0, 48(r1)
+; CHECK-NEXT:    xvf32gerpp acc1, v3, vs0
 ; CHECK-NEXT:    lxv v31, -48(r30) # 16-byte Folded Reload
 ; CHECK-NEXT:    lxv v30, -64(r30) # 16-byte Folded Reload
-; CHECK-NEXT:    xxmfacc acc0
+; CHECK-NEXT:    xxmfacc acc1
+; CHECK-NEXT:    xxlor vs0, vs4, vs4
+; CHECK-NEXT:    xxlor vs1, vs5, vs5
+; CHECK-NEXT:    xxlor vs2, vs6, vs6
+; CHECK-NEXT:    xxlor vs3, vs7, vs7
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lei137 wrote:

These extra copies are a result of using `acc1` vs `acc0` on line 29.  Any idea as to why this patch caused it to use `acc1` vs `acc0`?

https://github.com/llvm/llvm-project/pull/125533