[llvm] [DAGCombiner] Add pattern matching for negated subtraction in ABDU selection (PR #156217)

[Matt Arsenault via llvm-commits]

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@@ -367,12 +363,14 @@ define i64 @abd_cmp_i64(i64 %a, i64 %b) nounwind {
 define i128 @abd_cmp_i128(i128 %a, i128 %b) nounwind {
 ; CHECK-LABEL: abd_cmp_i128:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    subs x8, x2, x0
-; CHECK-NEXT:    sbc x9, x3, x1
-; CHECK-NEXT:    subs x10, x0, x2
-; CHECK-NEXT:    sbcs x11, x1, x3
-; CHECK-NEXT:    csel x0, x10, x8, lt
-; CHECK-NEXT:    csel x1, x11, x9, lt
+; CHECK-NEXT:    subs x8, x0, x2
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arsenm wrote:

This looks worse? 

https://github.com/llvm/llvm-project/pull/156217