[llvm] [VPlan] Simplify add x, (sub 0, y) -> sub x, y (PR #187228)

[Ramkumar Ramachandra via llvm-commits]

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@@ -875,14 +875,14 @@ define i32 @PR27246() {
 ; UNROLL-NO-IC-NEXT:    [[IND_END:%.*]] = sub i32 [[I_016]], [[N_VEC]]
 ; UNROLL-NO-IC-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <4 x i32> poison, i32 [[I_016]], i64 0
 ; UNROLL-NO-IC-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <4 x i32> [[DOTSPLATINSERT]], <4 x i32> poison, <4 x i32> zeroinitializer
-; UNROLL-NO-IC-NEXT:    [[INDUCTION:%.*]] = add nsw <4 x i32> [[DOTSPLAT]], <i32 0, i32 -1, i32 -2, i32 -3>
+; UNROLL-NO-IC-NEXT:    [[INDUCTION:%.*]] = sub nsw <4 x i32> [[DOTSPLAT]], <i32 0, i32 1, i32 2, i32 3>
 ; UNROLL-NO-IC-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; UNROLL-NO-IC:       vector.body:
 ; UNROLL-NO-IC-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
 ; UNROLL-NO-IC-NEXT:    [[VEC_IND:%.*]] = phi <4 x i32> [ [[INDUCTION]], [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
-; UNROLL-NO-IC-NEXT:    [[STEP_ADD:%.*]] = add <4 x i32> [[VEC_IND]], splat (i32 -4)
+; UNROLL-NO-IC-NEXT:    [[STEP_ADD:%.*]] = sub <4 x i32> [[VEC_IND]], splat (i32 4)
 ; UNROLL-NO-IC-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
-; UNROLL-NO-IC-NEXT:    [[VEC_IND_NEXT]] = add nsw <4 x i32> [[STEP_ADD]], splat (i32 -4)
+; UNROLL-NO-IC-NEXT:    [[VEC_IND_NEXT]] = sub <4 x i32> [[STEP_ADD]], splat (i32 4)
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artagnon wrote:

The original nsw on the add was incorrect: should be fixed by https://github.com/llvm/llvm-project/pull/187710

https://github.com/llvm/llvm-project/pull/187228