[llvm] [SelectionDAG] Fix condition used for unsigned subtraction overflow (PR #170896)

[via llvm-commits]

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@@ -75,23 +75,12 @@ define i32 @combine_uadd_not(i32 %a0, i32 %a1) {
 define <4 x i32> @combine_vec_uadd_not(<4 x i32> %a0, <4 x i32> %a1) {
 ; SSE-LABEL: combine_vec_uadd_not:
 ; SSE:       # %bb.0:
-; SSE-NEXT:    pxor %xmm2, %xmm2
-; SSE-NEXT:    psubd %xmm0, %xmm2
-; SSE-NEXT:    pmovsxbd {{.*#+}} xmm0 = [1,1,1,1]
-; SSE-NEXT:    pmaxud %xmm2, %xmm0
-; SSE-NEXT:    pcmpeqd %xmm2, %xmm0
-; SSE-NEXT:    blendvps %xmm0, %xmm2, %xmm1
 ; SSE-NEXT:    movaps %xmm1, %xmm0
 ; SSE-NEXT:    retq
 ;
 ; AVX-LABEL: combine_vec_uadd_not:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    vpxor %xmm2, %xmm2, %xmm2
-; AVX-NEXT:    vpsubd %xmm0, %xmm2, %xmm0
-; AVX-NEXT:    vpbroadcastd {{.*#+}} xmm2 = [1,1,1,1]
-; AVX-NEXT:    vpmaxud %xmm2, %xmm0, %xmm2
-; AVX-NEXT:    vpcmpeqd %xmm2, %xmm0, %xmm2
-; AVX-NEXT:    vblendvps %xmm2, %xmm0, %xmm1, %xmm0
+; AVX-NEXT:    vmovaps %xmm1, %xmm0
 ; AVX-NEXT:    retq
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aabhinavg1 wrote:

The first two instructions (vpcmpeqd + vblendvps) were doing a compare and conditional blend of vectors, while now it’s replaced by vmovaps, which just moves the vector directly. So effectively, the result is the same, but the code is simpler and shorter.

https://github.com/llvm/llvm-project/pull/170896