[llvm] [VPlan] Compute blend masks from minimum set of edge masks (PR #201783)

[Florian Hahn via llvm-commits]

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@@ -1145,14 +1146,16 @@ define float @reduction_conditional(ptr %A, ptr %B, ptr %C, float %S) {
 ; CHECK-INTERLEAVED-NEXT:    [[TMP16:%.*]] = select <4 x i1> [[TMP6]], <4 x i1> [[TMP8]], <4 x i1> zeroinitializer
 ; CHECK-INTERLEAVED-NEXT:    [[TMP17:%.*]] = fadd fast <4 x float> [[VEC_PHI]], [[WIDE_LOAD]]
 ; CHECK-INTERLEAVED-NEXT:    [[TMP18:%.*]] = fadd fast <4 x float> [[VEC_PHI1]], [[WIDE_LOAD2]]
+; CHECK-INTERLEAVED-NEXT:    [[TMP27:%.*]] = xor <4 x i1> [[TMP5]], splat (i1 true)
+; CHECK-INTERLEAVED-NEXT:    [[TMP28:%.*]] = xor <4 x i1> [[TMP6]], splat (i1 true)
 ; CHECK-INTERLEAVED-NEXT:    [[TMP20:%.*]] = select <4 x i1> [[TMP19]], <4 x i1> [[TMP11]], <4 x i1> zeroinitializer
 ; CHECK-INTERLEAVED-NEXT:    [[TMP22:%.*]] = select <4 x i1> [[TMP21]], <4 x i1> [[TMP12]], <4 x i1> zeroinitializer
-; CHECK-INTERLEAVED-NEXT:    [[PREDPHI:%.*]] = select <4 x i1> [[TMP20]], <4 x float> [[VEC_PHI]], <4 x float> [[TMP13]]
-; CHECK-INTERLEAVED-NEXT:    [[PREDPHI5:%.*]] = select <4 x i1> [[TMP15]], <4 x float> [[TMP17]], <4 x float> [[PREDPHI]]
-; CHECK-INTERLEAVED-NEXT:    [[PREDPHI6]] = select <4 x i1> [[TMP5]], <4 x float> [[PREDPHI5]], <4 x float> [[VEC_PHI]]
-; CHECK-INTERLEAVED-NEXT:    [[PREDPHI7:%.*]] = select <4 x i1> [[TMP22]], <4 x float> [[VEC_PHI1]], <4 x float> [[TMP14]]
-; CHECK-INTERLEAVED-NEXT:    [[PREDPHI8:%.*]] = select <4 x i1> [[TMP16]], <4 x float> [[TMP18]], <4 x float> [[PREDPHI7]]
-; CHECK-INTERLEAVED-NEXT:    [[PREDPHI9]] = select <4 x i1> [[TMP6]], <4 x float> [[PREDPHI8]], <4 x float> [[VEC_PHI1]]
+; CHECK-INTERLEAVED-NEXT:    [[TMP25:%.*]] = or <4 x i1> [[TMP20]], [[TMP27]]
+; CHECK-INTERLEAVED-NEXT:    [[TMP26:%.*]] = or <4 x i1> [[TMP22]], [[TMP28]]
+; CHECK-INTERLEAVED-NEXT:    [[PREDPHI:%.*]] = select <4 x i1> [[TMP25]], <4 x float> [[VEC_PHI]], <4 x float> [[TMP13]]
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fhahn wrote:

Yep in this particular case it is not an issue end-to-end, but it shows that in theory we can end up with more expensive compares instead of value select. But I'd expect this to only happen rarely in practice.

May be good to double-check the test-suite diffs to make sure that's not happening though

https://github.com/llvm/llvm-project/pull/201783