[llvm] [VPlan] Use VPlan operand order for VPBlendRecipes. (PR #139475)

[via llvm-commits]

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@@ -219,7 +219,7 @@ define void @test_blend_feeding_replicated_store_2(ptr noalias %src, ptr %dst, i
 ; CHECK-NEXT:    [[TMP4:%.*]] = xor <16 x i1> [[TMP3]], splat (i1 true)
 ; CHECK-NEXT:    [[TMP6:%.*]] = select <16 x i1> [[TMP4]], <16 x i1> [[TMP5]], <16 x i1> zeroinitializer
 ; CHECK-NEXT:    [[TMP7:%.*]] = or <16 x i1> [[TMP6]], [[TMP3]]
-; CHECK-NEXT:    [[PREDPHI:%.*]] = select <16 x i1> [[TMP6]], <16 x i8> zeroinitializer, <16 x i8> splat (i8 1)
+; CHECK-NEXT:    [[PREDPHI:%.*]] = select <16 x i1> [[TMP3]], <16 x i8> splat (i8 1), <16 x i8> zeroinitializer
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ayalz wrote:

Ah, ok, if TMP3 is false only some entries of PREDPHI are used/live - and then these must be set to 0; other entries may be set arbitrarily as in undef. Setting all to 0 seems a simpler solution.

Branches on invariant conditions (as in %c.0) could be optimized by loop unswitching or retained in the vectorize loop as being uniform.

https://github.com/llvm/llvm-project/pull/139475