[llvm] [VPlan] Introduce reduction selects for tail folding in foldTailByMasking. NFCI (PR #192987)

[David Sherwood via llvm-commits]

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@@ -292,7 +292,7 @@ define i32 @reduction(ptr noalias %p, i32 %n) {
 ; CHECK-NEXT:    Successor(s): vector.latch
 ; CHECK-EMPTY:
 ; CHECK-NEXT:    vector.latch:
-; CHECK-NEXT:      EMIT-SCALAR vp<[[VP8]]> = phi [ ir<%rdx.next>, vector.body.split ], [ ir<poison>, vector.body ]
+; CHECK-NEXT:      EMIT-SCALAR vp<[[VP8]]> = phi [ ir<%rdx.next>, vector.body.split ], [ ir<%rdx>, vector.body ]
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david-arm wrote:

Yeah I was just expecting to see some corresponding changes in IR tests too due to the difference in PHI.

https://github.com/llvm/llvm-project/pull/192987