[llvm] [VPlan] Introduce VPScalarPHIRecipe, use for can & EVL IV codegen (NFC). (PR #114305)

[via llvm-commits]

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@@ -359,6 +359,7 @@ class VPDef {
     VPFirstOrderRecurrencePHISC,
     VPWidenIntOrFpInductionSC,
     VPWidenPointerInductionSC,
+    VPScalarPHISC,
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ayalz wrote:

Would be good to keep (all header phi recipes in) some order...

https://github.com/llvm/llvm-project/pull/114305