[llvm] [VPlan] Verify and handle FOR legality during header phi creation (NFC). (PR #191298)

[Florian Hahn via llvm-commits]

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@@ -5,8 +5,9 @@
 define void @first_order_recurrence(ptr noalias %A, ptr noalias %B, i64 %TC) {
 ; IF-EVL: VPlan 'Initial VPlan for VF={1},UF>=1'
 ; IF-EVL-NOT: CURRENT-ITERATION-PHI
+; IF-EVL: VPlan 'Initial VPlan for VF={vscale x 1},UF={1}'
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fhahn wrote:

There are no users of the recurrence outside the loop, and the original version of the patch would always split for scalable VF = 1. Updated to only do so if there are users outside the loop region, thanks

https://github.com/llvm/llvm-project/pull/191298