[llvm] [VPlan] Add initial VPScalarEvolution, use to get trip count SCEV (NFC) (PR #94464)

[via llvm-commits]

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@@ -905,8 +905,9 @@ Value *getRuntimeVF(IRBuilderBase &B, Type *Ty, ElementCount VF) {
   return B.CreateElementCount(Ty, VF);
 }
 
-const SCEV *createTripCountSCEV(Type *IdxTy, PredicatedScalarEvolution &PSE,
-                                Loop *OrigLoop) {
+static const SCEV *createTripCountSCEV(Type *IdxTy,
+                                       PredicatedScalarEvolution &PSE,
+                                       Loop *OrigLoop) {
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ayalz wrote:

Possibly here or as follow-up:

The call to createTripCountSCEV() in LVP::selectEpilogueVectorizationFactor() has available VPlans from which to retrieve a TripCount VPValue and call the new API instead of continuing to call createTripCountSCEV().

The other two calls to createTripCountSCEV() are inside calls to VPlan::createInitialVPlan(), setting its first parameter; should they be inlined into createInitialVPlan() itself instead?
Thereby retiring createTripCountSCEV altogether, leaving only vputils::getSCEVExprForVPValue(Plan.getTripCount(), SE) as the way to obtain the SCEV of a loop's trip count.

https://github.com/llvm/llvm-project/pull/94464