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

[via llvm-commits]

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@@ -67,6 +69,15 @@ class VPTypeAnalysis {
 // Collect a VPlan's ephemeral recipes (those used only by an assume).
 void collectEphemeralRecipesForVPlan(VPlan &Plan,
                                      DenseSet<VPRecipeBase *> &EphRecipes);
+
+namespace vputils {
+
+/// Return the SCEV expression for \p V. Returns SCEVCouldNotCompute if no
+/// SCEV expression could be constructed.
+const SCEV *getSCEVExprForVPValue(VPValue *V, ScalarEvolution &SE);
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ayalz wrote:

Ok, +1 to reorganize all `vputils` functions in files of their own.

Most of these would presumably promote to a type system of VPValues, or other refinements like introducing an extract-first-lane as only user to capture `onlyFirstLaneUsed()`.

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