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

[via llvm-commits]

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@@ -60,3 +61,14 @@ bool vputils::isHeaderMask(const VPValue *V, VPlan &Plan) {
   return match(V, m_Binary<Instruction::ICmp>(m_VPValue(A), m_VPValue(B))) &&
          IsWideCanonicalIV(A) && B == Plan.getOrCreateBackedgeTakenCount();
 }
+
+const SCEV *vputils::getSCEVExprForVPValue(VPValue *V, ScalarEvolution &SE) {
+  if (V->isLiveIn())
+    return SE.getSCEV(V->getLiveInIRValue());
+
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ayalz wrote:

This seems to work well for Values at VPlan's boundary: can complement live-ins with live-out/VPIRInstructions which could also simply retrieve SE.getSCEV() of the instruction they wrap; as follow-up, along with concrete use.

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