[llvm] [VPlan] Verify plan before optimizations. NFC (PR #122678)

[Florian Hahn via llvm-commits]

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@@ -8837,6 +8837,8 @@ void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
   for (ElementCount VF = MinVF; ElementCount::isKnownLT(VF, MaxVFTimes2);) {
     VFRange SubRange = {VF, MaxVFTimes2};
     if (auto Plan = tryToBuildVPlanWithVPRecipes(SubRange)) {
+      assert(verifyVPlanIsValid(*Plan) && "VPlan is invalid");
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fhahn wrote:

better do this at the end of `tryToBuildVPlanWithVPRecipes`?

https://github.com/llvm/llvm-project/pull/122678