[VPlan] Improve comment (NFC)

Author: artagnon

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -2121,11 +2121,10 @@ static void licm(VPlan &Plan) {
 
   // Hoist any loop invariant recipes from the vector loop region to the
   // preheader. Preform a shallow traversal of the vector loop region, to
-  // exclude recipes in replicate regions.
+  // exclude recipes in replicate regions. Since the top-level blocks in the
+  // vector loop region are guaranteed to execute if the vector pre-header is,
+  // we don't need to check speculation safety.
   VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
-
-  // Since the vector loop region is guaranteed to execute, if the vector
-  // pre-header is, we don't need to check speculation safety.
   assert(Preheader->getSingleSuccessor() == LoopRegion &&
          "Expected vector prehader's successor to be the vector loop region");
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(