[VPlan] Tweak comment around assume

Author: artagnon

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -2124,7 +2124,8 @@ static void licm(VPlan &Plan) {
   // Return true if we do not know how to (mechanically) hoist a given recipe
   // out of a loop region.
   auto CannotHoistRecipe = [](VPRecipeBase &R) {
-    // Assumes don't alias anything or throw.
+    // Assumes don't alias anything or throw; as long as they're guaranteed to
+    // execute, they're safe to hoist.
     if (match(&R, m_Intrinsic<Intrinsic::assume>()))
       return false;