!fixup extend comment

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -5270,7 +5270,8 @@ LoopVectorizationCostModel::calculateRegisterUsage(ArrayRef<ElementCount> VFs) {
     for (Instruction *ToRemove : List)
       OpenIntervals.erase(ToRemove);
 
-    // Ignore instructions that are never used within the loop.
+    // Ignore instructions that are never used within the loop and do not have
+    // side-effects.
     if (!Ends.count(I) && !I->mayHaveSideEffects())
       continue;