LAA: add comment on stride units; address review

Author: artagnon

llvm/include/llvm/Analysis/LoopAccessAnalysis.h

@@ -365,6 +365,10 @@ class MemoryDepChecker {
   void mergeInStatus(VectorizationSafetyStatus S);
 
   struct DepDistanceStrideAndSizeInfo {
+    // Strides could either be scaled (in bytes, taking the size of the
+    // underlying type into account), or unscaled (in indexing units; unscaled
+    // stride = scaled stride / size of underlying type). Here, strides are
+    // unscaled.
     const SCEV *Dist;
     uint64_t MaxStride;
     std::optional<uint64_t> CommonStride;