RegionInfo: use a range-based for loop [NFCI]

Change-Id: I9985d72191a2b0680195032acf8a14ad2ba954ed

Differential Revision: https://reviews.llvm.org/D92932

llvm/include/llvm/Analysis/RegionInfoImpl.h

@@ -585,10 +585,8 @@ bool RegionInfoBase<Tr>::isRegion(BlockT *entry, BlockT *exit) const {
   // Exit is the header of a loop that contains the entry. In this case,
   // the dominance frontier must only contain the exit.
   if (!DT->dominates(entry, exit)) {
-    for (typename DST::iterator SI = entrySuccs->begin(),
-                                SE = entrySuccs->end();
-         SI != SE; ++SI) {
-      if (*SI != exit && *SI != entry)
+    for (BlockT *successor : *entrySuccs) {
+      if (successor != exit && successor != entry)
         return false;
     }