[DSE] Fix bug in updating MadeChange flag

[junbuml]

Summary

The MadeChange flag should be ORed to keep the previous result.

[mcrosier]

LGTM. Thanks for fixing this, Jun.

llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp

for (auto OI : IOL) {
     assert(isRemovable(EarlierWrite) && "Expect only removable instruction");
     assert(Loc.Size != MemoryLocation::UnknownSize && "Unexpected mem loc");
 
     const Value *Ptr = Loc.Ptr->stripPointerCasts();
     int64_t EarlierStart = 0;
     int64_t EarlierSize = int64_t(Loc.Size);
     GetPointerBaseWithConstantOffset(Ptr, EarlierStart, DL);
     OverlapIntervalsTy &IntervalMap = OI.second;
-    Changed =
+    Changed |=
         tryToShortenEnd(EarlierWrite, IntervalMap, EarlierStart, EarlierSize);
     if (IntervalMap.empty())
       continue;
     Changed |=
         tryToShortenBegin(EarlierWrite, IntervalMap, EarlierStart, EarlierSize);
   }
   return Changed;
 }
while (InstDep.isDef() || InstDep.isClobber()) {
                    ((OR == OverwriteBegin &&
                      isShortenableAtTheBeginning(DepWrite)))) {
           assert(!EnablePartialOverwriteTracking && "Do not expect to perform "
                                                     "when partial-overwrite "
                                                     "tracking is enabled");
           int64_t EarlierSize = DepLoc.Size;
           int64_t LaterSize = Loc.Size;
           bool IsOverwriteEnd = (OR == OverwriteEnd);
-          MadeChange = tryToShorten(DepWrite, DepWriteOffset, EarlierSize,
+          MadeChange |= tryToShorten(DepWrite, DepWriteOffset, EarlierSize,
                                     InstWriteOffset, LaterSize, IsOverwriteEnd);
         }
       }
 
       // If this is a may-aliased store that is clobbering the store value, we
       // can keep searching past it for another must-aliased pointer that stores
       // to the same location.  For example, in:
       //   store -> P