[PATCH] Fix MemoryDependenceAnalysis in cases where QueryInstr is a CmpXchg or a AtomicRMW

[Philip Reames]

LGTM

================
Comment at: lib/Analysis/MemoryDependenceAnalysis.cpp:456
@@ -456,1 +455,3 @@
+        }
+        else if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst)) {
           if (!QuerySI->isSimple())
----------------
nitpick: } else if (c) {

http://reviews.llvm.org/D5019