diff --git a/llvm/include/llvm/IR/Instructions.h b/llvm/include/llvm/IR/Instructions.h
--- a/llvm/include/llvm/IR/Instructions.h
+++ b/llvm/include/llvm/IR/Instructions.h
@@ -5310,6 +5310,10 @@
   }
 };
 
+//===----------------------------------------------------------------------===//
+//                          Helper functions
+//===----------------------------------------------------------------------===//
+
 /// A helper function that returns the pointer operand of a load or store
 /// instruction. Returns nullptr if not load or store.
 inline const Value *getLoadStorePointerOperand(const Value *V) {
@@ -5365,6 +5369,24 @@
   return cast<StoreInst>(I)->getValueOperand()->getType();
 }
 
+/// A helper function that returns an atomic operation's sync scope; returns
+/// None if it is not an atomic operation.
+inline Optional<SyncScope::ID> getAtomicSyncScopeID(const Instruction *I) {
+  if (!I->isAtomic())
+    return None;
+  if (auto *AI = dyn_cast<LoadInst>(I))
+    return AI->getSyncScopeID();
+  if (auto *AI = dyn_cast<StoreInst>(I))
+    return AI->getSyncScopeID();
+  if (auto *AI = dyn_cast<FenceInst>(I))
+    return AI->getSyncScopeID();
+  if (auto *AI = dyn_cast<AtomicCmpXchgInst>(I))
+    return AI->getSyncScopeID();
+  if (auto *AI = dyn_cast<AtomicRMWInst>(I))
+    return AI->getSyncScopeID();
+  llvm_unreachable("unhandled atomic operation");
+}
+
 //===----------------------------------------------------------------------===//
 //                              FreezeInst Class
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
--- a/llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
@@ -526,19 +526,14 @@
   Local.clear();
 }
 
-static bool isAtomic(Instruction *I) {
+static bool isTsanAtomic(const Instruction *I) {
   // TODO: Ask TTI whether synchronization scope is between threads.
-  if (LoadInst *LI = dyn_cast<LoadInst>(I))
-    return LI->isAtomic() && LI->getSyncScopeID() != SyncScope::SingleThread;
-  if (StoreInst *SI = dyn_cast<StoreInst>(I))
-    return SI->isAtomic() && SI->getSyncScopeID() != SyncScope::SingleThread;
-  if (isa<AtomicRMWInst>(I))
-    return true;
-  if (isa<AtomicCmpXchgInst>(I))
-    return true;
-  if (isa<FenceInst>(I))
-    return true;
-  return false;
+  auto SSID = getAtomicSyncScopeID(I);
+  if (!SSID.hasValue())
+    return false;
+  if (isa<LoadInst>(I) || isa<StoreInst>(I))
+    return SSID.getValue() != SyncScope::SingleThread;
+  return true;
 }
 
 void ThreadSanitizer::InsertRuntimeIgnores(Function &F) {
@@ -580,7 +575,7 @@
   // Traverse all instructions, collect loads/stores/returns, check for calls.
   for (auto &BB : F) {
     for (auto &Inst : BB) {
-      if (isAtomic(&Inst))
+      if (isTsanAtomic(&Inst))
         AtomicAccesses.push_back(&Inst);
       else if (isa<LoadInst>(Inst) || isa<StoreInst>(Inst))
         LocalLoadsAndStores.push_back(&Inst);