diff --git a/compiler-rt/test/dfsan/event_callbacks.c b/compiler-rt/test/dfsan/event_callbacks.c
--- a/compiler-rt/test/dfsan/event_callbacks.c
+++ b/compiler-rt/test/dfsan/event_callbacks.c
@@ -57,6 +57,13 @@
   fprintf(stderr, "Label %u copied to memory\n", Start[0]);
 }
 
+void __dfsan_cmp_callback(dfsan_label CombinedLabel) {
+  if (!CombinedLabel)
+    return;
+
+  fprintf(stderr, "Label %u used for branching\n", CombinedLabel);
+}
+
 #else
 // Compile this code with DFSan and -dfsan-event-callbacks to insert the
 // callbacks.
@@ -82,12 +89,14 @@
   volatile int Sink = I;
 
   // CHECK: Label 1 loaded from memory
+  // CHECK: Label 1 used for branching
   assert(Sink == 1);
 
   // CHECK: Label 2 stored to memory
   Sink = J;
 
   // CHECK: Label 2 loaded from memory
+  // CHECK: Label 2 used for branching
   assert(Sink == 2);
 
   // CHECK: Label 2 loaded from memory
@@ -95,8 +104,12 @@
   Sink += I;
 
   // CHECK: Label 3 loaded from memory
+  // CHECK: Label 3 used for branching
   assert(Sink == 3);
 
+  // CHECK: Label 3 used for branching
+  assert(I != J);
+
   LenArgv = strlen(Argv[1]);
   LabelArgv = dfsan_create_label("Argv", 0);
   dfsan_set_label(LabelArgv, Argv[1], LenArgv);
diff --git a/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
--- a/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
@@ -163,14 +163,15 @@
     cl::Hidden);
 
 // Experimental feature that inserts callbacks for certain data events.
-// Currently callbacks are only inserted for loads, stores, and memory transfers
-// (i.e. memcpy and memmove).
+// Currently callbacks are only inserted for loads, stores, memory transfers
+// (i.e. memcpy and memmove), and comparisons.
 //
 // If this flag is set to true, the user must provide definitions for the
 // following callback functions:
 //   void __dfsan_load_callback(dfsan_label Label);
 //   void __dfsan_store_callback(dfsan_label Label);
 //   void __dfsan_mem_transfer_callback(dfsan_label *Start, size_t Len);
+//   void __dfsan_cmp_callback(dfsan_label CombinedLabel);
 static cl::opt<bool> ClEventCallbacks(
     "dfsan-event-callbacks",
     cl::desc("Insert calls to __dfsan_*_callback functions on data events."),
@@ -359,7 +360,7 @@
   FunctionType *DFSanSetLabelFnTy;
   FunctionType *DFSanNonzeroLabelFnTy;
   FunctionType *DFSanVarargWrapperFnTy;
-  FunctionType *DFSanLoadStoreCallbackFnTy;
+  FunctionType *DFSanLoadStoreCmpCallbackFnTy;
   FunctionType *DFSanMemTransferCallbackFnTy;
   FunctionCallee DFSanUnionFn;
   FunctionCallee DFSanCheckedUnionFn;
@@ -371,6 +372,7 @@
   FunctionCallee DFSanLoadCallbackFn;
   FunctionCallee DFSanStoreCallbackFn;
   FunctionCallee DFSanMemTransferCallbackFn;
+  FunctionCallee DFSanCmpCallbackFn;
   MDNode *ColdCallWeights;
   DFSanABIList ABIList;
   DenseMap<Value *, Function *> UnwrappedFnMap;
@@ -457,7 +459,10 @@
     return DFSF.F->getParent()->getDataLayout();
   }
 
-  void visitOperandShadowInst(Instruction &I);
+  // Combines shadow values for all of I's operands. Returns the combined shadow
+  // value.
+  Value *visitOperandShadowInst(Instruction &I);
+
   void visitUnaryOperator(UnaryOperator &UO);
   void visitBinaryOperator(BinaryOperator &BO);
   void visitCastInst(CastInst &CI);
@@ -602,7 +607,7 @@
       Type::getVoidTy(*Ctx), None, /*isVarArg=*/false);
   DFSanVarargWrapperFnTy = FunctionType::get(
       Type::getVoidTy(*Ctx), Type::getInt8PtrTy(*Ctx), /*isVarArg=*/false);
-  DFSanLoadStoreCallbackFnTy =
+  DFSanLoadStoreCmpCallbackFnTy =
       FunctionType::get(Type::getVoidTy(*Ctx), ShadowTy, /*isVarArg=*/false);
   Type *DFSanMemTransferCallbackArgs[2] = {ShadowPtrTy, IntptrTy};
   DFSanMemTransferCallbackFnTy =
@@ -809,11 +814,13 @@
                                                   DFSanVarargWrapperFnTy);
 
   DFSanLoadCallbackFn = Mod->getOrInsertFunction("__dfsan_load_callback",
-                                                 DFSanLoadStoreCallbackFnTy);
-  DFSanStoreCallbackFn = Mod->getOrInsertFunction("__dfsan_store_callback",
-                                                  DFSanLoadStoreCallbackFnTy);
+                                                 DFSanLoadStoreCmpCallbackFnTy);
+  DFSanStoreCallbackFn = Mod->getOrInsertFunction(
+      "__dfsan_store_callback", DFSanLoadStoreCmpCallbackFnTy);
   DFSanMemTransferCallbackFn = Mod->getOrInsertFunction(
       "__dfsan_mem_transfer_callback", DFSanMemTransferCallbackFnTy);
+  DFSanCmpCallbackFn = Mod->getOrInsertFunction("__dfsan_cmp_callback",
+                                                DFSanLoadStoreCmpCallbackFnTy);
 
   std::vector<Function *> FnsToInstrument;
   SmallPtrSet<Function *, 2> FnsWithNativeABI;
@@ -828,7 +835,8 @@
         &i != DFSanVarargWrapperFn.getCallee()->stripPointerCasts() &&
         &i != DFSanLoadCallbackFn.getCallee()->stripPointerCasts() &&
         &i != DFSanStoreCallbackFn.getCallee()->stripPointerCasts() &&
-        &i != DFSanMemTransferCallbackFn.getCallee()->stripPointerCasts())
+        &i != DFSanMemTransferCallbackFn.getCallee()->stripPointerCasts() &&
+        &i != DFSanCmpCallbackFn.getCallee()->stripPointerCasts())
       FnsToInstrument.push_back(&i);
   }
 
@@ -1212,9 +1220,10 @@
   return Shadow;
 }
 
-void DFSanVisitor::visitOperandShadowInst(Instruction &I) {
+Value *DFSanVisitor::visitOperandShadowInst(Instruction &I) {
   Value *CombinedShadow = DFSF.combineOperandShadows(&I);
   DFSF.setShadow(&I, CombinedShadow);
+  return CombinedShadow;
 }
 
 // Generates IR to load shadow corresponding to bytes [Addr, Addr+Size), where
@@ -1451,7 +1460,13 @@
 
 void DFSanVisitor::visitCastInst(CastInst &CI) { visitOperandShadowInst(CI); }
 
-void DFSanVisitor::visitCmpInst(CmpInst &CI) { visitOperandShadowInst(CI); }
+void DFSanVisitor::visitCmpInst(CmpInst &CI) {
+  Value *CombinedShadow = visitOperandShadowInst(CI);
+  if (ClEventCallbacks) {
+    IRBuilder<> IRB(&CI);
+    IRB.CreateCall(DFSF.DFS.DFSanCmpCallbackFn, CombinedShadow);
+  }
+}
 
 void DFSanVisitor::visitGetElementPtrInst(GetElementPtrInst &GEPI) {
   visitOperandShadowInst(GEPI);