Index: lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -89,6 +89,7 @@
 static const char *const kAsanModuleDtorName = "asan.module_dtor";
 static const uint64_t kAsanCtorAndDtorPriority = 1;
 static const char *const kAsanReportErrorTemplate = "__asan_report_";
+static const char *const kAsanApplyToGlobalsName = "__asan_apply_to_globals";
 static const char *const kAsanRegisterGlobalsName = "__asan_register_globals";
 static const char *const kAsanUnregisterGlobalsName =
     "__asan_unregister_globals";
@@ -546,6 +547,7 @@
   Function *AsanUnpoisonGlobals;
   Function *AsanRegisterGlobals;
   Function *AsanUnregisterGlobals;
+  Function *AsanApplyToGlobals;
 };
 
 // Stack poisoning does not play well with exception handling.
@@ -1298,6 +1300,13 @@
       M.getOrInsertFunction(kAsanUnregisterGlobalsName, IRB.getVoidTy(),
                             IntptrTy, IntptrTy, nullptr));
   AsanUnregisterGlobals->setLinkage(Function::ExternalLinkage);
+
+  if (TargetTriple.isOSBinFormatMachO()) {
+    AsanApplyToGlobals = checkSanitizerInterfaceFunction(
+        M.getOrInsertFunction(kAsanApplyToGlobalsName,
+        IRB.getVoidTy(), IntptrTy, IntptrTy, nullptr));
+    AsanApplyToGlobals->setLinkage(Function::ExternalLinkage);
+  }
 }
 
 // This function replaces all global variables with new variables that have
@@ -1406,17 +1415,58 @@
     DEBUG(dbgs() << "NEW GLOBAL: " << *NewGlobal << "\n");
   }
 
-  ArrayType *ArrayOfGlobalStructTy = ArrayType::get(GlobalStructTy, n);
-  GlobalVariable *AllGlobals = new GlobalVariable(
-      M, ArrayOfGlobalStructTy, false, GlobalVariable::InternalLinkage,
-      ConstantArray::get(ArrayOfGlobalStructTy, Initializers), "");
+
+  GlobalVariable *AllGlobals = nullptr;
+
+  // On Mach-O platforms, we emit the global metadata in a way that allows the
+  // linker to properly strip dead globals.
+  if (TargetTriple.isOSBinFormatMachO()) {
+    // We use AllGlobals as a dummy symbol which lets us look up the header
+    // of the library that contains it later.
+    AllGlobals = new GlobalVariable(
+        M, IntptrTy, false, GlobalVariable::InternalLinkage,
+        ConstantInt::get(IntptrTy, 0), "");
+    
+    // We also emit a structure which binds the liveness of the global
+    // variable to the metadata struct.
+    StructType *LivenessTy = StructType::get(IntptrTy, IntptrTy, nullptr);
+
+    for (size_t i = 0; i < n; i++) {
+      GlobalVariable *Metadata = new GlobalVariable(
+          M, GlobalStructTy, false, GlobalVariable::InternalLinkage,
+          Initializers[i], "");
+      Metadata->setSection("__DATA,__asan_globals,regular");
+      Metadata->setAlignment(1); // don't leave padding in between
+
+      auto LivenessBinder = ConstantStruct::get(LivenessTy,
+          Initializers[i]->getAggregateElement(0u),
+          ConstantExpr::getPointerCast(Metadata, IntptrTy),
+          nullptr);
+      GlobalVariable *Liveness = new GlobalVariable(
+          M, LivenessTy, false, GlobalVariable::InternalLinkage,
+          LivenessBinder, "");
+      Liveness->setSection("__DATA,__asan_liveness,regular,live_support");
+    }
+  } else {
+    ArrayType *ArrayOfGlobalStructTy = ArrayType::get(GlobalStructTy, n);
+    AllGlobals = new GlobalVariable(
+        M, ArrayOfGlobalStructTy, false, GlobalVariable::InternalLinkage,
+        ConstantArray::get(ArrayOfGlobalStructTy, Initializers), "");
+  }
 
   // Create calls for poisoning before initializers run and unpoisoning after.
   if (HasDynamicallyInitializedGlobals)
     createInitializerPoisonCalls(M, ModuleName);
-  IRB.CreateCall(AsanRegisterGlobals,
-                 {IRB.CreatePointerCast(AllGlobals, IntptrTy),
-                  ConstantInt::get(IntptrTy, n)});
+
+  if (TargetTriple.isOSBinFormatMachO()) {
+    IRB.CreateCall(AsanApplyToGlobals,
+                   {IRB.CreatePointerCast(AsanRegisterGlobals, IntptrTy),
+                    IRB.CreatePointerCast(AllGlobals, IntptrTy)});
+  } else {
+    IRB.CreateCall(AsanRegisterGlobals,
+                   {IRB.CreatePointerCast(AllGlobals, IntptrTy),
+                    ConstantInt::get(IntptrTy, n)});
+  }
 
   // We also need to unregister globals at the end, e.g. when a shared library
   // gets closed.
@@ -1425,9 +1475,17 @@
                        GlobalValue::InternalLinkage, kAsanModuleDtorName, &M);
   BasicBlock *AsanDtorBB = BasicBlock::Create(*C, "", AsanDtorFunction);
   IRBuilder<> IRB_Dtor(ReturnInst::Create(*C, AsanDtorBB));
-  IRB_Dtor.CreateCall(AsanUnregisterGlobals,
-                      {IRB.CreatePointerCast(AllGlobals, IntptrTy),
-                       ConstantInt::get(IntptrTy, n)});
+
+  if (TargetTriple.isOSBinFormatMachO()) {
+    IRB_Dtor.CreateCall(AsanApplyToGlobals,
+                        {IRB.CreatePointerCast(AsanUnregisterGlobals, IntptrTy),
+                         IRB.CreatePointerCast(AllGlobals, IntptrTy)});
+  } else {
+    IRB_Dtor.CreateCall(AsanUnregisterGlobals,
+                        {IRB.CreatePointerCast(AllGlobals, IntptrTy),
+                         ConstantInt::get(IntptrTy, n)});
+  }
+
   appendToGlobalDtors(M, AsanDtorFunction, kAsanCtorAndDtorPriority);
 
   DEBUG(dbgs() << M);