Index: lib/CodeGen/GlobalMerge.cpp
===================================================================
--- lib/CodeGen/GlobalMerge.cpp
+++ lib/CodeGen/GlobalMerge.cpp
@@ -73,10 +73,10 @@
 
 #define DEBUG_TYPE "global-merge"
 
-static cl::opt<bool>
+static cl::opt<cl::boolOrDefault>
 EnableGlobalMerge("enable-global-merge", cl::Hidden,
                   cl::desc("Enable global merge pass"),
-                  cl::init(true));
+                  cl::init(cl::BOU_UNSET));
 
 static cl::opt<bool>
 EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden,
@@ -278,8 +278,25 @@
   }
 }
 
+static bool shouldEnableGlobalMergeForModule(const Module &M) {
+  Metadata *FlagMD = M.getModuleFlag("Global Merge");
+
+  // If not explicitly specified otherwise, enable the pass.
+  if (!FlagMD)
+    return true;
+
+  ConstantAsMetadata *Flag = dyn_cast<ConstantAsMetadata>(FlagMD);
+  if (!Flag || !isa<ConstantInt>(Flag->getValue()))
+    report_fatal_error("Unexpected type for \"Global Merge\" module flag "
+                       "value, should be an integer constant!");
+
+  return !cast<ConstantInt>(Flag->getValue())->isZero();
+}
+
 bool GlobalMerge::doInitialization(Module &M) {
-  if (!EnableGlobalMerge)
+  if (EnableGlobalMerge == cl::BOU_FALSE ||
+      (EnableGlobalMerge == cl::BOU_UNSET &&
+       !shouldEnableGlobalMergeForModule(M)))
     return false;
 
   DenseMap<unsigned, SmallVector<GlobalVariable*, 16> > Globals, ConstGlobals,
Index: test/CodeGen/AArch64/global-merge-moduleflag-disabled.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/global-merge-moduleflag-disabled.ll
@@ -0,0 +1,21 @@
+; RUN: llc %s -mtriple=aarch64-none-linux-gnu -o - | FileCheck %s --check-prefix=CHECK-NGM
+; RUN: llc %s -mtriple=aarch64-none-linux-gnu -enable-global-merge -o - | FileCheck %s --check-prefix=CHECK-GM
+; RUN: llc %s -mtriple=aarch64-none-linux-gnu -enable-global-merge=false -o - | FileCheck %s --check-prefix=CHECK-NGM
+
+@m = internal global i32 0, align 4
+@n = internal global i32 0, align 4
+
+define void @f1(i32 %a1, i32 %a2) {
+  store i32 %a1, i32* @m, align 4
+  store i32 %a2, i32* @n, align 4
+  ret void
+}
+
+!0 = !{ i32 4, !"Global Merge", i32 0 }
+!llvm.module.flags = !{ !0 }
+
+;CHECK-GM:	.type	_MergedGlobals,@object  // @_MergedGlobals
+;CHECK-GM:	.local	_MergedGlobals
+;CHECK-GM:	.comm	_MergedGlobals,8,8
+
+;CHECK-NGM-NOT:	MergedGlobals
Index: test/CodeGen/AArch64/global-merge-moduleflag-enabled.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/global-merge-moduleflag-enabled.ll
@@ -0,0 +1,21 @@
+; RUN: llc %s -mtriple=aarch64-none-linux-gnu -o - | FileCheck %s --check-prefix=CHECK-GM
+; RUN: llc %s -mtriple=aarch64-none-linux-gnu -enable-global-merge -o - | FileCheck %s --check-prefix=CHECK-GM
+; RUN: llc %s -mtriple=aarch64-none-linux-gnu -enable-global-merge=false -o - | FileCheck %s --check-prefix=CHECK-NGM
+
+@m = internal global i32 0, align 4
+@n = internal global i32 0, align 4
+
+define void @f1(i32 %a1, i32 %a2) {
+  store i32 %a1, i32* @m, align 4
+  store i32 %a2, i32* @n, align 4
+  ret void
+}
+
+!0 = !{ i32 1, !"Global Merge", i32 1 }
+!llvm.module.flags = !{ !0 }
+
+;CHECK-GM:	.type	_MergedGlobals,@object  // @_MergedGlobals
+;CHECK-GM:	.local	_MergedGlobals
+;CHECK-GM:	.comm	_MergedGlobals,8,8
+
+;CHECK-NGM-NOT:	MergedGlobals