Index: include/llvm/CodeGen/TargetInstrInfo.h
===================================================================
--- include/llvm/CodeGen/TargetInstrInfo.h
+++ include/llvm/CodeGen/TargetInstrInfo.h
@@ -1686,6 +1686,11 @@
         "Target didn't implement TargetInstrInfo::insertOutlinerPrologue!");
   }
 
+  /// Return true if the function should be outlined from by default.
+  virtual bool shouldOutlineFromFunctionByDefault(MachineFunction &MF) const {
+    return false;
+  }
+
   /// Return true if the function can safely be outlined from.
   /// A function \p MF is considered safe for outlining if an outlined function
   /// produced from instructions in F will produce a program which produces the
Index: lib/CodeGen/MachineOutliner.cpp
===================================================================
--- lib/CodeGen/MachineOutliner.cpp
+++ lib/CodeGen/MachineOutliner.cpp
@@ -88,6 +88,18 @@
 STATISTIC(NumOutlined, "Number of candidates outlined");
 STATISTIC(FunctionsCreated, "Number of functions created");
 
+// If passed in, enable the MachineOutliner on all functions except for
+// linkonceodrs by default.
+// FIXME: This should be changed to something that describes *what* you want to
+// outline from. By default, the target decides if there's anything it wants
+// to outline from. The user should be able to override this if they wish. E.g,
+// -outline-from=all, -outline-from=size, -outline-from=minsize...
+static cl::opt<bool> EnableMachineOutliner(
+    "enable-machine-outliner",
+    cl::Hidden,
+    cl::desc("Enable the machine outliner on all functions"),
+    cl::init(false));
+
 // Set to true if the user wants the outliner to run on linkonceodr linkage
 // functions. This is false by default because the linker can dedupe linkonceodr
 // functions. Since the outliner is confined to a single module (modulo LTO),
@@ -1439,7 +1451,6 @@
   // If the user specifies that they want to outline from linkonceodrs, set
   // it here.
   OutlineFromLinkOnceODRs = EnableLinkOnceODROutlining;
-
   InstructionMapper Mapper;
 
   // Build instruction mappings for each function in the module. Start by
@@ -1460,6 +1471,13 @@
     if (!MF)
       continue;
 
+    // If the user hasn't specified that they want to enable the outliner, then
+    // check if the target wants this function to be outlined from.
+    if (!EnableMachineOutliner &&
+        !TII->shouldOutlineFromFunctionByDefault(*MF)) {
+      continue;
+    }
+
     // We have a MachineFunction. Ask the target if it's suitable for outlining.
     // If it isn't, then move on to the next Function in the module.
     if (!TII->isFunctionSafeToOutlineFrom(*MF, OutlineFromLinkOnceODRs))
Index: lib/CodeGen/TargetPassConfig.cpp
===================================================================
--- lib/CodeGen/TargetPassConfig.cpp
+++ lib/CodeGen/TargetPassConfig.cpp
@@ -111,9 +111,9 @@
     cl::desc("Verify generated machine code"),
     cl::init(false),
     cl::ZeroOrMore);
-static cl::opt<bool> EnableMachineOutliner("enable-machine-outliner",
+static cl::opt<bool> DisableMachineOutliner("disable-machine-outliner",
     cl::Hidden,
-    cl::desc("Enable machine outliner"));
+    cl::desc("Disable machine outliner"));
 // Enable or disable FastISel. Both options are needed, because
 // FastISel is enabled by default with -fast, and we wish to be
 // able to enable or disable fast-isel independently from -O0.
@@ -901,7 +901,7 @@
   addPass(&XRayInstrumentationID, false);
   addPass(&PatchableFunctionID, false);
 
-  if (EnableMachineOutliner)
+  if (!DisableMachineOutliner)
     addPass(createMachineOutlinerPass());
 
   // Add passes that directly emit MI after all other MI passes.
Index: lib/Target/AArch64/AArch64InstrInfo.h
===================================================================
--- lib/Target/AArch64/AArch64InstrInfo.h
+++ lib/Target/AArch64/AArch64InstrInfo.h
@@ -238,7 +238,7 @@
 
   /// AArch64 supports the MachineOutliner.
   bool useMachineOutliner() const override { return true; }
-  
+  bool shouldOutlineFromFunctionByDefault(MachineFunction &MF) const override;
   bool
   canOutlineWithoutLRSave(MachineBasicBlock::iterator &CallInsertionPt) const;
   bool isFunctionSafeToOutlineFrom(MachineFunction &MF,
Index: lib/Target/AArch64/AArch64InstrInfo.cpp
===================================================================
--- lib/Target/AArch64/AArch64InstrInfo.cpp
+++ lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -5004,6 +5004,11 @@
                              FrameID);
 }
 
+bool AArch64InstrInfo::shouldOutlineFromFunctionByDefault(
+    MachineFunction &MF) const {
+  return MF.getFunction().optForMinSize();
+}
+
 bool AArch64InstrInfo::isFunctionSafeToOutlineFrom(
     MachineFunction &MF, bool OutlineFromLinkOnceODRs) const {
   const Function &F = MF.getFunction();
Index: test/CodeGen/AArch64/machine-outliner-calls.mir
===================================================================
--- test/CodeGen/AArch64/machine-outliner-calls.mir
+++ test/CodeGen/AArch64/machine-outliner-calls.mir
@@ -8,7 +8,7 @@
     ret void
   }
   
-  attributes #0 = { noredzone }
+  attributes #0 = { noredzone minsize }
 ...
 ---
 
Index: test/CodeGen/AArch64/machine-outliner-flags.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/machine-outliner-flags.ll
@@ -0,0 +1,9 @@
+; RUN: llc %s -debug-pass=Structure -mtriple arm64---- -o - 2>&1 | FileCheck %s -check-prefix=DEFAULT
+; RUN: llc %s -debug-pass=Structure -disable-machine-outliner -mtriple arm64---- -o - 2>&1 | FileCheck %s -check-prefix=DISABLED
+
+; Ensure that the MachineOutliner is added by default in arm64
+; DEFAULT: Machine Outliner
+; DISABLED-NOT: Machine Outliner
+
+define void @foo(float %x) #0 { ret void }
+attributes #0 = { noredzone minsize }
Index: test/CodeGen/AArch64/machine-outliner.mir
===================================================================
--- test/CodeGen/AArch64/machine-outliner.mir
+++ test/CodeGen/AArch64/machine-outliner.mir
@@ -15,7 +15,7 @@
     ret void
   }
   
-  attributes #0 = { noinline noredzone "no-frame-pointer-elim"="true" }
+  attributes #0 = { minsize noinline noredzone "no-frame-pointer-elim"="true" }
 ...
 ---
 # This test ensures that we