diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index 710ca7a..2560c9f 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -636,10 +636,75 @@
   DISALLOW_COPY_AND_ASSIGN(ArraySetSlowPathARM);
 };
 
+// Abstract base class for read barrier slow paths marking a reference
+// `ref`.
+//
+// Argument `entrypoint` must be a register location holding the read
+// barrier marking runtime entry point to be invoked.
+class ReadBarrierMarkSlowPathBaseARM : public SlowPathCodeARM {
+ protected:
+  ReadBarrierMarkSlowPathBaseARM(HInstruction* instruction, Location ref, Location entrypoint)
+      : SlowPathCodeARM(instruction), ref_(ref), entrypoint_(entrypoint) {
+    DCHECK(kEmitCompilerReadBarrier);
+  }
+
+  const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkSlowPathBaseARM"; }
+
+  // Generate assembly code calling the read barrier marking runtime
+  // entry point (ReadBarrierMarkRegX).
+  void GenerateReadBarrierMarkRuntimeCall(CodeGenerator* codegen) {
+    Register ref_reg = ref_.AsRegister<Register>();
+
+    // No need to save live registers; it's taken care of by the
+    // entrypoint. Also, there is no need to update the stack mask,
+    // as this runtime call will not trigger a garbage collection.
+    CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen);
+    DCHECK_NE(ref_reg, SP);
+    DCHECK_NE(ref_reg, LR);
+    DCHECK_NE(ref_reg, PC);
+    // IP is used internally by the ReadBarrierMarkRegX entry point
+    // as a temporary, it cannot be the entry point's input/output.
+    DCHECK_NE(ref_reg, IP);
+    DCHECK(0 <= ref_reg && ref_reg < kNumberOfCoreRegisters) << ref_reg;
+    // "Compact" slow path, saving two moves.
+    //
+    // Instead of using the standard runtime calling convention (input
+    // and output in R0):
+    //
+    //   R0 <- ref
+    //   R0 <- ReadBarrierMark(R0)
+    //   ref <- R0
+    //
+    // we just use rX (the register containing `ref`) as input and output
+    // of a dedicated entrypoint:
+    //
+    //   rX <- ReadBarrierMarkRegX(rX)
+    //
+    if (entrypoint_.IsValid()) {
+      arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this);
+      __ blx(entrypoint_.AsRegister<Register>());
+    } else {
+      // Entrypoint is not already loaded, load from the thread.
+      int32_t entry_point_offset =
+          CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg);
+      // This runtime call does not require a stack map.
+      arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this);
+    }
+  }
+
+  // The location (register) of the marked object reference.
+  const Location ref_;
+
+  // The location of the entrypoint if it is already loaded.
+  const Location entrypoint_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathBaseARM);
+};
+
 // Slow path marking an object reference `ref` during a read
 // barrier. The field `obj.field` in the object `obj` holding this
-// reference does not get updated by this slow path after marking (see
-// ReadBarrierMarkAndUpdateFieldSlowPathARM below for that).
+// reference does not get updated by this slow path after marking.
 //
 // This means that after the execution of this slow path, `ref` will
 // always be up-to-date, but `obj.field` may not; i.e., after the
@@ -651,12 +716,12 @@
 // If `entrypoint` is a valid location it is assumed to already be
 // holding the entrypoint. The case where the entrypoint is passed in
 // is when the decision to mark is based on whether the GC is marking.
-class ReadBarrierMarkSlowPathARM : public SlowPathCodeARM {
+class ReadBarrierMarkSlowPathARM : public ReadBarrierMarkSlowPathBaseARM {
  public:
   ReadBarrierMarkSlowPathARM(HInstruction* instruction,
                              Location ref,
                              Location entrypoint = Location::NoLocation())
-      : SlowPathCodeARM(instruction), ref_(ref), entrypoint_(entrypoint) {
+      : ReadBarrierMarkSlowPathBaseARM(instruction, ref, entrypoint) {
     DCHECK(kEmitCompilerReadBarrier);
   }
 
@@ -664,15 +729,77 @@
 
   void EmitNativeCode(CodeGenerator* codegen) OVERRIDE {
     LocationSummary* locations = instruction_->GetLocations();
+    DCHECK(locations->CanCall());
+    if (kIsDebugBuild) {
+      Register ref_reg = ref_.AsRegister<Register>();
+      DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg)) << ref_reg;
+    }
+    DCHECK(instruction_->IsLoadClass() || instruction_->IsLoadString())
+        << "Unexpected instruction in read barrier marking slow path: "
+        << instruction_->DebugName();
+
+    __ Bind(GetEntryLabel());
+    GenerateReadBarrierMarkRuntimeCall(codegen);
+    __ b(GetExitLabel());
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARM);
+};
+
+// Slow path loading `obj`'s lock word, loading a reference from
+// object `*(obj + offset + (index << scale_factor))` into `ref`, and
+// marking `ref` if `obj` is gray according to the lock word (Baker
+// read barrier). The field `obj.field` in the object `obj` holding
+// this reference does not get updated by this slow path after marking
+// (see LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM
+// below for that).
+//
+// This means that after the execution of this slow path, `ref` will
+// always be up-to-date, but `obj.field` may not; i.e., after the
+// flip, `ref` will be a to-space reference, but `obj.field` will
+// probably still be a from-space reference (unless it gets updated by
+// another thread, or if another thread installed another object
+// reference (different from `ref`) in `obj.field`).
+//
+// Argument `entrypoint` must be a register location holding the read
+// barrier marking runtime entry point to be invoked.
+class LoadReferenceWithBakerReadBarrierSlowPathARM : public ReadBarrierMarkSlowPathBaseARM {
+ public:
+  LoadReferenceWithBakerReadBarrierSlowPathARM(HInstruction* instruction,
+                                               Location ref,
+                                               Register obj,
+                                               uint32_t offset,
+                                               Location index,
+                                               ScaleFactor scale_factor,
+                                               bool needs_null_check,
+                                               Register temp,
+                                               Location entrypoint)
+      : ReadBarrierMarkSlowPathBaseARM(instruction, ref, entrypoint),
+        obj_(obj),
+        offset_(offset),
+        index_(index),
+        scale_factor_(scale_factor),
+        needs_null_check_(needs_null_check),
+        temp_(temp) {
+    DCHECK(kEmitCompilerReadBarrier);
+    DCHECK(kUseBakerReadBarrier);
+  }
+
+  const char* GetDescription() const OVERRIDE {
+    return "LoadReferenceWithBakerReadBarrierSlowPathARM";
+  }
+
+  void EmitNativeCode(CodeGenerator* codegen) OVERRIDE {
+    LocationSummary* locations = instruction_->GetLocations();
     Register ref_reg = ref_.AsRegister<Register>();
     DCHECK(locations->CanCall());
     DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg)) << ref_reg;
+    DCHECK_NE(ref_reg, temp_);
     DCHECK(instruction_->IsInstanceFieldGet() ||
            instruction_->IsStaticFieldGet() ||
            instruction_->IsArrayGet() ||
            instruction_->IsArraySet() ||
-           instruction_->IsLoadClass() ||
-           instruction_->IsLoadString() ||
            instruction_->IsInstanceOf() ||
            instruction_->IsCheckCast() ||
            (instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()) ||
@@ -686,158 +813,202 @@
              instruction_->AsArrayGet()->GetArray()->IsIntermediateAddress()));
 
     __ Bind(GetEntryLabel());
-    // No need to save live registers; it's taken care of by the
-    // entrypoint. Also, there is no need to update the stack mask,
-    // as this runtime call will not trigger a garbage collection.
-    CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen);
-    DCHECK_NE(ref_reg, SP);
-    DCHECK_NE(ref_reg, LR);
-    DCHECK_NE(ref_reg, PC);
-    // IP is used internally by the ReadBarrierMarkRegX entry point
-    // as a temporary, it cannot be the entry point's input/output.
-    DCHECK_NE(ref_reg, IP);
-    DCHECK(0 <= ref_reg && ref_reg < kNumberOfCoreRegisters) << ref_reg;
-    // "Compact" slow path, saving two moves.
+
+    // When using MaybeGenerateReadBarrierSlow, the read barrier call is
+    // inserted after the original load. However, in fast path based
+    // Baker's read barriers, we need to perform the load of
+    // mirror::Object::monitor_ *before* the original reference load.
+    // This load-load ordering is required by the read barrier.
+    // The fast path/slow path (for Baker's algorithm) should look like:
     //
-    // Instead of using the standard runtime calling convention (input
-    // and output in R0):
+    //   uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState();
+    //   lfence;  // Load fence or artificial data dependency to prevent load-load reordering
+    //   HeapReference<mirror::Object> ref = *src;  // Original reference load.
+    //   bool is_gray = (rb_state == ReadBarrier::GrayState());
+    //   if (is_gray) {
+    //     ref = entrypoint(ref);  // ref = ReadBarrier::Mark(ref);  // Runtime entry point call.
+    //   }
     //
-    //   R0 <- ref
-    //   R0 <- ReadBarrierMark(R0)
-    //   ref <- R0
-    //
-    // we just use rX (the register containing `ref`) as input and output
-    // of a dedicated entrypoint:
-    //
-    //   rX <- ReadBarrierMarkRegX(rX)
-    //
-    if (entrypoint_.IsValid()) {
-      arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this);
-      __ blx(entrypoint_.AsRegister<Register>());
-    } else {
-      // Entrypoint is not already loaded, load from the thread.
-      int32_t entry_point_offset =
-          CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg);
-      // This runtime call does not require a stack map.
-      arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this);
+    // Note: the original implementation in ReadBarrier::Barrier is
+    // slightly more complex as it performs additional checks that we do
+    // not do here for performance reasons.
+
+    // /* int32_t */ monitor = obj->monitor_
+    uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value();
+    __ LoadFromOffset(kLoadWord, temp_, obj_, monitor_offset);
+    if (needs_null_check_) {
+      codegen->MaybeRecordImplicitNullCheck(instruction_);
     }
+    // /* LockWord */ lock_word = LockWord(monitor)
+    static_assert(sizeof(LockWord) == sizeof(int32_t),
+                  "art::LockWord and int32_t have different sizes.");
+
+    // Introduce a dependency on the lock_word including the rb_state,
+    // which shall prevent load-load reordering without using
+    // a memory barrier (which would be more expensive).
+    // `obj` is unchanged by this operation, but its value now depends
+    // on `temp`.
+    __ add(obj_, obj_, ShifterOperand(temp_, LSR, 32));
+
+    // The actual reference load.
+    // A possible implicit null check has already been handled above.
+    CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen);
+    arm_codegen->GenerateRawReferenceLoad(
+        instruction_, ref_, obj_, offset_, index_, scale_factor_, /* needs_null_check */ false);
+
+    // Mark the object `ref` when `obj` is gray.
+    //
+    // if (rb_state == ReadBarrier::GrayState())
+    //   ref = ReadBarrier::Mark(ref);
+    //
+    // Given the numeric representation, it's enough to check the low bit of the
+    // rb_state. We do that by shifting the bit out of the lock word with LSRS
+    // which can be a 16-bit instruction unlike the TST immediate.
+    static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0");
+    static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1");
+    __ Lsrs(temp_, temp_, LockWord::kReadBarrierStateShift + 1);
+    __ b(GetExitLabel(), CC);  // Carry flag is the last bit shifted out by LSRS.
+    GenerateReadBarrierMarkRuntimeCall(codegen);
+
     __ b(GetExitLabel());
   }
 
  private:
-  // The location (register) of the marked object reference.
-  const Location ref_;
+  // The register containing the object holding the marked object reference field.
+  Register obj_;
+  // The offset, index and scale factor to access the reference in `obj_`.
+  uint32_t offset_;
+  Location index_;
+  ScaleFactor scale_factor_;
+  // Is a null check required?
+  bool needs_null_check_;
+  // A temporary register used to hold the lock word of `obj_`.
+  Register temp_;
 
-  // The location of the entrypoint if already loaded.
-  const Location entrypoint_;
-
-  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARM);
+  DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierSlowPathARM);
 };
 
-// Slow path marking an object reference `ref` during a read barrier,
-// and if needed, atomically updating the field `obj.field` in the
-// object `obj` holding this reference after marking (contrary to
-// ReadBarrierMarkSlowPathARM above, which never tries to update
-// `obj.field`).
+// Slow path loading `obj`'s lock word, loading a reference from
+// object `*(obj + offset + (index << scale_factor))` into `ref`, and
+// marking `ref` if `obj` is gray according to the lock word (Baker
+// read barrier). If needed, this slow path also atomically updates
+// the field `obj.field` in the object `obj` holding this reference
+// after marking (contrary to
+// LoadReferenceWithBakerReadBarrierSlowPathARM above, which never
+// tries to update `obj.field`).
 //
 // This means that after the execution of this slow path, both `ref`
 // and `obj.field` will be up-to-date; i.e., after the flip, both will
 // hold the same to-space reference (unless another thread installed
 // another object reference (different from `ref`) in `obj.field`).
 //
-// If `entrypoint` is a valid location it is assumed to already be
-// holding the entrypoint. The case where the entrypoint is passed in
-// is when the decision to mark is based on whether the GC is marking.
-class ReadBarrierMarkAndUpdateFieldSlowPathARM : public SlowPathCodeARM {
+// Argument `entrypoint` must be a register location holding the read
+// barrier marking runtime entry point to be invoked.
+class LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM
+    : public ReadBarrierMarkSlowPathBaseARM {
  public:
-  ReadBarrierMarkAndUpdateFieldSlowPathARM(HInstruction* instruction,
-                                           Location ref,
-                                           Register obj,
-                                           Location field_offset,
-                                           Register temp1,
-                                           Register temp2,
-                                           Location entrypoint = Location::NoLocation())
-      : SlowPathCodeARM(instruction),
-        ref_(ref),
+  LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM(HInstruction* instruction,
+                                                             Location ref,
+                                                             Register obj,
+                                                             uint32_t offset,
+                                                             Location index,
+                                                             ScaleFactor scale_factor,
+                                                             bool needs_null_check,
+                                                             Register temp1,
+                                                             Register temp2,
+                                                             Location entrypoint)
+      : ReadBarrierMarkSlowPathBaseARM(instruction, ref, entrypoint),
         obj_(obj),
-        field_offset_(field_offset),
+        offset_(offset),
+        index_(index),
+        scale_factor_(scale_factor),
+        needs_null_check_(needs_null_check),
         temp1_(temp1),
-        temp2_(temp2),
-        entrypoint_(entrypoint) {
+        temp2_(temp2) {
     DCHECK(kEmitCompilerReadBarrier);
+    DCHECK(kUseBakerReadBarrier);
   }
 
-  const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkAndUpdateFieldSlowPathARM"; }
+  const char* GetDescription() const OVERRIDE {
+    return "LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM";
+  }
 
   void EmitNativeCode(CodeGenerator* codegen) OVERRIDE {
     LocationSummary* locations = instruction_->GetLocations();
     Register ref_reg = ref_.AsRegister<Register>();
     DCHECK(locations->CanCall());
     DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg)) << ref_reg;
-    // This slow path is only used by the UnsafeCASObject intrinsic.
+    DCHECK_NE(ref_reg, temp1_);
+
+    // This slow path is only used by the UnsafeCASObject intrinsic at the moment.
     DCHECK((instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()))
         << "Unexpected instruction in read barrier marking and field updating slow path: "
         << instruction_->DebugName();
     DCHECK(instruction_->GetLocations()->Intrinsified());
     DCHECK_EQ(instruction_->AsInvoke()->GetIntrinsic(), Intrinsics::kUnsafeCASObject);
-    DCHECK(field_offset_.IsRegisterPair()) << field_offset_;
+    DCHECK_EQ(offset_, 0u);
+    DCHECK_EQ(scale_factor_, ScaleFactor::TIMES_1);
+    // The location of the offset of the marked reference field within `obj_`.
+    Location field_offset = index_;
+    DCHECK(field_offset.IsRegisterPair()) << field_offset;
 
     __ Bind(GetEntryLabel());
 
-    // Save the old reference.
+    // /* int32_t */ monitor = obj->monitor_
+    uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value();
+    __ LoadFromOffset(kLoadWord, temp1_, obj_, monitor_offset);
+    if (needs_null_check_) {
+      codegen->MaybeRecordImplicitNullCheck(instruction_);
+    }
+    // /* LockWord */ lock_word = LockWord(monitor)
+    static_assert(sizeof(LockWord) == sizeof(int32_t),
+                  "art::LockWord and int32_t have different sizes.");
+
+    // Introduce a dependency on the lock_word including the rb_state,
+    // which shall prevent load-load reordering without using
+    // a memory barrier (which would be more expensive).
+    // `obj` is unchanged by this operation, but its value now depends
+    // on `temp1`.
+    __ add(obj_, obj_, ShifterOperand(temp1_, LSR, 32));
+
+    // The actual reference load.
+    // A possible implicit null check has already been handled above.
+    CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen);
+    arm_codegen->GenerateRawReferenceLoad(
+        instruction_, ref_, obj_, offset_, index_, scale_factor_, /* needs_null_check */ false);
+
+    // Mark the object `ref` when `obj` is gray.
+    //
+    // if (rb_state == ReadBarrier::GrayState())
+    //   ref = ReadBarrier::Mark(ref);
+    //
+    // Given the numeric representation, it's enough to check the low bit of the
+    // rb_state. We do that by shifting the bit out of the lock word with LSRS
+    // which can be a 16-bit instruction unlike the TST immediate.
+    static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0");
+    static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1");
+    __ Lsrs(temp1_, temp1_, LockWord::kReadBarrierStateShift + 1);
+    __ b(GetExitLabel(), CC);  // Carry flag is the last bit shifted out by LSRS.
+
+    // Save the old value of the reference before marking it.
     // Note that we cannot use IP to save the old reference, as IP is
     // used internally by the ReadBarrierMarkRegX entry point, and we
     // need the old reference after the call to that entry point.
     DCHECK_NE(temp1_, IP);
     __ Mov(temp1_, ref_reg);
 
-    // No need to save live registers; it's taken care of by the
-    // entrypoint. Also, there is no need to update the stack mask,
-    // as this runtime call will not trigger a garbage collection.
-    CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen);
-    DCHECK_NE(ref_reg, SP);
-    DCHECK_NE(ref_reg, LR);
-    DCHECK_NE(ref_reg, PC);
-    // IP is used internally by the ReadBarrierMarkRegX entry point
-    // as a temporary, it cannot be the entry point's input/output.
-    DCHECK_NE(ref_reg, IP);
-    DCHECK(0 <= ref_reg && ref_reg < kNumberOfCoreRegisters) << ref_reg;
-    // "Compact" slow path, saving two moves.
-    //
-    // Instead of using the standard runtime calling convention (input
-    // and output in R0):
-    //
-    //   R0 <- ref
-    //   R0 <- ReadBarrierMark(R0)
-    //   ref <- R0
-    //
-    // we just use rX (the register containing `ref`) as input and output
-    // of a dedicated entrypoint:
-    //
-    //   rX <- ReadBarrierMarkRegX(rX)
-    //
-    if (entrypoint_.IsValid()) {
-      arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this);
-      __ blx(entrypoint_.AsRegister<Register>());
-    } else {
-      // Entrypoint is not already loaded, load from the thread.
-      int32_t entry_point_offset =
-          CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg);
-      // This runtime call does not require a stack map.
-      arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this);
-    }
+    GenerateReadBarrierMarkRuntimeCall(codegen);
 
     // If the new reference is different from the old reference,
-    // update the field in the holder (`*(obj_ + field_offset_)`).
+    // update the field in the holder (`*(obj_ + field_offset)`).
     //
     // Note that this field could also hold a different object, if
     // another thread had concurrently changed it. In that case, the
     // LDREX/SUBS/ITNE sequence of instructions in the compare-and-set
     // (CAS) operation below would abort the CAS, leaving the field
     // as-is.
-    Label done;
     __ cmp(temp1_, ShifterOperand(ref_reg));
-    __ b(&done, EQ);
+    __ b(GetExitLabel(), EQ);
 
     // Update the the holder's field atomically.  This may fail if
     // mutator updates before us, but it's OK.  This is achieved
@@ -850,7 +1021,7 @@
     // The UnsafeCASObject intrinsic uses a register pair as field
     // offset ("long offset"), of which only the low part contains
     // data.
-    Register offset = field_offset_.AsRegisterPairLow<Register>();
+    Register offset = field_offset.AsRegisterPairLow<Register>();
     Register expected = temp1_;
     Register value = ref_reg;
     Register tmp_ptr = IP;       // Pointer to actual memory.
@@ -900,25 +1071,27 @@
       }
     }
 
-    __ Bind(&done);
     __ b(GetExitLabel());
   }
 
  private:
-  // The location (register) of the marked object reference.
-  const Location ref_;
   // The register containing the object holding the marked object reference field.
   const Register obj_;
-  // The location of the offset of the marked reference field within `obj_`.
-  Location field_offset_;
-
+  // The offset, index and scale factor to access the reference in `obj_`.
+  uint32_t offset_;
+  Location index_;
+  ScaleFactor scale_factor_;
+  // Is a null check required?
+  bool needs_null_check_;
+  // A temporary register used to hold the lock word of `obj_`; and
+  // also to hold the original reference value, when the reference is
+  // marked.
   const Register temp1_;
+  // A temporary register used in the implementation of the CAS, to
+  // update the object's reference field.
   const Register temp2_;
 
-  // The location of the entrypoint if already loaded.
-  const Location entrypoint_;
-
-  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkAndUpdateFieldSlowPathARM);
+  DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM);
 };
 
 // Slow path generating a read barrier for a heap reference.
@@ -7310,13 +7483,11 @@
   DCHECK(kEmitCompilerReadBarrier);
   DCHECK(kUseBakerReadBarrier);
 
-  // After loading the reference from `obj.field` into `ref`, query
-  // `art::Thread::Current()->GetIsGcMarking()` to decide whether we
-  // need to enter the slow path to mark the reference. This
-  // optimistic strategy (we expect the GC to not be marking most of
-  // the time) does not check `obj`'s lock word (to see if it is a
-  // gray object or not), so may sometimes mark an already marked
-  // object.
+  // Query `art::Thread::Current()->GetIsGcMarking()` to decide
+  // whether we need to enter the slow path to mark the reference.
+  // Then, in the slow path, check the gray bit in the lock word of
+  // the reference's holder (`obj`) to decide whether to mark `ref` or
+  // not.
   //
   // Note that we do not actually check the value of `GetIsGcMarking()`;
   // instead, we load into `temp3` the read barrier mark entry point
@@ -7324,14 +7495,19 @@
   // that `GetIsGcMarking()` is false, and vice versa.
   //
   //   temp3 = Thread::Current()->pReadBarrierMarkReg ## root.reg()
-  //   HeapReference<mirror::Object> ref = *src;  // Original reference load.
   //   if (temp3 != nullptr) {  // <=> Thread::Current()->GetIsGcMarking()
   //     // Slow path.
-  //     ref = temp3(ref);  // ref = ReadBarrier::Mark(ref);  // Runtime entry point call.
+  //     uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState();
+  //     lfence;  // Load fence or artificial data dependency to prevent load-load reordering
+  //     HeapReference<mirror::Object> ref = *src;  // Original reference load.
+  //     bool is_gray = (rb_state == ReadBarrier::GrayState());
+  //     if (is_gray) {
+  //       ref = temp3(ref);  // ref = ReadBarrier::Mark(ref);  // Runtime entry point call.
+  //     }
+  //   } else {
+  //     HeapReference<mirror::Object> ref = *src;  // Original reference load.
   //   }
 
-  // TODO: This temp register is only necessary when
-  // `always_update_field` is true; make it optional (like `temp2`).
   Register temp_reg = temp.AsRegister<Register>();
 
   // Slow path marking the object `ref` when the GC is marking. The
@@ -7340,18 +7516,37 @@
   SlowPathCodeARM* slow_path;
   if (always_update_field) {
     DCHECK(temp2 != nullptr);
-    // ReadBarrierMarkAndUpdateFieldSlowPathARM only supports address
-    // of the form `obj + field_offset`, where `obj` is a register and
-    // `field_offset` is a register pair (of which only the lower half
-    // is used). Thus `offset` and `scale_factor` above are expected
-    // to be null in this code path.
+    // LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM only
+    // supports address of the form `obj + field_offset`, where `obj`
+    // is a register and `field_offset` is a register pair (of which
+    // only the lower half is used). Thus `offset` and `scale_factor`
+    // above are expected to be null in this code path.
     DCHECK_EQ(offset, 0u);
     DCHECK_EQ(scale_factor, ScaleFactor::TIMES_1);
-    slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkAndUpdateFieldSlowPathARM(
-        instruction, ref, obj, /* field_offset */ index, temp_reg, *temp2, /* entrypoint */ temp3);
+    Location field_offset = index;
+    slow_path =
+        new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM(
+            instruction,
+            ref,
+            obj,
+            offset,
+            /* index */ field_offset,
+            scale_factor,
+            needs_null_check,
+            temp_reg,
+            *temp2,
+            /* entrypoint */ temp3);
   } else {
-    slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkSlowPathARM(
-        instruction, ref, /* entrypoint */ temp3);
+    slow_path = new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierSlowPathARM(
+        instruction,
+        ref,
+        obj,
+        offset,
+        index,
+        scale_factor,
+        needs_null_check,
+        temp_reg,
+        /* entrypoint */ temp3);
   }
   AddSlowPath(slow_path);
 
@@ -7361,11 +7556,11 @@
   // Loading the entrypoint does not require a load acquire since it is only changed when
   // threads are suspended or running a checkpoint.
   __ LoadFromOffset(kLoadWord, temp3.AsRegister<Register>(), TR, entry_point_offset);
-  // The reference load.
-  GenerateRawReferenceLoad(instruction, ref, obj, offset, index, scale_factor, needs_null_check);
   // The entrypoint is null when the GC is not marking, this prevents one load compared to
   // checking GetIsGcMarking.
   __ CompareAndBranchIfNonZero(temp3.AsRegister<Register>(), slow_path->GetEntryLabel());
+  // Fast path: just load the reference.
+  GenerateRawReferenceLoad(instruction, ref, obj, offset, index, scale_factor, needs_null_check);
   __ Bind(slow_path->GetExitLabel());
 }
 
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index c2cf0de..a3732ef 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -633,10 +633,73 @@
   }
 }
 
+// Abstract base class for read barrier slow paths marking a reference
+// `ref`.
+//
+// Argument `entrypoint` must be a register location holding the read
+// barrier marking runtime entry point to be invoked.
+class ReadBarrierMarkSlowPathBaseARM64 : public SlowPathCodeARM64 {
+ protected:
+  ReadBarrierMarkSlowPathBaseARM64(HInstruction* instruction, Location ref, Location entrypoint)
+      : SlowPathCodeARM64(instruction), ref_(ref), entrypoint_(entrypoint) {
+    DCHECK(kEmitCompilerReadBarrier);
+  }
+
+  const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkSlowPathBaseARM64"; }
+
+  // Generate assembly code calling the read barrier marking runtime
+  // entry point (ReadBarrierMarkRegX).
+  void GenerateReadBarrierMarkRuntimeCall(CodeGenerator* codegen) {
+    // No need to save live registers; it's taken care of by the
+    // entrypoint. Also, there is no need to update the stack mask,
+    // as this runtime call will not trigger a garbage collection.
+    CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen);
+    DCHECK_NE(ref_.reg(), LR);
+    DCHECK_NE(ref_.reg(), WSP);
+    DCHECK_NE(ref_.reg(), WZR);
+    // IP0 is used internally by the ReadBarrierMarkRegX entry point
+    // as a temporary, it cannot be the entry point's input/output.
+    DCHECK_NE(ref_.reg(), IP0);
+    DCHECK(0 <= ref_.reg() && ref_.reg() < kNumberOfWRegisters) << ref_.reg();
+    // "Compact" slow path, saving two moves.
+    //
+    // Instead of using the standard runtime calling convention (input
+    // and output in W0):
+    //
+    //   W0 <- ref
+    //   W0 <- ReadBarrierMark(W0)
+    //   ref <- W0
+    //
+    // we just use rX (the register containing `ref`) as input and output
+    // of a dedicated entrypoint:
+    //
+    //   rX <- ReadBarrierMarkRegX(rX)
+    //
+    if (entrypoint_.IsValid()) {
+      arm64_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this);
+      __ Blr(XRegisterFrom(entrypoint_));
+    } else {
+      // Entrypoint is not already loaded, load from the thread.
+      int32_t entry_point_offset =
+          CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArm64PointerSize>(ref_.reg());
+      // This runtime call does not require a stack map.
+      arm64_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this);
+    }
+  }
+
+  // The location (register) of the marked object reference.
+  const Location ref_;
+
+  // The location of the entrypoint if it is already loaded.
+  const Location entrypoint_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathBaseARM64);
+};
+
 // Slow path marking an object reference `ref` during a read
 // barrier. The field `obj.field` in the object `obj` holding this
-// reference does not get updated by this slow path after marking (see
-// ReadBarrierMarkAndUpdateFieldSlowPathARM64 below for that).
+// reference does not get updated by this slow path after marking.
 //
 // This means that after the execution of this slow path, `ref` will
 // always be up-to-date, but `obj.field` may not; i.e., after the
@@ -648,14 +711,12 @@
 // If `entrypoint` is a valid location it is assumed to already be
 // holding the entrypoint. The case where the entrypoint is passed in
 // is when the decision to mark is based on whether the GC is marking.
-class ReadBarrierMarkSlowPathARM64 : public SlowPathCodeARM64 {
+class ReadBarrierMarkSlowPathARM64 : public ReadBarrierMarkSlowPathBaseARM64 {
  public:
   ReadBarrierMarkSlowPathARM64(HInstruction* instruction,
                                Location ref,
                                Location entrypoint = Location::NoLocation())
-      : SlowPathCodeARM64(instruction),
-        ref_(ref),
-        entrypoint_(entrypoint) {
+      : ReadBarrierMarkSlowPathBaseARM64(instruction, ref, entrypoint) {
     DCHECK(kEmitCompilerReadBarrier);
   }
 
@@ -666,12 +727,75 @@
     DCHECK(locations->CanCall());
     DCHECK(ref_.IsRegister()) << ref_;
     DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_.reg())) << ref_.reg();
+    DCHECK(instruction_->IsLoadClass() || instruction_->IsLoadString())
+        << "Unexpected instruction in read barrier marking slow path: "
+        << instruction_->DebugName();
+
+    __ Bind(GetEntryLabel());
+    GenerateReadBarrierMarkRuntimeCall(codegen);
+    __ B(GetExitLabel());
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARM64);
+};
+
+// Slow path loading `obj`'s lock word, loading a reference from
+// object `*(obj + offset + (index << scale_factor))` into `ref`, and
+// marking `ref` if `obj` is gray according to the lock word (Baker
+// read barrier). The field `obj.field` in the object `obj` holding
+// this reference does not get updated by this slow path after marking
+// (see LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64
+// below for that).
+//
+// This means that after the execution of this slow path, `ref` will
+// always be up-to-date, but `obj.field` may not; i.e., after the
+// flip, `ref` will be a to-space reference, but `obj.field` will
+// probably still be a from-space reference (unless it gets updated by
+// another thread, or if another thread installed another object
+// reference (different from `ref`) in `obj.field`).
+//
+// Argument `entrypoint` must be a register location holding the read
+// barrier marking runtime entry point to be invoked.
+class LoadReferenceWithBakerReadBarrierSlowPathARM64 : public ReadBarrierMarkSlowPathBaseARM64 {
+ public:
+  LoadReferenceWithBakerReadBarrierSlowPathARM64(HInstruction* instruction,
+                                                 Location ref,
+                                                 Register obj,
+                                                 uint32_t offset,
+                                                 Location index,
+                                                 size_t scale_factor,
+                                                 bool needs_null_check,
+                                                 bool use_load_acquire,
+                                                 Register temp,
+                                                 Location entrypoint)
+      : ReadBarrierMarkSlowPathBaseARM64(instruction, ref, entrypoint),
+        obj_(obj),
+        offset_(offset),
+        index_(index),
+        scale_factor_(scale_factor),
+        needs_null_check_(needs_null_check),
+        use_load_acquire_(use_load_acquire),
+        temp_(temp) {
+    DCHECK(kEmitCompilerReadBarrier);
+    DCHECK(kUseBakerReadBarrier);
+  }
+
+  const char* GetDescription() const OVERRIDE {
+    return "LoadReferenceWithBakerReadBarrierSlowPathARM64";
+  }
+
+  void EmitNativeCode(CodeGenerator* codegen) OVERRIDE {
+    LocationSummary* locations = instruction_->GetLocations();
+    DCHECK(locations->CanCall());
+    DCHECK(ref_.IsRegister()) << ref_;
+    DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_.reg())) << ref_.reg();
+    DCHECK(obj_.IsW());
+    DCHECK_NE(ref_.reg(), LocationFrom(temp_).reg());
     DCHECK(instruction_->IsInstanceFieldGet() ||
            instruction_->IsStaticFieldGet() ||
            instruction_->IsArrayGet() ||
            instruction_->IsArraySet() ||
-           instruction_->IsLoadClass() ||
-           instruction_->IsLoadString() ||
            instruction_->IsInstanceOf() ||
            instruction_->IsCheckCast() ||
            (instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()) ||
@@ -684,88 +808,138 @@
     DCHECK(!(instruction_->IsArrayGet() &&
              instruction_->AsArrayGet()->GetArray()->IsIntermediateAddress()));
 
+    // Temporary register `temp_`, used to store the lock word, must
+    // not be IP0 nor IP1, as we may use them to emit the reference
+    // load (in the call to GenerateRawReferenceLoad below), and we
+    // need the lock word to still be in `temp_` after the reference
+    // load.
+    DCHECK_NE(LocationFrom(temp_).reg(), IP0);
+    DCHECK_NE(LocationFrom(temp_).reg(), IP1);
+
     __ Bind(GetEntryLabel());
-    // No need to save live registers; it's taken care of by the
-    // entrypoint. Also, there is no need to update the stack mask,
-    // as this runtime call will not trigger a garbage collection.
-    CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen);
-    DCHECK_NE(ref_.reg(), LR);
-    DCHECK_NE(ref_.reg(), WSP);
-    DCHECK_NE(ref_.reg(), WZR);
-    // IP0 is used internally by the ReadBarrierMarkRegX entry point
-    // as a temporary, it cannot be the entry point's input/output.
-    DCHECK_NE(ref_.reg(), IP0);
-    DCHECK(0 <= ref_.reg() && ref_.reg() < kNumberOfWRegisters) << ref_.reg();
-    // "Compact" slow path, saving two moves.
+
+    // When using MaybeGenerateReadBarrierSlow, the read barrier call is
+    // inserted after the original load. However, in fast path based
+    // Baker's read barriers, we need to perform the load of
+    // mirror::Object::monitor_ *before* the original reference load.
+    // This load-load ordering is required by the read barrier.
+    // The fast path/slow path (for Baker's algorithm) should look like:
     //
-    // Instead of using the standard runtime calling convention (input
-    // and output in W0):
+    //   uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState();
+    //   lfence;  // Load fence or artificial data dependency to prevent load-load reordering
+    //   HeapReference<mirror::Object> ref = *src;  // Original reference load.
+    //   bool is_gray = (rb_state == ReadBarrier::GrayState());
+    //   if (is_gray) {
+    //     ref = entrypoint(ref);  // ref = ReadBarrier::Mark(ref);  // Runtime entry point call.
+    //   }
     //
-    //   W0 <- ref
-    //   W0 <- ReadBarrierMark(W0)
-    //   ref <- W0
-    //
-    // we just use rX (the register containing `ref`) as input and output
-    // of a dedicated entrypoint:
-    //
-    //   rX <- ReadBarrierMarkRegX(rX)
-    //
-    if (entrypoint_.IsValid()) {
-      arm64_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this);
-      __ Blr(XRegisterFrom(entrypoint_));
-    } else {
-      // Entrypoint is not already loaded, load from the thread.
-      int32_t entry_point_offset =
-          CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArm64PointerSize>(ref_.reg());
-      // This runtime call does not require a stack map.
-      arm64_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this);
+    // Note: the original implementation in ReadBarrier::Barrier is
+    // slightly more complex as it performs additional checks that we do
+    // not do here for performance reasons.
+
+    // /* int32_t */ monitor = obj->monitor_
+    uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value();
+    __ Ldr(temp_, HeapOperand(obj_, monitor_offset));
+    if (needs_null_check_) {
+      codegen->MaybeRecordImplicitNullCheck(instruction_);
     }
+    // /* LockWord */ lock_word = LockWord(monitor)
+    static_assert(sizeof(LockWord) == sizeof(int32_t),
+                  "art::LockWord and int32_t have different sizes.");
+
+    // Introduce a dependency on the lock_word including rb_state,
+    // to prevent load-load reordering, and without using
+    // a memory barrier (which would be more expensive).
+    // `obj` is unchanged by this operation, but its value now depends
+    // on `temp`.
+    __ Add(obj_.X(), obj_.X(), Operand(temp_.X(), LSR, 32));
+
+    // The actual reference load.
+    // A possible implicit null check has already been handled above.
+    CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen);
+    arm64_codegen->GenerateRawReferenceLoad(instruction_,
+                                            ref_,
+                                            obj_,
+                                            offset_,
+                                            index_,
+                                            scale_factor_,
+                                            /* needs_null_check */ false,
+                                            use_load_acquire_);
+
+    // Mark the object `ref` when `obj` is gray.
+    //
+    //   if (rb_state == ReadBarrier::GrayState())
+    //     ref = ReadBarrier::Mark(ref);
+    //
+    // Given the numeric representation, it's enough to check the low bit of the rb_state.
+    static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0");
+    static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1");
+    __ Tbz(temp_, LockWord::kReadBarrierStateShift, GetExitLabel());
+    GenerateReadBarrierMarkRuntimeCall(codegen);
+
     __ B(GetExitLabel());
   }
 
  private:
-  // The location (register) of the marked object reference.
-  const Location ref_;
+  // The register containing the object holding the marked object reference field.
+  Register obj_;
+  // The offset, index and scale factor to access the reference in `obj_`.
+  uint32_t offset_;
+  Location index_;
+  size_t scale_factor_;
+  // Is a null check required?
+  bool needs_null_check_;
+  // Should this reference load use Load-Acquire semantics?
+  bool use_load_acquire_;
+  // A temporary register used to hold the lock word of `obj_`.
+  Register temp_;
 
-  // The location of the entrypoint if it is already loaded.
-  const Location entrypoint_;
-
-  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARM64);
+  DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierSlowPathARM64);
 };
 
-// Slow path marking an object reference `ref` during a read barrier,
-// and if needed, atomically updating the field `obj.field` in the
-// object `obj` holding this reference after marking (contrary to
-// ReadBarrierMarkSlowPathARM64 above, which never tries to update
-// `obj.field`).
+// Slow path loading `obj`'s lock word, loading a reference from
+// object `*(obj + offset + (index << scale_factor))` into `ref`, and
+// marking `ref` if `obj` is gray according to the lock word (Baker
+// read barrier). If needed, this slow path also atomically updates
+// the field `obj.field` in the object `obj` holding this reference
+// after marking (contrary to
+// LoadReferenceWithBakerReadBarrierSlowPathARM64 above, which never
+// tries to update `obj.field`).
 //
 // This means that after the execution of this slow path, both `ref`
 // and `obj.field` will be up-to-date; i.e., after the flip, both will
 // hold the same to-space reference (unless another thread installed
 // another object reference (different from `ref`) in `obj.field`).
 //
-// If `entrypoint` is a valid location it is assumed to already be
-// holding the entrypoint. The case where the entrypoint is passed in
-// is when the decision to mark is based on whether the GC is marking.
-class ReadBarrierMarkAndUpdateFieldSlowPathARM64 : public SlowPathCodeARM64 {
+// Argument `entrypoint` must be a register location holding the read
+// barrier marking runtime entry point to be invoked.
+class LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64
+    : public ReadBarrierMarkSlowPathBaseARM64 {
  public:
-  ReadBarrierMarkAndUpdateFieldSlowPathARM64(HInstruction* instruction,
-                                             Location ref,
-                                             Register obj,
-                                             Location field_offset,
-                                             Register temp,
-                                             Location entrypoint = Location::NoLocation())
-      : SlowPathCodeARM64(instruction),
-        ref_(ref),
+  LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64(HInstruction* instruction,
+                                                               Location ref,
+                                                               Register obj,
+                                                               uint32_t offset,
+                                                               Location index,
+                                                               size_t scale_factor,
+                                                               bool needs_null_check,
+                                                               bool use_load_acquire,
+                                                               Register temp,
+                                                               Location entrypoint)
+      : ReadBarrierMarkSlowPathBaseARM64(instruction, ref, entrypoint),
         obj_(obj),
-        field_offset_(field_offset),
-        temp_(temp),
-        entrypoint_(entrypoint) {
+        offset_(offset),
+        index_(index),
+        scale_factor_(scale_factor),
+        needs_null_check_(needs_null_check),
+        use_load_acquire_(use_load_acquire),
+        temp_(temp) {
     DCHECK(kEmitCompilerReadBarrier);
+    DCHECK(kUseBakerReadBarrier);
   }
 
   const char* GetDescription() const OVERRIDE {
-    return "ReadBarrierMarkAndUpdateFieldSlowPathARM64";
+    return "LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64";
   }
 
   void EmitNativeCode(CodeGenerator* codegen) OVERRIDE {
@@ -774,70 +948,90 @@
     DCHECK(locations->CanCall());
     DCHECK(ref_.IsRegister()) << ref_;
     DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_.reg())) << ref_.reg();
-    // This slow path is only used by the UnsafeCASObject intrinsic.
+    DCHECK(obj_.IsW());
+    DCHECK_NE(ref_.reg(), LocationFrom(temp_).reg());
+
+    // This slow path is only used by the UnsafeCASObject intrinsic at the moment.
     DCHECK((instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()))
         << "Unexpected instruction in read barrier marking and field updating slow path: "
         << instruction_->DebugName();
     DCHECK(instruction_->GetLocations()->Intrinsified());
     DCHECK_EQ(instruction_->AsInvoke()->GetIntrinsic(), Intrinsics::kUnsafeCASObject);
-    DCHECK(field_offset_.IsRegister()) << field_offset_;
+    DCHECK_EQ(offset_, 0u);
+    DCHECK_EQ(scale_factor_, 0u);
+    DCHECK_EQ(use_load_acquire_, false);
+    // The location of the offset of the marked reference field within `obj_`.
+    Location field_offset = index_;
+    DCHECK(field_offset.IsRegister()) << field_offset;
+
+    // Temporary register `temp_`, used to store the lock word, must
+    // not be IP0 nor IP1, as we may use them to emit the reference
+    // load (in the call to GenerateRawReferenceLoad below), and we
+    // need the lock word to still be in `temp_` after the reference
+    // load.
+    DCHECK_NE(LocationFrom(temp_).reg(), IP0);
+    DCHECK_NE(LocationFrom(temp_).reg(), IP1);
 
     __ Bind(GetEntryLabel());
 
-    // Save the old reference.
+    // /* int32_t */ monitor = obj->monitor_
+    uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value();
+    __ Ldr(temp_, HeapOperand(obj_, monitor_offset));
+    if (needs_null_check_) {
+      codegen->MaybeRecordImplicitNullCheck(instruction_);
+    }
+    // /* LockWord */ lock_word = LockWord(monitor)
+    static_assert(sizeof(LockWord) == sizeof(int32_t),
+                  "art::LockWord and int32_t have different sizes.");
+
+    // Introduce a dependency on the lock_word including rb_state,
+    // to prevent load-load reordering, and without using
+    // a memory barrier (which would be more expensive).
+    // `obj` is unchanged by this operation, but its value now depends
+    // on `temp`.
+    __ Add(obj_.X(), obj_.X(), Operand(temp_.X(), LSR, 32));
+
+    // The actual reference load.
+    // A possible implicit null check has already been handled above.
+    CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen);
+    arm64_codegen->GenerateRawReferenceLoad(instruction_,
+                                            ref_,
+                                            obj_,
+                                            offset_,
+                                            index_,
+                                            scale_factor_,
+                                            /* needs_null_check */ false,
+                                            use_load_acquire_);
+
+    // Mark the object `ref` when `obj` is gray.
+    //
+    //   if (rb_state == ReadBarrier::GrayState())
+    //     ref = ReadBarrier::Mark(ref);
+    //
+    // Given the numeric representation, it's enough to check the low bit of the rb_state.
+    static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0");
+    static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1");
+    __ Tbz(temp_, LockWord::kReadBarrierStateShift, GetExitLabel());
+
+    // Save the old value of the reference before marking it.
     // Note that we cannot use IP to save the old reference, as IP is
     // used internally by the ReadBarrierMarkRegX entry point, and we
     // need the old reference after the call to that entry point.
     DCHECK_NE(LocationFrom(temp_).reg(), IP0);
     __ Mov(temp_.W(), ref_reg);
 
-    // No need to save live registers; it's taken care of by the
-    // entrypoint. Also, there is no need to update the stack mask,
-    // as this runtime call will not trigger a garbage collection.
-    CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen);
-    DCHECK_NE(ref_.reg(), LR);
-    DCHECK_NE(ref_.reg(), WSP);
-    DCHECK_NE(ref_.reg(), WZR);
-    // IP0 is used internally by the ReadBarrierMarkRegX entry point
-    // as a temporary, it cannot be the entry point's input/output.
-    DCHECK_NE(ref_.reg(), IP0);
-    DCHECK(0 <= ref_.reg() && ref_.reg() < kNumberOfWRegisters) << ref_.reg();
-    // "Compact" slow path, saving two moves.
-    //
-    // Instead of using the standard runtime calling convention (input
-    // and output in W0):
-    //
-    //   W0 <- ref
-    //   W0 <- ReadBarrierMark(W0)
-    //   ref <- W0
-    //
-    // we just use rX (the register containing `ref`) as input and output
-    // of a dedicated entrypoint:
-    //
-    //   rX <- ReadBarrierMarkRegX(rX)
-    //
-    if (entrypoint_.IsValid()) {
-      arm64_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this);
-      __ Blr(XRegisterFrom(entrypoint_));
-    } else {
-      // Entrypoint is not already loaded, load from the thread.
-      int32_t entry_point_offset =
-          CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArm64PointerSize>(ref_.reg());
-      // This runtime call does not require a stack map.
-      arm64_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this);
-    }
+    GenerateReadBarrierMarkRuntimeCall(codegen);
 
     // If the new reference is different from the old reference,
-    // update the field in the holder (`*(obj_ + field_offset_)`).
+    // update the field in the holder (`*(obj_ + field_offset)`).
     //
     // Note that this field could also hold a different object, if
     // another thread had concurrently changed it. In that case, the
     // LDXR/CMP/BNE sequence of instructions in the compare-and-set
     // (CAS) operation below would abort the CAS, leaving the field
     // as-is.
-    vixl::aarch64::Label done;
     __ Cmp(temp_.W(), ref_reg);
-    __ B(eq, &done);
+    __ B(eq, GetExitLabel());
 
     // Update the the holder's field atomically.  This may fail if
     // mutator updates before us, but it's OK.  This is achieved
@@ -850,7 +1044,7 @@
 
     // Convenience aliases.
     Register base = obj_.W();
-    Register offset = XRegisterFrom(field_offset_);
+    Register offset = XRegisterFrom(field_offset);
     Register expected = temp_.W();
     Register value = ref_reg;
     Register tmp_ptr = temps.AcquireX();    // Pointer to actual memory.
@@ -894,24 +1088,26 @@
       }
     }
 
-    __ Bind(&done);
     __ B(GetExitLabel());
   }
 
  private:
-  // The location (register) of the marked object reference.
-  const Location ref_;
   // The register containing the object holding the marked object reference field.
   const Register obj_;
-  // The location of the offset of the marked reference field within `obj_`.
-  Location field_offset_;
-
+  // The offset, index and scale factor to access the reference in `obj_`.
+  uint32_t offset_;
+  Location index_;
+  size_t scale_factor_;
+  // Is a null check required?
+  bool needs_null_check_;
+  // Should this reference load use Load-Acquire semantics?
+  bool use_load_acquire_;
+  // A temporary register used to hold the lock word of `obj_`; and
+  // also to hold the original reference value, when the reference is
+  // marked.
   const Register temp_;
 
-  // The location of the entrypoint if it is already loaded.
-  const Location entrypoint_;
-
-  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkAndUpdateFieldSlowPathARM64);
+  DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64);
 };
 
 // Slow path generating a read barrier for a heap reference.
@@ -2442,6 +2638,9 @@
                                                        LocationSummary::kNoCall);
   if (object_array_get_with_read_barrier && kUseBakerReadBarrier) {
     locations->SetCustomSlowPathCallerSaves(RegisterSet::Empty());  // No caller-save registers.
+    // We need a temporary register for the read barrier marking slow
+    // path in CodeGeneratorARM64::GenerateArrayLoadWithBakerReadBarrier.
+    locations->AddTemp(Location::RequiresRegister());
   }
   locations->SetInAt(0, Location::RequiresRegister());
   locations->SetInAt(1, Location::RegisterOrConstant(instruction->InputAt(1)));
@@ -2477,7 +2676,7 @@
 
   if (type == Primitive::kPrimNot && kEmitCompilerReadBarrier && kUseBakerReadBarrier) {
     // Object ArrayGet with Baker's read barrier case.
-    Register temp = temps.AcquireW();
+    Register temp = WRegisterFrom(locations->GetTemp(0));
     // Note that a potential implicit null check is handled in the
     // CodeGeneratorARM64::GenerateArrayLoadWithBakerReadBarrier call.
     codegen_->GenerateArrayLoadWithBakerReadBarrier(
@@ -5773,13 +5972,11 @@
   // `instruction->IsArrayGet()` => `!use_load_acquire`.
   DCHECK(!instruction->IsArrayGet() || !use_load_acquire);
 
-  // After loading the reference from `obj.field` into `ref`, query
-  // `art::Thread::Current()->GetIsGcMarking()` to decide whether we
-  // need to enter the slow path to mark the reference. This
-  // optimistic strategy (we expect the GC to not be marking most of
-  // the time) does not check `obj`'s lock word (to see if it is a
-  // gray object or not), so may sometimes mark an already marked
-  // object.
+  // Query `art::Thread::Current()->GetIsGcMarking()` to decide
+  // whether we need to enter the slow path to mark the reference.
+  // Then, in the slow path, check the gray bit in the lock word of
+  // the reference's holder (`obj`) to decide whether to mark `ref` or
+  // not.
   //
   // Note that we do not actually check the value of `GetIsGcMarking()`;
   // instead, we load into `temp2` the read barrier mark entry point
@@ -5787,10 +5984,17 @@
   // that `GetIsGcMarking()` is false, and vice versa.
   //
   //   temp2 = Thread::Current()->pReadBarrierMarkReg ## root.reg()
-  //   HeapReference<mirror::Object> ref = *src;  // Original reference load.
   //   if (temp2 != nullptr) {  // <=> Thread::Current()->GetIsGcMarking()
   //     // Slow path.
-  //     ref = temp2(ref);  // ref = ReadBarrier::Mark(ref);  // Runtime entry point call.
+  //     uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState();
+  //     lfence;  // Load fence or artificial data dependency to prevent load-load reordering
+  //     HeapReference<mirror::Object> ref = *src;  // Original reference load.
+  //     bool is_gray = (rb_state == ReadBarrier::GrayState());
+  //     if (is_gray) {
+  //       ref = temp2(ref);  // ref = ReadBarrier::Mark(ref);  // Runtime entry point call.
+  //     }
+  //   } else {
+  //     HeapReference<mirror::Object> ref = *src;  // Original reference load.
   //   }
 
   // Slow path marking the object `ref` when the GC is marking. The
@@ -5799,17 +6003,38 @@
   Location temp2_loc = LocationFrom(temp2);
   SlowPathCodeARM64* slow_path;
   if (always_update_field) {
-    // ReadBarrierMarkAndUpdateFieldSlowPathARM64 only supports
-    // address of the form `obj + field_offset`, where `obj` is a
-    // register and `field_offset` is a register. Thus `offset` and
-    // `scale_factor` above are expected to be null in this code path.
+    // LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64
+    // only supports address of the form `obj + field_offset`, where
+    // `obj` is a register and `field_offset` is a register. Thus
+    // `offset` and `scale_factor` above are expected to be null in
+    // this code path.
     DCHECK_EQ(offset, 0u);
     DCHECK_EQ(scale_factor, 0u);  /* "times 1" */
-    slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkAndUpdateFieldSlowPathARM64(
-        instruction, ref, obj, /* field_offset */ index, temp, /* entrypoint */ temp2_loc);
+    Location field_offset = index;
+    slow_path =
+        new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64(
+            instruction,
+            ref,
+            obj,
+            offset,
+            /* index */ field_offset,
+            scale_factor,
+            needs_null_check,
+            use_load_acquire,
+            temp,
+            /* entrypoint */ temp2_loc);
   } else {
-    slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkSlowPathARM64(
-        instruction, ref, /* entrypoint */ temp2_loc);
+    slow_path = new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierSlowPathARM64(
+        instruction,
+        ref,
+        obj,
+        offset,
+        index,
+        scale_factor,
+        needs_null_check,
+        use_load_acquire,
+        temp,
+        /* entrypoint */ temp2_loc);
   }
   AddSlowPath(slow_path);
 
@@ -5819,12 +6044,12 @@
   // Loading the entrypoint does not require a load acquire since it is only changed when
   // threads are suspended or running a checkpoint.
   __ Ldr(temp2, MemOperand(tr, entry_point_offset));
-  // The reference load.
-  GenerateRawReferenceLoad(
-      instruction, ref, obj, offset, index, scale_factor, needs_null_check, use_load_acquire);
   // The entrypoint is null when the GC is not marking, this prevents one load compared to
   // checking GetIsGcMarking.
   __ Cbnz(temp2, slow_path->GetEntryLabel());
+  // Fast path: just load the reference.
+  GenerateRawReferenceLoad(
+      instruction, ref, obj, offset, index, scale_factor, needs_null_check, use_load_acquire);
   __ Bind(slow_path->GetExitLabel());
 }
 
diff --git a/compiler/optimizing/code_generator_arm_vixl.cc b/compiler/optimizing/code_generator_arm_vixl.cc
index c92a056..5506f31 100644
--- a/compiler/optimizing/code_generator_arm_vixl.cc
+++ b/compiler/optimizing/code_generator_arm_vixl.cc
@@ -657,10 +657,75 @@
   DISALLOW_COPY_AND_ASSIGN(ArraySetSlowPathARMVIXL);
 };
 
+// Abstract base class for read barrier slow paths marking a reference
+// `ref`.
+//
+// Argument `entrypoint` must be a register location holding the read
+// barrier marking runtime entry point to be invoked.
+class ReadBarrierMarkSlowPathBaseARMVIXL : public SlowPathCodeARMVIXL {
+ protected:
+  ReadBarrierMarkSlowPathBaseARMVIXL(HInstruction* instruction, Location ref, Location entrypoint)
+      : SlowPathCodeARMVIXL(instruction), ref_(ref), entrypoint_(entrypoint) {
+    DCHECK(kEmitCompilerReadBarrier);
+  }
+
+  const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkSlowPathBaseARMVIXL"; }
+
+  // Generate assembly code calling the read barrier marking runtime
+  // entry point (ReadBarrierMarkRegX).
+  void GenerateReadBarrierMarkRuntimeCall(CodeGenerator* codegen) {
+    vixl32::Register ref_reg = RegisterFrom(ref_);
+
+    // No need to save live registers; it's taken care of by the
+    // entrypoint. Also, there is no need to update the stack mask,
+    // as this runtime call will not trigger a garbage collection.
+    CodeGeneratorARMVIXL* arm_codegen = down_cast<CodeGeneratorARMVIXL*>(codegen);
+    DCHECK(!ref_reg.Is(sp));
+    DCHECK(!ref_reg.Is(lr));
+    DCHECK(!ref_reg.Is(pc));
+    // IP is used internally by the ReadBarrierMarkRegX entry point
+    // as a temporary, it cannot be the entry point's input/output.
+    DCHECK(!ref_reg.Is(ip));
+    DCHECK(ref_reg.IsRegister()) << ref_reg;
+    // "Compact" slow path, saving two moves.
+    //
+    // Instead of using the standard runtime calling convention (input
+    // and output in R0):
+    //
+    //   R0 <- ref
+    //   R0 <- ReadBarrierMark(R0)
+    //   ref <- R0
+    //
+    // we just use rX (the register containing `ref`) as input and output
+    // of a dedicated entrypoint:
+    //
+    //   rX <- ReadBarrierMarkRegX(rX)
+    //
+    if (entrypoint_.IsValid()) {
+      arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this);
+      __ Blx(RegisterFrom(entrypoint_));
+    } else {
+      // Entrypoint is not already loaded, load from the thread.
+      int32_t entry_point_offset =
+          CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg.GetCode());
+      // This runtime call does not require a stack map.
+      arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this);
+    }
+  }
+
+  // The location (register) of the marked object reference.
+  const Location ref_;
+
+  // The location of the entrypoint if already loaded.
+  const Location entrypoint_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathBaseARMVIXL);
+};
+
 // Slow path marking an object reference `ref` during a read
 // barrier. The field `obj.field` in the object `obj` holding this
-// reference does not get updated by this slow path after marking (see
-// ReadBarrierMarkAndUpdateFieldSlowPathARM below for that).
+// reference does not get updated by this slow path after marking.
 //
 // This means that after the execution of this slow path, `ref` will
 // always be up-to-date, but `obj.field` may not; i.e., after the
@@ -671,13 +736,13 @@
 //
 // If `entrypoint` is a valid location it is assumed to already be
 // holding the entrypoint. The case where the entrypoint is passed in
-// when the decision to mark is based on whether the GC is marking.
-class ReadBarrierMarkSlowPathARMVIXL : public SlowPathCodeARMVIXL {
+// is when the decision to mark is based on whether the GC is marking.
+class ReadBarrierMarkSlowPathARMVIXL : public ReadBarrierMarkSlowPathBaseARMVIXL {
  public:
   ReadBarrierMarkSlowPathARMVIXL(HInstruction* instruction,
                                  Location ref,
                                  Location entrypoint = Location::NoLocation())
-      : SlowPathCodeARMVIXL(instruction), ref_(ref), entrypoint_(entrypoint) {
+      : ReadBarrierMarkSlowPathBaseARMVIXL(instruction, ref, entrypoint) {
     DCHECK(kEmitCompilerReadBarrier);
   }
 
@@ -685,6 +750,67 @@
 
   void EmitNativeCode(CodeGenerator* codegen) OVERRIDE {
     LocationSummary* locations = instruction_->GetLocations();
+    DCHECK(locations->CanCall());
+    DCHECK(ref_.IsRegister()) << ref_;
+    DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_.reg())) << ref_.reg();
+    DCHECK(instruction_->IsLoadClass() || instruction_->IsLoadString())
+        << "Unexpected instruction in read barrier marking slow path: "
+        << instruction_->DebugName();
+
+    __ Bind(GetEntryLabel());
+    GenerateReadBarrierMarkRuntimeCall(codegen);
+    __ B(GetExitLabel());
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARMVIXL);
+};
+
+// Slow path loading `obj`'s lock word, loading a reference from
+// object `*(obj + offset + (index << scale_factor))` into `ref`, and
+// marking `ref` if `obj` is gray according to the lock word (Baker
+// read barrier). The field `obj.field` in the object `obj` holding
+// this reference does not get updated by this slow path after marking
+// (see LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL
+// below for that).
+//
+// This means that after the execution of this slow path, `ref` will
+// always be up-to-date, but `obj.field` may not; i.e., after the
+// flip, `ref` will be a to-space reference, but `obj.field` will
+// probably still be a from-space reference (unless it gets updated by
+// another thread, or if another thread installed another object
+// reference (different from `ref`) in `obj.field`).
+//
+// Argument `entrypoint` must be a register location holding the read
+// barrier marking runtime entry point to be invoked.
+class LoadReferenceWithBakerReadBarrierSlowPathARMVIXL : public ReadBarrierMarkSlowPathBaseARMVIXL {
+ public:
+  LoadReferenceWithBakerReadBarrierSlowPathARMVIXL(HInstruction* instruction,
+                                                   Location ref,
+                                                   vixl32::Register obj,
+                                                   uint32_t offset,
+                                                   Location index,
+                                                   ScaleFactor scale_factor,
+                                                   bool needs_null_check,
+                                                   vixl32::Register temp,
+                                                   Location entrypoint)
+      : ReadBarrierMarkSlowPathBaseARMVIXL(instruction, ref, entrypoint),
+        obj_(obj),
+        offset_(offset),
+        index_(index),
+        scale_factor_(scale_factor),
+        needs_null_check_(needs_null_check),
+        temp_(temp) {
+    DCHECK(kEmitCompilerReadBarrier);
+    DCHECK(kUseBakerReadBarrier);
+  }
+
+  const char* GetDescription() const OVERRIDE {
+    return "LoadReferenceWithBakerReadBarrierSlowPathARMVIXL";
+  }
+
+  void EmitNativeCode(CodeGenerator* codegen) OVERRIDE {
+    LocationSummary* locations = instruction_->GetLocations();
     vixl32::Register ref_reg = RegisterFrom(ref_);
     DCHECK(locations->CanCall());
     DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg.GetCode())) << ref_reg;
@@ -692,8 +818,6 @@
            instruction_->IsStaticFieldGet() ||
            instruction_->IsArrayGet() ||
            instruction_->IsArraySet() ||
-           instruction_->IsLoadClass() ||
-           instruction_->IsLoadString() ||
            instruction_->IsInstanceOf() ||
            instruction_->IsCheckCast() ||
            (instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()) ||
@@ -706,90 +830,133 @@
     DCHECK(!(instruction_->IsArrayGet() &&
              instruction_->AsArrayGet()->GetArray()->IsIntermediateAddress()));
 
+    // Temporary register `temp_`, used to store the lock word, must
+    // not be IP, as we may use it to emit the reference load (in the
+    // call to GenerateRawReferenceLoad below), and we need the lock
+    // word to still be in `temp_` after the reference load.
+    DCHECK(!temp_.Is(ip));
+
     __ Bind(GetEntryLabel());
-    // No need to save live registers; it's taken care of by the
-    // entrypoint. Also, there is no need to update the stack mask,
-    // as this runtime call will not trigger a garbage collection.
+
+    // When using MaybeGenerateReadBarrierSlow, the read barrier call is
+    // inserted after the original load. However, in fast path based
+    // Baker's read barriers, we need to perform the load of
+    // mirror::Object::monitor_ *before* the original reference load.
+    // This load-load ordering is required by the read barrier.
+    // The fast path/slow path (for Baker's algorithm) should look like:
+    //
+    //   uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState();
+    //   lfence;  // Load fence or artificial data dependency to prevent load-load reordering
+    //   HeapReference<mirror::Object> ref = *src;  // Original reference load.
+    //   bool is_gray = (rb_state == ReadBarrier::GrayState());
+    //   if (is_gray) {
+    //     ref = entrypoint(ref);  // ref = ReadBarrier::Mark(ref);  // Runtime entry point call.
+    //   }
+    //
+    // Note: the original implementation in ReadBarrier::Barrier is
+    // slightly more complex as it performs additional checks that we do
+    // not do here for performance reasons.
+
     CodeGeneratorARMVIXL* arm_codegen = down_cast<CodeGeneratorARMVIXL*>(codegen);
-    DCHECK(!ref_reg.Is(sp));
-    DCHECK(!ref_reg.Is(lr));
-    DCHECK(!ref_reg.Is(pc));
-    // IP is used internally by the ReadBarrierMarkRegX entry point
-    // as a temporary, it cannot be the entry point's input/output.
-    DCHECK(!ref_reg.Is(ip));
-    DCHECK(ref_reg.IsRegister()) << ref_reg;
-    // "Compact" slow path, saving two moves.
-    //
-    // Instead of using the standard runtime calling convention (input
-    // and output in R0):
-    //
-    //   R0 <- ref
-    //   R0 <- ReadBarrierMark(R0)
-    //   ref <- R0
-    //
-    // we just use rX (the register containing `ref`) as input and output
-    // of a dedicated entrypoint:
-    //
-    //   rX <- ReadBarrierMarkRegX(rX)
-    //
-    if (entrypoint_.IsValid()) {
-      arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this);
-      __ Blx(RegisterFrom(entrypoint_));
-    } else {
-      // Entrypoint is not already loaded, load from the thread.
-      int32_t entry_point_offset =
-          CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg.GetCode());
-      // This runtime call does not require a stack map.
-      arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this);
+
+    // /* int32_t */ monitor = obj->monitor_
+    uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value();
+    arm_codegen->GetAssembler()->LoadFromOffset(kLoadWord, temp_, obj_, monitor_offset);
+    if (needs_null_check_) {
+      codegen->MaybeRecordImplicitNullCheck(instruction_);
     }
+    // /* LockWord */ lock_word = LockWord(monitor)
+    static_assert(sizeof(LockWord) == sizeof(int32_t),
+                  "art::LockWord and int32_t have different sizes.");
+
+    // Introduce a dependency on the lock_word including the rb_state,
+    // which shall prevent load-load reordering without using
+    // a memory barrier (which would be more expensive).
+    // `obj` is unchanged by this operation, but its value now depends
+    // on `temp`.
+    __ Add(obj_, obj_, Operand(temp_, ShiftType::LSR, 32));
+
+    // The actual reference load.
+    // A possible implicit null check has already been handled above.
+    arm_codegen->GenerateRawReferenceLoad(
+        instruction_, ref_, obj_, offset_, index_, scale_factor_, /* needs_null_check */ false);
+
+    // Mark the object `ref` when `obj` is gray.
+    //
+    //   if (rb_state == ReadBarrier::GrayState())
+    //     ref = ReadBarrier::Mark(ref);
+    //
+    // Given the numeric representation, it's enough to check the low bit of the
+    // rb_state. We do that by shifting the bit out of the lock word with LSRS
+    // which can be a 16-bit instruction unlike the TST immediate.
+    static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0");
+    static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1");
+    __ Lsrs(temp_, temp_, LockWord::kReadBarrierStateShift + 1);
+    __ B(cc, GetExitLabel());  // Carry flag is the last bit shifted out by LSRS.
+    GenerateReadBarrierMarkRuntimeCall(codegen);
+
     __ B(GetExitLabel());
   }
 
  private:
-  // The location (register) of the marked object reference.
-  const Location ref_;
+  // The register containing the object holding the marked object reference field.
+  vixl32::Register obj_;
+  // The offset, index and scale factor to access the reference in `obj_`.
+  uint32_t offset_;
+  Location index_;
+  ScaleFactor scale_factor_;
+  // Is a null check required?
+  bool needs_null_check_;
+  // A temporary register used to hold the lock word of `obj_`.
+  vixl32::Register temp_;
 
-  // The location of the entrypoint if already loaded.
-  const Location entrypoint_;
-
-  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARMVIXL);
+  DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierSlowPathARMVIXL);
 };
 
-// Slow path marking an object reference `ref` during a read barrier,
-// and if needed, atomically updating the field `obj.field` in the
-// object `obj` holding this reference after marking (contrary to
-// ReadBarrierMarkSlowPathARM above, which never tries to update
-// `obj.field`).
+// Slow path loading `obj`'s lock word, loading a reference from
+// object `*(obj + offset + (index << scale_factor))` into `ref`, and
+// marking `ref` if `obj` is gray according to the lock word (Baker
+// read barrier). If needed, this slow path also atomically updates
+// the field `obj.field` in the object `obj` holding this reference
+// after marking (contrary to
+// LoadReferenceWithBakerReadBarrierSlowPathARMVIXL above, which never
+// tries to update `obj.field`).
 //
 // This means that after the execution of this slow path, both `ref`
 // and `obj.field` will be up-to-date; i.e., after the flip, both will
 // hold the same to-space reference (unless another thread installed
 // another object reference (different from `ref`) in `obj.field`).
 //
-// If `entrypoint` is a valid location it is assumed to already be
-// holding the entrypoint. The case where the entrypoint is passed in
-// when the decision to mark is based on whether the GC is marking.
-class ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL : public SlowPathCodeARMVIXL {
+//
+// Argument `entrypoint` must be a register location holding the read
+// barrier marking runtime entry point to be invoked.
+class LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL
+    : public ReadBarrierMarkSlowPathBaseARMVIXL {
  public:
-  ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL(HInstruction* instruction,
-                                               Location ref,
-                                               vixl32::Register obj,
-                                               Location field_offset,
-                                               vixl32::Register temp1,
-                                               vixl32::Register temp2,
-                                               Location entrypoint = Location::NoLocation())
-      : SlowPathCodeARMVIXL(instruction),
-        ref_(ref),
+  LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL(HInstruction* instruction,
+                                                                 Location ref,
+                                                                 vixl32::Register obj,
+                                                                 uint32_t offset,
+                                                                 Location index,
+                                                                 ScaleFactor scale_factor,
+                                                                 bool needs_null_check,
+                                                                 vixl32::Register temp1,
+                                                                 vixl32::Register temp2,
+                                                                 Location entrypoint)
+      : ReadBarrierMarkSlowPathBaseARMVIXL(instruction, ref, entrypoint),
         obj_(obj),
-        field_offset_(field_offset),
+        offset_(offset),
+        index_(index),
+        scale_factor_(scale_factor),
+        needs_null_check_(needs_null_check),
         temp1_(temp1),
-        temp2_(temp2),
-        entrypoint_(entrypoint) {
+        temp2_(temp2) {
     DCHECK(kEmitCompilerReadBarrier);
+    DCHECK(kUseBakerReadBarrier);
   }
 
   const char* GetDescription() const OVERRIDE {
-    return "ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL";
+    return "LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL";
   }
 
   void EmitNativeCode(CodeGenerator* codegen) OVERRIDE {
@@ -797,70 +964,83 @@
     vixl32::Register ref_reg = RegisterFrom(ref_);
     DCHECK(locations->CanCall());
     DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg.GetCode())) << ref_reg;
-    // This slow path is only used by the UnsafeCASObject intrinsic.
+    DCHECK_NE(ref_.reg(), LocationFrom(temp1_).reg());
+
+    // This slow path is only used by the UnsafeCASObject intrinsic at the moment.
     DCHECK((instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()))
         << "Unexpected instruction in read barrier marking and field updating slow path: "
         << instruction_->DebugName();
     DCHECK(instruction_->GetLocations()->Intrinsified());
     DCHECK_EQ(instruction_->AsInvoke()->GetIntrinsic(), Intrinsics::kUnsafeCASObject);
-    DCHECK(field_offset_.IsRegisterPair()) << field_offset_;
+    DCHECK_EQ(offset_, 0u);
+    DCHECK_EQ(scale_factor_, ScaleFactor::TIMES_1);
+    Location field_offset = index_;
+    DCHECK(field_offset.IsRegisterPair()) << field_offset;
+
+    // Temporary register `temp1_`, used to store the lock word, must
+    // not be IP, as we may use it to emit the reference load (in the
+    // call to GenerateRawReferenceLoad below), and we need the lock
+    // word to still be in `temp1_` after the reference load.
+    DCHECK(!temp1_.Is(ip));
 
     __ Bind(GetEntryLabel());
 
-    // Save the old reference.
+    CodeGeneratorARMVIXL* arm_codegen = down_cast<CodeGeneratorARMVIXL*>(codegen);
+
+    // /* int32_t */ monitor = obj->monitor_
+    uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value();
+    arm_codegen->GetAssembler()->LoadFromOffset(kLoadWord, temp1_, obj_, monitor_offset);
+    if (needs_null_check_) {
+      codegen->MaybeRecordImplicitNullCheck(instruction_);
+    }
+    // /* LockWord */ lock_word = LockWord(monitor)
+    static_assert(sizeof(LockWord) == sizeof(int32_t),
+                  "art::LockWord and int32_t have different sizes.");
+
+    // Introduce a dependency on the lock_word including the rb_state,
+    // which shall prevent load-load reordering without using
+    // a memory barrier (which would be more expensive).
+    // `obj` is unchanged by this operation, but its value now depends
+    // on `temp`.
+    __ Add(obj_, obj_, Operand(temp1_, ShiftType::LSR, 32));
+
+    // The actual reference load.
+    // A possible implicit null check has already been handled above.
+    arm_codegen->GenerateRawReferenceLoad(
+        instruction_, ref_, obj_, offset_, index_, scale_factor_, /* needs_null_check */ false);
+
+    // Mark the object `ref` when `obj` is gray.
+    //
+    //   if (rb_state == ReadBarrier::GrayState())
+    //     ref = ReadBarrier::Mark(ref);
+    //
+    // Given the numeric representation, it's enough to check the low bit of the
+    // rb_state. We do that by shifting the bit out of the lock word with LSRS
+    // which can be a 16-bit instruction unlike the TST immediate.
+    static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0");
+    static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1");
+    __ Lsrs(temp1_, temp1_, LockWord::kReadBarrierStateShift + 1);
+    __ B(cc, GetExitLabel());  // Carry flag is the last bit shifted out by LSRS.
+
+    // Save the old value of the reference before marking it.
     // Note that we cannot use IP to save the old reference, as IP is
     // used internally by the ReadBarrierMarkRegX entry point, and we
     // need the old reference after the call to that entry point.
     DCHECK(!temp1_.Is(ip));
     __ Mov(temp1_, ref_reg);
 
-    // No need to save live registers; it's taken care of by the
-    // entrypoint. Also, there is no need to update the stack mask,
-    // as this runtime call will not trigger a garbage collection.
-    CodeGeneratorARMVIXL* arm_codegen = down_cast<CodeGeneratorARMVIXL*>(codegen);
-    DCHECK(!ref_reg.Is(sp));
-    DCHECK(!ref_reg.Is(lr));
-    DCHECK(!ref_reg.Is(pc));
-    // IP is used internally by the ReadBarrierMarkRegX entry point
-    // as a temporary, it cannot be the entry point's input/output.
-    DCHECK(!ref_reg.Is(ip));
-    DCHECK(ref_reg.IsRegister()) << ref_reg;
-    // "Compact" slow path, saving two moves.
-    //
-    // Instead of using the standard runtime calling convention (input
-    // and output in R0):
-    //
-    //   R0 <- ref
-    //   R0 <- ReadBarrierMark(R0)
-    //   ref <- R0
-    //
-    // we just use rX (the register containing `ref`) as input and output
-    // of a dedicated entrypoint:
-    //
-    //   rX <- ReadBarrierMarkRegX(rX)
-    //
-    if (entrypoint_.IsValid()) {
-      arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this);
-      __ Blx(RegisterFrom(entrypoint_));
-    } else {
-      // Entrypoint is not already loaded, load from the thread.
-      int32_t entry_point_offset =
-          CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg.GetCode());
-      // This runtime call does not require a stack map.
-      arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this);
-    }
+    GenerateReadBarrierMarkRuntimeCall(codegen);
 
     // If the new reference is different from the old reference,
-    // update the field in the holder (`*(obj_ + field_offset_)`).
+    // update the field in the holder (`*(obj_ + field_offset)`).
     //
     // Note that this field could also hold a different object, if
     // another thread had concurrently changed it. In that case, the
     // LDREX/SUBS/ITNE sequence of instructions in the compare-and-set
     // (CAS) operation below would abort the CAS, leaving the field
     // as-is.
-    vixl32::Label done;
     __ Cmp(temp1_, ref_reg);
-    __ B(eq, &done, /* far_target */ false);
+    __ B(eq, GetExitLabel());
 
     // Update the the holder's field atomically.  This may fail if
     // mutator updates before us, but it's OK.  This is achieved
@@ -874,7 +1054,7 @@
     // The UnsafeCASObject intrinsic uses a register pair as field
     // offset ("long offset"), of which only the low part contains
     // data.
-    vixl32::Register offset = LowRegisterFrom(field_offset_);
+    vixl32::Register offset = LowRegisterFrom(field_offset);
     vixl32::Register expected = temp1_;
     vixl32::Register value = ref_reg;
     vixl32::Register tmp_ptr = temps.Acquire();       // Pointer to actual memory.
@@ -930,25 +1110,27 @@
       }
     }
 
-    __ Bind(&done);
     __ B(GetExitLabel());
   }
 
  private:
-  // The location (register) of the marked object reference.
-  const Location ref_;
   // The register containing the object holding the marked object reference field.
   const vixl32::Register obj_;
-  // The location of the offset of the marked reference field within `obj_`.
-  Location field_offset_;
-
+  // The offset, index and scale factor to access the reference in `obj_`.
+  uint32_t offset_;
+  Location index_;
+  ScaleFactor scale_factor_;
+  // Is a null check required?
+  bool needs_null_check_;
+  // A temporary register used to hold the lock word of `obj_`; and
+  // also to hold the original reference value, when the reference is
+  // marked.
   const vixl32::Register temp1_;
+  // A temporary register used in the implementation of the CAS, to
+  // update the object's reference field.
   const vixl32::Register temp2_;
 
-  // The location of the entrypoint if already loaded.
-  const Location entrypoint_;
-
-  DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL);
+  DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL);
 };
 
 // Slow path generating a read barrier for a heap reference.
@@ -7392,13 +7574,11 @@
   DCHECK(kEmitCompilerReadBarrier);
   DCHECK(kUseBakerReadBarrier);
 
-  // After loading the reference from `obj.field` into `ref`, query
-  // `art::Thread::Current()->GetIsGcMarking()` to decide whether we
-  // need to enter the slow path to mark the reference. This
-  // optimistic strategy (we expect the GC to not be marking most of
-  // the time) does not check `obj`'s lock word (to see if it is a
-  // gray object or not), so may sometimes mark an already marked
-  // object.
+  // Query `art::Thread::Current()->GetIsGcMarking()` to decide
+  // whether we need to enter the slow path to mark the reference.
+  // Then, in the slow path, check the gray bit in the lock word of
+  // the reference's holder (`obj`) to decide whether to mark `ref` or
+  // not.
   //
   // Note that we do not actually check the value of `GetIsGcMarking()`;
   // instead, we load into `temp3` the read barrier mark entry point
@@ -7406,14 +7586,19 @@
   // that `GetIsGcMarking()` is false, and vice versa.
   //
   //   temp3 = Thread::Current()->pReadBarrierMarkReg ## root.reg()
-  //   HeapReference<mirror::Object> ref = *src;  // Original reference load.
   //   if (temp3 != nullptr) {  // <=> Thread::Current()->GetIsGcMarking()
   //     // Slow path.
-  //     ref = temp3(ref);  // ref = ReadBarrier::Mark(ref);  // Runtime entry point call.
+  //     uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState();
+  //     lfence;  // Load fence or artificial data dependency to prevent load-load reordering
+  //     HeapReference<mirror::Object> ref = *src;  // Original reference load.
+  //     bool is_gray = (rb_state == ReadBarrier::GrayState());
+  //     if (is_gray) {
+  //       ref = temp3(ref);  // ref = ReadBarrier::Mark(ref);  // Runtime entry point call.
+  //     }
+  //   } else {
+  //     HeapReference<mirror::Object> ref = *src;  // Original reference load.
   //   }
 
-  // TODO: This temp register is only necessary when
-  // `always_update_field` is true; make it optional (like `temp2`).
   vixl32::Register temp_reg = RegisterFrom(temp);
 
   // Slow path marking the object `ref` when the GC is marking. The
@@ -7422,18 +7607,37 @@
   SlowPathCodeARMVIXL* slow_path;
   if (always_update_field) {
     DCHECK(temp2 != nullptr);
-    // ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL only supports address
-    // of the form `obj + field_offset`, where `obj` is a register and
-    // `field_offset` is a register pair (of which only the lower half
-    // is used). Thus `offset` and `scale_factor` above are expected
-    // to be null in this code path.
+    // LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL
+    // only supports address of the form `obj + field_offset`, where
+    // `obj` is a register and `field_offset` is a register pair (of
+    // which only the lower half is used). Thus `offset` and
+    // `scale_factor` above are expected to be null in this code path.
     DCHECK_EQ(offset, 0u);
     DCHECK_EQ(scale_factor, ScaleFactor::TIMES_1);
-    slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL(
-        instruction, ref, obj, /* field_offset */ index, temp_reg, *temp2, /* entrypoint */ temp3);
+    Location field_offset = index;
+    slow_path =
+        new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL(
+            instruction,
+            ref,
+            obj,
+            offset,
+            /* index */ field_offset,
+            scale_factor,
+            needs_null_check,
+            temp_reg,
+            *temp2,
+            /* entrypoint */ temp3);
   } else {
-    slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkSlowPathARMVIXL(
-        instruction, ref, /* entrypoint */ temp3);
+    slow_path = new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierSlowPathARMVIXL(
+        instruction,
+        ref,
+        obj,
+        offset,
+        index,
+        scale_factor,
+        needs_null_check,
+        temp_reg,
+        /* entrypoint */ temp3);
   }
   AddSlowPath(slow_path);
 
@@ -7443,11 +7647,11 @@
   // Loading the entrypoint does not require a load acquire since it is only changed when
   // threads are suspended or running a checkpoint.
   GetAssembler()->LoadFromOffset(kLoadWord, RegisterFrom(temp3), tr, entry_point_offset);
-  // The reference load.
-  GenerateRawReferenceLoad(instruction, ref, obj, offset, index, scale_factor, needs_null_check);
   // The entrypoint is null when the GC is not marking, this prevents one load compared to
   // checking GetIsGcMarking.
   __ CompareAndBranchIfNonZero(RegisterFrom(temp3), slow_path->GetEntryLabel());
+  // Fast path: just load the reference.
+  GenerateRawReferenceLoad(instruction, ref, obj, offset, index, scale_factor, needs_null_check);
   __ Bind(slow_path->GetExitLabel());
 }
 
diff --git a/compiler/optimizing/intrinsics_arm64.cc b/compiler/optimizing/intrinsics_arm64.cc
index 46751bf..934ba1b 100644
--- a/compiler/optimizing/intrinsics_arm64.cc
+++ b/compiler/optimizing/intrinsics_arm64.cc
@@ -853,7 +853,6 @@
   DCHECK((type == Primitive::kPrimInt) ||
          (type == Primitive::kPrimLong) ||
          (type == Primitive::kPrimNot));
-  MacroAssembler* masm = codegen->GetVIXLAssembler();
   Location base_loc = locations->InAt(1);
   Register base = WRegisterFrom(base_loc);      // Object pointer.
   Location offset_loc = locations->InAt(2);
@@ -863,8 +862,7 @@
 
   if (type == Primitive::kPrimNot && kEmitCompilerReadBarrier && kUseBakerReadBarrier) {
     // UnsafeGetObject/UnsafeGetObjectVolatile with Baker's read barrier case.
-    UseScratchRegisterScope temps(masm);
-    Register temp = temps.AcquireW();
+    Register temp = WRegisterFrom(locations->GetTemp(0));
     codegen->GenerateReferenceLoadWithBakerReadBarrier(invoke,
                                                        trg_loc,
                                                        base,
@@ -901,6 +899,9 @@
                                                            kIntrinsified);
   if (can_call && kUseBakerReadBarrier) {
     locations->SetCustomSlowPathCallerSaves(RegisterSet::Empty());  // No caller-save registers.
+    // We need a temporary register for the read barrier marking slow
+    // path in CodeGeneratorARM64::GenerateReferenceLoadWithBakerReadBarrier.
+    locations->AddTemp(Location::RequiresRegister());
   }
   locations->SetInAt(0, Location::NoLocation());        // Unused receiver.
   locations->SetInAt(1, Location::RequiresRegister());
@@ -2381,9 +2382,14 @@
     // Temporary register IP0, obtained from the VIXL scratch register
     // pool, cannot be used in ReadBarrierSystemArrayCopySlowPathARM64
     // (because that register is clobbered by ReadBarrierMarkRegX
-    // entry points). Get an extra temporary register from the
-    // register allocator.
+    // entry points). It cannot be used in calls to
+    // CodeGeneratorARM64::GenerateFieldLoadWithBakerReadBarrier
+    // either. For these reasons, get a third extra temporary register
+    // from the register allocator.
     locations->AddTemp(Location::RequiresRegister());
+  } else {
+    // Cases other than Baker read barriers: the third temporary will
+    // be acquired from the VIXL scratch register pool.
   }
 }
 
@@ -2494,11 +2500,12 @@
     // We use a block to end the scratch scope before the write barrier, thus
     // freeing the temporary registers so they can be used in `MarkGCCard`.
     UseScratchRegisterScope temps(masm);
-    // Note: Because it is acquired from VIXL's scratch register pool,
-    // `temp3` might be IP0, and thus cannot be used as `ref` argument
-    // of CodeGeneratorARM64::GenerateFieldLoadWithBakerReadBarrier
-    // calls below (see ReadBarrierMarkSlowPathARM64 for more details).
-    Register temp3 = temps.AcquireW();
+    Register temp3;
+    if (kEmitCompilerReadBarrier && kUseBakerReadBarrier) {
+      temp3 = WRegisterFrom(locations->GetTemp(2));
+    } else {
+      temp3 = temps.AcquireW();
+    }
 
     if (!optimizations.GetDoesNotNeedTypeCheck()) {
       // Check whether all elements of the source array are assignable to the component
@@ -2704,19 +2711,7 @@
 
     Register src_curr_addr = temp1.X();
     Register dst_curr_addr = temp2.X();
-    Register src_stop_addr;
-    if (kEmitCompilerReadBarrier && kUseBakerReadBarrier) {
-      // Temporary register IP0, obtained from the VIXL scratch
-      // register pool as `temp3`, cannot be used in
-      // ReadBarrierSystemArrayCopySlowPathARM64 (because that
-      // register is clobbered by ReadBarrierMarkRegX entry points).
-      // So another temporary register allocated by the register
-      // allocator instead.
-      DCHECK_EQ(LocationFrom(temp3).reg(), IP0);
-      src_stop_addr = XRegisterFrom(locations->GetTemp(2));
-    } else {
-      src_stop_addr = temp3.X();
-    }
+    Register src_stop_addr = temp3.X();
 
     GenSystemArrayCopyAddresses(masm,
                                 Primitive::kPrimNot,
@@ -2760,10 +2755,11 @@
       __ Cmp(src_curr_addr, src_stop_addr);
       __ B(&done, eq);
 
-      Register tmp = temps.AcquireW();
       // Make sure `tmp` is not IP0, as it is clobbered by
       // ReadBarrierMarkRegX entry points in
       // ReadBarrierSystemArrayCopySlowPathARM64.
+      temps.Exclude(ip0);
+      Register tmp = temps.AcquireW();
       DCHECK_NE(LocationFrom(tmp).reg(), IP0);
 
       // /* int32_t */ monitor = src->monitor_