Enable concurrent sweep on MIPS and ARM64.

runtime/vm/stub_code_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 1022 matching lines @@
   __ tsti(TMP, Immediate(1 << RawObject::kRememberedBit));
   __ b(&add_to_buffer, EQ);
   __ ret();
 
   __ Bind(&add_to_buffer);
   // Save values being destroyed.
   __ Push(R1);
   __ Push(R2);
   __ Push(R3);
 
-  __ orri(R2, TMP, Immediate(1 << RawObject::kRememberedBit));
-  __ StoreFieldToOffset(R2, R0, Object::tags_offset());
+  // Atomically set the remembered bit of the object header.
+  ASSERT(Object::tags_offset() == 0);
+  __ sub(R3, R0, Operand(kHeapObjectTag));
+  // R3: Untagged address of header word (ldxr/stxr do not support offsets).
+  Label retry;
+  __ Bind(&retry);
+  __ ldxr(R2, R3);
+  __ orri(R2, R2, Immediate(1 << RawObject::kRememberedBit));
+  __ stxr(R1, R2, R3);
+  __ cmp(R1, Operand(1));
+  __ b(&retry, EQ);
 
   // Load the StoreBuffer block out of the thread. Then load top_ out of the
   // StoreBufferBlock and add the address to the pointers_.
   __ LoadFromOffset(R1, THR, Thread::store_buffer_block_offset());
   __ LoadFromOffset(R2, R1, StoreBufferBlock::top_offset(), kUnsignedWord);
   __ add(R3, R1, Operand(R2, LSL, 3));
   __ StoreToOffset(R0, R3, StoreBufferBlock::pointers_offset());
 
   // Increment top_ and check for overflow.
   // R2: top_.
@@ skipping 1130 matching lines @@
   __ Bind(&miss);
   __ LoadIsolate(R2);
   __ ldr(CODE_REG, Address(R2, Isolate::ic_miss_code_offset()));
   __ ldr(R1, FieldAddress(CODE_REG, Code::entry_point_offset()));
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64