Moves the top_ and end_ words of the Scavenger into mutator thread.

runtime/vm/assembler_arm64.cc

Index: runtime/vm/assembler_arm64.cc
diff --git a/runtime/vm/assembler_arm64.cc b/runtime/vm/assembler_arm64.cc
index 9b9b1b134fff4ac5fb2ab672c8cb8eb1f79a91c4..bd5d8cf3bc36a3b483d49482aeae57a3a6f403b5 100644
--- a/runtime/vm/assembler_arm64.cc
+++ b/runtime/vm/assembler_arm64.cc
@@ -1260,21 +1260,20 @@ void Assembler::TryAllocate(const Class& cls,
     // allocation call site.
     NOT_IN_PRODUCT(MaybeTraceAllocation(cls.id(), temp_reg, failure));
     const intptr_t instance_size = cls.instance_size();
-    Heap::Space space = Heap::kNew;
-    ldr(temp_reg, Address(THR, Thread::heap_offset()));
-    ldr(instance_reg, Address(temp_reg, Heap::TopOffset(space)));
+    NOT_IN_PRODUCT(Heap::Space space = Heap::kNew);
+    ldr(instance_reg, Address(THR, Thread::top_offset()));
     // TODO(koda): Protect against unsigned overflow here.
     AddImmediateSetFlags(instance_reg, instance_reg, instance_size);
 
     // instance_reg: potential next object start.
-    ldr(TMP, Address(temp_reg, Heap::EndOffset(space)));
+    ldr(TMP, Address(THR, Thread::end_offset()));
     CompareRegisters(TMP, instance_reg);
     // fail if heap end unsigned less than or equal to instance_reg.
     b(failure, LS);
 
     // Successfully allocated the object, now update top to point to
     // next object start and store the class in the class field of object.
-    str(instance_reg, Address(temp_reg, Heap::TopOffset(space)));
+    str(instance_reg, Address(THR, Thread::top_offset()));
 
     ASSERT(instance_size >= kHeapObjectTag);
     AddImmediate(instance_reg, -instance_size + kHeapObjectTag);
@@ -1305,23 +1304,22 @@ void Assembler::TryAllocateArray(intptr_t cid,
     // (i.e. the allocation stub) which will allocate the object and trace the
     // allocation call site.
     NOT_IN_PRODUCT(MaybeTraceAllocation(cid, temp1, failure));
-    Heap::Space space = Heap::kNew;
-    ldr(temp1, Address(THR, Thread::heap_offset()));
+    NOT_IN_PRODUCT(Heap::Space space = Heap::kNew);
     // Potential new object start.
-    ldr(instance, Address(temp1, Heap::TopOffset(space)));
+    ldr(instance, Address(THR, Thread::top_offset()));
     AddImmediateSetFlags(end_address, instance, instance_size);
     b(failure, CS);  // Fail on unsigned overflow.
 
     // Check if the allocation fits into the remaining space.
     // instance: potential new object start.
     // end_address: potential next object start.
-    ldr(temp2, Address(temp1, Heap::EndOffset(space)));
+    ldr(temp2, Address(THR, Thread::end_offset()));
     cmp(end_address, Operand(temp2));
     b(failure, CS);
 
     // Successfully allocated the object(s), now update top to point to
     // next object start and initialize the object.
-    str(end_address, Address(temp1, Heap::TopOffset(space)));
+    str(end_address, Address(THR, Thread::top_offset()));
     add(instance, instance, Operand(kHeapObjectTag));
     LoadImmediate(temp2, instance_size);
     NOT_IN_PRODUCT(UpdateAllocationStatsWithSize(cid, temp2, space));