Skip write barriers in the fast case when setting up local context.

src/arm64/full-codegen-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "v8.h"
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "code-stubs.h"
 #include "codegen.h"
@@ skipping 193 matching lines @@
       }
     }
   }
 
   bool function_in_register_x1 = true;
 
   int heap_slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
   if (heap_slots > 0) {
     // Argument to NewContext is the function, which is still in x1.
     Comment cmnt(masm_, "[ Allocate context");
+    bool need_write_barrier = true;
     if (FLAG_harmony_scoping && info->scope()->is_global_scope()) {
       __ Mov(x10, Operand(info->scope()->GetScopeInfo()));
       __ Push(x1, x10);
       __ CallRuntime(Runtime::kHiddenNewGlobalContext, 2);
     } else if (heap_slots <= FastNewContextStub::kMaximumSlots) {
       FastNewContextStub stub(isolate(), heap_slots);
       __ CallStub(&stub);
+      // Result of FastNewContextStub is always in new space.
+      need_write_barrier = false;
     } else {
       __ Push(x1);
       __ CallRuntime(Runtime::kHiddenNewFunctionContext, 1);
     }
     function_in_register_x1 = false;
     // Context is returned in x0.  It replaces the context passed to us.
     // It's saved in the stack and kept live in cp.
     __ Mov(cp, x0);
     __ Str(x0, MemOperand(fp, StandardFrameConstants::kContextOffset));
     // Copy any necessary parameters into the context.
     int num_parameters = info->scope()->num_parameters();
     for (int i = 0; i < num_parameters; i++) {
       Variable* var = scope()->parameter(i);
       if (var->IsContextSlot()) {
         int parameter_offset = StandardFrameConstants::kCallerSPOffset +
             (num_parameters - 1 - i) * kPointerSize;
         // Load parameter from stack.
         __ Ldr(x10, MemOperand(fp, parameter_offset));
         // Store it in the context.
         MemOperand target = ContextMemOperand(cp, var->index());
         __ Str(x10, target);
 
         // Update the write barrier.
-        __ RecordWriteContextSlot(
-            cp, target.offset(), x10, x11, kLRHasBeenSaved, kDontSaveFPRegs);
+        if (need_write_barrier) {
+          __ RecordWriteContextSlot(
+              cp, target.offset(), x10, x11, kLRHasBeenSaved, kDontSaveFPRegs);
+        } else if (FLAG_debug_code) {
+          Label done;
+          __ JumpIfInNewSpace(cp, &done);
+          __ Abort(kExpectedNewSpaceObject);
+          __ bind(&done);
+        }
       }
     }
   }
 
   Variable* arguments = scope()->arguments();
   if (arguments != NULL) {
     // Function uses arguments object.
     Comment cmnt(masm_, "[ Allocate arguments object");
     if (!function_in_register_x1) {
       // Load this again, if it's used by the local context below.
@@ skipping 4630 matching lines @@
   return previous_;
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM64