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

src/arm64/lithium-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"
 
 #include "arm64/lithium-codegen-arm64.h"
 #include "arm64/lithium-gap-resolver-arm64.h"
 #include "code-stubs.h"
 #include "stub-cache.h"
@@ skipping 676 matching lines @@
   }
 
   if (info()->saves_caller_doubles()) {
     SaveCallerDoubles();
   }
 
   // Allocate a local context if needed.
   int heap_slots = info()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
   if (heap_slots > 0) {
     Comment(";;; Allocate local context");
+    bool need_write_barrier = true;
     // Argument to NewContext is the function, which is in x1.
     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);
     }
     RecordSafepoint(Safepoint::kNoLazyDeopt);
     // 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 = scope()->num_parameters();
     for (int i = 0; i < num_parameters; i++) {
       Variable* var = scope()->parameter(i);
       if (var->IsContextSlot()) {
         Register value = x0;
         Register scratch = x3;
 
         int parameter_offset = StandardFrameConstants::kCallerSPOffset +
             (num_parameters - 1 - i) * kPointerSize;
         // Load parameter from stack.
         __ Ldr(value, MemOperand(fp, parameter_offset));
         // Store it in the context.
         MemOperand target = ContextMemOperand(cp, var->index());
         __ Str(value, target);
         // Update the write barrier. This clobbers value and scratch.
-        __ RecordWriteContextSlot(cp, target.offset(), value, scratch,
-                                  GetLinkRegisterState(), kSaveFPRegs);
+        if (need_write_barrier) {
+          __ RecordWriteContextSlot(cp, target.offset(), value, scratch,
+                                    GetLinkRegisterState(), kSaveFPRegs);
+        } else if (FLAG_debug_code) {
+          Label done;
+          __ JumpIfInNewSpace(cp, &done);
+          __ Abort(kExpectedNewSpaceObject);
+          __ bind(&done);
+        }
       }
     }
     Comment(";;; End allocate local context");
   }
 
   // Trace the call.
   if (FLAG_trace && info()->IsOptimizing()) {
     // We have not executed any compiled code yet, so cp still holds the
     // incoming context.
     __ CallRuntime(Runtime::kTraceEnter, 0);
@@ skipping 5270 matching lines @@
   __ Ldr(result, FieldMemOperand(object, JSObject::kPropertiesOffset));
   // Index is equal to negated out of object property index plus 1.
   __ Sub(result, result, Operand::UntagSmiAndScale(index, kPointerSizeLog2));
   __ Ldr(result, FieldMemOperand(result,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ Bind(deferred->exit());
   __ Bind(&done);
 }
 
 } }  // namespace v8::internal