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

src/arm/lithium-codegen-arm.cc

 // Copyright 2012 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 "arm/lithium-codegen-arm.h"
 #include "arm/lithium-gap-resolver-arm.h"
 #include "code-stubs.h"
 #include "stub-cache.h"
@@ skipping 161 matching lines @@
   }
 
   if (info()->saves_caller_doubles()) {
     SaveCallerDoubles();
   }
 
   // Possibly allocate a local context.
   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 r1.
     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(r1);
       __ CallRuntime(Runtime::kHiddenNewFunctionContext, 1);
     }
     RecordSafepoint(Safepoint::kNoLazyDeopt);
     // Context is returned in both r0 and cp.  It replaces the context
     // passed to us.  It's saved in the stack and kept live in cp.
     __ mov(cp, r0);
     __ str(r0, 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()) {
         int parameter_offset = StandardFrameConstants::kCallerSPOffset +
             (num_parameters - 1 - i) * kPointerSize;
         // Load parameter from stack.
         __ ldr(r0, MemOperand(fp, parameter_offset));
         // Store it in the context.
         MemOperand target = ContextOperand(cp, var->index());
         __ str(r0, target);
         // Update the write barrier. This clobbers r3 and r0.
-        __ RecordWriteContextSlot(
-            cp,
-            target.offset(),
-            r0,
-            r3,
-            GetLinkRegisterState(),
-            kSaveFPRegs);
+        if (need_write_barrier) {
+          __ RecordWriteContextSlot(
+              cp,
+              target.offset(),
+              r0,
+              r3,
+              GetLinkRegisterState(),
+              kSaveFPRegs);
+        } else if (FLAG_debug_code) {
+          Label done;
+          __ JumpIfInNewSpace(cp, r0, &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 5596 matching lines @@
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(deferred->exit());
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal