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

src/ia32/full-codegen-ia32.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"
 
 #if V8_TARGET_ARCH_IA32
 
 #include "code-stubs.h"
 #include "codegen.h"
@@ skipping 180 matching lines @@
       }
     }
   }
 
   bool function_in_register = true;
 
   // Possibly allocate a local context.
   int heap_slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
   if (heap_slots > 0) {
     Comment cmnt(masm_, "[ Allocate context");
+    bool need_write_barrier = true;
     // Argument to NewContext is the function, which is still in edi.
     if (FLAG_harmony_scoping && info->scope()->is_global_scope()) {
       __ push(edi);
       __ Push(info->scope()->GetScopeInfo());
       __ 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(edi);
       __ CallRuntime(Runtime::kHiddenNewFunctionContext, 1);
     }
     function_in_register = false;
     // Context is returned in eax.  It replaces the context passed to us.
     // It's saved in the stack and kept live in esi.
     __ mov(esi, eax);
     __ mov(Operand(ebp, StandardFrameConstants::kContextOffset), eax);
 
     // Copy parameters into context if necessary.
     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.
         __ mov(eax, Operand(ebp, parameter_offset));
         // Store it in the context.
         int context_offset = Context::SlotOffset(var->index());
         __ mov(Operand(esi, context_offset), eax);
         // Update the write barrier. This clobbers eax and ebx.
-        __ RecordWriteContextSlot(esi,
-                                  context_offset,
-                                  eax,
-                                  ebx,
-                                  kDontSaveFPRegs);
+        if (need_write_barrier) {
+          __ RecordWriteContextSlot(esi,
+                                    context_offset,
+                                    eax,
+                                    ebx,
+                                    kDontSaveFPRegs);
+        } else if (FLAG_debug_code) {
+          Label done;
+          __ JumpIfInNewSpace(esi, eax, &done, Label::kNear);
+          __ 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) {
       __ push(edi);
@@ skipping 4546 matching lines @@
   ASSERT_EQ(isolate->builtins()->OsrAfterStackCheck()->entry(),
             Assembler::target_address_at(call_target_address,
                                          unoptimized_code));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32