Slightly faster variant of Array.push.

src/ia32/stub-cache-ia32.cc

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1233 matching lines @@
   } else {
     // Get the elements array of the object.
     __ mov(ebx, FieldOperand(edx, JSArray::kElementsOffset));
 
     // Check that the elements are in fast mode (not dictionary).
     __ cmp(FieldOperand(ebx, HeapObject::kMapOffset),
            Immediate(Factory::fixed_array_map()));
     __ j(not_equal, &miss);
 
     if (argc == 1) {  // Otherwise fall through to call builtin.
-      Label call_builtin, exit, with_rset_update,
-            attempt_to_grow_elements, finish_push;
+      Label call_builtin, exit, with_rset_update, attempt_to_grow_elements;
 
       // Get the array's length into eax and calculate new length.
       __ mov(eax, FieldOperand(edx, JSArray::kLengthOffset));
       STATIC_ASSERT(kSmiTagSize == 1);
       STATIC_ASSERT(kSmiTag == 0);
       __ add(Operand(eax), Immediate(argc << 1));
 
       // Get the element's length into ecx.
       __ mov(ecx, FieldOperand(ebx, FixedArray::kLengthOffset));
       __ SmiTag(ecx);
 
       // Check if we could survive without allocation.
       __ cmp(eax, Operand(ecx));
       __ j(greater, &attempt_to_grow_elements);
 
       // Save new length.
       __ mov(FieldOperand(edx, JSArray::kLengthOffset), eax);
 
       // Push the element.
       __ lea(edx, FieldOperand(ebx,
                                eax, times_half_pointer_size,
                                FixedArray::kHeaderSize - argc * kPointerSize));
       __ mov(ecx, Operand(esp, argc * kPointerSize));
       __ mov(Operand(edx, 0), ecx);
 
-      __ bind(&finish_push);
-
       // Check if value is a smi.
       __ test(ecx, Immediate(kSmiTagMask));
       __ j(not_zero, &with_rset_update);
 
       __ bind(&exit);
       __ ret((argc + 1) * kPointerSize);
 
       __ bind(&with_rset_update);
 
       __ InNewSpace(ebx, ecx, equal, &exit);
@@ skipping 18 matching lines @@
                                FixedArray::kHeaderSize - argc * kPointerSize));
       __ cmp(edx, Operand(ecx));
       __ j(not_equal, &call_builtin);
       __ add(Operand(ecx), Immediate(kAllocationDelta * kPointerSize));
       __ cmp(ecx, Operand::StaticVariable(new_space_allocation_limit));
       __ j(greater, &call_builtin);
 
       // We fit and could grow elements.
       __ mov(Operand::StaticVariable(new_space_allocation_top), ecx);
       __ mov(ecx, Operand(esp, argc * kPointerSize));
+
+      // Push the argument...
       __ mov(Operand(edx, 0), ecx);
+      // ... and fill the rest with holes.
       for (int i = 1; i < kAllocationDelta; i++) {
         __ mov(Operand(edx, i * kPointerSize),
-               Immediate(Factory::undefined_value()));
+               Immediate(Factory::the_hole_value()));
       }
 
       // Restore receiver to edx as finish sequence assumes it's here.
       __ mov(edx, Operand(esp, (argc + 1) * kPointerSize));
 
       // Increment element's and array's sizes.
       __ add(FieldOperand(ebx, FixedArray::kLengthOffset),
              Immediate(kAllocationDelta));
       __ mov(FieldOperand(edx, JSArray::kLengthOffset), eax);
 
-      __ jmp(&finish_push);
+      // Elements are in new space, so no remembered set updates are necessary.
+      __ ret((argc + 1) * kPointerSize);
 
       __ bind(&call_builtin);
     }
 
     __ TailCallExternalReference(ExternalReference(Builtins::c_ArrayPush),
                                  argc + 1,
                                  1);
   }
 
   __ bind(&miss);
@@ skipping 1078 matching lines @@
   __ jmp(generic_construct_stub, RelocInfo::CODE_TARGET);
 
   // Return the generated code.
   return GetCode();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal