Initialize pre-allocated fields of JSObject with undefined.

src/arm/builtins-arm.cc

 // Copyright 2011 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 732 matching lines @@
       __ str(r6, MemOperand(r5, kPointerSize, PostIndex));
 
       // Fill all the in-object properties with the appropriate filler.
       // r1: constructor function
       // r2: initial map
       // r3: object size (in words)
       // r4: JSObject (not tagged)
       // r5: First in-object property of JSObject (not tagged)
       __ add(r6, r4, Operand(r3, LSL, kPointerSizeLog2));  // End of object.
       ASSERT_EQ(3 * kPointerSize, JSObject::kHeaderSize);
-      { Label loop, entry;
-        if (count_constructions) {
-          // To allow for truncation.
-          __ LoadRoot(r7, Heap::kOnePointerFillerMapRootIndex);
-        } else {
-          __ LoadRoot(r7, Heap::kUndefinedValueRootIndex);
+      __ LoadRoot(r7, Heap::kUndefinedValueRootIndex);
+      if (count_constructions) {
+        __ ldr(r0, FieldMemOperand(r2, Map::kInstanceSizesOffset));
+        __ Ubfx(r0, r0, Map::kPreAllocatedPropertyFieldsByte * 8, 8);
+        __ add(r0, r5, Operand(r0, LSL, kPointerSizeLog2));
+        // r0: offset of first field after pre-allocated fields
+        if (FLAG_debug_code) {
+          __ cmp(r0, r6);
+          __ Assert(le, "Unexpected number of pre-allocated property fields.");
         }
-        __ b(&entry);
-        __ bind(&loop);
-        __ str(r7, MemOperand(r5, kPointerSize, PostIndex));
-        __ bind(&entry);
-        __ cmp(r5, r6);
-        __ b(lt, &loop);
+        __ InitializeFieldsWithFiller(r5, r0, r7);
+        // To allow for truncation.
+        __ LoadRoot(r7, Heap::kOnePointerFillerMapRootIndex);
       }
+      __ InitializeFieldsWithFiller(r5, r6, r7);
 
       // Add the object tag to make the JSObject real, so that we can continue
       // and jump into the continuation code at any time from now on. Any
       // failures need to undo the allocation, so that the heap is in a
       // consistent state and verifiable.
       __ add(r4, r4, Operand(kHeapObjectTag));
 
       // Check if a non-empty properties array is needed. Continue with
       // allocated object if not fall through to runtime call if it is.
       // r1: constructor function
@@ skipping 937 matching lines @@
   __ bind(&dont_adapt_arguments);
   __ Jump(r3);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM