Try aligning unboxed double array backing store in allocation or scavenge promotion.

src/ia32/codegen-ia32.cc

 // Copyright 2012 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 379 matching lines @@
   __ j(equal, &only_change_map);
 
   __ push(eax);
   __ push(ebx);
 
   __ mov(edi, FieldOperand(edi, FixedArray::kLengthOffset));
 
   // Allocate new FixedDoubleArray.
   // edx: receiver
   // edi: length of source FixedArray (smi-tagged)
-  __ lea(esi, Operand(edi, times_4, FixedDoubleArray::kHeaderSize));
+  __ lea(esi, Operand(edi, times_4, FixedDoubleArray::kHeaderSize + kPointerSize));

[Erik Corry, 2012/04/16 14:35:19]

Lint?

[Vyacheslav Egorov (Chromium), 2012/04/30 14:39:11]

Done.

   __ AllocateInNewSpace(esi, eax, ebx, no_reg, &gc_required, TAG_OBJECT);
 
+  Label aligned, aligned_done;
+  __ test(eax, Immediate(0x6));

[Erik Corry, 2012/04/16 14:35:19]

It seems strange to test the 2 bit here when we know it is always zero.

+  __ j(zero, &aligned, Label::kNear);
+  __ mov(FieldOperand(eax, 0),
+         Immediate(masm->isolate()->factory()->one_pointer_filler_map()));
+  __ add(eax, Immediate(kPointerSize));
+  __ j(zero, &aligned_done, Label::kNear);

[Erik Corry, 2012/04/16 14:35:19]

Why is this branch conditional?

[Vyacheslav Egorov (Chromium), 2012/04/30 14:39:11]

Done.

+
+  __ bind(&aligned);
+  __ mov(Operand(eax, esi, times_1, -kPointerSize-1),
+         Immediate(masm->isolate()->factory()->one_pointer_filler_map()));
+
+  __ bind(&aligned_done);
+
   // eax: destination FixedDoubleArray
   // edi: number of elements
   // edx: receiver
   __ mov(FieldOperand(eax, HeapObject::kMapOffset),
          Immediate(masm->isolate()->factory()->fixed_double_array_map()));
   __ mov(FieldOperand(eax, FixedDoubleArray::kLengthOffset), edi);
   __ mov(esi, FieldOperand(edx, JSObject::kElementsOffset));
   // Replace receiver's backing store with newly created FixedDoubleArray.
   __ mov(FieldOperand(edx, JSObject::kElementsOffset), eax);
   __ mov(ebx, eax);
@@ skipping 324 matching lines @@
                                   times_1,
                                   SeqAsciiString::kHeaderSize));
   __ bind(&done);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32