[Mac] Tighten up objc zombie dealloc implementation.

[Mac] Tighten up objc zombie dealloc implementation.

Enabling the zombie code in release causes Perf(2) to regress.
Reviewing |ZombieDealloc()|, I notice that object_setClass() is
implemented with a memory barrier.  The objc runtime doesn't use it in
deallocation, so move to direct access.

BUG=none
TEST=none

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=48857

[Avi (use Gerrit), 2010-06-03 19:16:51]

LG

http://codereview.chromium.org/2605004/diff/1/2
File chrome/browser/cocoa/objc_zombie.mm (right):

http://codereview.chromium.org/2605004/diff/1/2#newcode157
chrome/browser/cocoa/objc_zombie.mm:157: self->isa = g_zombieClass;
Huh. isa is still public in the objc2 runtime? If this compiles on 64, go for
it. If not you might have to ifdef __LP64__ it.

[Scott Hess - ex-Googler, 2010-06-03 19:46:32]

Is this a "check-in then make sure on 64-bit", or "make sure on 64-bit then
check-in"?  Thanks.

http://codereview.chromium.org/2605004/diff/1/2
File chrome/browser/cocoa/objc_zombie.mm (right):

http://codereview.chromium.org/2605004/diff/1/2#newcode157
chrome/browser/cocoa/objc_zombie.mm:157: self->isa = g_zombieClass;
On 2010/06/03 19:16:51, Avi wrote:
> Huh. isa is still public in the objc2 runtime? If this compiles on 64, go for
> it. If not you might have to ifdef __LP64__ it.

Not sure what you mean.  struct objc_class has OBJC2_UNAVAILABLE annotations,
but struct objc_object just has Class isa with no annotations.

This code should never be called in 64-bit due to the nlist stuff not being
adapted yet.  I'm trying to figure out how to compile 64-bit, but:
   GYP_DEFINES="target_arch=x64" gclient sync
doesn't seem to change from i386.

[Avi (use Gerrit), 2010-06-03 19:49:31]

This was a "this works on the new runtime!?" comment. If this is not
expected to work on 64 anyway, then it has my OK.

Avi

On Thu, Jun 3, 2010 at 3:46 PM, <shess@chromium.org> wrote:

> Is this a "check-in then make sure on 64-bit", or "make sure on 64-bit then
> check-in"?  Thanks.
>
>
>
> http://codereview.chromium.org/2605004/diff/1/2
> File chrome/browser/cocoa/objc_zombie.mm (right):
>
> http://codereview.chromium.org/2605004/diff/1/2#newcode157
> chrome/browser/cocoa/objc_zombie.mm:157: self->isa = g_zombieClass;
> On 2010/06/03 19:16:51, Avi wrote:
>
>> Huh. isa is still public in the objc2 runtime? If this compiles on 64,
>>
> go for
>
>> it. If not you might have to ifdef __LP64__ it.
>>
>
> Not sure what you mean.  struct objc_class has OBJC2_UNAVAILABLE
> annotations, but struct objc_object just has Class isa with no
> annotations.
>
> This code should never be called in 64-bit due to the nlist stuff not
> being adapted yet.  I'm trying to figure out how to compile 64-bit, but:
>   GYP_DEFINES="target_arch=x64" gclient sync
> doesn't seem to change from i386.
>
>
> http://codereview.chromium.org/2605004/show
>