- Update the header word atomically on ia32.

- Update the header word atomically on ia32.

R=koda@google.com

Committed: https://code.google.com/p/dart/source/detail?r=40855

[Ivan Posva, 2014-10-01 20:20:46]

iposva@google.com changed reviewers:
+ koda@google.com

[koda, 2014-10-01 21:01:23]

lgtm with suggestion

https://codereview.chromium.org/624473003/diff/1/runtime/vm/stub_code_ia32.cc
File runtime/vm/stub_code_ia32.cc (right):

https://codereview.chromium.org/624473003/diff/1/runtime/vm/stub_code_ia32.cc...
runtime/vm/stub_code_ia32.cc:1079: __ LockCmpxchgl(FieldAddress(EDX,
Object::tags_offset()), ECX);
Consider reminding the reader that this compares with EAX.

https://codereview.chromium.org/624473003/diff/1/runtime/vm/stub_code_ia32.cc...
runtime/vm/stub_code_ia32.cc:1080: __ j(NOT_EQUAL, &reload);
This jump is currently never exercised, which is bad, but I'm still not sure
there's a good way to get coverage for it.

I suppose you could add a flag that inserts a runtime call that tweaks the tags
between the load and the CAS, but that's probably too invasive.

[Ivan Posva, 2014-10-01 21:11:58]

https://codereview.chromium.org/624473003/diff/1/runtime/vm/stub_code_ia32.cc
File runtime/vm/stub_code_ia32.cc (right):

https://codereview.chromium.org/624473003/diff/1/runtime/vm/stub_code_ia32.cc...
runtime/vm/stub_code_ia32.cc:1079: __ LockCmpxchgl(FieldAddress(EDX,
Object::tags_offset()), ECX);
On 2014/10/01 21:01:23, koda wrote:
> Consider reminding the reader that this compares with EAX.

Added.

https://codereview.chromium.org/624473003/diff/1/runtime/vm/stub_code_ia32.cc...
runtime/vm/stub_code_ia32.cc:1080: __ j(NOT_EQUAL, &reload);
On 2014/10/01 21:01:23, koda wrote:
> This jump is currently never exercised, which is bad, but I'm still not sure
> there's a good way to get coverage for it.
> 
> I suppose you could add a flag that inserts a runtime call that tweaks the
tags
> between the load and the CAS, but that's probably too invasive.

Yes, too invasive. I'd rather make this not dead code.

[Ivan Posva, 2014-10-01 21:12:19]

Committed patchset #2 (id:20001) manually as r40855 (presubmit successful).