On Wed, Jan 13, 2010 at 8:34 PM, Antoine Labour <pi...@google.com> wrote:
>
> On Wed, Jan 13, 2010 at 10:06 AM, Stephen White <senorbla...@chromium.org>
> wrote:
>>
>> On Wed, Jan 13, 2010 at 12:19 PM, Dan Kegel <d...@kegel.com> wrote:
>>>
>>> On Wed, Jan 13, 2010 at 9:12 AM, Stephen White <senorbla...@chromium.org>
>>> wrote:
>>> > 2) Most of the supposed performance advantage of strict aliasing rules
>>> > is
>>> > probably taken care of by memory disambiguation in modern (ie., Core2
>>> > and
>>> > later) CPUs.
>>>
>>> I kind of doubt that. Disallowing aliasing lets the compiler do
>>> a number of high-level optimizations that the chip could never do on its
>>> own.
>>> See e.g.
>>>
>>> http://cellperformance.beyond3d.com/articles/2006/06/understanding-strict-aliasing.html
>>
>> (As a side note, I find this example somewhat contrived: if this were
>> performance-critical code, the programmer would pull the dereference out of
>> the loop anyway, not rely on the compiler to do it.)
>> That said, the "data-driven" answer would be to run perf benchmarks with
>> and without strict aliasing, and see the effect. It might even help us find
>> some hotspots which we could improve under MSVC.
>>>
>>> I'm for -fstrict-aliasing except for third_party.
>>
>> Whichever is decided, I think making it explicit would make life easier
>> for the people on different compiler versions.
>> Stephen
>
> I have a bias towards -fstrict-aliasing, but whichever the choice, I think
> we should have the same default for all the compiler versions (i.e. forcing
> it either way).
> For Chrome OS, we will use gcc 4.4 so we'll get more exposure in-house to
> that particular compiler.
I'm one try-server run away from possibly turning -fno-strict-aliasing on for
all linux/bsd gcc: http://codereview.chromium.org/519034
>From a "process" standpoint, given that there is some disagreement here
is someone going to come find me with a clue bat if I commit this?
Get your votes in now! :)
--Craig
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