I had a short discussion with the gcc community on IRC. After having
this discussion I think it would be of great benefit if -xsafe=mem
would be available for -xO3 and the compiler would more aggressively
issue such speculative read accesses because other platforms greatly
benefit from such instructions, making up to 30% of the load
instructions in heavily branched applications like firefox. The Sun
Studio compiler may be much too conservative since it was written in
days when a CPU had much less bandwidth than the CPU of today.
Olga
2010/3/31 Darryl Gove <darryl.g...@oracle.com>:
> I'd guess that since it enables the compiler to perform speculative memory
> accesses, in theory it could cause additional page faults that were not
> originally there. So it's probably most appropriate in the situation where
> the compiler has profile feedback information that indicates that the load
> will eventually be performed.
>
> Regards,
>
> Darryl.
>
>
> On 3/30/2010 8:36 PM, ольга крыжановская wrote:
>>
>> Why does this option require -xO5 and not a lesser level like -xO3?
>> Why is this not the default in ON?
>>
>> Olga
>>
>> On Tue, Mar 30, 2010 at 6:45 AM, Darryl Gove<darryl.g...@oracle.com>
>> wrote:
>>>
>>> Hi,
>>>
>>> The flag basically means that memory traps don't get forwarded to the
>>> application. So the kernel still gets to handle the trap, but the app
>>> won't
>>> segfault if you access a bad address.
>>>
>>> The option is basically to allow the compiler to use speculative memory
>>> accesses.
>>>
>>> Regards,
>>>
>>> Darryl.
>>>
>>>
>>> On 3/28/2010 2:42 PM, ольга крыжановская wrote:
>>>>
>>>> Does -xsafe=mem work with mmap() for files? From the documentation it
>>>> says that -xsafe=mem turns of the memory traps. Does that include
>>>> traps used by the kernel to serve files mapped into mmap() into the
>>>> process address space?
>>>>
>>>> Olga
>>>
>>> _______________________________________________
>>> tools-compilers mailing list
>>> tools-compil...@opensolaris.org
>>
>>
>>
>
>
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