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Re: Ignored optimization command
On Sun, Feb 24, 2013 at 1:07 PM, Kirk Liberty <kirk.liberty@gmail.com> wrote:
> On Sun, Feb 24, 2013 at 6:10 AM, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
>> On 24 February 2013 00:23, Kirk Liberty wrote:
>>> Hi all,
>>>
>>> I'm trying to use g++ to compile a function with optimization O2
>>> except for one function I want at O3. I'm not having any luck with
>>> __attribute__ or #pragma. I am using GCC version 4.7.2. With
>>> __attribute__ I am getting a warning that the directive was ignored,
>>> and with #pragma I am simply not seeing the speedup expected.
>>
>> Maybe the optimizer simply doesn't make the code any faster.
>
> When I globally use O3 I see about a 3 times speedup in that function.
>
>>> Here's what I've tried.
>>> bool* getStreamBool(uint64_t num) __attribute__ ((optimize("-O3"))) {...}
>>
>> I think this should be "O3" or just "3", without the dash.
>
> I have tried it without the dash, but not without the "O".
> I seem to have broken my <cmath> and <random> files so I can't try it right now.
>
I was able to try it with just "3", I did not notice any difference.
> Kirk
Kirk