[Mesa-dev] [PATCH] glsl: optimize list handling in opt_dead_code

[Jan Ziak]

On Tue, Oct 18, 2016 at 3:12 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> On 18.10.2016 15:07, Jan Ziak wrote:
>>
>> On Tue Oct 18 09:29:59 UTC 2016, Eero Tamminen wrote:
>>>
>>> On 18.10.2016 01:07, Jan Ziak wrote:
>>>>
>>>> - The total number of executed instructions goes down from 64.184 to
>>>> 63.797
>>>>   giga-instructions when Mesa is compiled with "gcc -O0 ..."
>>>
>>>
>>> Please don't do performance related decisions based on data from
>>> compiling code with optimizations disabled.  Use -O2 or -O3 (or even
>>> better, check both).
>>
>>
>> Options -O2 and -O3 interfere with profiling tools.
>
>>
>>
>> I will try using -Og the next time.
>
>
> Just stop and use proper profiling tools like perf that can work with
> optimized tools. You may have to compile with -fno-omit-frame-pointer, but
> anything more than that is going to distort your measurement results so much
> that they're worthless.
>
> Nicolai

The function from -O0, -O1, -O2 to number-of-instructions (or to
number-of-cycles) is in the vast majority of cases a monotonically
decreasing function.

Are you saying that this rule does not hold in the case of this patch?

Jan