compiled programs significantly slower after upgrading

Jeff Law law@redhat.com
Wed Apr 18 21:50:00 GMT 2018


On 04/18/2018 03:45 PM, Dennis Clarke wrote:
> On 18/04/18 05:28 PM, Jack Stalnaker wrote:
>> I upgraded gcc from 4.8.2 to 7.3.0. I also upgraded binutils to 2.30
>> (from
>> the default installed on scientific linux 5).
>>
>> Unfortunately, the executable I get is now 5 times slower consistently. I
>> have changed nothing about the code itself. I have not changed any
>> compilation options either. I'm honestly shocked by such a dramatic
>> slowdown. Has something changed significantly between these two versions?
>>
>> I realize I haven't given any information about the code itself (it's
>> a mix
>> of fortran and c), but the important thing is the significant slowdown
>> when
>> only the compilation chain has changed.
>>
>> Can anyone give me any insight as to what might be happening or how to
>> address it?
>>
> 
> With no code at all to consider ?  Not likely.   Take a look at your
> optimization options and your settings for "march/mtune" etc in case
> you had those.  Look at the actual online manual for 7.3.0 and check
> your options as a LOT has changed and a lot deprecated.
Given a 5x slowdown, it's not likely arch/tuning options.  But without
code there's really nothing we can do -- even reasonable speculation is
impossible.

jeff



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