[Python-Dev] first post introduction and question regarding lto

[Nick Coghlan]

On 9 August 2017 at 17:52, Antoine Pitrou <solipsis at pitrou.net> wrote:
> On Wed, 9 Aug 2017 13:36:28 +1000
> Nick Coghlan <ncoghlan at gmail.com> wrote:
>> On 8 August 2017 at 10:12, Gregory P. Smith <greg at krypto.org> wrote:
>> > I don't know whether it is beneficial or not - but having the capability to
>> > build LTO without PGO seems reasonable. I can review any pull requests
>> > altering configure.ac and Makefile.pre.in to make such a change.
>>
>> Being able to separate them seems useful even if it's just from the
>> performance research perspective of comparing "PGO only", "LTO only"
>> and "PGO+LTO".
>
> That does not mean "LTO only" deserves a configure option, though.  PGO
> is difficult to set up manually so it's fair that we provide dedicated
> build support for it.  LTO should just be a matter of tweaking CFLAGS
> and LDFLAGS.

I wouldn't be confident in my own ability to get those right for gcc,
let alone getting them right for clang as well. Whereas if the
"--with-lto" configure option just works, then I'd never need to worry
about it :)

It also means that if folks *do* investigate this, it eliminates a
class of configuration bugs (i.e. "you didn't actually enable LTO
correctly in your testing").

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia