On 9 August 2017 at 17:52, Antoine Pitrou <solip...@pitrou.net> wrote:
> On Wed, 9 Aug 2017 13:36:28 +1000
> Nick Coghlan <ncogh...@gmail.com> wrote:
>> On 8 August 2017 at 10:12, Gregory P. Smith <g...@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").
Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia
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