From: Junio C Hamano <gitster@pobox.com>
Date: Fri, 03 Feb 2012 00:58:09 GMT
Subject: Re: [PATCH, RFC] Fix build problems related to profile-directed optimization
Message-ID: <7vvcnou40u.fsf@alter.siamese.dyndns.org>
In-Reply-To: <20120202201226.GA1032@thunk.org>

Ted Ts'o <tytso@mit.edu> writes:

> ...
> At least in theory, it should be possible to have something which
> supports both PROFILE_GEN/PROFILE_USE as well as a combined
> PROFILE_BUILD.
>
> The hard part is that PROFILE_BUILD requires a multi-pass process; you
> need to build with one set of CFLAGS, then run the sample workload to
> get the data for your feedback directed optimizations, and then re-run
> the build with another set of CFLAGS.

Yeah, I can see how that forces us to some kludgy solution, but I tend to
agree that the separation between GEN/USE is a good thing.

> I think what we could to check
> for PROFILE_BUILD, and if it is set, do the first PROFILE_GEN / make
> test commands as part of the top-level Makefile's all: rule, and then
> do the normal build after that.

Yeah, something like that would emulate the "make profile-all" well enough
for people not to notice the change while giving us the flexibility of
GEN/USE separation. I kinda like it.

Thanks.