[PATCH 01/10] Makefile: v2 Allow LTO to be disabled for a build

[Tom Rini]

On Mon, Apr 11, 2022 at 03:46:04PM -0600, Simon Glass wrote:
> Hi Andrew,
> 
> On Thu, 31 Mar 2022 at 04:29, Andrew Scull <ascull at google.com> wrote:
> >
> > On Sun, 27 Mar 2022 at 21:27, Simon Glass <sjg at chromium.org> wrote:
> > >
> > > LTO (Link-Time Optimisation) is an very useful feature which can
> > > significantly reduce the size of U-Boot binaries. So far it has been
> > > made available for selected ARM boards and sandbox.
> > >
> > > However, incremental builds are much slower when LTO is used. For example,
> > > an incremental build of sandbox takes 2.1 seconds on my machine, but 6.7
> > > seconds with LTO enabled.
> >
> > This is something that has been bothering me too. I'd resorted to adding
> > `# CONFIG_LTO is not set` to sandbox_defconfig because I couldn't work
> > out how to stop .config being regenerated each build. But then the
> > diff gets in the way and is difficult to manage.
> >
> > > Add a LTO_BUILD=n parameter to the build, so it can be disabled during
> > > development if needed, for faster builds.
> >
> > If you go the build parameter route rather than config route to
> > address this, could the flag be consistent e.g. with NO_SDL=1, which
> > would mean NO_LTO=1?
> 
> That seems OK to me. Would you like to do that and send a new version?
> 
> Here is a better version of the patch to use as a starting point:
> 
> https://source.denx.de/u-boot/custodians/u-boot-dm/-/commit/2d4ebfb0e8e86a1b347e6cbd4dbec9a4eb745bd5
> 
> Tom, please consider dropping your objection to this. I have already
> shown that it makes a dramatic difference to incremental build time
> for any board...

Yeah, OK, reworked to be consistent with now we do SDL is workable.

-- 
Tom
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