[Mesa-dev] Meson's default build type

[Chad Versace]

On Mon 06 Nov 2017, Eric Engestrom wrote:
> On Monday, 2017-11-06 08:07:21 -0800, Chad Versace wrote:
> > On Thu 02 Nov 2017, Dylan Baker wrote:
> > > Quoting Matt Turner (2017-11-02 10:06:43)
> > > > On Thu, Nov 2, 2017 at 9:51 AM, Michel Dänzer <michel at daenzer.net> wrote:
> > > > > FWIW, my vote is for debugoptimized: Assertions are enabled and there's
> > > > > debugging information useful for bug reports, but performance should be
> > > > > decent.
> > > > 
> > > > If debugoptimized turns on DEBUG, then I don't think performance will
> > > > be decent as that enables paths like nir_validate. Maybe we should
> > > > change debugoptimized to not do that. Not sure.
> > > > 
> > > > I think some of the messaging got confused -- autotools does specify
> > > > -g in the default CFLAGS, but that doesn't really mean it's a useful
> > > > debug build. -g -O2 is really a release build, with debugging symbols.
> > > 
> > > debugoptimized does turn on DEBUG. Last time I tried (which was a while ago),
> > > if asserts are enabled but DEBUG is not mesa couldn't be compiled, as asserts
> > > used members of structs that only exist when DEBUG is set. Maybe that's a
> > > situation that deserves being revisited.
> > 
> > I vote for debugoptimized, where debuoptimized contains CFLAGS='-g -O2'.
> 
> This is already the default behaviour on meson [1]
> 
> [1] http://mesonbuild.com/Running-Meson.html#configuring-the-source
> 
> > The user gets a build that's suitable for everyday use (-O2) and it the
> > user can submit meaningful bug reports (-g).
> > 
> > To -DDEBUG or not to -DDEBUG... Since I want to ensure that users with
> > a self-built Mesa have a Mesa that's suitable for everyday use, I think
> > the default build should *not* contain assertions that severely impact
> > performance. So I vote against -DDEBUG; or, at a minimum, we could keep
> > -DDEBUG and somehow disable the slooooooow assertions in debugoptimized.
> 
> assert()s are controlled by the standard NDEBUG, which is not tied to
> Mesa's DEBUG.
> 
> Mesa's autotools, having only two build types, locally defines NDEBUG
> when --enable-debug is not given, kind of tying the two together.
> Meson on the other hand uses the build option `b_ndebug` to control
> NDEBUG, which defaults to `false` (ie. "don't compile out asserts").
> 
> Mesa's DEBUG is currently enabled in Meson on both `debug` and
> `debugoptimized` builds. We could limit it to `debug` only, removing
> DEBUG code in `debugoptimized` but keeping assert()s.
> 
> Does that sound like a good middle-ground?

Thanks for explaining all that. Your proposal sounds good to me.