[Mesa-dev] [PATCH 08/12] meson doesn't use env vars, WAS: configure.ac: deprecate --with-llvm-prefix

[Dylan Baker]

Quoting Jan Vesely (2018-11-07 10:39:48)
> On Tue, 2018-11-06 at 12:09 +0000, Emil Velikov wrote:
> > On Thu, 1 Nov 2018 at 16:13, Michel Dänzer <michel at daenzer.net> wrote:
> > > On 2018-11-01 5:03 p.m., Jan Vesely wrote:
> > > > On Wed, 2018-10-31 at 18:40 +0000, Emil Velikov wrote:
> > > > > On Wed, 31 Oct 2018 at 17:41, Jan Vesely <jan.vesely at rutgers.edu> wrote:
> > > > > > On Wed, 2018-10-31 at 17:22 +0000, Emil Velikov wrote:
> > > > > > > On Wed, 31 Oct 2018 at 16:24, Michel Dänzer <michel at daenzer.net> wrote:
> > > > > > > > On 2018-10-31 5:19 p.m., Jan Vesely wrote:
> > > > > > > > > This might be a stupid question; is the LLVM_CONFIG env var remembered
> > > > > > > > > between reconfigure (touch configure.ac; make) or do I need to provide
> > > > > > > > > it explicitly every time configure is run?
> > > > > > > > 
> > > > > > > > I don't know the answer, but agree that would be a minimum requirement
> > > > > > > > for this change.
> > > > > > > > 
> > > > > > > Nope, yet it's not really a minimum. LLVM_CONFIG has been around for
> > > > > > > years, it will work for any Mesa checkout since its inception.
> > > > > > > You can safely bisect Mesa and things will just work.
> > > > > > 
> > > > > > The question is; Do I have to do "LLVM_CONFIG=..." make every time
> > > > > > bisect changes configure.ac?
> > > > > > 
> > > > > You can do (although there's other options if this one seems weird)
> > > > > 
> > > > > $ LLVM_CONFIG=... ../autogen.sh
> > > > 
> > > > That does not answer my question.
> > > > 
> > > > suppose the following sequence:
> > > > $ LLVM_CONFIG=/usr/local/llvm-4/bin/llvm-config ../mesa-src/autogen.sh
> > > > ...
> > > >         llvm:            yes
> > > >         llvm-config:     /usr/local/llvm-4/bin/llvm-config
> > > >         llvm-version:    4.0.1
> > > > ...
> > > > $ make -j128
> > > > $ touch ../mesa-src/configure.ac
> > > > $ make -j128
> > > > ...
> > > >         llvm:            yes
> > > >         llvm-config:     /usr/bin/llvm-config
> > > >         llvm-version:    7.0.0
> > > > ...
> > > > 
> > > > the second reconfigure silently reverted back to system default llvm.
> > > > That's a loss of capabilty for me.
> > > 
> > > Thanks for checking, Jan. That's a NAK from me for this patch in the
> > > current form.
> > > 
> > > FWIW, LLVM_CONFIG is available in the generated Makefiles, so it might
> > > not be too hard to make this work with the environment variable. I don't
> > > know the preferred way to do that however.
> > > 
> > Right, I misread the usecase :-( Sorry about that.
> > The following works like a charm:
> > 
> > .../autogen.sh ac_cv_path_LLVM_CONFIG=/...
> > make
> > touch .../configure.ac
> > make
> 
> ouch, that's rather ugly. What is the reason to prefer env var vs.
> proper option (like --with-llvm-config)?
> meson also seems to prefer env var for some reason.

Actually, we (meson) made the concious choice not to use env vars, our solution
is config files (like cross files) for native compilation. They work just like
cross file, but for native compilation (load at initial configuration, don't
reload change on subsequent reconfigurations):

$ cat llvm-4.0
[binaries]
llvm-config = /usr/local/lib/llvm-4.0/bin/llvm-config

$ meson build --native-file llvm-4.0

Hopefully this series in the in the final stretch and can land shortly, and be
present in 0.49.0

Dylan
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