llvm dev - Sep 2021 - RFC: Deprecate config.guess

Hi,

I was looking into fixing host detection (which is currently done using
config.guess) for my operating system and came across these old
reviews[1][2] with objections to updating it due to its license.

If we can't update config.guess any more that I would like to propose that
we (eventually) remove it completely.

I've submitted this patch[3], which turns off config.guess by default
and tries to determine the host triple using the host compiler.  Given
all the different combinations for triples, I don't know if there is
any better way to test this than to turn it off and wait for the bug
reports.  My hope is that over time, we will be able to replace the
functionality from config.guess that users actually care about and
at some point we'll be able to remove config.guess completely.

Thanks,
Tom

[1] https://reviews.llvm.org/D55445
[2] https://reviews.llvm.org/D99625
[3] https://reviews.llvm.org/D109837

On Wed, 15 Sept 2021 at 17:55, Tom Stellard via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> I've submitted this patch[3], which turns off config.guess by default
> and tries to determine the host triple using the host compiler.  Given
> all the different combinations for triples, I don't know if there is
> any better way to test this than to turn it off and wait for the bug
> reports.
>
I think this is a good change and one that we should really work on, but
I'm not sure compiler front-ends are a drop-in replacement for all
variations.

Perhaps add the option and make it ON by default for now, which will still
work for all current platforms, and add the possibility of turning guessing
OFF and allowing those that aren't supported by out very old config.guess
version to use the compiler.

Fixing the triple in the front-end isn't really trivial, there are a number
of replacements on the triple until it hits the middle-end, so this may
actually create problems that aren't easy to fix down the line.

Just like moving from automake to CMake, I think we need to do this slowly
and changing buildbots until all are running the new format, then we change
the default behaviour.

cheers,
--renato
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