[Bug bootstrap/56259] GCC's configure script has a hard-coded setting of 'with_gmp' for FreeBSD

["novulae at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56259

--- Comment #3 from Caleb Sunstrum <novulae at hotmail dot com> 2013-02-20 01:47:02 UTC ---
(In reply to comment #2)
> This block of code was added to handle a special case seen on FreeBSD:
> (a) on some versions of FreeBSD circa 2004, the system installed copy of gmp.h
> was too old to support gcc
> (b) by default, FreeBSD ports system installs into /usr/local

Is there a reason why /path/to/gcc-source/configure --with-gmp=/usr/local
doesn't work? I don't have access to these older FreeBSDs, so I can't comment.

> 
> I note that the claimed serious side effects only happen when one installed gmp
> from ports (or otherwise installed it into /usr/local) *and* one attempted to
> build a gcc with a copy of gmp co-located with gcc source.

At the very least, this hack should propagate the settings downstream to mpfr
and mpc. But since --with-gmp=/usr/local will (should) do the same thing, I
don't see why it's necessary.

> 
> We need to think about the default user (which will likely not unpack gmp, mpfr
> and mpc) into the gcc source tree.

While I agree the default use case is important, I think it's more important to
note that there is nothing to suggest that this hack in play, and diagnosing
the failures + the unexpected side effects is quite difficult to do. I only
noticed this when trying to figure out why MPFR and MPC were failing to build
with GMP and tracing through the configure script.

Conversely, if no --with-gmp is specified and the default GMP is too old, one
could add additional text to the warning when configure fails - stating that
the GMP found in the default location is too old, and they may wish to specify
--with-gmp=/usr/local (if GMP exists there), or to build GMP from source as
part of GCC.