[PATCH] PR jit/64780: configure: --enable-host-shared and the jit

[Jeff Law]

On 01/27/15 10:17, David Malcolm wrote:
> Currently the jit requires you to specify --enable-host-shared, or the
> build eventually fails with  linker errors (this is something of a FAQ
> for people trying out the jit).
>
> We seem to have two choices here:
>
> (A) default to --enable-host-shared when jit is an enabled language
> (B) have the toplevel configure reject jit as language if
>      --enable-host-shared is not supplied.
>
> FWIW apparently Darwin defaults to position-independent code, so it's not
> explicitly needed there.
>
> I think (B) is the better option for us, since there is a performance
> cost: there are people who perform benchmarking of GCC (and publish
> their results on prominent websites).  If they turn on the jit and use
> the same configuration to do their benchmarking of the rest of GCC,
> they'll see GCC 5 be apparently slower than earlier releases.  This
> is sufficiently subtle that I don't think it's reasonable to simply
> document it and expect 3rd-party reviewers to see such a note in the
> documentation before benchmarking.
>
> The attached patch implements (B), with a note in the error message
> recommending that people configure and build GCC twice to avoid the
> performance hit, so that it can be self-documenting.
>
> Tested by hand with various combinations of values for
> --enable-host-shared and --enable-languages.
>
> OK for stage 4?
>
> 	PR jit/64780
> 	* configure.ac: Require the user to explicitly specify
> 	--enable-host-shared if the jit is enabled.
> 	* configure: Regenerate.
OK.
jeff