Hi,
Currently, the Makefile fragment for ARM aprofile multilib is using a
substractive approach. It specifies a set of options to be combined (eg.
-march=armv7-a,armv7ve,armv8-a, with
-mfpu=vfpv3-d16,neon,vfpv4-d16,neon-fpv4,neon-fp-armv8) using MULTILIB_OPTIONS
and then specifies which combination should *not* be built with
MULTILIB_EXCEPTIONS.
This patch replaces that approach by an additive one: using MULTILIB_REQUIRED to
specify the combinations we *do* want. This approach is more scalable and
maintainable:
1) Scalability
The substractive approach (MULTILIB_EXCEPTIONS) is doable today because there is
only 3 -march and 5 -mfpu options in t-aprofile. Yet it needs already 22
MULTILIB_EXCEPTIONS to define the set of multilib to be built. Adding new
architecture or new mfpu would make that worse. Since we only care about a small
number of combinations (each mfpu is used with only one march), it makes more
sense to specify what we want. The new approach only needs 9 MULTILIB_REQUIRED
lines.
2) Maintainability
Adding one new architecture or vfp option means adding exceptions for all
combinations which does not make sense with that option (eg. if we add mfpu=foo
we'll have to exclude all the march we don't want to mix with foo). It forces us
to think about all combinations involved with this new option and thinking about
the combinations in it that we do not want. Basically we have to do the work of
genmultilib in our mind. MULTILIB_REQUIRED on the other hand would allow us to
just specify the combination involving that new option that we care about which
is likely to be more obvious IMHO.
Patch is in attachment. ChangeLog entry is as follows:
*** gcc/ChangeLog ***
2016-08-01 Thomas Preud'homme <thomas.preudhomme@arm.com>
* config/arm/t-aprofile (MULTILIB_EXCEPTIONS): Rewrite into ...
(MULTILIB_REQUIRED): This by specifying multilib needing to be built
rather than those that should not be built.
The output of "tree lib/gcc/arm-none-eabi/7.0.0" before and after the patch
shows that the same set of multilib is being built.
Is this ok for trunk?
Best regards,
Thomas