Re: Add .def file for public target instructions

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Jul 1, 2015 at 11:39 AM, Trevor Saunders <tbsaunde@tbsaunde.org> wrote:
> On Tue, Jun 23, 2015 at 07:41:42PM +0100, Richard Sandiford wrote:
>> [A fair bit later than promised, sorry...]
>>
>> Mikhail posted a patch to make genflags generate the default HAVE_foo
>> and gen_foo definitions that have recently been added to defaults.h:
>>
>>   https://gcc.gnu.org/ml/gcc-patches/2015-06/msg00723.html
>>
>> I agree it'd be a good idea to generate this kind of thing automatically,
>> but I think we should take the opportunity to move the interface to the
>> target structure.  I.e.:
>>
>>   HAVE_foo -> targetm.have_foo ()
>>   gen_foo -> targetm.gen_foo ()
>>
>> This should move us closer to the pipedream goal of supporting multiple
>> targets at once.  It should also mean that only the target code depends
>> on insn-flags.h.
>
> using targetm. certainly seems like an improvement.  I wonder if it
> would be faster to stick this data on a per function object.  I think
> that would mean you could compute what insns are available once when the
> function is created and afterwards all checks would only needed to be
> reading computed values.

I think the memory cost of this is prohibitive.

Richard.

> Trev
>