On 2/6/25 4:54 PM, Richard Sandiford wrote:
Vladimir Makarov<vmaka...@redhat.com> writes:
This is a complicated problem resulted in many tries to fix it in some
general way.
In general I am agree with Surya's approach to scale cost of reg
saves/restores somehow. But the general approach, although solved some
problems, also created a lot of new ones. May be because IRA does not
take some other aspects of using callee saved regs. And some of them
were addressed by other patches. e.g. recently proposed by Surya and one
for PR118497.
I also agree with Richard Sandiford's comment that we should avoid
introducing the new hooks for RA and I actually tried to stick to this
policy for a long time. But I don't see another solution to introducing
the new hook in this case. It is hard to figure out generally in RA
that saves/restores will be insns different from ld/st (e.g. x86
push/pop) and that they will be cheaper.
So after some time to think about the patch I decided to approve the RA
part of the patch. I also hope that the work on this problem will
continue (e.g. improving default and target hook implementations and
documentation how to better use it).
For the record, I strongly object to this. The hook just seems like a
complete hack to me. Even if we accept that there is target-specific
information in play, the hook isn't providing that information.
In contrast to what you said above, my objection isn't to having hooks
-- those are often needed and good. What bothers me is that the hook
isn't well designed. Hooks should provide information rather than
override code by brute force.
On the other hand, I accept that you're (rightly!) the maintainer.
I also don't like the hook implementation for x86-64 (although this is a
matter of target maintainers). All these costs look voodoo and random
to me.
But this problem is longing for more than half year. I spent a lot of
time too on this. Patches were submitted and reverted and nobody did
find so far any solution satisfying all GCC tests. If somebody finds a
solution without the hook, I will be glad to get rid off the hook. Also
the related PRs are marked as P1 ones, it means people think they are
important (I am not sure about this myself). Without fixing them (or
downgrading them) there will be no GCC release. So I am in difficult
situation with these PRs and need some resolution.
