Re: AIX regression due to DFA scheduler merge

[Vladimir Makarov <vmakarov at redhat dot com>]

law@redhat.com wrote:
> 
>  In message <3CF7DA0F.B8C69795@redhat.com>, Vladimir Makarov writes:
>  > >         If I understand Jeff's earlier comment correctly, the local-alloc
>  > > problem may help with the latent bugs uncovered in the proposed
>  > > SCHED_GROUP fix.  The SCHED_GROUP patch is necessary for other reasons, so
>  > > we may need *both* fixes.
>  >
>  >   I've just read email thread about the SCHED_GROUP patch.  The idea is
>  > clear and its implementation should prevent the bug occurring.  So I
>  > don't think that  the local-alloc problem may help with the latent bugs
>  > uncovered in the proposed SCHED_GROUP fix".
>  >
>  >   Also I don't think SCHED_GROUP patch is good for all processors and
>  > tests.  It remove probability to generate a better insn schedules.
>  > Although there are cases (when the register pressure is too high) when
>  > better insn schedules result in worse code.  This is standard conflict
>  > of separate insn scheduler and register allocator.  It can be solved by
>  > some their integration not rejecting opportunities in one optimization.
>  > So I don't like the SCHED_GROUP patch (its libcall part).
>  >
>  >   Although the idea not to move clobber too far is right, but it should
>  > be solved not by making all LIBCALL as SCHED_GROUP.  At least it is
>  > better to make only clobber and the 1st insn used the register as a
>  > SCHED_GROUP.
> BTW, I should also mention that I think libcall blocks suck and they should
> be eliminated in the long term.  But they're going to be around for a while
> so we should do something sensible with them.

They definitely suck as many other RTL features.