Re: [PATCH] i386: Separate costs of pseudo registers from hard registers

["H.J. Lu" <hjl.tools@gmail.com>]

On Fri, Aug 9, 2019 at 3:01 PM Jeff Law <law@redhat.com> wrote:
>
> On 7/23/19 3:57 PM, H.J. Lu wrote:
> [ Snip ]
> > Here is the updated patch to improve register allocator and RTL
> > expressions independently.
> >
> > Any comments?
> >
> > Thanks.
> >
> >
> > -- H.J.
> >
> >
> > 0001-i386-Separate-costs-of-pseudo-registers-from-hard-re.patch
> >
> > From 79834daf252cecfc3ee51acd864641d2cdaff733 Mon Sep 17 00:00:00 2001
> > From: "H.J. Lu" <hjl.tools@gmail.com>
> > Date: Fri, 14 Jun 2019 13:30:16 -0700
> > Subject: [PATCH] i386: Separate costs of pseudo registers from hard registers
> >
> > processor_costs has costs of RTL expressions with pseudo registers and
> > and costs of hard register moves:
> >
> > 1. Costs of RTL expressions are used to generate the most efficient RTL
> > operations with pseudo registers.
> >
> > 2. Costs of hard register moves are used by register allocator to
> > decide how to allocate and move hard registers.
> >
> > Since relative costs of pseudo register load and store versus pseudo
> > register moves in RTL expressions can be different from relative costs
> > of hard registers, we should separate costs of RTL expressions with
> > pseudo registers from costs of hard registers so that register allocator
> > and RTL expressions can be improved independently.
> >
> > This patch moves costs of hard register moves to the new hard_register
> > field and duplicates costs of moves which are also used for costs of RTL
> > expressions.
> >
> >       PR target/90878
> >       * config/i386/i386.c (inline_memory_move_cost): Use hard_register
> >       for costs of hard register moves.
> >       (ix86_register_move_cost): Likewise.
> >       * config/i386/i386.h (processor_costs): Move costs of hard
> >       register moves to hard_register.  Add int_load, int_store,
> >       xmm_move, ymm_move, zmm_move, sse_to_integer, integer_to_sse,
> >       sse_load, sse_store, sse_unaligned_load and sse_unaligned_store
> >       for costs of RTL expressions.
> >       * config/i386/x86-tune-costs.h: Move costs of hard register
> >       moves to hard_register.  Duplicate int_load, int_store,
> >       xmm_move, ymm_move, zmm_move, sse_to_integer, integer_to_sse,
> >       sse_load, sse_store for costs of RTL expressions.
> This looks reasonable to me.  If you haven't had objections from Jan or
> Uros, go ahead and commit it.

Will do.

> I'm assuming this patch isn't supposed to actually change anything yet
> and a subsequent patch will twiddle some of the costs, particularly for
> skylake.
>

We have a one-line followup patch to actually fix:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90878

Thanks.

-- 
H.J.