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From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Wed, 16 Sep 2020 08:11:28 -0700
Message-ID: <CAMe9rOo1dzHmaGThbpcsjd6u-KxTS9xBf6_cTsNq8xZ7L0RoWA@mail.gmail.com>
Subject: Re: [PATCH] IRA: Don't make a global register eliminable
To: "H.J. Lu" <hjl.tools@gmail.com>, GCC Patches <gcc-patches@gcc.gnu.org>, 
 Vladimir Makarov <vmakarov@redhat.com>,
 Richard Sandiford <richard.sandiford@arm.com>
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On Wed, Sep 16, 2020 at 7:46 AM Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> "H.J. Lu" <hjl.tools@gmail.com> writes:
> > On Tue, Sep 15, 2020 at 7:44 AM Richard Sandiford
> > <richard.sandiford@arm.com> wrote:
> >>
> >> Thanks for looking at this.
> >>
> >> "H.J. Lu" <hjl.tools@gmail.com> writes:
> >> > commit 1bcb4c4faa4bd6b1c917c75b100d618faf9e628c
> >> > Author: Richard Sandiford <richard.sandiford@arm.com>
> >> > Date:   Wed Oct 2 07:37:10 2019 +0000
> >> >
> >> >     [LRA] Don't make eliminable registers live (PR91957)
> >> >
> >> > didn't make eliminable registers live which breaks
> >> >
> >> > register void *cur_pro asm("reg");
> >> >
> >> > where "reg" is an eliminable register.  Make fixed eliminable registers
> >> > live to fix it.
> >>
> >> I don't think fixedness itself is the issue here: it's usual for at
> >> least some registers involved in eliminations to be fixed registers.
> >>
> >> I think what makes this case different is instead that cur_pro/ebp
> >> is a global register.  But IMO things have already gone wrong if we
> >> think that a global register is eliminable.
> >>
> >> So I wonder if instead we should check global_regs at the beginning of:
> >>
> >>       for (i = 0; i < fp_reg_count; i++)
> >>         if (!TEST_HARD_REG_BIT (crtl->asm_clobbers,
> >>                                 HARD_FRAME_POINTER_REGNUM + i))
> >>           {
> >>             SET_HARD_REG_BIT (eliminable_regset,
> >>                               HARD_FRAME_POINTER_REGNUM + i);
> >>             if (frame_pointer_needed)
> >>               SET_HARD_REG_BIT (ira_no_alloc_regs,
> >>                                 HARD_FRAME_POINTER_REGNUM + i);
> >>           }
> >>         else if (frame_pointer_needed)
> >>           error ("%s cannot be used in %<asm%> here",
> >>                  reg_names[HARD_FRAME_POINTER_REGNUM + i]);
> >>         else
> >>           df_set_regs_ever_live (HARD_FRAME_POINTER_REGNUM + i, true);
> >>
> >> (ira_setup_eliminable_regset), and handle the global_regs[] case in
> >> the same way as the else case, i.e. short-circuiting both of the ifs.
> >>
> >
> > Like this?
>
> Sorry for the delay.  I was testing this in parallel.
>
> Bootstrapped & regression-tested on x86_64-linux-gnu.
>

Thanks.

-- 
H.J.