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?

Thanks.

-- 
H.J.