Re: [PATCH] x86-64: Find a scratch register for large model profiling

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

On Thu, Feb 1, 2024 at 10:32 AM Jakub Jelinek <jakub@redhat.com> wrote:
>
> On Thu, Feb 01, 2024 at 10:15:30AM -0800, H.J. Lu wrote:
> > --- a/gcc/config/i386/i386.cc
> > +++ b/gcc/config/i386/i386.cc
> > @@ -22749,6 +22749,31 @@ current_fentry_section (const char **name)
> >    return true;
> >  }
> >
> > +/* Return an unused caller-saved register at entry for profile.  */
> > +
> > +static int
> > +x86_64_select_profile_regnum (bool r11_ok ATTRIBUTE_UNUSED)
> > +{
> > +  int i;
>
> Why not just return R10_REG here if flag_entry != 0 (i.e. keep existing
> behavior unless emitting profiler after prologue)?

Fixed in v2.

> > +  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
> > +    if (GENERAL_REGNO_P (i)
> > +#ifdef NO_PROFILE_COUNTERS
> > +     && (r11_ok || i != R11_REG)
> > +#else
> > +     && i != R11_REG
> > +#endif
> > +     && (!REX2_INT_REGNO_P (i) || TARGET_APX_EGPR)
> > +     && !fixed_regs[i]
> > +     && call_used_regs[i]
> > +     && !df_regs_ever_live_p (i))
>
> Also, isn't this too restrictive?
> I mean, all we care about is whether there is some register
> which is not live across the NOTE_INSN_PROLOG_END note, no?
> I.e. doesn't contain any of function's argument that are used later,
> and isn't set in the prologue to be used later.  E.g. call used
> register which is just saved to stack in the prologue might be just fine.

Fixed in v2.

> > +      return i;
> > +
> > +  sorry ("No register available for profiling %<-mcmodel=large%s%>",
>
> Diagnostics shouldn't start with capital letter.
>
> > +      ix86_cmodel == CM_LARGE_PIC ? " -fPIC" : "");
> > +
> > +  return INVALID_REGNUM;
> > +}
> > +
> >  /* Output assembler code to FILE to increment profiler label # LABELNO
> >     for profiling a function entry.  */
> >  void
>
>         Jakub
>


-- 
H.J.