0001-Part-1.-Add-generic-part-for-Intel-CET-enabling

[Tsimbalist, Igor V]

> -----Original Message-----
> From: Tsimbalist, Igor V
> Sent: Tuesday, September 12, 2017 5:59 PM
> To: 'Jeff Law' <law@redhat.com>; 'gcc-patches@gcc.gnu.org' <gcc-
> patches@gcc.gnu.org>
> Cc: Tsimbalist, Igor V <igor.v.tsimbalist@intel.com>
> Subject: RE: 0001-Part-1.-Add-generic-part-for-Intel-CET-enabling
> 
> 
> > -----Original Message-----
> > From: Jeff Law [mailto:law@redhat.com]
> > Sent: Friday, August 25, 2017 10:50 PM
> > To: Tsimbalist, Igor V <igor.v.tsimbalist@intel.com>; 'gcc-
> > patches@gcc.gnu.org' <gcc-patches@gcc.gnu.org>
> > Subject: Re: 0001-Part-1.-Add-generic-part-for-Intel-CET-enabling
> >
> > On 08/01/2017 02:56 AM, Tsimbalist, Igor V wrote:
> > > Part#1. Add generic part for Intel CET enabling.
> > >
>
> > Q. Do we need to do anything with ICF (identical code folding) and CFE?
> > Given two functions which have the same implementation in gimple,
> > except that one has a notrack indirect call and the other has a
> > tracked indirect call, what is proper behavior?  I think we'd keep
> > them separate which implies we need to make sure the notrack attribute
> > is part of the ICF hashing implementation.  It'd probably even be
> > worth building a test for this :-)
> Are you talking about a case when such two functions are inlined? Or there is
> a possibility to merge function bodies if they are identical?
> 
> I agree with you that the functions should be kept separate. I haven't looked
> into such optimization in gcc so I need to learn it.
I thought over this case and my conclusion is that nothing has to be done regarding ICF.

First of all let's sync on a case we are talking about. A code template could look like

fn1 definition
{
  <some code>
}

fn2 definition with notrack attribute
{
  <the same code as in fn1>
}

func definition
{
  <calling fn1>...<calling fn2>
}

Is it the case you are talking about? Let's consider different scenarios:

1) calls to fn1 and fn2 are direct calls. In that case 'notrack' has no effect on direct calls as they are
assumed to be save (it applies to indirect calls only). ICF can be done here;
2) one of calls is an indirect call or both calls are indirect calls. If compiler can prove what exact functions
are called then indirect call(s) can be replaced by direct call(s) and that gives us the case 1);
3) if compiler cannot prove what function is called it will keep the indirect call and so there is nothing
to do for ICF here. 

Thanks,
Igor

> 
> > >  }
> > >
> > >
> > > +/* Return true if call GS is marked as no-track.  */
> > > +
> > > +static inline bool
> > > +gimple_call_with_notrack_p (const gcall *gs) {
> > > +  return (gs->subcode & GF_CALL_WITH_NOTRACK) != 0; }
> > > +
> > > +static inline bool
> > > +gimple_call_with_notrack_p (const gimple *gs) {
> > > +  const gcall *gc = GIMPLE_CHECK2<const gcall *> (gs);
> > > +  return gimple_call_with_notrack_p (gc); }
> > Agree with Richi WRT avoiding gimple * overloads.
> Fixed.
> 
> Thanks,
> Igor
> 
> >
> >
> > Jeff