Re: mn10300, invariants on DEP_PRO/DEP_CON and on TARGET_SCHED_ADJUST_COST params

[David Malcolm <dmalcolm at redhat dot com>]

On Fri, 2014-07-11 at 10:13 +1200, Maxim Kuvyrkov wrote:
> On Jul 9, 2014, at 8:21 AM, David Malcolm <dmalcolm@redhat.com> wrote:
> 
> > [CCing nickc, who wrote the mn10300 hook in question]
> > 
> > I'm experimenting with separating out instructions from expressions in
> > RTL; see [1] for more info on that.
> > 
> > I noticed that mn10300 has this implementation of a target hook:
> >  #define TARGET_SCHED_ADJUST_COST mn10300_adjust_sched_cost
> > 
> > Within mn10300_adjust_sched_cost (where "insn" and "dep" are the first
> > and third parameters respectively), there's this code:
> > 
> >  if (GET_CODE (insn) == PARALLEL)
> >    insn = XVECEXP (insn, 0, 0);
> > 
> >  if (GET_CODE (dep) == PARALLEL)
> >    dep = XVECEXP (dep, 0, 0);
> > 
> > However, I believe that these params of this hook ("insn") always
> > satisfy INSN_CHAIN_CODE_P, and so can't have code PARALLEL.  [Nick: did
> > those conditionals ever get triggered, or was this defensive coding?]
> 
> From what I can tell these are remnants from the early days of
> haifa-sched (10+ years ago).  I would be very surprised if scheduler
> didn't ICE on a PARALLEL of INSNs (not to be confused with a PARALLEL
> as INSN_PATTERN).

Thanks.  In my experimental patch series [1] I've gone ahead and removed
those checks.

> > Specifically, the hook is called from haifa-sched.c:dep_cost_1 on the
> > DEP_CON and DEP_PRO of a dep_t.
> > 
> > It's my belief that DEP_CON and DEP_PRO always satisfy INSN_CHAIN_CODE_P
> > - and on every other config so far that seems to be the case.
> > 
> > Is my belief about DEP_CON/DEP_PRO correct?  (or, at least, consistent
> > with other gcc developers' views on the matter :))  My patch kit [2] has
> > this expressed in the type system as of [3], so if I'm incorrect about
> > this I'd prefer to know ASAP.
> 
> Yes, it is correct.

Thanks; that's reassuring.

> > 
> > Similarly, do the first and third params of TARGET_SCHED_ADJUST_COST
> > also satisfy INSN_CHAIN_CODE_P?
> > 
> 
> Yes, since they are always derived from DEP_CON / DEP_PRO.

(nods)

Thanks again
Dave

[1] fwiw, latest work-in-progress of instructions vs expressions:
http://dmalcolm.fedorapeople.org/gcc/patch-backups/rtx-classes/v12/
with the removal of the redundant checks for PARALLEL in:
http://dmalcolm.fedorapeople.org/gcc/patch-backups/rtx-classes/v12/0205-FIXME-config-mn10300-Fix-for-target.def-patch.patch