[Bug rtl-optimization/32296] [4.3 Regression] Bootstrap failure in stage1 on hppa*-*-*

["spark at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #6 from spark at gcc dot gnu dot org  2007-06-12 23:07 -------
(In reply to comment #5)
> Subject: Re:  [4.3 Regression] Bootstrap failure in stage1 on hppa*-*-*
> 
> > @@ -4384,7 +4385,7 @@ hppa_can_use_return_insn_p (void)
> >  {
> >    return (reload_completed
> >           && (compute_frame_size (get_frame_size (), 0) ? 0 : 1)
> > -         && ! df_regs_ever_live_p (2)
> > +         && df_hard_reg_used_count (2) == 1
> >           && ! frame_pointer_needed);
> >  }
> 
> Don't understand difference between df_regs_ever_live_p and
> f->hard_regs_live_count, and why you are checking for a count of 1.

hppa_can_use_return_insn_p() is called 
from "return" insn pattern in pa.md.
The pattern looks:

(define_insn "return"
  [(return)
   (use (reg:SI 2))
   (const_int 0)]
  "hppa_can_use_return_insn_p ()"
  "*

i.e. there's a use of reg 2.

Before dataflow branch got merged, regs_ever_live(2) was not true
for reg 2, even though it is used at the return (hence it's live
throughout the function body) - unless there's some other use
within the function.

Now, with df, we always have the correct and precise regs_ever_live.
Since the condition hppa_can_use_return_p() is checking 
is really that there are no other insn that uses reg 2
AND since we know the pattern has a use of reg 2,
checking the number of use count to be 1
checks effectively the same assertion.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32296