------- 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
