Re: Fix PR34916, 35519 Combine (Dataflow merge regression.)

[Andy H <hutchinsonandy at aim dot com>]

Please refer to PR35519 which contains a detailed explanation.

*http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35519*

If necessary, I can provide further clarification.

Anything is cheaper than the current bug but  I could not figure out a 
cheaper way to solve issue.

best regards


Richard Guenther wrote:
> On Tue, Mar 18, 2008 at 10:35 PM, Andy H <hutchinsonandy@aim.com> wrote:
>   
> > This patch fixes combine bugs. Now cleaned up with Change log entry.
> >
> >  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34916
> >  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35519
> >
> >  which appeared after dataflow merge (rev 125624).
> >
> >  Could this be committed please? I have tested with cygwin/AVR port and
> >  there were no regressions.
> >  I cannot test on other targets due to speed of Dejagnu under cygwin.
> >     
>
> That doesn't look cheap.  Also you don't explain how this happens in the
> first place.
>
> Richard.
>
>   
> >  PS I have assignment paperwork on file with FSF.
> >
> >
> >  2008-03-16 Andy Hutchinson <hutchinsonandy@aim.com>
> >
> >         PR rtl-optimization/34916
> >         PR middle-end/35519
> >          * combine.c (create_log_links): Do not create duplicate LOG_LINKS
> >          between instruction pairs.
> >
> >
> > Index: combine.c
> >  ===================================================================
> >  --- combine.c   (revision 133282)
> >  +++ combine.c   (working copy)
> >  @@ -976,8 +976,17 @@
> >                       assignments later.  */
> >                    if (regno >= FIRST_PSEUDO_REGISTER
> >                        || asm_noperands (PATTERN (use_insn)) < 0)
> >  -                    LOG_LINKS (use_insn) =
> >  -                      alloc_INSN_LIST (insn, LOG_LINKS (use_insn));
> >  +                    {
> >  +                        /* Don't add duplicates links between instructions. */
> >  +                        rtx links;
> >  +                        for (links = LOG_LINKS (use_insn); links; links = XEXP (links, 1))
> >  +                            if (insn == XEXP (links, 0))
> >  +                                break;
> >  +
> >  +                        if (!links)
> >  +                            LOG_LINKS (use_insn) =
> >  +                              alloc_INSN_LIST (insn, LOG_LINKS (use_insn));
> >  +                    }
> >                  }
> >                next_use[regno] = NULL_RTX;
> >              }
> >
> >
> >