Re: other/7814: incorrect scheduling for glibc-2.2.92 stpcpy test

[Glen Nakamura <glen@imodulo.com>]

The following reply was made to PR other/7814; it has been noted by GNATS.

From: Glen Nakamura <glen@imodulo.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Cc:  
Subject: Re: other/7814: incorrect scheduling for glibc-2.2.92 stpcpy test
Date: Mon, 2 Sep 2002 10:24:48 -1000

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7814
 Okay, I think the problem is that when we flush the dependency lists
 (e.g. when ?_length > MAX_PENDING_LIST_LENGTH), we end up with a single
 insn in the 'clobbers' list while the 'sets' and 'uses' lists are empty.
 Now, if there is another clobber insn before any set or use insn, it won't
 be dependent on any previous insn because the 'sets' and 'uses' lists
 are empty...  The problem is fixed by adding the last insn to the 'sets'
 list after flushing.
 
 - glen
 
 Here is the patch:
 
 ChangeLog
 ===================================================================
 2002-09-02  Glen Nakamura  <glen@imodulo.com>
 
 	* sched-deps.c (sched_analyze_insn): Make sure to add insn
 	to reg_last->sets after flushing the dependency lists to guarantee
 	that subsequent clobbers will be dependent on it.
 
 Index: sched-deps.c
 ===================================================================
 RCS file: /cvsroot/gcc/gcc/gcc/sched-deps.c,v
 retrieving revision 1.34.6.1
 diff -c -3 -p -u -r1.34.6.1 sched-deps.c
 --- sched-deps.c	19 Aug 2002 18:59:31 -0000	1.34.6.1
 +++ sched-deps.c	2 Sep 2002 06:35:15 -0000
 @@ -1118,8 +1118,6 @@ sched_analyze_insn (deps, x, insn, loop_
  	  EXECUTE_IF_SET_IN_REG_SET (reg_pending_clobbers, 0, i,
  	    {
  	      struct deps_reg *reg_last = &deps->reg_last[i];
 -	      add_dependence_list (insn, reg_last->sets, REG_DEP_OUTPUT);
 -	      add_dependence_list (insn, reg_last->uses, REG_DEP_ANTI);
  	      if (reg_last->uses_length > MAX_PENDING_LIST_LENGTH
  		  || reg_last->clobbers_length > MAX_PENDING_LIST_LENGTH)
  		{
 @@ -1129,6 +1127,7 @@ sched_analyze_insn (deps, x, insn, loop_
  						REG_DEP_ANTI);
  		  add_dependence_list_and_free (insn, &reg_last->clobbers,
  						REG_DEP_OUTPUT);
 +		  reg_last->sets = alloc_INSN_LIST (insn, reg_last->sets);
  		  reg_last->clobbers_length = 0;
  		  reg_last->uses_length = 0;
  		}