[Bug tree-optimization/17560] [4.0 Regression] Infinite recursion in tree-scalar-evolution with -Os

["sebastian dot pop at cri dot ensmp dot fr" <gcc-bugzilla@gcc.gnu.org>]

------- Additional Comments From sebastian dot pop at cri dot ensmp dot fr  2004-10-08 13:03 -------
Subject: Re:  [4.0 Regression] Infinite recursion in tree-scalar-evolution with -Os

> It seems to me that this can definitly happen in the case of irreducible
> regions...
> 
> Honza

Then the following patch solves the problem by avoiding the analysis
of these cycles.


Index: tree-scalar-evolution.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-scalar-evolution.c,v
retrieving revision 2.8
diff -c -c -3 -p -r2.8 tree-scalar-evolution.c
*** tree-scalar-evolution.c	1 Oct 2004 09:05:57 -0000	2.8
--- tree-scalar-evolution.c	8 Oct 2004 12:59:37 -0000
*************** tree chrec_dont_know;
*** 284,289 ****
--- 284,290 ----
  tree chrec_known;
  
  static bitmap already_instantiated;
+ static bitmap already_analyzed;
  
  static htab_t scalar_evolution_info;
  
*************** follow_ssa_edge_in_condition_phi (struct
*** 1398,1403 ****
--- 1399,1409 ----
  
    for (i = 1; i < PHI_NUM_ARGS (condition_phi); i++)
      {
+       /* Quickly give up when the evolution of one of the branches is
+ 	 not known.  */
+       if (*evolution_of_loop == chrec_dont_know)
+ 	return true;
+ 
        if (!follow_ssa_edge_in_condition_phi_branch (i, loop, condition_phi,
  						    halting_phi,
  						    &evolution_of_branch,
*************** analyze_scalar_evolution_1 (struct loop 
*** 1833,1838 ****
--- 1839,1853 ----
        goto set_and_end;
      }
  
+   /* Fail on irreducible CFGs.  */
+   if (bitmap_bit_p (already_analyzed, SSA_NAME_VERSION (var)))
+     {
+       res = chrec_dont_know;
+       goto set_and_end;
+     }
+   else
+     bitmap_set_bit (already_analyzed, SSA_NAME_VERSION (var));
+ 
    if (res != chrec_not_analyzed_yet)
      {
        if (loop != bb->loop_father)
*************** analyze_scalar_evolution_1 (struct loop 
*** 1870,1875 ****
--- 1885,1892 ----
  
   set_and_end:
  
+   bitmap_clear_bit (already_analyzed, SSA_NAME_VERSION (var));
+ 
    /* Keep the symbolic form.  */
    if (res == chrec_dont_know)
      res = var;
*************** scev_initialize (struct loops *loops)
*** 2450,2455 ****
--- 2467,2473 ----
    scalar_evolution_info = htab_create (100, hash_scev_info,
  				       eq_scev_info, del_scev_info);
    already_instantiated = BITMAP_XMALLOC ();
+   already_analyzed = BITMAP_XMALLOC ();
    
    initialize_scalar_evolutions_analyzer ();
  
*************** scev_finalize (void)
*** 2545,2549 ****
--- 2563,2568 ----
  {
    htab_delete (scalar_evolution_info);
    BITMAP_XFREE (already_instantiated);
+   BITMAP_XFREE (already_analyzed);
  }
  


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17560