[Bug tree-optimization/48189] [4.3/4.4/4.5/4.6/4.7 Regression] ICE: SIGFPE (division by zero) in in predict_loops () at predict.c:991 with --param max-predicted-iterations=0

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48189

Steven Bosscher <steven at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |steven at gcc dot gnu.org

--- Comment #3 from Steven Bosscher <steven at gcc dot gnu.org> 2011-04-10 
13:33:30 UTC ---
I'd say probability is zero i.e. never executed, as a special case. Or if you
consider the edge always taken, then the probability should be
REG_BR_PROB_BASE. 

But zero seems more consistent:

Index: predict.c
===================================================================
--- predict.c   (revision 172225)
+++ predict.c   (working copy)
@@ -988,7 +988,14 @@
          else
            continue;

-         probability = ((REG_BR_PROB_BASE + nitercst / 2) / nitercst);
+         if (nitercst == 0 && predictor == PRED_LOOP_ITERATIONS)
+           /* If the prediction for number of iterations is zero, the exits
+              will never be taken.  Only make this prediction if we are quite
+              sure that the loop will never roll, from analysis.  */
+           probability = 0;
+         else
+           probability = ((REG_BR_PROB_BASE + nitercst / 2) / nitercst);
+
          predict_edge (ex, predictor, probability);
        }
       VEC_free (edge, heap, exits);


Or maybe just not predict at all:

Index: predict.c
===================================================================
--- predict.c   (revision 172225)
+++ predict.c   (working copy)
@@ -988,6 +988,11 @@
          else
            continue;

+         /* If the prediction for number of iterations is zero, do not
+            predict the exit edges.  */
+         if (nitercst == 0)
+           continue;
+
          probability = ((REG_BR_PROB_BASE + nitercst / 2) / nitercst);
          predict_edge (ex, predictor, probability);
        }