Fix division by zero in loop splitting

Profile update I added to tree-ssa-loop-split can divide by zero in
situation that the conditional is predicted with 0 probability which
is triggered by jump threading update in the testcase.

gcc/ChangeLog:

	PR middle-end/110923
	* tree-ssa-loop-split.cc (split_loop): Watch for division by zero.

gcc/testsuite/ChangeLog:

	PR middle-end/110923
	* gcc.dg/tree-ssa/pr110923.c: New test.

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr110923.c b/gcc/testsuite/gcc.dg/tree-ssa/pr110923.c
new file mode 100644 (file)
index 0000000..8f5720a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr110923.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */ 
+/* { dg-options "-O3 -fdump-tree-lsplit-details-blocks" } */
+int a, b, c, d;
+int main() {
+  for (a = 0; a < 2; a++) {
+    if (b > 2)
+      c = 0;
+    if (b > a)
+      d = 0;
+  }
+  return 0;
+}
+/* { dg-final { scan-tree-dump-times "loop split" 1 "lsplit" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "lsplit" } } */

diff --git a/gcc/tree-ssa-loop-split.cc b/gcc/tree-ssa-loop-split.cc
index 2f7918c6e65adaad31caed9590c97d54e0e3aae0..64464802c1e565cfb7fdc3eaf880c3a9a8877ada 100644 (file)
--- a/gcc/tree-ssa-loop-split.cc
+++ b/gcc/tree-ssa-loop-split.cc
@@ -703,7 +703,7 @@ split_loop (class loop *loop1)
           split between of the two new loops.  Keep orignal estimate since
           it is likely better then completely dropping it.
 
-          TODO: If we know that onle of the new loops has constant
+          TODO: If we know that one of the new loops has constant
           number of iterations, we can do better.  We could also update
           upper bounds.  */
        if (loop1->any_estimate
@@ -713,11 +713,15 @@ split_loop (class loop *loop1)
                          ? true_edge->probability.to_sreal () : (sreal)1;
            sreal scale2 = false_edge->probability.reliable_p ()
                          ? false_edge->probability.to_sreal () : (sreal)1;
+           sreal div1 = loop1_prob.to_sreal ();
            /* +1 to get header interations rather than latch iterations and then
               -1 to convert back.  */
-           loop1->nb_iterations_estimate
-             = MAX ((((sreal)loop1->nb_iterations_estimate.to_shwi () + 1) * scale
-                    / loop1_prob.to_sreal ()).to_nearest_int () - 1, 0);
+           if (div1 != 0)
+             loop1->nb_iterations_estimate
+               = MAX ((((sreal)loop1->nb_iterations_estimate.to_shwi () + 1)
+                      * scale / div1).to_nearest_int () - 1, 0);
+           else
+             loop1->any_estimate = false;
            loop2->nb_iterations_estimate
              = MAX ((((sreal)loop2->nb_iterations_estimate.to_shwi () + 1) * scale2
                     / profile_probability::very_likely ().to_sreal ())