re PR tree-optimization/76490 (when use -O2 -fcheck-founds compiler appears to hang and consumes all memory)

2016-08-17  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/76490
	* tree-vrp.c (update_value_range): Preserve overflow infinities
	when intersecting with ranges from get_range_info.
	(operand_less_p): Handle overflow infinities correctly.
	(value_range_constant_singleton): Use vrp_operand_equal_p
	to handle overflow max/min correctly.
	(vrp_valueize): Likewise.
	(union_ranges): Likewise.
	(intersect_ranges): Likewise.
	(vrp_visit_phi_node): Improve iteration limitation to only
	apply when we'll possibly re-visit the PHI via a changed argument
	on the backedge.

	* gfortran.fortran-torture/compile/pr76490.f90: New testcase.
	* gcc.dg/pr52904.c: XFAIL.

From-SVN: r239529

1 files changed, 30 insertions, 16 deletions

diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index 6934914..a881013 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -774,8 +774,20 @@ update_value_range (const_tree var, value_range *new_vr)
 	{
 	  value_range nr;
 	  nr.type = rtype;
-	  nr.min = wide_int_to_tree (TREE_TYPE (var), min);
-	  nr.max = wide_int_to_tree (TREE_TYPE (var), max);
+	  /* Range info on SSA names doesn't carry overflow information
+	     so make sure to preserve the overflow bit on the lattice.  */
+	  if (new_vr->type == VR_RANGE
+	      && is_negative_overflow_infinity (new_vr->min)
+	      && wi::eq_p (new_vr->min, min))
+	    nr.min = new_vr->min;
+	  else
+	    nr.min = wide_int_to_tree (TREE_TYPE (var), min);
+	  if (new_vr->type == VR_RANGE
+	      && is_positive_overflow_infinity (new_vr->max)
+	      && wi::eq_p (new_vr->max, max))
+	    nr.max = new_vr->max;
+	  else
+	    nr.max = wide_int_to_tree (TREE_TYPE (var), max);
 	  nr.equiv = NULL;
 	  vrp_intersect_ranges (new_vr, &nr);
 	}
@@ -1138,7 +1150,10 @@ operand_less_p (tree val, tree val2)
 {
   /* LT is folded faster than GE and others.  Inline the common case.  */
   if (TREE_CODE (val) == INTEGER_CST && TREE_CODE (val2) == INTEGER_CST)
-    return tree_int_cst_lt (val, val2);
+    {
+      if (! is_positive_overflow_infinity (val2))
+	return tree_int_cst_lt (val, val2);
+    }
   else
     {
       tree tcmp;
@@ -1422,7 +1437,7 @@ static tree
 value_range_constant_singleton (value_range *vr)
 {
   if (vr->type == VR_RANGE
-      && operand_equal_p (vr->min, vr->max, 0)
+      && vrp_operand_equal_p (vr->min, vr->max)
       && is_gimple_min_invariant (vr->min))
     return vr->min;
 
@@ -7028,8 +7043,7 @@ vrp_valueize (tree name)
     {
       value_range *vr = get_value_range (name);
       if (vr->type == VR_RANGE
-	  && (vr->min == vr->max
-	      || operand_equal_p (vr->min, vr->max, 0)))
+	  && vrp_operand_equal_p (vr->min, vr->max))
 	return vr->min;
     }
   return name;
@@ -7995,8 +8009,8 @@ union_ranges (enum value_range_type *vr0type,
 	      enum value_range_type vr1type,
 	      tree vr1min, tree vr1max)
 {
-  bool mineq = operand_equal_p (*vr0min, vr1min, 0);
-  bool maxeq = operand_equal_p (*vr0max, vr1max, 0);
+  bool mineq = vrp_operand_equal_p (*vr0min, vr1min);
+  bool maxeq = vrp_operand_equal_p (*vr0max, vr1max);
 
   /* [] is vr0, () is vr1 in the following classification comments.  */
   if (mineq && maxeq)
@@ -8266,8 +8280,8 @@ intersect_ranges (enum value_range_type *vr0type,
 		  enum value_range_type vr1type,
 		  tree vr1min, tree vr1max)
 {
-  bool mineq = operand_equal_p (*vr0min, vr1min, 0);
-  bool maxeq = operand_equal_p (*vr0max, vr1max, 0);
+  bool mineq = vrp_operand_equal_p (*vr0min, vr1min);
+  bool maxeq = vrp_operand_equal_p (*vr0max, vr1max);
 
   /* [] is vr0, () is vr1 in the following classification comments.  */
   if (mineq && maxeq)
@@ -8725,7 +8739,7 @@ vrp_visit_phi_node (gphi *phi)
       print_gimple_stmt (dump_file, phi, 0, dump_flags);
     }
 
-  bool may_simulate_again = false;
+  bool may_simulate_backedge_again = false;
   edges = 0;
   for (i = 0; i < gimple_phi_num_args (phi); i++)
     {
@@ -8751,8 +8765,9 @@ vrp_visit_phi_node (gphi *phi)
 	      /* See if we are eventually going to change one of the args.  */
 	      gimple *def_stmt = SSA_NAME_DEF_STMT (arg);
 	      if (! gimple_nop_p (def_stmt)
-		  && prop_simulate_again_p (def_stmt))
-		may_simulate_again = true;
+		  && prop_simulate_again_p (def_stmt)
+		  && e->flags & EDGE_DFS_BACK)
+		may_simulate_backedge_again = true;
 
 	      vr_arg = *(get_value_range (arg));
 	      /* Do not allow equivalences or symbolic ranges to leak in from
@@ -8830,13 +8845,12 @@ vrp_visit_phi_node (gphi *phi)
      edge; this helps us avoid an overflow infinity for conditionals
      which are not in a loop.  If the old value-range was VR_UNDEFINED
      use the updated range and iterate one more time.  If we will not
-     simulate this PHI again with the same number of edges then iterate
-     one more time.  */
+     simulate this PHI again via the backedge allow us to iterate.  */
   if (edges > 0
       && gimple_phi_num_args (phi) > 1
       && edges == old_edges
       && lhs_vr->type != VR_UNDEFINED
-      && may_simulate_again)
+      && may_simulate_backedge_again)
     {
       /* Compare old and new ranges, fall back to varying if the
          values are not comparable.  */