[PATCH] Assuage ICE in VRP with [1, X] + UINT_MAX (PR tree-optimization/71031)

[Marek Polacek]

Since Bin's changes to the niter analysis in r231097, we find ourselves in
a situation where extract_range_from_binary_expr is given [1, od_5] + UINT_MAX
on type unsigned.  We combine the lower bounds, which is 1 + UINT_MAX = 0(OVF).
We then combine the upper bounds, because the max_op0 is not a constant, the
result of that is UINT_MAX.  That results in min overflow -- and an assert is
unhappy about that.  As suggested in the PR, a safe thing would be to change
the assert to dropping to varying.

Bootstrapped/regtested on x86_64-linux, ok for trunk and 6?

2016-05-19  Marek Polacek  <pola...@redhat.com>

        PR tree-optimization/71031
        * tree-vrp.c (extract_range_from_binary_expr_1): Drop to varying for
        min overflow or max underflow and remove an assert.

        * gcc.dg/tree-ssa/vrp100.c: New test.

diff --git gcc/testsuite/gcc.dg/tree-ssa/vrp100.c 
gcc/testsuite/gcc.dg/tree-ssa/vrp100.c
index e69de29..c0fe4b5 100644
--- gcc/testsuite/gcc.dg/tree-ssa/vrp100.c
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp100.c
@@ -0,0 +1,32 @@
+/* PR tree-optimization/71031 */
+/* { dg-do compile } */
+/* { dg-options "-Os" } */
+
+int zj;
+int **yr;
+
+void
+nn (void)
+{
+  unsigned int od = 4;
+
+  for (;;)
+    {
+      int lk;
+
+      for (lk = 0; lk < 2; ++lk)
+        {
+          static int cm;
+
+          zj = 0;
+          if (od == 0)
+            return;
+          ++od;
+          for (cm = 0; cm < 2; ++cm)
+            {
+              --od;
+              **yr = 0;
+            }
+        }
+    }
+}
diff --git gcc/tree-vrp.c gcc/tree-vrp.c
index 69e6248..791d738 100644
--- gcc/tree-vrp.c
+++ gcc/tree-vrp.c
@@ -2525,14 +2525,19 @@ extract_range_from_binary_expr_1 (value_range *vr,
                  set_value_range_to_varying (vr);
                  return;
                }
+             else if ((min_ovf == 1 && max_ovf == 0)
+                      || (min_ovf == 0 && max_ovf == -1))
+               {
+                 /* Min overflow or max underflow, drop to VR_VARYING.  */
+                 set_value_range_to_varying (vr);
+                 return;
+               }
              else
                {
                  /* Min underflow or max overflow.  The range kind
                     changes to VR_ANTI_RANGE.  */
                  bool covers = false;
                  wide_int tem = tmin;
-                 gcc_assert ((min_ovf == -1 && max_ovf == 0)
-                             || (max_ovf == 1 && min_ovf == 0));
                  type = VR_ANTI_RANGE;
                  tmin = tmax + 1;
                  if (wi::cmp (tmin, tmax, sgn) < 0)

        Marek