[PATCH] Improve PR78655

[Richard Biener]

The following implements parts of the suggested transforms in PR78655
by making code already in VRP actually trigger.  The patch doesn't
handle

void bar (int *x, int a)
{
  if (a != 0)
    {
      int *p = x + a;
      if (p == 0)
        link_error ();
    }
}

because a gets promoted to sizetype and the multiplied by 4 which
has defined overflow and thus gets us zero in the range for the
addend again.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2018-08-20  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/78655
        * tree-vrp.c (extract_range_from_binary_expr_1): Make
        pointer + offset nonnull if either operand is nonnull work.

        * gcc.dg/tree-ssa/evrp11.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/evrp11.c 
b/gcc/testsuite/gcc.dg/tree-ssa/evrp11.c
new file mode 100644
index 00000000000..f1373bd8683
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/evrp11.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-evrp" } */
+
+extern void link_error ();
+
+void foo (int *x)
+{
+  int *p = x + 1;
+  if (p == 0)
+    link_error ();
+}
+
+void bar (char *x, int a)
+{
+  if (a != 0)
+    {
+      char *p = x + a;
+      if (p == 0)
+       link_error ();
+    }
+}
+
+/* { dg-final { scan-tree-dump-not "link_error" "evrp" } }  */
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index d553a254878..2ddb0c2c197 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -1437,6 +1437,7 @@ extract_range_from_binary_expr_1 (value_range *vr,
       && code != PLUS_EXPR
       && code != MINUS_EXPR
       && code != RSHIFT_EXPR
+      && code != POINTER_PLUS_EXPR
       && (vr0.type == VR_VARYING
          || vr1.type == VR_VARYING
          || vr0.type != vr1.type
@@ -1467,7 +1468,11 @@ extract_range_from_binary_expr_1 (value_range *vr,
        {
          /* For pointer types, we are really only interested in asserting
             whether the expression evaluates to non-NULL.  */
-         if (range_is_nonnull (&vr0) || range_is_nonnull (&vr1))
+         if (range_is_nonnull (&vr0)
+             || range_is_nonnull (&vr1)
+             || (vr1.type == VR_RANGE
+                 && !symbolic_range_p (&vr1)
+                 && !range_includes_zero_p (vr1.min, vr1.max)))
            set_value_range_to_nonnull (vr, expr_type);
          else if (range_is_null (&vr0) && range_is_null (&vr1))
            set_value_range_to_null (vr, expr_type);