tree-optimization/112706 - missed simplification of condition

We lack a match.pd pattern recognizing ptr + o ==/!= ptr + o'.
The following extends handling we have for integral types to
pointers.

	PR tree-optimization/112706
	* match.pd (ptr + o ==/!=/- ptr + o'): New patterns.

	* gcc.dg/tree-ssa/pr112706.c: New testcase.

Author: rguenth

gcc/match.pd

@@ -2596,6 +2596,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
        && (TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0))
 	   || TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0))))
    (op @0 @1))))
+/* And similar for pointers.  */
+(for op (eq ne)
+ (simplify
+  (op (pointer_plus @0 @1) (pointer_plus @0 @2))
+  (op @1 @2)))
+(simplify
+ (pointer_diff (pointer_plus @0 @1) (pointer_plus @0 @2))
+ (if (TYPE_OVERFLOW_WRAPS (TREE_TYPE (@1)))
+  (convert (minus @1 @2))))
 
 /* X - Z < Y - Z is the same as X < Y when there is no overflow.  */
 (for op (lt le ge gt)

gcc/testsuite/gcc.dg/tree-ssa/pr112706.c

@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-fre1" } */
+
+int *ptr;
+void link_error ();
+void
+test ()
+{
+  int *ptr1 = ptr + 10;
+  int *ptr2 = ptr + 20;
+  if (ptr1 == ptr2)
+    link_error ();
+}
+
+/* { dg-final { scan-tree-dump-not "if" "fre1" } } */