[PATCH] Improve "str" + 2 > "str" folding (PR c++/71448)

[Jakub Jelinek]

Hi!

For the purposes of fold_comparison, various constants (in this case
STRING_CST) work the same as decls, in particular we know the objects
extents and can determine possible pointer wrapping.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk
(and maybe later for 6.x)?

2016-06-08  Jakub Jelinek  <ja...@redhat.com>
            Richard Biener  <rguent...@suse.de>

        PR c++/71448
        * fold-const.c (fold_comparison): Handle CONSTANT_CLASS_P (base0)
        the same as DECL_P (base0) for indirect_base0.  Use equality_code
        in one further place.

        * g++.dg/torture/pr71448.C: New test.

--- gcc/fold-const.c.jj 2016-06-06 19:39:40.000000000 +0200
+++ gcc/fold-const.c    2016-06-08 10:23:15.129178865 +0200
@@ -8527,9 +8527,9 @@ fold_comparison (location_t loc, enum tr
          if ((offset0 == offset1
               || (offset0 && offset1
                   && operand_equal_p (offset0, offset1, 0)))
-             && (code == EQ_EXPR
-                 || code == NE_EXPR
-                 || (indirect_base0 && DECL_P (base0))
+             && (equality_code
+                 || (indirect_base0
+                     && (DECL_P (base0) || CONSTANT_CLASS_P (base0)))
                  || POINTER_TYPE_OVERFLOW_UNDEFINED))
 
            {
@@ -8568,7 +8568,8 @@ fold_comparison (location_t loc, enum tr
             6.5.6/8 and /9 with respect to the signed ptrdiff_t.  */
          else if (bitpos0 == bitpos1
                   && (equality_code
-                      || (indirect_base0 && DECL_P (base0))
+                      || (indirect_base0
+                          && (DECL_P (base0) || CONSTANT_CLASS_P (base0)))
                       || POINTER_TYPE_OVERFLOW_UNDEFINED))
            {
              /* By converting to signed sizetype we cover middle-end pointer
--- gcc/testsuite/g++.dg/torture/pr71448.C.jj   2016-06-08 10:32:17.409952602 
+0200
+++ gcc/testsuite/g++.dg/torture/pr71448.C      2016-06-08 10:33:38.396872265 
+0200
@@ -0,0 +1,27 @@
+// PR c++/71448
+// { dg-do compile }
+// { dg-additional-options "-std=c++11" }
+
+static constexpr const char foo[] = "foo";
+static constexpr const char *bar = "bar";
+
+static_assert ((foo + 3 - foo) == 3, "check");
+static_assert (foo + 2 != foo, "check");
+static_assert (foo + 2 >= foo, "check");
+static_assert (3 + foo >= foo, "check");
+static_assert (foo <= foo + 2, "check");
+static_assert (foo <= 3 + foo, "check");
+static_assert (foo + 2 > foo, "check");
+static_assert (3 + foo > foo, "check");
+static_assert (foo < 2 + foo, "check");
+static_assert (foo < foo + 3, "check");
+static_assert ((bar + 3 - bar) == 3, "check");
+static_assert (bar + 2 != bar, "check");
+static_assert (2 + bar >= bar, "check");
+static_assert (bar + 3 >= bar, "check");
+static_assert (bar <= bar + 2, "check");
+static_assert (bar <= 3 + bar, "check");
+static_assert (bar + 2 > bar, "check");
+static_assert (3 + bar > bar, "check");
+static_assert (bar < 2 + bar, "check");
+static_assert (bar < bar + 3, "check");

        Jakub