Hi!
As the testcase shows, we also want to fold "abcd" + 3 != NULL
at constant time. The following patch fixes that.
Additionally, I think if !indirect_base0 then we basically want to compare
whether the base0's value rather than address is non-NULL, which we can't
optimize. All we can optimize is when indirect_base0 is true, i.e. we
want to ask whether base0's address + some constant offset is non-NULL.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2016-12-05 Jakub Jelinek <ja...@redhat.com>
PR c++/71537
* fold-const.c (fold_comparison): Assume CONSTANT_CLASS_P (base0)
plus offset is non-zero. For maybe_nonzero_address decl base0,
require indirect_base0.
* g++.dg/cpp0x/constexpr-71537.C: New test.
--- gcc/fold-const.c.jj 2016-11-23 16:47:32.000000000 +0100
+++ gcc/fold-const.c 2016-12-05 15:17:29.425739667 +0100
@@ -8419,14 +8419,16 @@ fold_comparison (location_t loc, enum tr
below follow the C++ rules with the additional property that
every object pointer compares greater than a null pointer.
*/
- else if (DECL_P (base0)
- && maybe_nonzero_address (base0) > 0
- /* Avoid folding references to struct members at offset 0 to
- prevent tests like '&ptr->firstmember == 0' from getting
- eliminated. When ptr is null, although the -> expression
- is strictly speaking invalid, GCC retains it as a matter
- of QoI. See PR c/44555. */
- && (offset0 == NULL_TREE && bitpos0 != 0)
+ else if (((DECL_P (base0)
+ && maybe_nonzero_address (base0) > 0
+ /* Avoid folding references to struct members at offset 0 to
+ prevent tests like '&ptr->firstmember == 0' from getting
+ eliminated. When ptr is null, although the -> expression
+ is strictly speaking invalid, GCC retains it as a matter
+ of QoI. See PR c/44555. */
+ && (offset0 == NULL_TREE && bitpos0 != 0))
+ || CONSTANT_CLASS_P (base0))
+ && indirect_base0
/* The caller guarantees that when one of the arguments is
constant (i.e., null in this case) it is second. */
&& integer_zerop (arg1))
--- gcc/testsuite/g++.dg/cpp0x/constexpr-71537.C.jj 2016-12-05
15:34:09.648000207 +0100
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-71537.C 2016-12-05
15:33:47.000000000 +0100
@@ -0,0 +1,18 @@
+// PR c++/71537
+// { dg-do compile { target c++11 } }
+
+constexpr int n[42] = {1};
+constexpr int x1 = n ? 1 : 0;
+constexpr int x2 = n + 1 ? 1 : 0;
+constexpr int x3 = "abc" ? 1 : 0;
+constexpr int x4 = "abc" + 1 ? 1 : 0;
+constexpr bool x5 = "abc" + 1;
+constexpr bool x6 = "abc" + 4;
+constexpr bool x7 = n + 42;
+static_assert (x1 == 1, "");
+static_assert (x2 == 1, "");
+static_assert (x3 == 1, "");
+static_assert (x4 == 1, "");
+static_assert (x5, "");
+static_assert (x6, "");
+static_assert (x7, "");
Jakub
