[Bug c++/70196] inconsistent constness of inequality of weak symbol addresses
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70196 Eric Gallager changed: What|Removed |Added See Also||https://gcc.gnu.org/bugzill ||a/show_bug.cgi?id=81453 --- Comment #6 from Eric Gallager --- (In reply to Eric Gallager from comment #5) > (In reply to Nathan Sidwell from comment #4) > > ordering comparison of pointers is only well-defined when the two pointers > > point into the same object (including one-past-the-end). [expr.ref]/4 > > > > Right, there's a warning from -Wextra for that, there's a bug to split it > off into its own warning, too... ...right, bug 81453
[Bug c++/70196] inconsistent constness of inequality of weak symbol addresses
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70196 --- Comment #5 from Eric Gallager --- (In reply to Nathan Sidwell from comment #4) > ordering comparison of pointers is only well-defined when the two pointers > point into the same object (including one-past-the-end). [expr.ref]/4 > Right, there's a warning from -Wextra for that, there's a bug to split it off into its own warning, too...
[Bug c++/70196] inconsistent constness of inequality of weak symbol addresses
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70196
--- Comment #4 from Nathan Sidwell ---
ordering comparison of pointers is only well-defined when the two pointers
point into the same object (including one-past-the-end). [expr.ref]/4
No object can have a NULL address.
The third bullet permits a compiler to /always/ return true (or false) for any
stricly ordered relational pointer comparison involving a null pointer
constant. (AFAICT even '(void *)0 < 0' is included in that). The -or-equal
operators coult be expanded to '(strict-order) | (equality-cmp)', and then
simplified based on what constant we chose the strict-order to always return.
Now, that said, I think the problematic statement in the example is:
constexpr int *q = &i;
That should probably be rejected, as it assigns the set {NULL, obj-addr} to q.
[Bug c++/70196] inconsistent constness of inequality of weak symbol addresses
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70196 Eric Gallager changed: What|Removed |Added CC||jason at gcc dot gnu.org, ||nathan at gcc dot gnu.org --- Comment #3 from Eric Gallager --- cc-ing C++ FE maintainers
[Bug c++/70196] inconsistent constness of inequality of weak symbol addresses
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70196
Eric Gallager changed:
What|Removed |Added
Status|UNCONFIRMED |NEW
Last reconfirmed||2017-08-28
CC||egallager at gcc dot gnu.org
Ever confirmed|0 |1
Known to fail||8.0
--- Comment #2 from Eric Gallager ---
Combined into a single testcase and confirmed:
$ cat 70196.cc && /usr/local/bin/g++ -c -S -Wall -Wextra -Wpedantic -xc++
70196.cc
extern __attribute__ ((weak)) int i;
constexpr int *p = 0;
constexpr int *q = &i;
static_assert (p == q, "p == q");
static_assert (!(q < p), "!(a < p)"); // accepted and true
static_assert (p <= q, "p <= q"); // accepted and true
template struct S { };
S s0; // accepted
S<&i == 0> s1; // rejected
70196.cc:6:1: error: non-constant condition for static assertion
static_assert (p == q, "p == q");
^
70196.cc:6:18: error: ‘((& i) == 0)’ is not a constant expression
static_assert (p == q, "p == q");
~~^~~~
70196.cc:12:10: warning: ordered comparison of pointer with integer zero
[-Wextra]
S s0; // accepted
^
70196.cc:13:10: error: template argument 1 is invalid
S<&i == 0> s1; // rejected
^
$
[Bug c++/70196] inconsistent constness of inequality of weak symbol addresses
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70196
Martin Sebor changed:
What|Removed |Added
Keywords||accepts-invalid
Known to fail||4.9.3, 5.3.0, 6.0
--- Comment #1 from Martin Sebor ---
All supported versions behave this way. This is also not specific to constexpr
but a more general issue. Below is a test case that doesn't involve constexpr.
$ cat v.c && /home/msebor/build/gcc-trunk-svn/gcc/xgcc
-B/home/msebor/build/gcc-trunk-svn/gcc -S -Wall -Wextra -Wpedantic -o/dev/null
-std=c++11 -xc++ v.c
extern __attribute__ ((weak)) int i;
template struct S { };
S s0; // accepted
S<&i == 0> s1; // rejected
v.c:5:10: warning: ordered comparison of pointer with integer zero [-Wextra]
S s0; // accepted
^
v.c:6:10: error: template argument 1 is invalid
S<&i == 0> s1; // rejected
^
