The _Relative_pointer_impl (and its const variant) implementation invokes
undefined behavior as it computes differences and compares pointers pointing
to different objects.
For example
int i;
RelPtr<int> p, q;
p.set(&i);
q.set(&i);
if (p == q)
will reconstruct pointer values based on the addresses of p and q. This
invokes undefined behavior.
The fix is to do all the pointer arithmetic and the comparisons using
an unsigned integer type (uintptr_t), not using char *.
Likely this causes 23_containers/vector/ext_pointer/modifiers/insert.cc
to fail on alias-improvements branch for i?86 (points-to analysis will
correctly conclude that the objects pointed to by the pointers returned
from get() point to different objects).
--
Summary: _Relative_pointer_impl invokes undefined behavior
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: critical
Priority: P3
Component: libstdc++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: rguenth at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38720
