https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70151
Bug ID: 70151
Summary: forming out of bounds constexpr pointer accepted
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
In the following program, the initializer of the constexpr pointer p has
undefined behavior. As a result, the initializer is not a /core constant
expression/ which makes the program ill-formed and subject to a requirement for
a diagnostic. However, GCC 6.0 and all supported versions before it that
implement constexpr silently accept it.
$ cat z.c && /home/msebor/build/gcc-trunk-svn/gcc/xg++
-B/home/msebor/build/gcc-trunk-svn/gcc -S z.c
constexpr int a [] = { 1 };
constexpr const int *p = a - 1;
The EDG eccp front end rejects the program with the following output:
"z.c", line 2: warning: pointer points outside of underlying object
constexpr const int *p = a - 1;
^
"z.c", line 2: error: expression must have a constant value
constexpr const int *p = a - 1;
^
"z.c", line 2: warning: variable "p" was declared but never referenced
constexpr const int *p = a - 1;
^
1 error detected in the compilation of "z.c".
