[Bug c/69972] New: duplicate integer overflow diagnostic in constant expressions

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69972

            Bug ID: 69972
           Summary: duplicate integer overflow diagnostic in constant
                    expressions
           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: ---

Both the C and the C++ front ends issue duplicate diagnostics for integer
overflows in constant expressions.  For example, in C:

$ /home/msebor/build/gcc-4.9.3/gcc/xgcc -B/home/msebor/build/gcc-4.9.3/gcc -S
-Wall -Wextra -Wpedantic -o/dev/null -xc x.c
x.c:1:24: warning: integer overflow in expression [-Woverflow]
 enum { e = __INT_MAX__ + 1 };
                        ^
x.c:1:8: warning: overflow in constant expression [-Woverflow]
 enum { e = __INT_MAX__ + 1 };
        ^

G++ issues two similar kinds of diagnostics for the following code, one
-Woverflow and another -fpermissive:

$ cat t.c && /build/gcc-trunk/gcc/xgcc -B /build/gcc-trunk/gcc -S -Wall -Wextra
-Wpedantic -o/dev/null -xc++ t.c
template <int N> struct S { };
S<(__INT_MAX__ + 1)> s;
t.c:2:16: warning: integer overflow in expression [-Woverflow]
 S<(__INT_MAX__ + 1)> s;
    ~~~~~~~~~~~~^~~
t.c:2:20: error: overflow in constant expression [-fpermissive]
 S<(__INT_MAX__ + 1)> s;
                    ^
t.c:2:20: note: in template argument for type ‘int’