[Bug c++/78964] gcc fails to detect pointless increment

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78964

--- Comment #2 from David Binderman <dcb314 at hotmail dot com> ---
>Why should it warn?

For all the same reasons as warning -Wunused-but-set-variable.

See the following code:

extern void g( int);

void f( int n)
{
        int m = 0;
        int m2 = 2;

        for (int i = 0; i < n; ++i)
        {
                g(i);
                ++m;
        }
        m2 = 3;
}

$ ~/gcc/results/bin/gcc -c -O2 -Wall jan02.cc
jan02.cc: In function ‘void f(int)’:
jan02.cc:7:6: warning: variable ‘m2’ set but not used
[-Wunused-but-set-variable]
  int m2 = 2;
      ^~
$ 

The compiler warns about m2, but not m. Anomaly.