[Bug middle-end/82365] stack locations are consolidated if noreturn function is on the path

["pinskia at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2017-09-30
          Component|other                       |middle-end
            Summary|excessive stack usage with  |stack locations are
                   |norreturn attribute         |consolidated if noreturn
                   |                            |function is on the path
     Ever confirmed|0                           |1
           Severity|normal                      |enhancement

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
here is a reduced testcase to show the issue a lot better:
#define __noreturn __attribute__((noreturn))

struct i2c_board_info {
        char type[20];
        char pad[100];
};

#ifdef NONORETURN
void fortify_panic();
#else
void fortify_panic() __noreturn;
#endif


int f(int a)
{
  if (a)
    fortify_panic();
}


void i2c_new_device(struct i2c_board_info *);
int em28xx_dvb_init(int model, int a, int b, int c, int d)
{
        switch (model) {
        case 1:{
                        struct i2c_board_info info = {};
                        f(a);
                        i2c_new_device(&info);
                        break;
                }
        case 2:{
                        struct i2c_board_info info = {};
                        f(b);
                        i2c_new_device(&info);
                        break;
                }
        case 3:{
                        struct i2c_board_info info = { };
                        f(c);
                        i2c_new_device(&info);
                        break;
                }
        case 4:{
                        struct i2c_board_info info = { };
                        f(d);
                        i2c_new_device(&info);
                        break;
                }
        }
        return 0;
}

Basically the noreturn function is not considered a barrier for the info so the
middle-end thinks all of the info can overlap in scope.