[Bug middle-end/54848] New: -ftrapv doesn't work when assigning to an integer with smaller size

[Bug middle-end/54848] New: -ftrapv doesn't work when assigning to an integer with smaller size

[mikulas at artax dot karlin.mff.cuni.cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54848

             Bug #: 54848
           Summary: -ftrapv doesn't work when assigning to an integer with
                    smaller size
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mikulas@artax.karlin.mff.cuni.cz
              Host: i686-pc-linux-gnu
            Target: i686-pc-linux-gnu
             Build: i686-pc-linux-gnu


When adding, subtracting or multiplying two integers and assigning the result
to a variable with smaller size, trap on overflow doesn't happen.

See for example this program:

#include <stdio.h>

int main(void)
{
        int a = 0x70000000;
        int b = 0x50000000;
        short c = a + b;
        printf("%x\n", c);
        return 0;
}

We compile the program without optimization and with -ftrapv, so that it should
crash because of integer overflow. But the program doesn't crash. If we replace
"short" with "int", an overflow crash happens correctly.

[Bug middle-end/54848] -ftrapv doesn't work when assigning to an integer with smaller size

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54848

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-10-08
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-10-08 10:43:53 UTC ---
Confirmed.  One of the many known issues with -ftrapv.

[Bug middle-end/54848] -ftrapv doesn't work when assigning to an integer with smaller size

[bruno at clisp dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54848

Bruno Haible <bruno at clisp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bruno at clisp dot org

--- Comment #2 from Bruno Haible <bruno at clisp dot org> ---
Another test case:

==================== u.c =====================
int
main ()
{
  unsigned short a = 0xeb64;
  unsigned short b = 0xf1e2;
  unsigned short c = a * b;
}
==============================================
$ gcc -ftrapv u.c
$ ./a.out; echo $?
0

Reproduced with gcc 14.1.0.