[Bug c/58490] New: __sync_bool_compare_and_swap sign bit failure

[erikvanderwerf at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58490

            Bug ID: 58490
           Summary: __sync_bool_compare_and_swap sign bit failure
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: erikvanderwerf at gmail dot com

The following lines cause an assertion failure on my arm device:

    unsigned short int x=0x8000;
    unsigned short int y=1; // or any other number
    char success = __sync_bool_compare_and_swap(&x, x, y);
    assert( success );  // ok
    assert( (x==y) );   // this fails when the highest bit in x is set

Using signed short int with negative numbers produces the same error. Using
older versions of gcc (e.g., 4.6) or when compiling for x86 it runs without
problems. 

I compiled using 'arm-linux-gnueabi-gcc-4.7 -Wall -static'. Here are some
details:

>> arm-linux-gnueabi-gcc-4.7 --version
arm-linux-gnueabi-gcc-4.7 (Debian 4.7.2-4) 4.7.2