[Bug rtl-optimization/69606] New: wrong code at -Os and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69606

            Bug ID: 69606
           Summary: wrong code at -Os and above on x86_64-linux-gnu
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The current gcc trunk miscompiles the following code on x86_64-linux-gnu at -Os
and above in both 32-bit and 64-bit modes.

This also affects 5.1.x and later, and is a regression from 4.9.x.


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 6.0.0 20160201 (experimental) [trunk revision 233027] (GCC) 
$ 
$ gcc-trunk -O1 small.c; ./a.out
$ gcc-4.9 -Os small.c; ./a.out
$ 
$ gcc-trunk -Os small.c
$ ./a.out
Floating point exception (core dumped)
$ gcc-5.3 -Os small.c
$ ./a.out
Floating point exception (core dumped)
$ gcc-5.2 -Os small.c
$ ./a.out
Floating point exception (core dumped)
$ gcc-5.1 -Os small.c
$ ./a.out
Floating point exception (core dumped)
$ 


-----------------------------


char a;
unsigned short b;
int c, d;
unsigned char e;

int
main ()
{
  int f = 1, g = ~a;
  if (b > f)
    {
      e = b; 
      d = b | e; 
      g = 0;
    }
  c = 1 % g;
  return 0; 
}