[Bug rtl-optimization/65383] New: wrong code at -O2 and -O3 on x86_64-linux

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65383

            Bug ID: 65383
           Summary: wrong code at -O2 and -O3 on x86_64-linux
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk mis-compiles the following code on x86_64-linux at -O2
and -O3 in both 32-bit and 64-bit modes. 

This is a regression from 4.6.x. 

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/5.0.0/lto-wrapper
Target: x86_64-unknown-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 5.0.0 20150310 (experimental) [trunk revision 221299] (GCC) 
$ 
$ gcc-trunk -Os small.c; ./a.out
0
$ gcc-4.6.4 -O2 small.c; ./a.out
0
$ 
$ gcc-trunk -O2 small.c
$ ./a.out
Segmentation fault (core dumped)
$ 


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



int printf (const char *, ...);

int a, b, c;

int
fn1 ()
{
  for (; a < 1; )
    {
      int d[10] = { 0 };
      if (((b < 2) < 1) < 1)
    return 0;
      c = d[3000];
    }
  return 0;
}

int
main ()
{
  fn1 ();
  printf ("%d\n", 0);
  return 0;
}