[Bug tree-optimization/59047] New: wrong code for bitfields at -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59047

            Bug ID: 59047
           Summary: wrong code for bitfields at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following testcase on x86_64-linux-gnu at
-O3 (in both 32-bit and 64-bit modes). 

This is a regression from 4.8.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/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure
--enable-languages=c,c++,objc,obj-c++,fortran,lto --disable-werror
--enable-checking=release --with-gmp=/usr/local/gcc-trunk
--with-mpfr=/usr/local/gcc-trunk --with-mpc=/usr/local/gcc-trunk
--with-cloog=/usr/local/gcc-trunk --prefix=/usr/local/gcc-trunk
Thread model: posix
gcc version 4.9.0 20131108 (experimental) [trunk revision 204560] (GCC) 
$ 
$ gcc-trunk -O2 small.c; a.out
1
$ gcc-4.8.2 -O3 small.c; a.out
1
$ 
$ gcc-trunk -O3 small.c; a.out
0
$ 


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


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

struct
{
  int f0;
  int f1:1;
  int f2:2;
} a = {0, 0, 1};

int b, c, *d, e, f;

int
fn1 ()
{
  for (; b < 1; ++b)
    {
      for (e = 0; e < 1; e = 1)
    {
      int **g = &d;
      *g = &c;
    } 
      *d = 0;
      f = a.f1;
      if (f)
    return 0;
    }
  return 0;
}

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