[Bug tree-optimization/58955] New: wrong code at -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58955

            Bug ID: 58955
           Summary: wrong code 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=none --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 20131031 (experimental) [trunk revision 204248] (GCC) 
$ 
$ gcc-trunk -O2 small.c; a.out
1
$ gcc-4.8 -O3 small.c; a.out
1 
$ gcc-trunk -O3 small.c; a.out
0
$ 

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


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

int a, b, c, d[4] = { 0, 0, 0, 1 };

int
main ()
{
  for (; a < 4; a++)
    {
      int e = d[a];
      for (c = 1; c < 1; c++);
      b = e;
      d[a] = 0;
    }
  printf ("%d\n", b);
  return 0;
}