[Bug tree-optimization/60115] 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=60115

            Bug ID: 60115
           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 mis-compiles the following code on x86_64-linux-gnu at
-O3 in both 32-bit and 64-bit modes.

This is a regression from 4.8.x.

Although the code has an out-of-bound array access, it isn't executed, so the
code is valid. 

$ 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 --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.9.0 20140207 (experimental) [trunk revision 207610] (GCC) 
$ 
$ gcc-trunk -O2 small.c; a.out
$ gcc-4.8 -O3 small.c; a.out
$ 
$ gcc-trunk -O3 small.c; a.out
Segmentation fault (core dumped)
$ 


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


int a, b[1];

int
main ()
{
 lbl:
  for (; a; a--)
    if (b[613])
      goto lbl;

  return 0;
}