[Bug lto/60319] New: wrong code (that hangs) by LTO at -Os and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60319

            Bug ID: 60319
           Summary: wrong code (that hangs) by LTO at -Os and above on
                    x86_64-linux-gnu
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following code when using LTO at -Os and
above on x86_64-linux-gnu (both 32-bit and 64-bit modes). 

This also affects the earlier versions of GCC from 4.6 to 4.8. 

$ 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 20140222 (experimental) [trunk revision 208040] (GCC) 
$ 
$ gcc-trunk -flto -O0 -c foo.c
$ gcc-trunk -flto -O0 -c main.c
$ 
$ gcc-trunk -flto -O1 foo.o main.o    
$ a.out
$ 
$ gcc-trunk -flto -Os foo.o main.o
$ a.out
^C
$ 
$ cat foo.c
void foo (char c) 
{
  for (c = 0; c >= 0; c++)
    ;
}
$ cat main.c
extern void foo (char c); 

int main () 
{ 
 foo(0);
 return 0;
}