[Bug middle-end/63774] New: wrong code at all optimization levels on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63774

            Bug ID: 63774
           Summary: wrong code at all optimization levels on
                    x86_64-linux-gnu
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following code on x86_64-linux at all
optimization levels in both 32-bit and 64-bit modes.  

This is a regression from 4.9.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 20141106 (experimental) [trunk revision 217200] (GCC) 

$ 
$ gcc-4.9 -O0 small.c; ./a.out
small.c: In function ‘fn1’:
small.c:7:3: warning: function returns address of local variable
[-Wreturn-local-addr]
   return &b;
   ^
$ 
$ gcc-trunk -O0 small.c     
small.c: In function ‘fn1’:
small.c:7:10: warning: function returns address of local variable
[-Wreturn-local-addr]
   return &b;
          ^
$ ./a.out
Aborted (core dumped)
$ 


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


int a, *c = &a; 

int *
fn1 ()
{
  int b;
  return &b;
}

int
main ()
{
  *c = (fn1 () != 0);

  if (a != 1)
    __builtin_abort (); 

  return 0;
}