[Bug lto/60461] New: LTO linking error at -Os (and above) on x86_64-linux-gnu

["su at cs dot ucdavis.edu" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60461

            Bug ID: 60461
           Summary: LTO linking error 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 following code triggers a linker error when it is compiled by the current
gcc trunk using LTO at -Os on x86_64-linux-gnu (in both 32-bit and 64-bit
modes). 

It also triggers the error at -O2 and -O3 in 32-bit mode. 

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 --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.9.0 20140307 (experimental) [trunk revision 208393] (GCC) 
$ 
$ gcc-trunk -Os small.c; a.out
$ gcc-trunk -flto -O1 small.c; a.out
$ gcc-4.8.2 -flto -Os small.c; a.out
$ 
$ gcc-trunk -flto -Os small.c
/tmp/ccv33rju.ltrans0.ltrans.o:ccv33rju.ltrans0.o:function fn2: error:
undefined reference to 'a'
collect2: error: ld returned 1 exit status
$ 


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


struct S
{
  int f1;
  int f2;
} a[1] = { {0, 0} }; 

int b, c;

static unsigned short fn1 (struct S);

void
fn2 ()
{
  for (; c;)
    ;
  b = 0;
  fn1 (a[0]);
}

unsigned short
fn1 (struct S p)
{
  if (p.f1)
    fn2 ();
  return 0;
}

int
main ()
{
  fn2 ();
  return 0;
}