[Bug tree-optimization/51117] [4.7 regression] rev.181172 causes glibc build failure

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51117

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-12-08 17:24:27 UTC ---
Created attachment 26025
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26025
gcc47-pr51117.patch

Untested fix.  This improves e.g.:
struct A { char buf[64]; };

void bar (A *);

void
foo ()
{
  {
    A a;
    bar (&a);
    if (a.buf[13])
      throw 1;
  }
  {
    A b;
    bar (&b);
    if (b.buf[13])
      throw 2;
  }
}

back to 4.6 generated code quality, but it doesn't already e.g.:
struct A
{
  char buf[64];
};
void bar (A *);
void
foo ()
{
  A c;
  bar (&c);
  try
  {
    {
      A a;
      bar (&a);
      if (a.buf[13])
throw 1;
      else if (a.buf[52])
throw 3;
    }
    {
      A b;
      bar (&b);
      if (b.buf[13])
throw 2;
    }
  }
  catch ( ...)
  {
    throw;
  }
}

I think it should be safe to move the clobbers to the EH destination of the
!stmt_can_throw_external (stmt) GIMPLE_RESX for that, but am not 100% sure
about that yet and would prefer to do it incrementally anyway.