Regression due to tree loop opt / expand weirdness

[Richard Kenner]

    Would changing the test in expand_expr_addr_expr from 
    
      if (!target.valid_pointer_mode (tmode))

    to

      if (tmode != Pmode && tmode != ptr_mode)

    be OK with you?  This should cause no change to ia64 ...

That looks wrong to me.  On ia64, Pmode is always DImode, but ptr_mode can
be either SImode or DImode depending on the *default* pointer size for
the configuration.  But we want to support both 32-bit and 64-bit pointers
for IA64 on at least some configurations (e.g., VMS) no matter what the
default is.

The target.valid_pointer_mode test does exactly the right thing and seems
to me to be the only thing that does.