alpha sjlj exception handling

[Jeffrey A Law]

  In message < 199711072009.MAA10173@cygnus.com >you write:
  > 	Where is this supposed to happen in the regular case of non-local goto?
  > 
  > A function that is the target of a non-local goto will have the global variable
  > current_function_has_nonlocal_label set.  local-alloc/global/reload all know
  > that if this variable is set, then pseudos whose lifetime crosses a function
  > call must be handled specially.
Correct.

This happens in local-alloc.c:find_free_reg

  /* Don't let a pseudo live in a reg across a function call
     if we might get a nonlocal goto.  */
  if (current_function_has_nonlocal_label
      && qty_n_calls_crossed[qty] > 0)
    return -1;

I assume global & reload have similar checks.


I brought up the question about call clobbered regs and their interaction
with the EH code and Kenner said it "couldn't happen" and he refused to
elaborate why.  Note this was with our old unwinder code, not sjlj exceptions.

I note that we now set current_function_has_nonlocal_label inside some
of our dwarf code for exception handling.  So for normal EH this problem
has been "solved".

However, I doubt it's been fixed for sjlj exceptions; seems to me if you
set current_function_has_nonlocal_label for sjlj exceptions then you should
be OK.

I would think it could be set unconditionally if EH is being used for now --
in the future we might consider turning it off if none of the EH regions
are actually used.


jeff