On Mon, Mar 20, 2006 at 04:03:08PM -0000, Dave Korn wrote:
> Do you happen to know off the top of your head when get_frame_size()
> becomes valid?
You don't get a good first-pass estimate until after all rtl
generation has been done. Which is later than you need.
Another possibility is to allocate an extra word high in the
stack frame for temporary storage in large frames w/ sibcalls
to functions using all arguments. Then you'd deallocate in
several steps:
scratchslot = argument
argument = stack frame size - small
sp += argument
argument = scratchslot
sp += small
This scheme has the advantage that you don't need to commit
to it until the last minute. Don't forget that you can also
handle "small" large values in a small number of steps. E.g.
for 65k:
sp += 32764
sp += 32764
sp += 1032
Which may well be faster than going through memory as above.
Of course, you wouldn't want to use this scheme for a 2mb frame.
r~
