[PATCH] Adjust call stmt cost for tailcalls

[Richard Guenther]

On Sat, 23 Jun 2012, Jan Hubicka wrote:

> > 
> > Tailcalls have no argument setup cost and no return value cost.
> > This patch adjusts estminate_num_insns to reflect that.
> > 
> > Honza, does this look correct?
> > 
> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
> > 
> > Thanks,
> > Richard.
> > 
> > 2012-06-20  Richard Guenther  <rguenther@suse.de>
> > 
> > 	* tree-inline.c (estimate_num_insns): Estimate call cost for
> > 	tailcalls properly.
> 
> Well, as discussed offline, this change should currently be no-op since
> we discover tail calls only very late in the game.
> 
> I am not sure I agree that the argument costs are zeroed out. I.e. the
> arguments are generally passed the same way as they would be for normal call,
> just they are homed at different place of the stack frame.
> (note that we mark by the tail call flag far more calls than those that
> are really expanded to tailcall because target limitations are checked only
> in calls.c).
> 
> Finally ipa-cp use estimate_move cost to estimate savings for propagating
> and I think there is risk in arriving to negative numbers when costs
> are not accounted at all calls.
> 
> So I am not sure we want to keep the patch in mainline in the current form...

I have reverted the patch.

Richard.