[PATCH GCC8][13/33]Rewrite cost computation of ivopts

[Bin Cheng <Bin dot Cheng at arm dot com>]

Hi,
This is the major part of this patch series.  It rewrites cost computation of ivopts using tree affine.
Apart from description given by cover message:
  A) New computation cost model.  Currently, there are big amount code trying to understand
     tree expression and estimate its computation cost.  The model is designed long ago
     for generic tree expressions.  In order to process generic expression (even address
     expression of array/memory references), it has code for too many corner cases.  The
     problem is it's somehow impossible to handle all complicated expressions, even with
     complicated logic in functions like get_computation_cost_at, difference_cost,
     ptr_difference_cost, get_address_cost and so on...  The second problem is it's hard
     to keep cost model consistent among special cases.  As special cases being added
     from time to time, the model is no long unified any more.  There are cases that right
     cost results in bad code, or vice versa, wrong cost results in good code.  Finally,
     it's difficult to add code for new cases.
     This patch introduces a new cost computation model by using tree affine.  Tree exprs
     are lowered to aff_tree which is simple arithmetic operation usually.  Code handling
     special cases is no longer necessary, which brings us quite simplicity.  It is also
     easier to compute consistent costs among different expressions using tree affine,
     which gives us a unified cost model.
This patch also fixes issue that cost computation for address type iv_use is inconsistent
with how it is re-rewritten in the end.  It greatly simplified cost computation.

Is it OK?

Thanks,
bin
2017-04-11  Bin Cheng  <bin.cheng@arm.com>

	* tree-ssa-loop-ivopts.c (get_loop_invariant_expr): Simplify.
	(adjust_setup_cost): New parameter supporting round up adjustment.
	(struct address_cost_data): Delete.
	(force_expr_to_var_cost): Don't bound cost with spill_cost.
	(split_address_cost, ptr_difference_cost): Delete.
	(difference_cost, compare_aff_trees, record_inv_expr): Delete.
	(struct ainc_cost_data): New struct.
	(get_address_cost_ainc): New function.
	(get_address_cost, get_computation_cost): Reimplement.
	(determine_group_iv_cost_address): Record inv_expr for all uses of
	a group.
	(determine_group_iv_cost_cond): Call get_loop_invariant_expr.
	(iv_ca_has_deps): Reimplemented to ...
	(iv_ca_more_deps): ... this.  Check if NEW_CP introduces more deps
	than OLD_CP.
	(iv_ca_extend): Call iv_ca_more_deps.

Attachment: 0013-rewrite-cost-computation-20170225.txt
Description: 0013-rewrite-cost-computation-20170225.txt