[GCC BACKPORT]Backport revision 254777 and 254778 to GCC 7 branch

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

Hi,
This patch backports revision 254777 and 254778 to GCC 7 branch.
Bootstrap and test on x86_64.  Is it OK?

Thanks,
bin

2017-12-18  Bin Cheng  <bin.cheng@arm.com>

	Backport from mainline
	2017-11-15  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/82726
	PR tree-optimization/70754
	* tree-predcom.c (order_drefs_by_pos): New function.
	(combine_chains): Move code setting has_max_use_after to...
	(try_combine_chains): ...here.  New parameter.  Sort combined chains
	according to position information.
	(tree_predictive_commoning_loop): Update call to above function.
	(update_pos_for_combined_chains, pcom_stmt_dominates_stmt_p): New.

	2017-11-15  Bin Cheng  <bin.cheng@arm.com>


	PR tree-optimization/82726
	Revert
	2017-01-23  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/70754
	* tree-predcom.c (stmt_combining_refs): New parameter INSERT_BEFORE.
	(reassociate_to_the_same_stmt): New parameter INSERT_BEFORE.  Insert
	combined stmt before it if not NULL.
	(combine_chains): Process refs reversely and compute dominance point
	for root ref.

	Revert
	2017-02-23  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/79663
	* tree-predcom.c (combine_chains): Process refs in reverse order
	only for ZERO length chains, and add explaining comment.

gcc/testsuite
2017-12-18  Bin Cheng  <bin.cheng@arm.com>

	Backport from mainline
	2017-11-15  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/82726
	* gcc.dg/tree-ssa/pr82726.c: New test.

Attachment: backport-r254778-r254777-GCC7.txt
Description: backport-r254778-r254777-GCC7.txt