backport: re PR tree-optimization/82726 (ICE in verify_ssa during GIMPLE pass: pcom)

backport: re PR tree-optimization/82726 (ICE in verify_ssa during GIMPLE pass: pcom)

	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.

	testsuite

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

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

	Backport from mainline
	2017-01-23  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/70754
	* gfortran.dg/pr70754.f90: New test.

From-SVN: r257291