[PR 78687] Set SRA grp_write lazily

[PR 78687] Set SRA grp_write lazily

2017-05-02  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/78687
	* tree-sra.c (access): New field parent.
	(process_subtree_disqualification): New function.
	(disqualify_candidate): Call it.
	(build_accesses_from_assign): Reset write flag if creating an
	assighnment link.
	(build_access_subtree): Fill in parent field and also prpagate
	down grp_write flag.
	(create_artificial_child_access): New parameter set_grp_write, set
	grp_write to its value.
	(propagate_subaccesses_across_link): Also propagate grp_write flag
	values.
	(propagate_all_subaccesses): Push the closest parent back to work
	queue if add_access_to_work_queue returned true.

testsuite/
	* g++.dg/tree-ssa/pr78687.C: New test.

From-SVN: r247497