revert: re PR tree-optimization/78496 (Missed opportunities for jump threading)

revert: re PR tree-optimization/78496 (Missed opportunities for jump threading)

2017-05-07  Jeff Law  <law@redhat.com>

	Revert:
	2017-05-06  Jeff Law  <law@redhat.com>
	PR tree-optimization/78496
	* tree-vrp.c (simplify_assert_expr_using_ranges): Remove debugging
	code.

	PR tree-optimization/78496
	* tree-vrp.c (simplify_assert_expr_using_ranges): New function.
	(simplify_stmt_using_ranges): Call it.
	(vrp_dom_walker::before_dom_children): Extract equivalences
	from an ASSERT_EXPR with an equality comparison against a
	constant.

	Revert:
	2017-05-06  Jeff Law  <law@redhat.com>
	PR tree-optimization/78496
	* gcc.dg/tree-ssa/ssa-thread-16.c: New test.
	* gcc.dg/tree-ssa/ssa-thread-17.c: New test.

From-SVN: r247727