PR tree-optimization/21417
	* tree-ssa-threadedge.c (thread_across_edge): Reject threading
	across a backedge if the control statement at the end of the
	block is data dependent on other statements in the same block.
	(record_temporary_equivalences_from_stmts): Remove over-conservative
	test for threading across backedges.

	* gcc.dg/tree-ssa/pr21417.c: New test.

From-SVN: r110785