re PR tree-optimization/77820 (A jump threading opportunity with conditionals)

re PR tree-optimization/77820 (A jump threading opportunity with conditionals)

	PR tree-optimization/77820
	* tree-ssa-threadedge.c
	(edge_forwards_cmp_to_conditional_jump_through_empty_bb_p): New
	function.
	(thread_across_edge): Add call to
	edge_forwards_cmp_to_conditional_jump_through_empty_bb_p.

	PR tree-optimization/77820
	* gcc.dg/tree-ssa/phi_on_compare-1.c: New testcase.
	* gcc.dg/tree-ssa/phi_on_compare-2.c: New testcase.
	* gcc.dg/tree-ssa/phi_on_compare-3.c: New testcase.
	* gcc.dg/tree-ssa/phi_on_compare-4.c: New testcase.
	* gcc.dg/tree-ssa/split-path-6.c: Update testcase.
	* gcc.target/sh/pr51244-20.c: Update testcase.

Co-Authored-By: Lijia He <helijia@linux.ibm.com>
From-SVN: r272261