re PR tree-optimization/15349 ([tree-ssa] Merge two phi nodes.)

re PR tree-optimization/15349 ([tree-ssa] Merge two phi nodes.)

	PR tree-optimization/15349
	* timevar.def (TV_TREE_MERGE_PHI): New.
	* tree-cfg.c (tree_forwarder_block_p): Add a new argument
	PHI_WANTED.
	(remove_forwarder_block, cleanup_forwarder_blocks): Adjust the
	calls to tree_forwarder_block_p.
	(remove_forwarder_block_with_phi, merge_phi_nodes,
	gate_merge_phi, pass_merge_phi): New.
	* tree-optimize.c (init_tree_optimization_passes): Add
	pass_merge_phi.
	* tree-pass.h: Add an extern for pass_merge_phi;

	PR tree-optimization/15349
	* testsuite/gcc.dg/tree-ssa/pr15349.c: New.

From-SVN: r93977