tree-predcom.c: Revise general description of the pass.

tree-predcom.c: Revise general description of the pass.

	* tree-predcom.c: Revise general description of the pass.
	(enum chain_type): New enum type for store elimination.
	(struct chain): New field supporting store elimination.
	(struct component): Ditto.
	(dump_chain): Dump store-stores chain.
	(release_chain): Release resources.
	(split_data_refs_to_components): Compute and create component
	contains only stores for elimination.
	(get_chain_last_ref_at): New function.
	(make_invariant_chain): Initialization.
	(make_rooted_chain): Specify chain type in parameter and record it.
	(add_looparound_copies): Skip for store-stores chain.
	(determine_roots_comp): Compute type of chain and pass it to
	make_rooted_chain.
	(initialize_root_vars_store_elim_2): New function.
	(finalize_eliminated_stores): New function.
	(remove_stmt): Handle store for elimination.
	(execute_pred_commoning_chain): Execute predictive commoning on
	store-store chains.
	(determine_unroll_factor): Skip unroll for store-stores chain.
	(prepare_initializers_chain_store_elim): New function.
	(prepare_initializers_chain): Hanlde store-store chain.
	(prepare_finalizers_chain, prepare_finalizers): New function.
	(tree_predictive_commoning_loop): Return integer value indicating
	if loop is unrolled or lcssa form is corrupted.
	(tree_predictive_commoning): Rewrite for lcssa form if necessary.

	gcc/testsuite
	* gcc.dg/tree-ssa/predcom-dse-1.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-2.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-3.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-4.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-5.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-6.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-7.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-8.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-9.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-10.c: New test.
	* gcc.dg/tree-ssa/predcom-dse-11.c: New test.

From-SVN: r250669