ipa: Implement a summary for callback edges

Currently in trunk, every edge contains a 16 bit field called
callback_id, which is used to link callback edges to their attributes,
from which all additional information is calculated as is needed.

This patch adds a new summary struct for callback edges, called
callback_info.  It allows us to remove callback_id from the main class
and aggregate all relevant information, without having to recalculate it
every single time.

gcc/ChangeLog:

	* Makefile.in: Add callback-info.o to OBJS.
	* attr-callback.cc (callback_fetch_attr_by_edge): Use fn_idx
	from the summary.
	(callback_get_arg_mapping): Replaced by
	callback_get_arg_mapping_from_attr and the summary field.
	(callback_get_arg_mapping_from_attr): New function, parses the
	attr and returns the computed argument mapping.
	(callback_fetch_fn_position): Delete, obsoleted by the summary.
	(callback_edge_useful_p): Check for the redirected flag in the
	summary instead of cgraph_node fields.
	* attr-callback.h (enum callback_position): Add comment.
	(enum arg_mapping_constants): New enum, defines the identifier
	for -1 in the arg_mapping vector.
	(callback_get_arg_mapping): Delete.
	(callback_fetch_fn_position): Delete.
	(callback_get_arg_mapping_from_attr): Add decl.
	* cgraph.cc (symbol_table::create_edge): Remove callback_id initializer.
	(cgraph_edge::make_callback): Initialize the callback_info
	summary, add necessary arguments.
	(cgraph_edge::redirect_callee): Set the redirected flag when
	redirecting a callback edge.
	(cgraph_edge::redirect_call_stmt_to_callee): Use the summary.
	(cgraph_node::verify_node): Remove callback_id checks.
	(cgraph_cc_finalize): Free the summaries.
	* cgraph.h: Remove callback_id from cgraph_edge, adjust decl of
	cgraph_edge::make_callback.
	* cgraphclones.cc (cgraph_edge::clone): Remove callback_id.
	* ipa-cp.cc (ipcp_driver): Initialize the summary sum.
	* ipa-prop.cc (ipa_compute_jump_functions_for_edge): Remove
	callback_id, adjust call to make_callback, use the summary.
	(ipa_analyze_node): Initialize the summary sum.
	(ipa_register_cgraph_hooks): Likewise.
	* lto-cgraph.cc (lto_output_edge): Remove callback_id, stream
	out the summary.
	(output_symtab): Initialize the summary sum.
	(input_edge): Remove callback_id, stream in the summary.
	(input_cgraph_1): Initialize the summary sum.
	* callback-info.cc: New file.
	* callback-info.h: New file.

Signed-off-by: Josef Melcr <josef.melcr@suse.com>