Simplify tree streaming.

Simplify tree streaming.

this patch cleans up tree streaming.  The code is prepared to stream nested
trees, but we only handle flat trees. As a result we have quite heavy function
to stream in/out tree reference which is used many times and shows up in
profile.

This patch adds stream_write_tree_ref/stream_read_tree_ref which is used to
stream references to trees that are required to exist in the cache or be
indexable.

The actual implementation is just a first cut.  I would like to make it more
compact. We used to stream 2 byte tag (as UHWI) + UHWI representing the index.
Now we stream one UHWI that represent type of reference + index for references
to cache, but still two integers for references to global stream.  This is
becaue the abstraction is not very helpful here and I want to clean this up
incrementally.

I would also like to get rid of the ref_p parameters which seems unnecessary for
flat streams.

This reduces around 7% of global stream, 3% when compressed.
More reduction will happen once the format is sanitized a bit.

from
[WPA] read 4597161 unshared trees
[WPA] read 2937414 mergeable SCCs of average size 1.364280
[WPA] 8604617 tree bodies read in total
[WPA] tree SCC table: size 524287, 247507 elements, collision ratio: 0.377468
[WPA] tree SCC max chain length 2 (size 1)
[WPA] Compared 2689907 SCCs, 184 collisions (0.000068)
[WPA] Merged 2689890 SCCs
[WPA] Merged 3722677 tree bodies
[WPA] Merged 632040 types
...
[WPA] Compression: 88124141 input bytes, 234906430 uncompressed bytes (ratio: 2.665631)
[WPA] Size of mmap'd section decls: 88124141 bytes
...
[WPA] Compression: 113758813 input bytes, 316149514 uncompressed bytes (ratio: 2.779121)
[WPA] Size of mmap'd section decls: 88124141 bytes
[WPA] Size of mmap'd section function_body: 14485721 bytes

to

[WPA] read 4597174 unshared trees
[WPA] read 2937413 mergeable SCCs of average size 1.364280
[WPA] 8604629 tree bodies read in total
[WPA] tree SCC table: size 524287, 247509 elements, collision ratio: 0.377458
[WPA] tree SCC max chain length 2 (size 1)
[WPA] Compared 2689904 SCCs, 183 collisions (0.000068)
[WPA] Merged 2689888 SCCs
[WPA] Merged 3722675 tree bodies
[WPA] Merged 632041 types
....
[WPA] Size of mmap'd section decls: 86177293 bytes
[WPA] Compression: 86177293 input bytes, 217625095 uncompressed bytes (ratio: 2.525318)
....
[WPA] Compression: 111682269 input bytes, 297228756 uncompressed bytes (ratio: 2.661378)
[WPA] Size of mmap'd section decls: 86177293 bytes
[WPA] Size of mmap'd section function_body: 14349032 bytes

gcc/ChangeLog:

	* lto-streamer-in.c (streamer_read_chain): Move here from
	tree-streamer-in.c.
	(stream_read_tree_ref): New.
	(lto_input_tree_1): Simplify.
	* lto-streamer-out.c (stream_write_tree_ref): New.
	(lto_write_tree_1): Simplify.
	(lto_output_tree_1): Simplify.
	(DFS::DFS_write_tree): Simplify.
	(streamer_write_chain): Move here from tree-stremaer-out.c.
	* lto-streamer.h (lto_output_tree_ref): Update prototype.
	(stream_read_tree_ref): Declare
	(stream_write_tree_ref): Declare
	* tree-streamer-in.c (streamer_read_chain): Update to use
	stream_read_tree_ref.
	(lto_input_ts_common_tree_pointers): Likewise.
	(lto_input_ts_vector_tree_pointers): Likewise.
	(lto_input_ts_poly_tree_pointers): Likewise.
	(lto_input_ts_complex_tree_pointers): Likewise.
	(lto_input_ts_decl_minimal_tree_pointers): Likewise.
	(lto_input_ts_decl_common_tree_pointers): Likewise.
	(lto_input_ts_decl_with_vis_tree_pointers): Likewise.
	(lto_input_ts_field_decl_tree_pointers): Likewise.
	(lto_input_ts_function_decl_tree_pointers): Likewise.
	(lto_input_ts_type_common_tree_pointers): Likewise.
	(lto_input_ts_type_non_common_tree_pointers): Likewise.
	(lto_input_ts_list_tree_pointers): Likewise.
	(lto_input_ts_vec_tree_pointers): Likewise.
	(lto_input_ts_exp_tree_pointers): Likewise.
	(lto_input_ts_block_tree_pointers): Likewise.
	(lto_input_ts_binfo_tree_pointers): Likewise.
	(lto_input_ts_constructor_tree_pointers): Likewise.
	(lto_input_ts_omp_clause_tree_pointers): Likewise.
	* tree-streamer-out.c (streamer_write_chain): Update to use
	stream_write_tree_ref.
	(write_ts_common_tree_pointers): Likewise.
	(write_ts_vector_tree_pointers): Likewise.
	(write_ts_poly_tree_pointers): Likewise.
	(write_ts_complex_tree_pointers): Likewise.
	(write_ts_decl_minimal_tree_pointers): Likewise.
	(write_ts_decl_common_tree_pointers): Likewise.
	(write_ts_decl_non_common_tree_pointers): Likewise.
	(write_ts_decl_with_vis_tree_pointers): Likewise.
	(write_ts_field_decl_tree_pointers): Likewise.
	(write_ts_function_decl_tree_pointers): Likewise.
	(write_ts_type_common_tree_pointers): Likewise.
	(write_ts_type_non_common_tree_pointers): Likewise.
	(write_ts_list_tree_pointers): Likewise.
	(write_ts_vec_tree_pointers): Likewise.
	(write_ts_exp_tree_pointers): Likewise.
	(write_ts_block_tree_pointers): Likewise.
	(write_ts_binfo_tree_pointers): Likewise.
	(write_ts_constructor_tree_pointers): Likewise.
	(write_ts_omp_clause_tree_pointers): Likewise.
	(streamer_write_tree_body): Likewise.
	(streamer_write_integer_cst): Likewise.
	* tree-streamer.h (streamer_read_chain):Declare.
	(streamer_write_chain):Declare.
	(streamer_write_tree_body): Update prototype.
	(streamer_write_integer_cst): Update prototype.