Improve LTO streaming dumps

this patch cleans up dumping of streaming so it is clear how dump is organized
and how much space individual components needs.

Compiling:

int a=1;
main()
{
  return a;
}

The output is now:

Creating output block for function_body
    Streaming tree  <result_decl 0x7ffff7457a50 D.1931>
     Start of LTO_trees of size 1
      Encoding indexable  <integer_type 0x7ffff7463000 sizetype>  as 0
     10 bytes

^^^ I do not think we should need 10 bytes to stream single indexable reference
to 0 :)

     Start of LTO_trees of size 1
      Encoding indexable  <integer_type 0x7ffff74630a8 bitsizetype>  as 1
     10 bytes
      Streaming header of  <result_decl 0x7ffff7457a50 D.1931>  to function_body
      Streaming body of  <result_decl 0x7ffff7457a50 D.1931>  to function_body
      Encoding indexable  <integer_type 0x7ffff74635e8 int>  as 2
      Encoding indexable  <function_decl 0x7ffff757b500 main>  as 0
      Streaming ref to  <integer_cst 0x7ffff744af18 32>
      Streaming ref to  <integer_cst 0x7ffff744af30 4>
    52 bytes

^^^ Instead of having multiple LTO_trees sections followed by the final tree
it would make a lot of sense to have only one LTO_trees where the first tree
is one lto_input_tree should return.  This is easy to arrange in DFS walk -
one does not need to pop after every SCC component but pop once at the end of
walk.  However this breaks handling of integer_csts because they may now
become of LTO_trees block and streamed as header + body.
This bypasses the separate code for shared integer_cst streaming.  I think
I want to stream everything into header and materialize the tree since it is not
part of SCC anyway.

    Streaming tree  <block 0x7ffff757e420>
      Streaming header of  <block 0x7ffff757e420>  to function_body
      Streaming body of  <block 0x7ffff757e420>  to function_body
    8 bytes
  Streaming gimple stmt _2 = a;
    Streaming ref to  <block 0x7ffff757e420>
    4 bytes
    Streaming tree  <mem_ref 0x7ffff7576f78>
     Start of LTO_trees of size 1
      Encoding indexable  <pointer_type 0x7ffff746b9d8>  as 3
     10 bytes
     Start of LTO_trees of size 1
      Streaming header of  <addr_expr 0x7ffff75893c0>  to function_body
      Streaming body of  <addr_expr 0x7ffff75893c0>  to function_body
      Encoding indexable  <var_decl 0x7ffff7fcfb40 a>  as 0
     15 bytes
      Streaming header of  <mem_ref 0x7ffff7576f78>  to function_body
      Streaming body of  <mem_ref 0x7ffff7576f78>  to function_body
      Streaming ref to  <addr_expr 0x7ffff75893c0>
      Streaming ref to  <integer_cst 0x7ffff75a3240 0>
    42 bytes
  Streaming gimple stmt return _2;

Outputting global stream
 0:  <function_decl 0x7ffff757b500 main>
    Streaming tree  <function_decl 0x7ffff757b500 main>
     Start of LTO_tree_scc of size 1
      Streaming header of  <optimization_node 0x7ffff744b000>  to decls
      Streaming body of  <optimization_node 0x7ffff744b000>  to decls
     576 bytes
     Start of LTO_tree_scc of size 1
      Streaming header of  <target_option_node 0x7ffff744a018>  to decls
      Streaming body of  <target_option_node 0x7ffff744a018>  to decls
     68 bytes
     Streaming single tree
      Streaming header of  <identifier_node 0x7ffff7577aa0 main>  to decls
      Streaming body of  <identifier_node 0x7ffff7577aa0 main>  to decls
     3 bytes
     Streaming single tree
      Streaming header of  <identifier_node 0x7ffff758a8c0 t.c>  to decls
      Streaming body of  <identifier_node 0x7ffff758a8c0 t.c>  to decls
     3 bytes
     Streaming single tree
      Streaming header of  <translation_unit_decl 0x7ffff7457ac8 t.c>  to decls
      Streaming body of  <translation_unit_decl 0x7ffff7457ac8 t.c>  to decls
      Streaming ref to  <identifier_node 0x7ffff758a8c0 t.c>
     22 bytes
     Start of LTO_tree_scc of size 1
      Streaming header of  <function_type 0x7ffff74717e0>  to decls
      Streaming body of  <function_type 0x7ffff74717e0>  to decls
      Streaming ref to  <integer_type 0x7ffff74635e8 int>
      Streaming ref to  <integer_cst 0x7ffff744adc8 8>
      Streaming ref to  <integer_cst 0x7ffff744ade0 1>
      Streaming ref to  <function_type 0x7ffff74717e0>
     38 bytes
     Start of LTO_tree_scc of size 1
      Streaming header of  <function_type 0x7ffff75832a0>  to decls
      Streaming body of  <function_type 0x7ffff75832a0>  to decls
      Streaming ref to  <integer_type 0x7ffff74635e8 int>
      Streaming ref to  <integer_cst 0x7ffff744adc8 8>
      Streaming ref to  <integer_cst 0x7ffff744ade0 1>
      Streaming ref to  <function_type 0x7ffff74717e0>
     38 bytes
     Start of LTO_tree_scc of size 1
      Streaming header of  <function_decl 0x7ffff757b500 main>  to decls
      Streaming body of  <function_decl 0x7ffff757b500 main>  to decls
      Streaming ref to  <function_type 0x7ffff75832a0>
      Streaming ref to  <identifier_node 0x7ffff7577aa0 main>
      Streaming ref to  <translation_unit_decl 0x7ffff7457ac8 t.c>
      Streaming ref to  <identifier_node 0x7ffff7577aa0 main>
      Streaming ref to  <target_option_node 0x7ffff744a018>
      Streaming ref to  <optimization_node 0x7ffff744b000>
     58 bytes
    806 bytes
 0:  <var_decl 0x7ffff7fcfb40 a>
    Streaming tree  <var_decl 0x7ffff7fcfb40 a>
     Streaming single tree
      Streaming header of  <identifier_node 0x7ffff758a870 a>  to decls
      Streaming body of  <identifier_node 0x7ffff758a870 a>  to decls
     3 bytes
     Streaming single tree
      Streaming ref to  <integer_type 0x7ffff7463000 sizetype>
     7 bytes
     Streaming single tree
      Streaming ref to  <integer_type 0x7ffff74630a8 bitsizetype>
     7 bytes
     Start of LTO_tree_scc of size 1
      Streaming header of  <var_decl 0x7ffff7fcfb40 a>  to decls
      Streaming body of  <var_decl 0x7ffff7fcfb40 a>  to decls
      Streaming ref to  <integer_type 0x7ffff74635e8 int>
      Streaming ref to  <identifier_node 0x7ffff758a870 a>
      Streaming ref to  <translation_unit_decl 0x7ffff7457ac8 t.c>
      Streaming ref to  <integer_cst 0x7ffff744af18 32>
      Streaming ref to  <integer_cst 0x7ffff744af30 4>
      Streaming ref to  <identifier_node 0x7ffff758a870 a>
      Streaming ref to  <integer_cst 0x7ffff7468090 1>
     49 bytes
    66 bytes

gcc/ChangeLog:

2020-05-22  Jan Hubicka  <hubicka@ucw.cz>

	* lto-section-out.c (lto_output_decl_index): Adjust dump indentation.
	* lto-streamer-out.c (create_output_block): Fix whitespace
	(lto_write_tree_1): Add (debug) dump.
	(DFS::DFS): Add dump.
	(DFS::DFS_write_tree_body): Do not dump here.
	(lto_output_tree): Improve dumping; do not stream ref when not needed.
	(produce_asm_for_decls): Fix whitespace.
	* tree-streamer-out.c (streamer_write_tree_header): Add dump.