Improve LTO streaming dumps

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.