[debug-early] emit locals early patchset

Gentlemen!

My apologies for the big patch.  In getting locals emitted early 
(parameters and locally scoped variables), I ran into many things which 
were in need of surgery, many of which couldn't happen without the 
other.  Consequently, I ended up fixing everything such that we are now 
back to no guality.exp failures for any language.

[Curiously, I hadn't noticed locals were not being dumped early because 
they were being picked up by the late dwarf pass.  Fixing this oversight 
is what caused this entire patch.]

There are a lot of changes here, and I would greatly appreciate 
feedback, so let me at least explain what's going on at a high level...

1. Changes to gen_subprogram_die() to handle early generation of locals, 
and amending location information on the second pass.  Everything else 
in this patch, basically stems from this change.

2. Changes to gen_variable_die() to handle multiple passes (early/late 
dwarf generation).

A lot of this is complicated by the fact that old_die's are cached and 
keyed by `tree', but an abstract instance and an inline instance share 
trees, while dwarf2out_abstract_function() sets DECL_ABSTRACT_P behind 
the scenes.

The current support (and my changes) maintain this shared and delicate 
design.  I wonder whether we could simplify a lot of this code by 
unsharing these trees, but this may be beyond the scope of this work. 
Richi perhaps you can comment?

3. I've removed deferred_locations.  With multiple dwarf passes we can 
do without them.

4. I have commented a lot of dwarf2out.c throughout .  Dwarf generation 
is this big mystery, and my brain is small.  I've commented things as 
I've learned them.  Hopefully it can help those unfortunate souls who 
come after me.

5. Variable-lengthed array types need special treatment.  Even though 
they can be early dumped, location information may not be available 
until late dwarf.  I've modified gen_type_die*() and friends to work 
with variable-lengthed arrays.  Now we will early generate the 
DW_TAG_subrange_type, but fill in the location at late dwarf.

6. Handle dual passes through gen_lexical_block_die(), while handling 
inlining gracefully.

Here I use a new tree bit (BLOCK_DIE) to store the DIE<->block 
relationship.  This will have to be adapted and streamed for LTO.

For that matter, LTO as a whole needs addressing, but I want to get the 
non-LTO version working before I dive into dwarf streaming, and removing 
all these ancillary data structures in dwarf2out.  Right now, LTO is 
working but only because everything gets recreated by the late dwarf 
pass, thus it's working as in mainline.

Phew... that's basically it.

Kind words greatly appreciated.  Basically I'm looking for feedback and 
positive reinforcement that this is all eventually useful :).

Aldy

p.s. Committed to branch.
commit 850d7f8460c1be9865ba4c45c6c56c346b4199e0
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Fri Oct 10 13:34:04 2014 -0700

    	* cp/decl2.c (emit_debug_for_namespace): Emit debugging for all
    	decls, not just some.
    	* debug.h (dwarf2out_mark_early_dies): Remove.
    	* dwarf2out.c (deferred_locations_struct): Remove.
    	(deferred_locations_list): Remove.
    	(early_dwarf_dumping): New.
    	(struct limbo_die_struct): Document better.
    	(abbrev_die_table_in_use): Same.
    	(new_die): Set dumped_early bit while early dwarf dumping.
    	(print_die): Print additional information if DIE was dumped early.
    	(mark_early_dies_helper): Remove.
    	(dwarf2out_mark_early_dies): Remove.
    	(dwarf2out_dump_early_debug_stats): Dump to asm_out_file.
    	(check_die_inline): Fix comment.
    	(defer_location): Remove.
    	(add_subscript_info): Reuse previously generated
    	DW_TAG_subrange_type.  Only set bounds that are unset.
    	(gen_array_type_die): Handle variable-lengthed arrays that have
    	been early dumped.
    	(gen_formal_parameter_die): Create a new DIE if the cached die has
    	a different context.
    	(gen_subprogram_die): Document better.
    	Early exit on cached declarations.
    	Even if we have a cached DIE with locations, recurse on to its
    	locals.
    	Handle specifications even if DIE was early dumped.
    	Only generate prototype parameters once.
    	Move setting of calling convention earlier.
    	Process locals regardless of DECL_STRUCT_FUNCTION.
    	(gen_variable_die): Handle multiple passes with cached results.
    	Remove defer_location calls.
    	Abstract specification check into its own function...
    	(decl_will_get_specification_p): ...here.
    	(gen_lexical_block_die): Cache previously generated block DIEs in
    	BLOCK_DIE field of tree structure.
    	Handle early dwarf generation and multiple passes through this
    	function.
    	(gen_type_die_with_usage): Variable-lengthed types may be
    	incomplete even if TREE_ASM_WRITTEN.
    	(dwarf2out_early_global_decl): Set early_dwarf_dumping.
    	Document better.
    	(dwarf2out_late_global_decl): Document better.
    	(dwarf2out_finish): Remove deferred_locations_list use.
    	* toplev.c (compile_file): Do not call dwarf2out_mark_early_dies.
    	* tree-core.h (struct tree_block): Add `die' field.
    	* tree.h (BLOCK_DIE): New.

[debug-early] emit locals early patchset

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