[patch] split FRAME variables back into pieces

[Eric Botcazou]

Hi,

this transformation has been in our tree for a couple of years and was 
originally developed for SPARKSkein (http://www.skein-hash.info/node/48), 
which is the implementation in SPARK (subset of Ada) of the Skein algorithm.

When nested functions access local variables of their parent, the compiler 
creates a special FRAME local variable in the parent, which represents the 
non-local frame, and puts into it all the variables accessed non-locally.

If these nested functions are later inlined into their parent, these FRAME 
variables generally remain unmodified and this has various drawbacks:
 1) the frame of the parent is unnecessarily large,
 2) scalarization of aggregates put into the FRAME variables is hindered,
 3) debug info for scalars put into the FRAME variables is poor since VTA only 
works on GIMPLE registers.

The attached patch makes it so that the compiler splits FRAME variables back 
into pieces when all the nested functions have been inlined.  The natural 
place to implement the transformation would probably be the SRA pass, but this 
would require a special path to work around all the heuristics and the pass is 
already complicated enough (sorry Martin ;-)  The transformation is therefore 
implemented as a sub-pass of execute_update_addresses_taken for technical 
reasons exposed in the patch.

Tested on x86-64/Linux, OK for the mainline?


2012-09-19  Eric Botcazou  <ebotcazou@adacore.com>

	* tree.h (DECL_NONLOCAL_FRAME): New macro.
	* gimple.c (gimple_ior_addresses_taken_1): Handle non-local frame
	structures specially.
	* tree-nested.c (get_frame_type): Set DECL_NONLOCAL_FRAME.
	* tree-ssa.c (lookup_decl_for_field): New static function.
	(split_nonlocal_frames_op): Likewise.
	(execute_update_addresses_taken): Break up non-local frame structures
	into variables when possible.
	* tree-streamer-in.c (unpack_ts_decl_common_value_fields): Stream in
	DECL_NONLOCAL_FRAME flag.
	* tree-streamer-out.c (pack_ts_decl_common_value_fields): Stream out
	DECL_NONLOCAL_FRAME flag.


2012-09-19  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc.dg/nested-func-9.c: New test.


-- 
Eric Botcazou
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