[Ada] Improve run time performance for large array reset

[Arnaud Charlet <charlet at adacore dot com>]

This patch makes the compiler generate faster code to reset a large array of
integers to 0 by means of an aggregate with a single Others choice and, more
generally, to set a large array of storage units to a single value by the
same means, for example:

  type Arr is array (1 .. 10000) of Integer;
  A : Arr := (others => 0);

Tested on x86_64-pc-linux-gnu, committed on trunk

2014-07-30  Eric Botcazou  <ebotcazou@adacore.com>

	* exp_aggr.adb (Aggr_Assignment_OK_For_Backend): New predicate.
	(Expand_Array_Aggregate): Also enable in-place expansion for
	code generated by the compiler.  For an object declaration,
	set the kind of the object in addition to its type.  If an
	in-place assignment is to be generated and it can be directly
	done by the back-end, do not expand the aggregate.
	* fe.h (Is_Others_Aggregate): Declare.
	* gcc-interface/trans.c
	(gnat_to_gnu) <N_Assignment_Statement>: Add support for an
	aggregate with a single Others choice on the RHS by means of
	__builtin_memset.  Tidy up.

Attachment: difs
Description: Text document