This patch recognizes additional cases of aggregates in assignment statements
that can be built in place and do not require the creation of temporaries.
This optimization prevents stack overflows. The patch covers aggregates for
arrays of arrays and multidimensional arrays whose components are static and
where the target of the assignment is a selected component or an indexed
component that is side-effect free.

Given the following:

with ess; use ess;
procedure P is
begin
   This_Ptr.Data_Pool := (others => (others => 0));

   for I in 1 .. 5 loop
      for J in Data_Buffer_Type'range loop
         This_Ptr.Data_Pool (I) (J) := 0;
      end loop;
   end loop;

   This_Ptr.all := Empty_R;
end P;

Compiling p.adb with stack usage:

    gcc -S -gnatp -O2 -fstack-usage p.adb

Must produce a file p.su containing:

   p.adb:6:1:P     32      static

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

2010-10-07  Ed Schonberg  <schonberg@adacore.com>

	* exp_aggr.adb (Expand_Array_Aggregate): Recognize additional cases
	where an aggregate in an assignment can be built directly into the
	target, and does not require the creation of a temporary that may
	overflow the stack.