[COMMITTED] ada: Fix memory explosion on aggregate of nested packed array type

["Marc Poulhiès" <poulhies@adacore.com>]

From: Eric Botcazou <ebotcazou@adacore.com>

It occurs at compile time on an aggregate of a 2-dimensional packed array
type whose component type is itself a packed array, because the compiler
is trying to pack the intermediate aggregate and ends up rewriting a bunch
of subcomponents.  This optimization was originally devised for the case of
a scalar component type so the change adds this restriction.

gcc/ada/

	* exp_aggr.adb (Is_Two_Dim_Packed_Array): Return true only if the
	component type of the array is scalar.

Tested on x86_64-pc-linux-gnu, committed on master.

---
 gcc/ada/exp_aggr.adb | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gcc/ada/exp_aggr.adb b/gcc/ada/exp_aggr.adb
index dffc5ab721d..cd5cc0b7669 100644
--- a/gcc/ada/exp_aggr.adb
+++ b/gcc/ada/exp_aggr.adb
@@ -306,7 +306,7 @@ package body Exp_Aggr is
    --  N is the N_Aggregate node to be expanded.
 
    function Is_Two_Dim_Packed_Array (Typ : Entity_Id) return Boolean;
-   --  For two-dimensional packed aggregates with constant bounds and constant
+   --  For 2D packed array aggregates with constant bounds and constant scalar
    --  components, it is preferable to pack the inner aggregates because the
    --  whole matrix can then be presented to the back-end as a one-dimensional
    --  list of literals. This is much more efficient than expanding into single
@@ -8563,9 +8563,11 @@ package body Exp_Aggr is
 
    function Is_Two_Dim_Packed_Array (Typ : Entity_Id) return Boolean is
       C : constant Uint := Component_Size (Typ);
+
    begin
       return Number_Dimensions (Typ) = 2
         and then Is_Bit_Packed_Array (Typ)
+        and then Is_Scalar_Type (Component_Type (Typ))
         and then C in Uint_1 | Uint_2 | Uint_4; -- False if No_Uint
    end Is_Two_Dim_Packed_Array;
 
-- 
2.40.0