This patch optimizes the initialization and allocation of scalar array objects
when pragma Initialize_Scalars is in effect. The patch also extends the syntax
and semantics of pragma Initialize_Scalars to allow for the specification of
invalid values pertaining to families of scalar types. The new syntax is as
follows:

   pragma Initialize_Scalars
     [ ( TYPE_VALUE_PAIR {, TYPE_VALUE_PAIR} ) ];

   TYPE_VALUE_PAIR ::=
     SCALAR_TYPE => static_EXPRESSION

   SCALAR_TYPE :=
     Short_Float
   | Float
   | Long_Float
   | Long_Long_Flat
   | Signed_8
   | Signed_16
   | Signed_32
   | Signed_64
   | Unsigned_8
   | Unsigned_16
   | Unsigned_32
   | Unsigned_64

Depending on the value specified by pragma Initialize_Scalars, the backend may
optimize the creation of the scalar array object into a fast memset.

------------
-- Source --
------------

--  gnat.adc

pragma Initialize_Scalars
  (Short_Float     => 0.0,
   Float           => 0.0,
   Long_Float      => 0.0,
   Long_Long_Float => 0.0,
   Signed_8        => 0,
   Signed_16       => 0,
   Signed_32       => 0,
   Signed_64       => 0,
   Unsigned_8      => 0,
   Unsigned_16     => 0,
   Unsigned_32     => 0,
   Unsigned_64     => 0);

--  types.ads

with System;

package Types is
   Max : constant := 10_000;
   subtype Big is Integer range 1 .. Max;

   type Byte is range 0 .. 255;
   for Byte'Size use System.Storage_Unit;

   type Byte_Arr_1 is array (1 .. Max) of Byte;
   type Byte_Arr_2 is array (Big) of Byte;
   type Byte_Arr_3 is array (Integer range <>) of Byte;
   type Byte_Arr_4 is array (Integer range <>,
                             Integer range <>) of Byte;
   type Constr_Arr_1 is array (1 .. Max) of Integer;
   type Constr_Arr_2 is array (Big) of Integer;
   type Constr_Arr_3 is array (1 .. Max, 1 .. Max) of Integer;
   type Constr_Arr_4 is array (Big, Big) of Integer;

   type Unconstr_Arr_1 is array (Integer range <>) of Integer;
   type Unconstr_Arr_2 is array (Integer range <>,
                                 Integer range <>) of Integer;

   subtype Subt_Arr_1 is Unconstr_Arr_1 (1 .. Max);
   subtype Subt_Arr_2 is Unconstr_Arr_1 (Big);
   subtype Subt_Arr_3 is Unconstr_Arr_2 (1 .. Max, 1 .. Max);
   subtype Subt_Arr_4 is Unconstr_Arr_2 (Big, Big);

   subtype Subt_Str_1 is String (1 .. Max);
   subtype Subt_Str_2 is String (Big);

   type Byte_Arr_1_Ptr     is access Byte_Arr_1;
   type Byte_Arr_2_Ptr     is access Byte_Arr_2;
   type Byte_Arr_3_Ptr     is access Byte_Arr_3;
   type Byte_Arr_4_Ptr     is access Byte_Arr_4;
   type Constr_Arr_1_Ptr   is access Constr_Arr_1;
   type Constr_Arr_2_Ptr   is access Constr_Arr_2;
   type Constr_Arr_3_Ptr   is access Constr_Arr_3;
   type Constr_Arr_4_Ptr   is access Constr_Arr_4;
   type Unconstr_Arr_1_Ptr is access Unconstr_Arr_1;
   type Unconstr_Arr_2_Ptr is access Unconstr_Arr_2;
   type Subt_Arr_1_Ptr     is access Subt_Arr_1;
   type Subt_Arr_2_Ptr     is access Subt_Arr_2;
   type Subt_Arr_3_Ptr     is access Subt_Arr_3;
   type Subt_Arr_4_Ptr     is access Subt_Arr_4;
   type Str_Ptr            is access String;
   type Subt_Str_1_Ptr     is access Subt_Str_1;
   type Subt_Str_2_Ptr     is access Subt_Str_2;
end Types;

--  main.adb

with Types; use Types;

procedure Main is
   Byte_Arr_1_Obj     : Byte_Arr_1;
   Byte_Arr_2_Obj     : Byte_Arr_2;
   Byte_Arr_3_Obj     : Byte_Arr_3 (1 .. Max);
   Byte_Arr_4_Obj     : Byte_Arr_3 (Big);
   Byte_Arr_5_Obj     : Byte_Arr_4 (1 .. Max, 1 .. Max);
   Byte_Arr_6_Obj     : Byte_Arr_4 (Big, Big);
   Constr_Arr_1_Obj   : Constr_Arr_1;
   Constr_Arr_2_Obj   : Constr_Arr_2;
   Constr_Arr_3_Obj   : Constr_Arr_3;
   Constr_Arr_4_Obj   : Constr_Arr_4;
   Unconstr_Arr_1_Obj : Unconstr_Arr_1 (1 .. Max);
   Unconstr_Arr_2_Obj : Unconstr_Arr_1 (Big);
   Unconstr_Arr_3_Obj : Unconstr_Arr_2 (1 .. Max, 1 .. Max);
   Unconstr_Arr_4_Obj : Unconstr_Arr_2 (Big, Big);
   Subt_Arr_1_Obj     : Subt_Arr_1;
   Subt_Arr_2_Obj     : Subt_Arr_2;
   Subt_Arr_3_Obj     : Subt_Arr_3;
   Subt_Arr_4_Obj     : Subt_Arr_4;
   Str_1_Obj          : String (1 .. Max);
   Str_2_Obj          : String (Big);
   Subt_Str_1_Obj     : Subt_Str_1;
   Subt_Str_2_Obj     : Subt_Str_2;

   Byte_Arr_1_Ptr_Obj     : Byte_Arr_1_Ptr     := new Byte_Arr_1;
   Byte_Arr_2_Ptr_Obj     : Byte_Arr_2_Ptr     := new Byte_Arr_2;
   Byte_Arr_3_Ptr_Obj     : Byte_Arr_3_Ptr     := new Byte_Arr_3 (1 .. Max);
   Byte_Arr_4_Ptr_Obj     : Byte_Arr_3_Ptr     := new Byte_Arr_3 (Big);
   Byte_Arr_5_Ptr_Obj     : Byte_Arr_4_Ptr     :=
                              new Byte_Arr_4 (1 .. Max, 1 .. Max);
   Byte_Arr_6_Ptr_Obj     : Byte_Arr_4_Ptr     := new Byte_Arr_4 (Big, Big);
   Constr_Arr_1_Ptr_Obj   : Constr_Arr_1_Ptr   := new Constr_Arr_1;
   Constr_Arr_2_Ptr_Obj   : Constr_Arr_2_Ptr   := new Constr_Arr_2;
   Constr_Arr_3_Ptr_Obj   : Constr_Arr_3_Ptr   := new Constr_Arr_3;
   Constr_Arr_4_Ptr_Obj   : Constr_Arr_4_Ptr   := new Constr_Arr_4;
   Unconstr_Arr_1_Ptr_Obj : Unconstr_Arr_1_Ptr :=
                              new Unconstr_Arr_1 (1 .. Max);
   Unconstr_Arr_2_Ptr_Obj : Unconstr_Arr_1_Ptr := new Unconstr_Arr_1 (Big);
   Unconstr_Arr_3_Ptr_Obj : Unconstr_Arr_2_Ptr :=
                              new Unconstr_Arr_2 (1 .. Max, 1 .. Max);
   Unconstr_Arr_4_Ptr_Obj : Unconstr_Arr_2_Ptr :=
                              new Unconstr_Arr_2 (Big, Big);
   Subt_Arr_1_Ptr_Obj     : Subt_Arr_1_Ptr     := new Subt_Arr_1;
   Subt_Arr_2_Ptr_Obj     : Subt_Arr_2_Ptr     := new Subt_Arr_2;
   Subt_Arr_3_Ptr_Obj     : Subt_Arr_3_Ptr     := new Subt_Arr_3;
   Subt_Arr_4_Ptr_Obj     : Subt_Arr_4_Ptr     := new Subt_Arr_4;
   Str_Ptr_1_Obj          : Str_Ptr            := new String (1 .. Max);
   Str_Ptr_2_Obj          : Str_Ptr            := new String (Big);
   Subt_Str_1_Ptr_Obj     : Subt_Str_1_Ptr     := new Subt_Str_1;
   Subt_Str_2_Ptr_Obj     : Subt_Str_2_Ptr     := new Subt_Str_2;
begin null; end Main;

----------------------------
-- Compilation and output --
----------------------------

$ gcc -c -S -gnatDG -gnatws main.adb
$ grep -c "others => types__TbyteB!(0));" main.adb.dg
$ grep -c "others => integer!(0));" main.adb.dg
$ grep -c "others => character!(0));" main.adb.dg
$ grep -c "others => types__TbyteB!(0));" main.adb.dg
$ grep -c "memset" main.s
8
12
8
8
44

2018-05-22  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* exp_aggr.adb (Aggr_Assignment_OK_For_Backend): Strip away any
	conversions before extracting the value of the expression.
	* exp_ch3.adb (Default_Initialize_Object): Optimize the default
	initialization of an array of scalars.
	(Get_Simple_Init_Val): Add processing for array types. Remove the
	processing of strings because this case is already handled by the array
	case.
	(Needs_Simple_Initialization): Moved to Sem_Util.
	(Simple_Init_Array_Type): New routine.
	(Simple_Init_Initialize_Scalars_Type): Reimplemented to use the new
	facilities from Sem_Util.
	(Simple_Initialization_OK): New routine.
	* exp_ch3.ads (Needs_Simple_Initialization): Moved to Sem_Util.
	* exp_ch4.adb (Expand_N_Allocator): Optimize the default allocation of
	an array of scalars.
	* sem_prag.adb (Analyze_Float_Value): New routine.
	(Analyze_Integer_Value): New routine.
	(Analyze_Pragma): Reimplement the analysis of pragma Initialize_Scalars
	to handled the extended form of the pragma.
	(Analyze_Type_Value_Pair): New routine.
	* sem_util.adb: Add invalid value-related data structures.
	(Examine_Array_Bounds): New routine.
	(Has_Static_Array_Bounds): Reimplemented.
	(Has_Static_Non_Empty_Array_Bounds): New routine.
	(Invalid_Scalar_Value): New routine.
	(Needs_Simple_Initialization): Moved from Exp_Ch3.
	(Set_Invalid_Scalar_Value): New routines.
	* sem_util.ads (Has_Static_Non_Empty_Array_Bounds): New routine.
	(Invalid_Scalar_Value): New routine.
	(Needs_Simple_Initialization): Moved from Exp_Ch3.
	(Set_Invalid_Scalar_Value): New routines.
	* snames.ads-tmpl: Add names for the salar type families used by pragma
	Initialize_Scalars.

From-SVN: r260529