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From: kenner@vlsi1.ultra.nyu.edu (Richard Kenner)
Message-Id: <10401191915.AA01080@vlsi1.ultra.nyu.edu>
To: dnovillo@redhat.com
Subject: Re: [RFC] Contributing tree-ssa to mainline
Cc: gcc@gcc.gnu.org
X-SW-Source: 2004-01/txt/msg01353.txt.bz2

    Well, I know nothing about Ada so I'm not sure what you mean by that
    remark.  That's why I was asking for specific examples.  Annotated, if
    possible.

OK.  Here's a test program:

procedure Tparray (X: Integer) is
   type Barr is array (Integer range <>) of Boolean;
   pragma Pack (Barr);		-- So we have a packed array of 1 bit
   Y: constant Integer := 31;	-- Here's a variable whose value we know.

   subtype Barr1 is Barr(1..X); -- This type has variable size.
   subtype Barr2 is Barr(1..Y); -- ... and this one has a fixed size (31 bits).

   --  Now we have two identical functions, one on each type.

   function F1 (A, B : Barr1) return Barr1 is
      Arr: Barr1 := A;
   begin
      Arr (2) := False;
      return Arr xor B;
   end F1;

   function F2 (A, B : Barr2) return Barr2 is
      Arr: Barr2 := A;
   begin
      Arr (2) := False;
      return Arr xor B;
   end F2;
begin
   null;
end Tparray;

Now here's the Ada expanded code for this.  Note the very different forms
of tparray__f1 and tparray__f2:

Source recreated from tree for Tparray (body)
---------------------------------------------

with system.system__unsigned_types;
with system.system__bit_ops;
with system;
with system.system__secondary_stack;

procedure tparray (x : integer) is
   type tparray__barr is array (-16#8000_0000# .. 16#7FFF_FFFF#
     range <>) of boolean;
   pragma pack (tparray__barr);
   y : constant integer := 31;
   subtype tparray__barr1 is tparray__barr (1 .. x);
   subtype tparray__barr2 is tparray__barr (1 .. 31);
   freeze tparray__barr []
   freeze tparray__barr1 []
   freeze tparray__barr2 []
   
   function tparray__f1 (a : tparray__barr1; b : tparray__barr1)
     return tparray__barr1 is
      arr : tparray__barr1 := a;
   begin
      arr (0) := system__unsigned_types__packed_byte!(arr (0) and 16#FD#);
      null;
      T3b : tparray__barr1;
      system__bit_ops__bit_xor (arr'address, tparray__Tbarr1P1'
        range_length, b'address, tparray__Tbarr1P1'range_length, T3b'
        address);
      return T3b;
   end tparray__f1;
   
   function tparray__f2 (a : tparray__barr2; b : tparray__barr2)
     return tparray__barr2 is
      arr : tparray__barr2 := a;
   begin
      arr := tparray__barr2___XP1!(arr and 16#FFFF_FFFD#);
      null;
      return tparray__barr2!(arr xor b);
   end tparray__f2;
begin
   null;
   return;
end tparray;