Re: GNAT (GCC) Profile Guided Compilation

[Keean Schupke <keean.schupke@googlemail.com>]

On Wednesday, 18 July 2012 11:01:11 UTC+1, Georg Bauhaus  wrote:
> On 15.07.12 10:27, Keean Schupke wrote:
> > function F(N : Node, V : Value) return Boolean is begin (
> >     return (N.Enum = Const) or else ((N.Enum = V) = (N.Number = 0));
> > )
> > 
> > B : constant Boolean = F(N1, V) 
> >     and then F(N2, V)
> >     and then F(N3, V)
> >     and then F(N4, V);
> > 
> 
> FWIW, I have two observations after playing with the above function:
> 
> Using different ways of supplying the variables to F and to functions
> like it, two things seemed to have noticeable influence:
> 
> 1) making the Node record limited (good)
> 2) supplying the values, not the record, to F (possibly good)
> 
> The results have varied a lot with everything (CPU, compiler, switches, ...),
> and I haven't checked the indirections for correctness; in any case,
> plain F (record components) did well.
> 
> with System;
> package News_23.Choice is
> 
>    function F  (N : Node; V : Value) return Boolean;
>    function FA (N : Node; V : Value) return Boolean;
>    function FP1 (p : System.Address; V : Value) return Boolean;
>    function FP2 (p : System.Address; V : Value) return Boolean;
>    function FP3 (p : System.Address; V : Value) return Boolean;
>    function F_3_Args (Enum   : Value;
> 		      Number : Numeric;
> 		      V	     : Value) return Boolean;
> private
>    Const : constant Value := Two;
> end News_23.choice;
> 
> with System.Address_To_Access_Conversions, System.Storage_Elements;
> with Ada.Unchecked_Conversion;
> package body News_23.Choice is
> 
>    use System.Storage_Elements;
>    Enum_Offset : constant := 4 * Storage_Element'Size;
>    Number_Offset : constant := 8 * Storage_Element'Size;
> 
>    function F(N : Node; V : Value) return Boolean is begin
>      return (N.Enum = Const) or else ((N.Enum = V) = (N.Number = 0));
>    end;
> 
>    package Value_P is new System.Address_To_Access_Conversions
>      (Object => Value);
>    package Numeric_P is new System.Address_To_Access_Conversions
>      (Object => Numeric);
> 
>    function FA(N : Node; V : Value) return Boolean is
>    begin
>       declare
> --	 Enm : Value_P.Object_Pointer renames Value_P.To_Pointer (N'Address +
> N.Enum'Position);
> --	 Num : Numeric_P.Object_Pointer renames Numeric_P.To_Pointer (N'Address +
> N.Number'Position);
> 	 Enm : Value_P.Object_Pointer renames Value_P.To_Pointer (N'Address +
> Enum_Offset);
> 	 Num : Numeric_P.Object_Pointer renames Numeric_P.To_Pointer (N'Address +
> Number_Offset);
>       begin
> 	 return (Enm.all = Const) or else ((Enm.all = V) = (Num.all = 0));
>       end;
>    end FA;
> 
>    function FP1 (P : System.Address; V : Value) return Boolean is
>       Enm : Value;
>       pragma Import (Ada, Enm);
>       for Enm'Address use P + Enum_Offset;
>       Num : Numeric;
>       pragma Import (Ada, Num);
>       for Num'Address use P + Number_Offset;
>    begin
>       pragma Inspection_Point (P);
>       return (Enm = Const) or else ((Enm = V) = (Num = 0));
>    end FP1;
> 
>    function FP2 (P : System.Address; V : Value) return Boolean is
>       Enm : Value;
>       pragma Import (Ada, Enm);
>       for Enm'Address use To_Address (To_Integer (P) + Enum_Offset);
>       Num : Numeric;
>       pragma Import (Ada, Num);
>       for Num'Address use To_Address (To_Integer (P) + Number_Offset);
>    begin
>       pragma Inspection_Point (P);
>       return (Enm = Const) or else ((Enm = V) = (Num = 0));
>    end FP2;
> 
>    type Adr is mod 2**Standard'Address_Size;
>    function To_N is new Ada.Unchecked_Conversion (System.Address, Adr);
>    function To_Adr is new Ada.Unchecked_Conversion (Adr, System.Address);
> 
>    function FP3 (P : System.Address; V : Value) return Boolean is
>       Enm : Value;
>       pragma Import (Ada, Enm);
>       for Enm'Address use To_Adr (To_N (P) + Enum_Offset);
>       Num : Numeric;
>       pragma Import (Ada, Num);
>       for Num'Address use To_Adr (To_N (P) + Number_Offset);
>    begin
>       pragma Inspection_Point (P);
>       return (Enm = Const) or else ((Enm = V) = (Num = 0));
>    end FP3;
> 
>    function F_3_Args(Enum : Value; Number : Numeric ; V : Value) return
> Boolean is begin
>      return (Enum = Const) or else ((Enum = V) = (Number = 0));
>    end F_3_Args;
> 
> end News_23.Choice;

I think if you use -O3 -gnatn (and pragma Inline(X)) the function will be inlined. Does it still make a difference then?

Cheers,
Keean.