[Lazarus] Example requested for TList and Sort using data type of Object (or record).

[Sven Barth]

On 11.05.2011 20:50, Graeme Geldenhuys wrote:
> On 11 May 2011 14:35, Sven Barth<pascaldragon at goo*****>  wrote:
>> function SortComponentsForName(Item1, Item2: Pointer): Integer;
>> var
>>   Comp1, Comp2: TComponent;
>> begin
>>   Comp1 := TComponent(Item1);
>>   Comp2 := TComponent(Item2);
>
>
> This is what I have always been using.... Is one method more efficient
>   (generated code) than the other?

The "absolute" version needs (in the example) 2 * SizeOf(Pointer) less 
stack space and also the two assignments aren't needed.

Example:

===source begin===

procedure Test1(aParam1, aParam2: Pointer);
var
   param1: TObject absolute aParam1;
   param2: TObject absolute aParam2;
begin
end;

procedure Test2(aParam1, aParam2: Pointer);
var
   param1: TObject;
   param2: TObject;
begin
   param1 := TObject(aParam1);
   param2 := TObject(aParam2);
end;

===source end===

The following code is generated on i386:

===assembler begin===

.section .text
         .balign 16,0x90
.globl  P$ABSOLUTETEST_TEST1$POINTER$POINTER
         .type   P$ABSOLUTETEST_TEST1$POINTER$POINTER, at function
P$ABSOLUTETEST_TEST1$POINTER$POINTER:
.Lc1:
# Temps allocated between ebp-8 and ebp-8
# [absolutetest.pas]
# [9] begin
         pushl   %ebp
.Lc3:
.Lc4:
         movl    %esp,%ebp
.Lc5:
         subl    $8,%esp
# Var aParam1 located at ebp-4
# Var aParam2 located at ebp-8
         movl    %eax,-4(%ebp)
         movl    %edx,-8(%ebp)
# [10] end;
         leave
         ret
.Lc2:
.Le0:
         .size   P$ABSOLUTETEST_TEST1$POINTER$POINTER, .Le0 - 
P$ABSOLUTETEST_TEST1$POINTER$POINTER

.section .text
         .balign 16,0x90
.globl  P$ABSOLUTETEST_TEST2$POINTER$POINTER
         .type   P$ABSOLUTETEST_TEST2$POINTER$POINTER, at function
P$ABSOLUTETEST_TEST2$POINTER$POINTER:
.Lc6:
# Temps allocated between ebp-16 and ebp-16
# [16] begin
         pushl   %ebp
.Lc8:
.Lc9:
         movl    %esp,%ebp
.Lc10:
         subl    $16,%esp
# Var aParam1 located at ebp-4
# Var aParam2 located at ebp-8
# Var param1 located at ebp-12
# Var param2 located at ebp-16
         movl    %eax,-4(%ebp)
         movl    %edx,-8(%ebp)
# [17] param1 := TObject(aParam1);
         movl    -4(%ebp),%eax
         movl    %eax,-12(%ebp)
# [18] param2 := TObject(aParam2);
         movl    -8(%ebp),%eax
         movl    %eax,-16(%ebp)
# [19] end;
         leave
         ret
.Lc7:
.Le1:
         .size   P$ABSOLUTETEST_TEST2$POINTER$POINTER, .Le1 - 
P$ABSOLUTETEST_TEST2$POINTER$POINTER

===assembler end===

Regards,
Sven