[fpc-pascal] Register variables slowing down floating point operations

[Marcos Douglas]

On Thu, May 12, 2011 at 3:54 PM, cobines <cobines at gmail.com> wrote:
> Hello.
>
> I have written the following program:
>
> program a;
> {$mode objfpc}
> uses
>  SysUtils;
> var
>  i: integer;
>  vd: double;
>  t: TDateTime;
>  max: int64;// = 100000000;
> begin
>  t := Now;
>  max := 100000000;
>  for i := 0 to max do
>    vd := i / max;
>  Writeln('Time: ', DateTimeToTimeStamp(Now - t).Time, ' ms');
> end.
>
> I'm running it on Windows XP i386, compiled with FPC 2.5.1 17430.
>
> # fpc -O a.pas
> ...
> # a.exe
> Time: 1462 ms
>
> # fpc -O3 a.pas
> ...
> # a.exe
> Time: 3325 ms
>
> It is slower with optimizations.

I did this test.
My env is FPC 2.4.3 (/fixes_2_4)

Result:
-O   = run in 891 ms
-O1 = run in 875 ms
-O2 = run in 1656 ms
-O3 = run in 1625 ms

And now?

Marcos Douglas