[fpc-pascal] UnicodeString comparison performance

[OBones]

Hello all,

As I'm moving further into my experiments with FreePascal 2.6.0, I have 
run into a strange issue related to UnicodeString comparisons.
Basically, I'm comparing the result of a function with a constant value 
and find that the comparison is faster if I first assign the result of 
the function to a local variable. The speed difference is around 25% 
slower for the version that does a direct comparison.
It seems it comes from an unnecessary transliteration in the comparison, 
but I can't figure out if it's really this and how to circumvent this.
I have pasted a program at the end of this message, it is a simplified 
version of the code I have, but it shows the issue quite well here.
Rewriting all code that does that to use a local variable is not 
desirable, I would very much prefer if there was some sort of compiler 
option/switch to get similar results in both cases.
All this is done using the x86 and x64 windows compilers.

Thanks in advance for your help and patience.

Regards
Olivier
=====================================================

program test;

uses
   SysUtils;

const
   LoopCount = 100000000;

function GetSomeString: UnicodeString;
begin
   Result := 'Tmp';
end;

function Direct: Double; register;
var
   i: Integer;
begin
   Result:= 0;
   for i := 1 to LoopCount do
   begin
     if GetSomeString = 'Z' then
     begin
       Result:= 33;
       Exit;
     end;
   end;
   Result:= 77;
end;

function Indirect: Double; register;
var
   i: Integer;
   S: UnicodeString;
begin
   Result:= 0;
   for i := 1 to LoopCount do
   begin
     S := GetSomeString;
     if S = 'Z' then
     begin
       Result := 33;
       Exit;
     end;
   end;
   Result:= 77;
end;

function TimeToMs(Value: TDateTime): string;
begin
   Result := FormatDateTime('ss.zzz', Value);
end;

procedure DoTest;
var
   StartTime: TDateTime;
begin
   StartTime := Now;
   Direct;
   WriteLn('Direct:   ' + TimeToMs(Now - StartTime));

   StartTime := Now;
   Indirect;
   WriteLn('Indirect: ' + TimeToMs(Now - StartTime));
end;

begin
   DoTest;
end.