Thank you Sven.
Unfortunately I can't find a way to compress the information in few lines
without losing important information. I've already done that mistake in the
first mail, now I'll try to fully explain why I'm interested in the way these
registers are allocated. Even if the mail is long I've tried to write it as
readable as possible. I'll try to explain, step by step, with the help of 3
versions of a common function. I've chosen the pos function.
HERE IS THE ORIGINAL VERSION. YOU CAN SKIP THE PASCAL CODE.
{Elapsed time for this function in tests:6830ms.
# Var $result located in register r14
# Var i located in register rbx
# Var MaxLen located in register r13
# Var pc located in register r12
Temps allocated between rsp+16 and rsp+48}
Function PosORIGINAL(Const Substr : AnsiString; Const Source : AnsiString) :
SizeInt;
var
i,MaxLen : SizeInt;
pc : pchar;
begin
RESULT:=0;
if Length(SubStr)0 then
begin
MaxLen:=Length(source)-Length(SubStr);
i:=0;
pc:=@source[1];
while (i=MaxLen) do
begin
inc(i);
if (SubStr[1]=pc^) and
(CompareByte(Substr[1],pc^,Length(SubStr))=0) then
begin
RESULT:=i;
exit;
end;
inc(pc);
end;
end;
end;
HERE COMES THE FIRST MODIFIED VERSION OF THE ORIGINAL FUNCTION. YOU CAN SKIP
THE PASCAL CODE.
{Compared with PosORIGINAL, variable MaxLen has been removed, the while
loop has been replaced with a for loop and if Length(SubStr)0 then is
replaced by if Length(SubStr)0 then.
Elapsed time for this function in tests:6000ms. That's ~800ms faster than
original function.
# Var $result located in register r12
# Var pc located in register r14
# Var I located in register rbx
Temps allocated between rsp+16 and rsp+48}
{Function PosFASTER(Const Substr:AnsiString; Const Source:AnsiString):SizeInt;
var pc:pchar;
I:SIZEINT;
begin
if Length(SubStr)0 then
begin
pc:=@source[1];
for I:=1 to (Length(source)-Length(SubStr)+1) do
if (SubStr[1]=pc^)and(CompareByte(Substr[1],pc^,Length(SubStr))=0) then
exit(I) else inc(pc);
end;
RESULT:=0;
end;}
HERE COMES THE VERSION I'D LIKE TO RUN FASTEST. YOU CAN SKIP THE PASCAL CODE.
{Compared with function PosFASTER, variable I:SIZEINT has been removed and
replaced with result.
Elapsed time for this function in tests:6600ms. WHICH IS NOT WHAT I WANTED!!!
# Temps allocated between rsp+16 and rsp+40
# Var $result located in register r13
# Var pc located in register rbx}
Function PosWISHTORUNFASTEST(Const Substr:AnsiString; Const
Source:AnsiString):SizeInt;
var pc:pchar;
begin
if Length(SubStr)0 then
begin
pc:=@source[1];
for RESULT:=1 to (Length(source)-Length(SubStr)+1) do
if (SubStr[1]=pc^)and(CompareByte(Substr[1],pc^,Length(SubStr))=0) then
exit else inc(pc);
end;
RESULT:=0;
end;
CONCLUSION
The second version(PosFASTER) runs noticeable faster(6000ms.) compared to
the original version(6800ms). I wish the third version(PosWISHTORUNFASTEST) to
run even faster(less than 6000ms in my tests). Why? Because by removing the
variable I:SIZEINT; I consider I make the job easier to the compiler. Instead
of running faster, the third version(PosWISHTORUNFASTEST) runs significantly
slower(6600ms) than the second version(PosFASTER)(6000ms). There are two
possible reasons for this slowdown:
1)I hit the if...then...else anomaly again, but I strongly doubt this is
the reason of the slowdown.
2)Using r13(result) is slower than rbx(I). If this is the case then I'd
like a solution for these situations. In my mind I have three approaches:
a) When function result is used in a for loop, try to assign a better
register.
b) If the first approach is not good, then give the programmer the chance to
act as a child: I would like one of these registers for a variable, or I don't
want a register in the r12-r15 range for the function result. I think C has a
directive register for variables, I don't know much about it.
c) If none of the above is ok, then please explain how can I identify the
functions that can use the result in for loops without penalties regarding
speed. For example I've noticed that if a function doesn't contain a call to
another function or procedure than, a int64 result is returned in rax, not r12,
which should be ok for me, see Function Pos(c : Char; Const s : AnsiString) :
SizeInt;.
I'm not much interested in while loops as I'm interested in for ones. I
hope I've explained better this time.
Thank you for patience.
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