Peter Vreman wrote:
>>>(astonishing that ShortStrings are slower than AnsiStrings in this
>>>example
>>
>>in delphi).
>>
>>Not really. Delphi is silently upcasting your shortstrings to AnsiStrings
>>in
>>the background. You would probably have to recompile the VCL to get around
>>this ;-)
>
>
> I've commited a few small fixes to improve performance, please try again
> with current 2.1.1 from svn
It's enough to get as fast as D7 :) I guess to get more speed we need:
1) subroutine generation without entry/exit code
2) better register allocation for small procedures
else we can't compete with the hand optimized assembler routines of the delphi
rtl: fpc_unique_string is used a lot here which looks like:
.globl fpc_ansistr_unique
fpc_ansistr_unique:
.globl FPC_ANSISTR_UNIQUE
FPC_ANSISTR_UNIQUE:
# Temps allocated between ebp-8 and ebp+0
pushl %ebp
movl %esp,%ebp
subl $8,%esp
movl %ebx,-8(%ebp)
movl %esi,-4(%ebp)
# Var S located in register
# Var $result located in register
movl %eax,%ebx
# [437] pointer(result) := pointer(s);
movl (%ebx),%esi
# [438] If Pointer(S)=Nil then
testl %esi,%esi
je .L4159
.L4164:
# [440] if PAnsiRec(Pointer(S)-Firstoff)^.Ref<>1 then
movl (%ebx),%eax
subl $8,%eax
movl (%eax),%eax
cmpl $1,%eax
je .L4166
# [441] result:=fpc_truely_ansistr_unique(s);
movl %ebx,%eax
call SYSTEM_FPC_TRUELY_ANSISTR_UNIQUE$POINTER$$POINTER
movl %eax,%esi
.L4166:
.L4159:
# [442] end;
movl %esi,%eax
movl -8(%ebp),%ebx
movl -4(%ebp),%esi
leave
ret
Making it "frameless" safes 4 instructions.
Being able to put result into eax saves at least another 4. result could be put
in eax if the compiler recognizes that it doesn't have to save result while the
fpc_truely_ansistr_unique(s) call because result is assigned after it. Is this
doable (Daniel, Peter)?
Further, using ebx for s isn't necessary because after the
fpc_truely_ansistr_unique call s isn't used anymore. Could save another 2
instructions.
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