digitalmars.D - foreach is slower than for?
- Stanislav Blinov (55/55) Sep 08 2010 I was wondering about it for some time:
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(10/65)
Sep 08 2010
Dnia 08-09-2010 o 23:12:55 Stanislav Blinov
- Justin Johansson (6/15) Sep 09 2010 Is there a roadmap for what things are more urgent? The OP has a
- Jesse PHillips (4/10) Sep 09 2010 There is a somewhat official road map[1]. It isn't really set up by impo...
- Andrej Mitrovic (9/19) Sep 09 2010 Are the ones listed under "Known D2" official?
- Stanislav Blinov (7/28) Sep 09 2010 Well, I actually didn't ask 'what's the point of foreach is if it's
- Jonathan M Davis (17/47) Sep 09 2010 I don't know about the case with arrays, but if foreach is using opApply...
- Stanislav Blinov (2/76) Sep 09 2010 Thanks, I hoped I'd see this kind of answer. :)
I was wondering about it for some time:
void foreach_loop(int arr[100])
{
foreach(i,a; arr)
{
auto e = a;
}
}
void for_loop(int arr[100])
{
for (int i = 0; i < 100; ++i)
{
auto e = arr[i];
}
}
compiled with -O -release yields this:
.text.void main.foreach_loop(int[100]) segment
assume CS:.text.void main.foreach_loop(int[100])
void main.foreach_loop(int[100]):
push EBP
mov EBP,ESP
sub ESP,8
mov EAX,064h
lea ECX,8[EBP]
xor EDX,EDX
mov -8[EBP],EAX
mov -4[EBP],ECX
cmp -8[EBP],EDX
je L23
L1B: add EDX,1
cmp EDX,-8[EBP]
jb L1B
L23: mov ESP,EBP
pop EBP
ret 0190h
nop
nop
nop
.text.void main.foreach_loop(int[100]) ends
.text.void main.for_loop(int[100]) segment
assume CS:.text.void main.for_loop(int[100])
void main.for_loop(int[100]):
push EBP
mov EBP,ESP
xor EAX,EAX
L5: inc EAX
cmp EAX,064h
jb L5
pop EBP
ret 0190h
nop
.text.void main.for_loop(int[100]) ends
Without -O -release the difference is even greater
Is this normal? I mean, shouldn't the compiler optimize foreach a bit
more? Or is it that I simply misunderstand generated code?
Sep 08 2010
Dnia 08-09-2010 o 23:12:55 Stanislav Blinov <stanislav.blinov gmail.com>= = napisa=B3(a):I was wondering about it for some time: void foreach_loop(int arr[100]) { foreach(i,a; arr) { auto e =3D a; } } void for_loop(int arr[100]) { for (int i =3D 0; i < 100; ++i) { auto e =3D arr[i]; } } compiled with -O -release yields this: .text.void main.foreach_loop(int[100]) segment assume CS:.text.void main.foreach_loop(int[100]) void main.foreach_loop(int[100]): push EBP mov EBP,ESP sub ESP,8 mov EAX,064h lea ECX,8[EBP] xor EDX,EDX mov -8[EBP],EAX mov -4[EBP],ECX cmp -8[EBP],EDX je L23 L1B: add EDX,1 cmp EDX,-8[EBP] jb L1B L23: mov ESP,EBP pop EBP ret 0190h nop nop nop .text.void main.foreach_loop(int[100]) ends .text.void main.for_loop(int[100]) segment assume CS:.text.void main.for_loop(int[100]) void main.for_loop(int[100]): push EBP mov EBP,ESP xor EAX,EAX L5: inc EAX cmp EAX,064h jb L5 pop EBP ret 0190h nop .text.void main.for_loop(int[100]) ends Without -O -release the difference is even greater Is this normal? I mean, shouldn't the compiler optimize foreach a bit ==more? Or is it that I simply misunderstand generated code?Yes, it should; that was the point of having foreach in the language: http://www.d-programming-language.org/faq.html#foreach I think it's just that there's always plenty of more urgent things with = = DMD. Tomek
Sep 08 2010
On 9/09/2010 6:56 AM, Tomek Sowiński wrote:Is there a roadmap for what things are more urgent? The OP has a valid point in asking what is the point of the language. A decent roadmap would help newcomers and oldcomers alike to stay with the Holy Grail of D. JustinWithout -O -release the difference is even greater Is this normal? I mean, shouldn't the compiler optimize foreach a bit more? Or is it that I simply misunderstand generated code?Yes, it should; that was the point of having foreach in the language: http://www.d-programming-language.org/faq.html#foreach I think it's just that there's always plenty of more urgent things with DMD. Tomek
Sep 09 2010
Justin Johansson Wrote:Is there a roadmap for what things are more urgent? The OP has a valid point in asking what is the point of the language. A decent roadmap would help newcomers and oldcomers alike to stay with the Holy Grail of D. JustinThere is a somewhat official road map[1]. It isn't really set up by importance. Don has been doing a good job of updating it. I don't think the list is used by Walter as a checklist of things to do. It could definitely use a face lift on how the items should be organized. Currently compiling 64 bit binaries is priority. Which I think is scheduled for next release 2.049, currently compiles Phobos. 1. http://prowiki.org/wiki4d/wiki.cgi?LanguageDevel
Sep 09 2010
Andrej Mitrovic <andrej.mitrovich gmail.com> Are the ones listed under "Known D2" official? There's "Remove C-style declarations." Is this really scheduled for removal= ? On Thu, Sep 9, 2010 at 8:33 PM, Jesse PHillips <jessekphillips+D gmail.com> wrote:Justin Johansson Wrote:tance. Don has been doing a good job of updating it. I don't think the list= is used by Walter as a checklist of things to do. It could definitely use = a face lift on how the items should be organized.Is there a roadmap for what things are more urgent? =A0The OP has a valid point in asking what is the point of the language. =A0A decent roadmap would help newcomers and oldcomers alike to stay with the Holy Grail of D. JustinThere is a somewhat official road map[1]. It isn't really set up by impor=Currently compiling 64 bit binaries is priority. Which I think is schedul=ed for next release 2.049, currently compiles Phobos.1. http://prowiki.org/wiki4d/wiki.cgi?LanguageDevel
Sep 09 2010
Justin Johansson wrote:On 9/09/2010 6:56 AM, Tomek Sowiński wrote:Well, I actually didn't ask 'what's the point of foreach is if it's slower' :) I just wanted to find out if it's really as far as it can get, or is it simply not polished yet. Nevertheless, I agree that seeing some kind of roadmap would be nice, especially now when D2 is shaped to certain extent and someone would consider starting mean projects with it.Is there a roadmap for what things are more urgent? The OP has a valid point in asking what is the point of the language. A decent roadmap would help newcomers and oldcomers alike to stay with the Holy Grail of D. JustinWithout -O -release the difference is even greater Is this normal? I mean, shouldn't the compiler optimize foreach a bit more? Or is it that I simply misunderstand generated code?Yes, it should; that was the point of having foreach in the language: http://www.d-programming-language.org/faq.html#foreach I think it's just that there's always plenty of more urgent things with DMD. Tomek
Sep 09 2010
On Thursday, September 09, 2010 13:31:13 Stanislav Blinov wrote:Justin Johansson wrote:I don't know about the case with arrays, but if foreach is using opApply(),= it=20 uses a delegate, which is definitely going to be less efficient. Theoretica= lly,=20 opApply and its delegate could be inlined to replace the foreach and defini= tely=20 improve that efficiency (especially because that particular delegate will n= ever be=20 called anywhere else), but that's not currently done. So, there are definit= ely=20 things that can (and likely eventually will) be done to improve the efficie= ncy of=20 foreach as well as other basic stuff, but as said in another post, other st= uff has=20 higher priority. =2D Jonathan M DavisOn 9/09/2010 6:56 AM, Tomek Sowi=F1ski wrote:=20 Well, I actually didn't ask 'what's the point of foreach is if it's slower' :) I just wanted to find out if it's really as far as it can get, or is it simply not polished yet. =20 Nevertheless, I agree that seeing some kind of roadmap would be nice, especially now when D2 is shaped to certain extent and someone would consider starting mean projects with it.=20 Is there a roadmap for what things are more urgent? The OP has a valid point in asking what is the point of the language. A decent roadmap would help newcomers and oldcomers alike to stay with the Holy Grail of D. =20 JustinWithout -O -release the difference is even greater =20 Is this normal? I mean, shouldn't the compiler optimize foreach a bit more? Or is it that I simply misunderstand generated code?=20 Yes, it should; that was the point of having foreach in the language: http://www.d-programming-language.org/faq.html#foreach =20 I think it's just that there's always plenty of more urgent things with DMD. =20 =20 Tomek
Sep 09 2010
Tomek Sowiński wrote:Dnia 08-09-2010 o 23:12:55 Stanislav Blinov <stanislav.blinov gmail.com> napisał(a):Thanks, I hoped I'd see this kind of answer. :)I was wondering about it for some time: void foreach_loop(int arr[100]) { foreach(i,a; arr) { auto e = a; } } void for_loop(int arr[100]) { for (int i = 0; i < 100; ++i) { auto e = arr[i]; } } compiled with -O -release yields this: .text.void main.foreach_loop(int[100]) segment assume CS:.text.void main.foreach_loop(int[100]) void main.foreach_loop(int[100]): push EBP mov EBP,ESP sub ESP,8 mov EAX,064h lea ECX,8[EBP] xor EDX,EDX mov -8[EBP],EAX mov -4[EBP],ECX cmp -8[EBP],EDX je L23 L1B: add EDX,1 cmp EDX,-8[EBP] jb L1B L23: mov ESP,EBP pop EBP ret 0190h nop nop nop .text.void main.foreach_loop(int[100]) ends .text.void main.for_loop(int[100]) segment assume CS:.text.void main.for_loop(int[100]) void main.for_loop(int[100]): push EBP mov EBP,ESP xor EAX,EAX L5: inc EAX cmp EAX,064h jb L5 pop EBP ret 0190h nop .text.void main.for_loop(int[100]) ends Without -O -release the difference is even greater Is this normal? I mean, shouldn't the compiler optimize foreach a bit more? Or is it that I simply misunderstand generated code?Yes, it should; that was the point of having foreach in the language: http://www.d-programming-language.org/faq.html#foreach I think it's just that there's always plenty of more urgent things with DMD. Tomek
Sep 09 2010