www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - [SO] question on trivial function inlining

reply Benjamin Shropshire <ao pathlink.com> writes:
Anyone care to add more details?

http://stackoverflow.com/questions/1109995/do-getters-and-setters-impact-performance-in-c-d-java/1110324#1110324
Jul 10 2009
parent reply bearophile <bearophileHUGS lycos.com> writes:
Benjamin Shropshire:
 Anyone care to add more details?
 http://stackoverflow.com/questions/1109995/do-getters-and-setters-impact-performance-in-c-d-java/1110324#1110324
I think DMD is currently unable to de-virtualize virtual getters and setters. Virtual calls are a bit slower by itself, but they also don't allow inlining, so successive standard optimizations can't be done. So if such accesses to the attribute is a virtual call and this happens in a "hot" part of the code, then it may slow down your code significantly. (if it happens in non-hot parts of the code it has usually no effects. That's why Java Hot Spot doesn't need optimize all your code to produce a very fast program anyway). I have encouraged Frits van Bommel to improve the devirtualization capabilities of LDC: http://www.dsource.org/projects/ldc/changeset/1506%3A76936858d1c6 Now LDC is able to do that in few very simple situations, but most times the situation is unchanged compared to DMD. Eventually LLVM will improve, so this situation can improve by itself. But the front-end too may do something about this. Some documentation about this topic, something older: http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=B26C4304DB1DA05ECBD67CA7D9313511?doi=10.1.1.7.7766&rep=rep1&type=pdf Some more modern: http://ols.fedoraproject.org/GCC/Reprints-2006/namolaru-reprint.pdf Bye, bearophile
Jul 10 2009
parent reply BCS <ao pathlink.com> writes:
Reply to bearophile,

 Benjamin Shropshire:
 
 Anyone care to add more details?
 http://stackoverflow.com/questions/1109995/do-getters-and-setters-imp
 act-performance-in-c-d-java/1110324#1110324
[...]
 Bye,
 bearophile
Mind if I echo that back to SO?
Jul 10 2009
parent reply bearophile <bearophileHUGS lycos.com> writes:
BCS:
 Mind if I echo that back to SO?
OK, if you want you can copy it on the StackOverflow site (even if it's bad advertising for the D language and even if there are some small grammar errors in what I have written, I have written it quickly, and English isn't my first language) :-) But I'd also like to show that answer of mine to D developers, because (an improvement in) the front-end may help in devirtualizing some class methods. Bye, bearophile
Jul 10 2009
parent reply BCS <ao pathlink.com> writes:
Reply to bearophile,

 BCS:
 
 OK, if you want you can copy it on the StackOverflow
done there
 But I'd also like to show that answer of mine to D developers,
done here :)
Jul 10 2009
parent bearophile <bearophileHUGS lycos.com> writes:
BCS:
 But I'd also like to show that answer of mine to D developers,
done here :)
Do D devs take a look at this D.learn newsgroup, once in a while? :-) Anyway, just to be sure I have done four more little tests, that show an ideal situation. Real world situations are probably worse. version(Tango) import tango.stdc.stdio: printf; class Test1 { int x; } class Test2 { int _x; int x() { return this._x; } void x(int xx) { this._x = xx; } } void main() { auto t = new Test1; t.x = 4; printf("%d\n", t.x); } /* DMD ASM: _D16getters_setters15Test21xMFZi comdat mov EAX,8[EAX] ret _D16getters_setters15Test21xMFiZv comdat mov ECX,4[ESP] mov 8[EAX],ECX ret 4 main: push EAX mov EAX,offset FLAT:_D16getters_setters15Test17__ClassZ push EAX call near ptr __d_newclass mov ECX,offset FLAT:_D16getters_setters15Test26__vtblZ[020h] mov dword ptr 8[EAX],4 push dword ptr 8[EAX] push ECX call near ptr _printf add ESP,0Ch xor EAX,EAX pop ECX ret -------------------------- LDC ASM: _D7getset15Test21xMFZi: movl 8(%eax), %eax ret _D7getset15Test21xMFiZv: movl 4(%esp), %ecx movl %ecx, 8(%eax) ret $4 main: subl $12, %esp movl $4, 4(%esp) movl $.str2, (%esp) call printf xorl %eax, %eax addl $12, %esp ret $8 */ Here the LDC code is almost optimal, thanks to Frits van Bommel and others. ========================== Now with a (virtual) getter and setter: version(Tango) import tango.stdc.stdio: printf; class Test1 { int x; } class Test2 { int _x; int x() { return this._x; } void x(int xx) { this._x = xx; } } void main() { auto t = new Test2; t.x = 4; printf("%d\n", t.x); } /* DMD ASM: _D16getters_setters25Test21xMFZi comdat mov EAX,8[EAX] ret _D16getters_setters25Test21xMFiZv comdat mov ECX,4[ESP] mov 8[EAX],ECX ret 4 main: push EAX mov EAX,offset FLAT:_D16getters_setters25Test27__ClassZ push EBX push ESI push 4 push EAX call near ptr __d_newclass add ESP,4 mov ECX,[EAX] mov EBX,EAX call dword ptr 01Ch[ECX] mov EDX,[EBX] mov EAX,EBX call dword ptr 018h[EDX] mov ESI,offset FLAT:_D16getters_setters25Test26__vtblZ[020h] push EAX push ESI call near ptr _printf add ESP,8 xor EAX,EAX pop ESI pop EBX pop ECX ret --------------------- LDC ASM: _D7getset25Test21xMFZi: movl 8(%eax), %eax ret _D7getset25Test21xMFiZv: movl 4(%esp), %ecx movl %ecx, 8(%eax) ret $4 main: subl $12, %esp movl $_D7getset25Test27__ClassZ, (%esp) call _d_allocclass movl $_D7getset25Test26__vtblZ, (%eax) movl $0, 4(%eax) movl $4, 8(%eax) movl $4, 4(%esp) movl $.str2, (%esp) call printf xorl %eax, %eax addl $12, %esp ret $8 */ I like LDC and LDC developers (and LLVM) :-) If 't' is defined as a scoped class, then LDC produces this main: main: subl $20, %esp movl $_D8getset2b5Test26__vtblZ, 8(%esp) movl $0, 12(%esp) movl $4, 16(%esp) movl $4, 4(%esp) movl $.str2, (%esp) call printf leal 8(%esp), %eax movl %eax, (%esp) call _d_callfinalizer xorl %eax, %eax addl $20, %esp ret $8 That's better. But recently I have asked ChristianK to improve that some more, removing part of that call to _d_callfinalizer, leaving only a call to the monitor management: http://www.dsource.org/projects/ldc/ticket/339 */ Bye, bearophile
Jul 10 2009