Re: D 50% slower than C++. What I'm doing wrong?
Am Sat, 14 Apr 2012 19:31:40 -0700 schrieb Jonathan M Davis jmdavisp...@gmx.com: On Sunday, April 15, 2012 04:21:09 Joseph Rushton Wakeling wrote: On 14/04/12 23:03, q66 wrote: He also uses a class. And -noboundscheck should be automatically induced by -release. ... but the methods are marked as final -- shouldn't that substantially reduce any speed hit from using class instead of struct? In theory. If they don't override anything, then that signals to the compiler that they don't need to be virtual, in which case, they _shouldn't_ be virtual, but that's up to the compiler to optimize, and I don't know how good it is about that right now. cynicism May I point to this: http://d.puremagic.com/issues/show_bug.cgi?id=7865 /cynicism -- Marco
Re: D 50% slower than C++. What I'm doing wrong?
Am Sat, 14 Apr 2012 21:05:36 +0200
schrieb ReneSac renedu...@yahoo.com.br:
I have this simple binary arithmetic coder in C++ by Mahoney and
translated to D by Maffi. I added notrow, final and pure
and GC.disable where it was possible, but that didn't made much
difference. Adding const to the Predictor.p() (as in the C++
version) gave 3% higher performance. Here the two versions:
http://mattmahoney.net/dc/ -- original zip
http://pastebin.com/55x9dT9C -- Original C++ version.
http://pastebin.com/TYT7XdwX -- Modified D translation.
The problem is that the D version is 50% slower:
test.fpaq0 (16562521 bytes) - test.bmp (33159254 bytes)
Lang| Comp | Binary size | Time (lower is better)
C++ (g++) - 13kb - 2.42s (100%) -O3 -s
D(DMD) - 230kb - 4.46s (184%) -O -release -inline
D(GDC) -1322kb - 3.69s (152%) -O3 -frelease -s
The only diference I could see between the C++ and D versions is
that C++ has hints to the compiler about which functions to
inline, and I could't find anything similar in D. So I manually
inlined the encode and decode functions:
http://pastebin.com/N4nuyVMh - Manual inline
D(DMD) - 228kb - 3.70s (153%) -O -release -inline
D(GDC) -1318kb - 3.50s (144%) -O3 -frelease -s
Still, the D version is slower. What makes this speed diference?
Is there any way to side-step this?
Note that this simple C++ version can be made more than 2 times
faster with algoritimical and io optimizations, (ab)using
templates, etc. So I'm not asking for generic speed
optimizations, but only things that may make the D code more
equal to the C++ code.
I noticed the thread just now. I ported fast paq8 (fp8) to D, and with some
careful D-ification and optimization it runs a bit faster than the original C
program when compiled with the GCC on Linux x86_64, Core 2 Duo. As others said
the files are cached in RAM anyway if there is enough available, so you should
not be bound by your hard drive speed anyway.
I don't know about this version of paq you ported the coder from, but I try to
give you some hints on what I did to optimize the code.
- time portions of your main()
is the time actually spent at start up or in the compression?
- use structs, where you don't classes don't make your code cleaner
- where ever you have large arrays that you don't need initialized to .init,
write:
int[large number] arr = void;
double[large number] arr = void;
This disables default initialization, which may help you in inner loops.
Remember that C++ doesn't default initialize at all, so this is an obvious
way to lose performance against that language.
Also keep in mind that the .init for floating point types is NaN:
struct Foo { double[99] bar; }
Is not a block of binary zeroes and hence cannot be stored in a .bss
section in the executable, where it would not take any space at all.
struct Foo { double[99] bar = void; }
On the contrary will not bloat your executable by 7,6 MB!
Be cautious with:
class Foo { double[99] bar = void; }
Classes' .init don't go into .bss either way. Another reason to use a
struct where appropriate. (WARNING: Usage of .bss on Linux/MacOS is currently
broken in the compiler front-end. You'll only see the effect on Windows)
- Mahoney used an Array class in my version of paq, which allocates via calloc.
Do this as well. You can't win otherwise. Read up a bit on calloc if you want.
It generally 'allocates' a special zeroed out memory page multiple times.
No matter how much memory you ask for, it wont really allocate anything until
you *write* to it, at which point new memory is allocated for you and the
zero-page is copied into it.
The D GC on the other hand allocates that memory and writes zeroes to it
immediately.
The effect is two fold: First, the calloc version will use much less RAM, if
the 'allocated' buffers aren't fully used (e.g. you compressed a small file).
Second, the D GC version is slowed down by writing zeroes to all that memory.
At high compression levels, paq8 uses ~2 GB of memory that is calloc'ed. You
should _not_ try to use GC memory for that.
- If there are data structures that are designed to fit into a CPU cache-line
(I had one of those in paq8), make sure it still has the correct size in your
D version. static assert(Foo.sizeof == 64); helped me find a bug there that
resulted from switching from C bitfields to the D version (which is a library
solution in Phobos).
I hope that gives you some ideas what to look for. Good luck!
--
Marco
Re: D 50% slower than C++. What I'm doing wrong?
Marco Leise: I ported fast paq8 (fp8) to D, and with some careful D-ification and optimization it runs a bit faster than the original C program when compiled with the GCC on Linux x86_64, Core 2 Duo. I guess you mean GDC. With DMD, even if you are a good D programmer, it's not easy to beat that original C compressor :-) Do you have a link to your D version? Matt Mahoney is probably willing to put a link in his site to your D version. I don't know about this version of paq you ported the coder from, It was a very basic coder. The D GC on the other hand allocates that memory and writes zeroes to it immediately. Is this always done the first time the memory is allocated by the GC? The effect is two fold: First, the calloc version will use much less RAM, if the 'allocated' buffers aren't fully used (e.g. you compressed a small file). On the other hand in D you may allocate the memory in a more conscious way. static assert(Foo.sizeof == 64); helped me find a bug there that resulted from switching from C bitfields to the D version (which is a library solution in Phobos). The Phobos D bitfields aren't required to mimic C, but that's an interesting case. Maybe it's a difference interesting to be taken a look at. Do you have the code of the two C-D versions? Bye, bearophile
Re: D 50% slower than C++. What I'm doing wrong?
DMC = Digital Mars Compiler? Does Mingw/GDC uses that? I think that both, g++ and GDC compiled binaries, use the mingw runtime, but I'm not sure also. you right, only dmd uses dmc environment, gdc uses mingw's. And I don't think it is I/O bound. It is only around 10MB/s, whereas my HD can do ~100MB/s. Furthermore, on files more compressible, where the speed was higher, the difference between D and C++ was higher too. And if is in fact I/O bound, then D is MORE than 50% slower than C++. to minimize system load and I/O impact, run the same file in the loop, like 5-10 times, it will be located in kernel cache. The difference is likely because of differences in external C libraries. Both, the D and C++ versions, use C's stdio library. What is the difference? probably because gdc backend make worse job on optimizing D AST vs C++ AST. I've got following results: C:\Decho off FF=a.doc C++ compress a.doc a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.36 s. a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.36 s. a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.33 s. a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.34 s. a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.34 s. C++ decompress a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.50 s. a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.51 s. a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.51 s. a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.50 s. a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.50 s. D compress a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.11 s. a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.08 s. a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.08 s. D decompress a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.17 s. a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.19 s. a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.19 s. a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.22 s. a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.25 s. Done So, what's up? I'm used the same backend too, but DMC (-o -6) vs DMD (-release -inline -O -noboundscheck). I don't know DMC optimization flags, so probably results might be better for it. Lets try to compile by MS CL (-Ox) C:\Decho off FF=a.doc C++ compress a.doc a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.03 s. a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.02 s. a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.04 s. a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.03 s. a.doc (2694428 bytes) - a.doc.cmp (1459227 bytes) in 1.01 s. C++ decompress a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.08 s. a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.06 s. a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.07 s. a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.07 s. a.doc.cmp (1459227 bytes) - a.doc.cmp.or (2694428 bytes) in 1.07 s. D compress a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.08 s. a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) - a.doc.dmp (1459227 bytes) in 1.09 s. D decompress a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.15 s. a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.17 s. a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.19 s. a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.17 s. a.doc.dmp (1459227 bytes) - a.doc.dmp.or (2694428 bytes) in 1.17 s. Done Much better for C++, but D is not so worse and about 1.1*C++ too. What we see - different compiler, different story. We should not compare languages for performance but compilers! So many differencies in compilers and environment and definetelly C++ is much more mature for performance now but also D has own benefits (faster development/debugging and more reliable code). Thanks, Oleg. PS. BTW, this code still can be optimized quite a lot.
Re: D 50% slower than C++. What I'm doing wrong?
Are you on linux/windows/mac? On Saturday, 14 April 2012 at 19:05:40 UTC, ReneSac wrote: I have this simple binary arithmetic coder in C++ by Mahoney and translated to D by Maffi. I added notrow, final and pure and GC.disable where it was possible, but that didn't made much difference. Adding const to the Predictor.p() (as in the C++ version) gave 3% higher performance. Here the two versions: http://mattmahoney.net/dc/ -- original zip http://pastebin.com/55x9dT9C -- Original C++ version. http://pastebin.com/TYT7XdwX -- Modified D translation. The problem is that the D version is 50% slower: test.fpaq0 (16562521 bytes) - test.bmp (33159254 bytes) Lang| Comp | Binary size | Time (lower is better) C++ (g++) - 13kb - 2.42s (100%) -O3 -s D(DMD) - 230kb - 4.46s (184%) -O -release -inline D(GDC) -1322kb - 3.69s (152%) -O3 -frelease -s The only diference I could see between the C++ and D versions is that C++ has hints to the compiler about which functions to inline, and I could't find anything similar in D. So I manually inlined the encode and decode functions: http://pastebin.com/N4nuyVMh - Manual inline D(DMD) - 228kb - 3.70s (153%) -O -release -inline D(GDC) -1318kb - 3.50s (144%) -O3 -frelease -s Still, the D version is slower. What makes this speed diference? Is there any way to side-step this? Note that this simple C++ version can be made more than 2 times faster with algoritimical and io optimizations, (ab)using templates, etc. So I'm not asking for generic speed optimizations, but only things that may make the D code more equal to the C++ code.
Re: D 50% slower than C++. What I'm doing wrong?
On Sat, 14 Apr 2012 22:31:40 -0400, Jonathan M Davis jmdavisp...@gmx.com
wrote:
On Sunday, April 15, 2012 04:21:09 Joseph Rushton Wakeling wrote:
On 14/04/12 23:03, q66 wrote:
He also uses a class. And -noboundscheck should be automatically
induced
by
-release.
... but the methods are marked as final -- shouldn't that substantially
reduce any speed hit from using class instead of struct?
In theory. If they don't override anything, then that signals to the
compiler
that they don't need to be virtual, in which case, they _shouldn't_ be
virtual, but that's up to the compiler to optimize, and I don't know how
good
it is about that right now.
You are misunderstanding something. Final functions can be in the vtable,
and still not be called via the vtable.
i.e.:
class C
{
int foo() { return 1; }
}
class D : C
{
override final int foo() { return 2; }
}
void main()
{
auto d = new D;
C c = d;
assert(d.foo() == 2); // non-virtual, inline-able call.
assert(c.foo() == 2); // virtual call
}
Disclaimer -- I haven't examined any of the code being discussed or the
issues contained in this thread. I just wanted to point out this
misunderstanding.
-Steve
Re: D 50% slower than C++. What I'm doing wrong?
On Monday, 16 April 2012 at 07:28:25 UTC, Andrea Fontana wrote: Are you on linux/windows/mac? Windows. My main question is now *WHY* D is slower than C++ in this program? The code is identical (even the same C functions) in the performance-critical parts, I'm using the same compiler backend (gdc/g++), and D was supposed to a fast compilable language. Yet it is up to 50% slower. What is D doing more than C++ in this program, that accounts for the lost CPU cycles? Or what prevents the D program to be optimized to the C++ level? The D front-end?
Re: D 50% slower than C++. What I'm doing wrong?
On 04/17/2012 12:24 AM, ReneSac wrote: On Monday, 16 April 2012 at 07:28:25 UTC, Andrea Fontana wrote: Are you on linux/windows/mac? Windows. DMC runtime ! My main question is now *WHY* D is slower than C++ in this program? The code is identical (even the same C functions) No. They are not the same. The performance difference is probably explained by the dmc runtime vs. glibc difference, because your biased results are not reproducible on a linux system where glibc is used for both versions. in the performance-critical parts, I'm using the same compiler backend (gdc/g++), and D was supposed to a fast compilable language. /was/is/s Yet it is up to 50% slower. This is a fallacy. Benchmarks can only compare implementations, not languages. Furthermore, it is usually the case that benchmarks that have surprising results don't measure what they intend to measure. Your program is apparently rather I/O bound. What is D doing more than C++ in this program, that accounts for the lost CPU cycles? Or what prevents the D program to be optimized to the C++ level? The D front-end? The difference is likely because of differences in external C libraries.
Re: D 50% slower than C++. What I'm doing wrong?
On Monday, 16 April 2012 at 22:58:08 UTC, Timon Gehr wrote: On 04/17/2012 12:24 AM, ReneSac wrote: Windows. DMC runtime ! DMC = Digital Mars Compiler? Does Mingw/GDC uses that? I think that both, g++ and GDC compiled binaries, use the mingw runtime, but I'm not sure also. No. They are not the same. The performance difference is probably explained by the dmc runtime vs. glibc difference, because your biased results are not reproducible on a linux system where glibc is used for both versions. Ok, I will benchmark on linux latter. This is a fallacy. Benchmarks can only compare implementations, not languages. Furthermore, it is usually the case that benchmarks that have surprising results don't measure what they intend to measure. Your program is apparently rather I/O bound. Yeah, I'm comparing the implementation, and I made it clear that it may be the GDC front-end that may be the bottleneck. And I don't think it is I/O bound. It is only around 10MB/s, whereas my HD can do ~100MB/s. Furthermore, on files more compressible, where the speed was higher, the difference between D and C++ was higher too. And if is in fact I/O bound, then D is MORE than 50% slower than C++. The difference is likely because of differences in external C libraries. Both, the D and C++ versions, use C's stdio library. What is the difference?
Re: D 50% slower than C++. What I'm doing wrong?
On Tuesday, 17 April 2012 at 01:30:30 UTC, ReneSac wrote: On Monday, 16 April 2012 at 22:58:08 UTC, Timon Gehr wrote: On 04/17/2012 12:24 AM, ReneSac wrote: Windows. DMC runtime ! DMC = Digital Mars Compiler? Does Mingw/GDC uses that? I think that both, g++ and GDC compiled binaries, use the mingw runtime, but I'm not sure also. No. They are not the same. The performance difference is probably explained by the dmc runtime vs. glibc difference, because your biased results are not reproducible on a linux system where glibc is used for both versions. Ok, I will benchmark on linux latter. This is a fallacy. Benchmarks can only compare implementations, not languages. Furthermore, it is usually the case that benchmarks that have surprising results don't measure what they intend to measure. Your program is apparently rather I/O bound. Yeah, I'm comparing the implementation, and I made it clear that it may be the GDC front-end that may be the bottleneck. And I don't think it is I/O bound. It is only around 10MB/s, whereas my HD can do ~100MB/s. Furthermore, on files more compressible, where the speed was higher, the difference between D and C++ was higher too. And if is in fact I/O bound, then D is MORE than 50% slower than C++. The difference is likely because of differences in external C libraries. Both, the D and C++ versions, use C's stdio library. What is the difference? Have you tried profiling it? On Windows you can use AMD CodeAnalyst for that, it works pretty well in my experience and it's free of charge.
Re: D 50% slower than C++. What I'm doing wrong?
On Sunday, 15 April 2012 at 02:56:21 UTC, Joseph Rushton Wakeling wrote: On Saturday, 14 April 2012 at 19:51:21 UTC, Joseph Rushton Wakeling wrote: GDC has all the regular gcc optimization flags available IIRC. The ones on the GDC man page are just the ones specific to GDC. I'm not talking about compiler flags, but the inline keyword in the C++ source code. I saw some discussion about @inline but it seems not implemented (yet?). Well, that is not a priority for D anyway. About compiler optimizations, -finline-functions and -fweb are part of -O3. I tried to compile with -no-bounds-check, but made no diference for DMD and GDC. It probably is part of -release as q66 said. Ah yes, you're right. I do wonder if your seeming speed differences are magnified because the whole operation is only 2-4 seconds long: if your algorithm were operating over a longer timeframe I think you'd likely find the relative speed differences decrease. (I have a memory of a program that took ~0.004s with a C/C++ version and 1s with D, and the difference seemed to be just startup time for the D program.) Well, this don't seem to be true: 1.2MB compressible encode: C++: 0.11s (100%) D-inl: 0.14s (127%) decode C++: 0.12s (100%) D-inl: 0.16s (133%) ~200MB compressible encode: C++: 17.2s (100%) D-inl: 21.5s (125%) decode: C++: 16.3s (100%) D-inl: 24,5s (150%) 3,8GB, barelly-compressible encode: C++: 412s (100%) D-inl: 512s (124%) What really amazes me is the difference between g++, DMD and GDC in size of the executable binary. 100 orders of magnitude! I have remarked it in another topic before, with a simple hello world. I need to update there, now that I got DMD working. BTW, it is 2 orders of magnitude. 3 remarks about the D code. One is that much of it still seems very C-ish; I'd be interested to see how speed and executable size differ if things like the file opening, or the reading of characters, are done with more idiomatic D code. Sounds stupid as the C stuff should be fastest, but I've been surprised sometimes at how using idiomatic D formulations can improve things. Well, it may indeed be faster, especially the IO that is dependent on things like buffering and so on. But for this I just wanted something as close as the C++ code as possible. Second remark is more of a query -- can Predictor.p() and .update really be marked as pure? Their result for a given input actually varies depending on the current values of cxt and ct, which are modified outside of function scope. Yeah, I don't know. I just did just throw those qualifiers against the compiler, and saw what sticks. And I was testing the decode speed specially to see easily if the output was corrupted. But maybe it haven't corrupted because the compiler don't optimize based on pure yet... there was no speed difference too.. so... Third remark -- again a query -- why the GC.disable ... ? Just to be sure that the speed difference wasn't caused by the GC. It didn't make any speed difference also, and it is indeed a bad idea.
Re: D 50% slower than C++. What I'm doing wrong?
On 15/04/12 09:23, ReneSac wrote:
What really amazes me is the difference between g++, DMD and GDC in size of
the executable binary. 100 orders of magnitude!
I have remarked it in another topic before, with a simple hello world. I need
to update there, now that I got DMD working. BTW, it is 2 orders of magnitude.
Ack. Yes, 2 orders of magnitude, 100 _times_ larger. That'll teach me to send
comments to a mailing list at an hour of the morning so late that it can be
called early. ;-)
Sounds stupid as the C stuff should be fastest, but I've been surprised
sometimes at how using idiomatic D formulations can improve things.
Well, it may indeed be faster, especially the IO that is dependent on things
like buffering and so on. But for this I just wanted something as close as the
C++ code as possible.
Fair dos. Seems worth trying the idiomatic alternatives before assuming the
speed difference is always going to be so great, though.
Yeah, I don't know. I just did just throw those qualifiers against the compiler,
and saw what sticks. And I was testing the decode speed specially to see easily
if the output was corrupted. But maybe it haven't corrupted because the compiler
don't optimize based on pure yet... there was no speed difference too.. so...
I think it's because although there's mutability outside the function, those
variables are still internal to the struct. e.g. if you try and compile this code:
int k = 23;
pure int twotimes(int a)
{
auto b = 2*a;
auto c = 2*k;
return b+c;
}
... it'll fail, but if you try and compile,
struct TwoTimes
{
int k = 23;
pure int twotimes(int a)
{
auto b = 2*a;
auto c = 2*k;
return b+c;
}
}
... the compiler accepts it. Whether that's because it's acceptably pure, or
because the compiler just doesn't detect this case of impurity, is another
matter. The int k is certainly mutable from outside the scope of the function,
so AFAICS it _should_ be disallowed.
Re: D 50% slower than C++. What I'm doing wrong?
On 15/04/12 10:29, Joseph Rushton Wakeling wrote: ... the compiler accepts it. Whether that's because it's acceptably pure, or because the compiler just doesn't detect this case of impurity, is another matter. The int k is certainly mutable from outside the scope of the function, so AFAICS it _should_ be disallowed. Meant to say: outside the scope of the struct.
Re: D 50% slower than C++. What I'm doing wrong?
On 15.04.2012 12:29, Joseph Rushton Wakeling wrote:
On 15/04/12 09:23, ReneSac wrote:
What really amazes me is the difference between g++, DMD and GDC in
size of
the executable binary. 100 orders of magnitude!
I have remarked it in another topic before, with a simple hello
world. I need
to update there, now that I got DMD working. BTW, it is 2 orders of
magnitude.
Ack. Yes, 2 orders of magnitude, 100 _times_ larger. That'll teach me to
send comments to a mailing list at an hour of the morning so late that
it can be called early. ;-)
Sounds stupid as the C stuff should be fastest, but I've been surprised
sometimes at how using idiomatic D formulations can improve things.
Well, it may indeed be faster, especially the IO that is dependent on
things
like buffering and so on. But for this I just wanted something as
close as the
C++ code as possible.
Fair dos. Seems worth trying the idiomatic alternatives before assuming
the speed difference is always going to be so great, though.
Yeah, I don't know. I just did just throw those qualifiers against the
compiler,
and saw what sticks. And I was testing the decode speed specially to
see easily
if the output was corrupted. But maybe it haven't corrupted because
the compiler
don't optimize based on pure yet... there was no speed difference
too.. so...
I think it's because although there's mutability outside the function,
those variables are still internal to the struct. e.g. if you try and
compile this code:
int k = 23;
pure int twotimes(int a)
{
auto b = 2*a;
auto c = 2*k;
return b+c;
}
... it'll fail, but if you try and compile,
struct TwoTimes
{
int k = 23;
pure int twotimes(int a)
{
auto b = 2*a;
auto c = 2*k;
return b+c;
}
}
Simple - it's called weakly pure. (it can modify this for instance)
It's allowed so that you can do:
pure int f(){
Twotimes t;
return t.towtime(1,1);
}
which is obviously normal/strongly pure. Of course, the compiler knows
what kind of purity each function has.
... the compiler accepts it. Whether that's because it's acceptably
pure, or because the compiler just doesn't detect this case of impurity,
is another matter. The int k is certainly mutable from outside the scope
of the function, so AFAICS it _should_ be disallowed.
--
Dmitry Olshansky
Re: D 50% slower than C++. What I'm doing wrong?
On Apr 15, 2012 4:30 AM, Joseph Rushton Wakeling joseph.wakel...@webdrake.net wrote: ... the compiler accepts it. Whether that's because it's acceptably pure, or because the compiler just doesn't detect this case of impurity, is another matter. The int k is certainly mutable from outside the scope of the function, so AFAICS it _should_ be disallowed. As far as I understand pure includes the hidden this parameter so it is pure if when you call it on the same structure with the same arguments you always get the same results. Although that seams pretty useless in the optimization standpoint because the function can modify it's own object between calls.
Re: D 50% slower than C++. What I'm doing wrong?
Le 15/04/2012 09:23, ReneSac a écrit : On Sunday, 15 April 2012 at 02:56:21 UTC, Joseph Rushton Wakeling wrote: On Saturday, 14 April 2012 at 19:51:21 UTC, Joseph Rushton Wakeling wrote: GDC has all the regular gcc optimization flags available IIRC. The I notice the 2D array is declared int ct[512][2]; // C++ int ct[2][512]; // D Any particular reason for this ? May this impede the cache utilization ? As for the executable size, the D compiler links the druntime and libraries statically in the binary while I would believe g++ links them dynamically.
Re: D 50% slower than C++. What I'm doing wrong?
On Sun, Apr 15, 2012 at 5:16 PM, Somedude lovelyd...@mailmetrash.com wrote: Le 15/04/2012 09:23, ReneSac a écrit : On Sunday, 15 April 2012 at 02:56:21 UTC, Joseph Rushton Wakeling wrote: On Saturday, 14 April 2012 at 19:51:21 UTC, Joseph Rushton Wakeling wrote: GDC has all the regular gcc optimization flags available IIRC. The I notice the 2D array is declared int ct[512][2]; // C++ int ct[2][512]; // D Not quite. It is declared int[2][512] ct; // not valid in C++ which is the same as Int ct[512][2], // also valid in C++ That's because you look at it as ((int)[2])[512] 512-sized array of 2-sized array of ints.
Re: D 50% slower than C++. What I'm doing wrong?
Le 15/04/2012 23:33, Ashish Myles a écrit : On Sun, Apr 15, 2012 at 5:16 PM, Somedude lovelyd...@mailmetrash.com wrote: Le 15/04/2012 09:23, ReneSac a écrit : On Sunday, 15 April 2012 at 02:56:21 UTC, Joseph Rushton Wakeling wrote: On Saturday, 14 April 2012 at 19:51:21 UTC, Joseph Rushton Wakeling wrote: GDC has all the regular gcc optimization flags available IIRC. The I notice the 2D array is declared int ct[512][2]; // C++ int ct[2][512]; // D Not quite. It is declared int[2][512] ct; // not valid in C++ which is the same as Int ct[512][2], // also valid in C++ That's because you look at it as ((int)[2])[512] 512-sized array of 2-sized array of ints. Oh right, sorry for this. It's a bit confusing.
Re: D 50% slower than C++. What I'm doing wrong?
Le 15/04/2012 23:41, Somedude a écrit : Le 15/04/2012 23:33, Ashish Myles a écrit : On Sun, Apr 15, 2012 at 5:16 PM, Somedude lovelyd...@mailmetrash.com wrote: Oh right, sorry for this. It's a bit confusing. Now apart from comparing the generated asm, I don't see.
Re: D 50% slower than C++. What I'm doing wrong?
On 04/15/2012 02:23 PM, Kevin Cox wrote:
On Apr 15, 2012 4:30 AM, Joseph Rushton Wakeling
joseph.wakel...@webdrake.net mailto:joseph.wakel...@webdrake.net wrote:
... the compiler accepts it. Whether that's because it's acceptably
pure, or because the compiler just doesn't detect this case of impurity,
is another matter. The int k is certainly mutable from outside the
scope of the function, so AFAICS it _should_ be disallowed.
As far as I understand pure includes the hidden this parameter so it
is pure if when you call it on the same structure with the same
arguments you always get the same results. Although that seams pretty
useless in the optimization standpoint
It is useful, because the guarantees it gives still are quite strong.
Besides, mutation of the receiver object can be explicitly disabled by
marking the method const or immutable; there is no reason why 'pure'
should imply 'const'.
because the function can modify
it's own object between calls.
S foo(int a)pure{
S x;
x.foo(a);
x.bar(a);
return x;
}
D 50% slower than C++. What I'm doing wrong?
I have this simple binary arithmetic coder in C++ by Mahoney and translated to D by Maffi. I added notrow, final and pure and GC.disable where it was possible, but that didn't made much difference. Adding const to the Predictor.p() (as in the C++ version) gave 3% higher performance. Here the two versions: http://mattmahoney.net/dc/ -- original zip http://pastebin.com/55x9dT9C -- Original C++ version. http://pastebin.com/TYT7XdwX -- Modified D translation. The problem is that the D version is 50% slower: test.fpaq0 (16562521 bytes) - test.bmp (33159254 bytes) Lang| Comp | Binary size | Time (lower is better) C++ (g++) - 13kb - 2.42s (100%) -O3 -s D(DMD) - 230kb - 4.46s (184%) -O -release -inline D(GDC) -1322kb - 3.69s (152%) -O3 -frelease -s The only diference I could see between the C++ and D versions is that C++ has hints to the compiler about which functions to inline, and I could't find anything similar in D. So I manually inlined the encode and decode functions: http://pastebin.com/N4nuyVMh - Manual inline D(DMD) - 228kb - 3.70s (153%) -O -release -inline D(GDC) -1318kb - 3.50s (144%) -O3 -frelease -s Still, the D version is slower. What makes this speed diference? Is there any way to side-step this? Note that this simple C++ version can be made more than 2 times faster with algoritimical and io optimizations, (ab)using templates, etc. So I'm not asking for generic speed optimizations, but only things that may make the D code more equal to the C++ code.
Re: D 50% slower than C++. What I'm doing wrong?
On 14/04/12 21:05, ReneSac wrote: Lang| Comp | Binary size | Time (lower is better) C++ (g++) - 13kb - 2.42s (100%) -O3 -s D (DMD) - 230kb - 4.46s (184%) -O -release -inline D (GDC) - 1322kb - 3.69s (152%) -O3 -frelease -s Try using extra optimizations for GDC. Actually, GDC has a dmd-like interface, gdmd, and gdmd -O -release -inline corresponds to gdc -O3 -fweb -frelease -finline-functions ... so there may be some optimizations you were missing. (If you call gdmd with the -vdmd flag, it will tell you exactly what gdc statement it's using.) The only diference I could see between the C++ and D versions is that C++ has hints to the compiler about which functions to inline, and I could't find anything similar in D. So I manually inlined the encode and decode functions: GDC has all the regular gcc optimization flags available IIRC. The ones on the GDC man page are just the ones specific to GDC. Still, the D version is slower. What makes this speed diference? Is there any way to side-step this? In my (brief and limited) experience GDC produced executables tend to have a noticeable but minor gap compared to equivalent g++ compiled C++ code -- nothing on the order of 150%. E.g. I have some simulation code which models a reputation system where users rate objects and are then in turn judged on the consistency of their ratings with the general consensus. A simulation with 1000 users and 1000 objects takes ~22s to run in C++, ~24s in D compiled with gdmd -O -release -inline. Scale that up to 2000 users and 1000 objects and it's 47s (C++) vs 53s (D). 2000 users and 2000 objects gives 1min 49s (C++) and 2min 4s (D). So, it's a gap, but not one to write home about really, especially when you count that D is safer and (I think) easier/faster to program in. It's true that DMD is much slower -- the GCC backend is much better at generating fast code. If I recall right the DMD backend's encoding of floating point operations is considerably less sophisticated. Note that this simple C++ version can be made more than 2 times faster with algoritimical and io optimizations, (ab)using templates, etc. So I'm not asking for generic speed optimizations, but only things that may make the D code more equal to the C++ code. I'm sure you can make various improvements to your D code in a similar way, and there are some things that improve in D when written in idiomatic D style as opposed to a more C++ish way of doing things (e.g. if you want to copy 1 vector to another, as happens in my code, write x[] = y[] instead of doing any kind of loop). Best wishes, -- Joe
Re: D 50% slower than C++. What I'm doing wrong?
On Saturday, 14 April 2012 at 19:05:40 UTC, ReneSac wrote: I have this simple binary arithmetic coder in C++ by Mahoney and translated to D by Maffi. I added notrow, final and pure and GC.disable where it was possible, but that didn't made much difference. Adding const to the Predictor.p() (as in the C++ version) gave 3% higher performance. Here the two versions: http://mattmahoney.net/dc/ -- original zip http://pastebin.com/55x9dT9C -- Original C++ version. http://pastebin.com/TYT7XdwX -- Modified D translation. The problem is that the D version is 50% slower: test.fpaq0 (16562521 bytes) - test.bmp (33159254 bytes) Lang| Comp | Binary size | Time (lower is better) C++ (g++) - 13kb - 2.42s (100%) -O3 -s D(DMD) - 230kb - 4.46s (184%) -O -release -inline D(GDC) -1322kb - 3.69s (152%) -O3 -frelease -s The only diference I could see between the C++ and D versions is that C++ has hints to the compiler about which functions to inline, and I could't find anything similar in D. So I manually inlined the encode and decode functions: http://pastebin.com/N4nuyVMh - Manual inline D(DMD) - 228kb - 3.70s (153%) -O -release -inline D(GDC) -1318kb - 3.50s (144%) -O3 -frelease -s Still, the D version is slower. What makes this speed diference? Is there any way to side-step this? Note that this simple C++ version can be made more than 2 times faster with algoritimical and io optimizations, (ab)using templates, etc. So I'm not asking for generic speed optimizations, but only things that may make the D code more equal to the C++ code. I wrote a version http://codepad.org/phpLP7cx based on the C++ one. My commands used to compile: g++46 -O3 -s fpaq0.cpp -o fpaq0cpp dmd -O -release -inline -noboundscheck fpaq0.d G++ 4.6, dmd 2.059. I did 5 tests for each: test.fpaq0 (34603008 bytes) - test.bmp (34610367 bytes) The C++ average result was 9.99 seconds (varying from 9.98 to 10.01) The D average result was 12.00 seconds (varying from 11.98 to 12.01) That means there is 16.8 percent difference in performance that would be cleared out by usage of gdc (which I don't have around currently).
Re: D 50% slower than C++. What I'm doing wrong?
Forgot to mention specs: Dualcore Athlon II X2 240 (2.8GHz), 4GB RAM, FreeBSD 9 x64, both compilers are 64bit.
Re: D 50% slower than C++. What I'm doing wrong?
Le 14/04/2012 21:53, q66 a écrit : On Saturday, 14 April 2012 at 19:05:40 UTC, ReneSac wrote: I have this simple binary arithmetic coder in C++ by Mahoney and translated to D by Maffi. I added notrow, final and pure and GC.disable where it was possible, but that didn't made much difference. Adding const to the Predictor.p() (as in the C++ version) gave 3% higher performance. Here the two versions: http://mattmahoney.net/dc/ -- original zip http://pastebin.com/55x9dT9C -- Original C++ version. http://pastebin.com/TYT7XdwX -- Modified D translation. The problem is that the D version is 50% slower: test.fpaq0 (16562521 bytes) - test.bmp (33159254 bytes) Lang| Comp | Binary size | Time (lower is better) C++ (g++) - 13kb - 2.42s (100%) -O3 -s D(DMD) - 230kb - 4.46s (184%) -O -release -inline D(GDC) -1322kb - 3.69s (152%) -O3 -frelease -s The only diference I could see between the C++ and D versions is that C++ has hints to the compiler about which functions to inline, and I could't find anything similar in D. So I manually inlined the encode and decode functions: http://pastebin.com/N4nuyVMh - Manual inline D(DMD) - 228kb - 3.70s (153%) -O -release -inline D(GDC) -1318kb - 3.50s (144%) -O3 -frelease -s Still, the D version is slower. What makes this speed diference? Is there any way to side-step this? Note that this simple C++ version can be made more than 2 times faster with algoritimical and io optimizations, (ab)using templates, etc. So I'm not asking for generic speed optimizations, but only things that may make the D code more equal to the C++ code. I wrote a version http://codepad.org/phpLP7cx based on the C++ one. My commands used to compile: g++46 -O3 -s fpaq0.cpp -o fpaq0cpp dmd -O -release -inline -noboundscheck fpaq0.d G++ 4.6, dmd 2.059. I did 5 tests for each: test.fpaq0 (34603008 bytes) - test.bmp (34610367 bytes) The C++ average result was 9.99 seconds (varying from 9.98 to 10.01) The D average result was 12.00 seconds (varying from 11.98 to 12.01) That means there is 16.8 percent difference in performance that would be cleared out by usage of gdc (which I don't have around currently). The code is nearly identical (there is a slight difference in update(), where he accesses the array once more than you), but the main difference I see is the -noboundscheck compilation option on DMD.
Re: D 50% slower than C++. What I'm doing wrong?
On Saturday, 14 April 2012 at 20:58:01 UTC, Somedude wrote: Le 14/04/2012 21:53, q66 a écrit : On Saturday, 14 April 2012 at 19:05:40 UTC, ReneSac wrote: I have this simple binary arithmetic coder in C++ by Mahoney and translated to D by Maffi. I added notrow, final and pure and GC.disable where it was possible, but that didn't made much difference. Adding const to the Predictor.p() (as in the C++ version) gave 3% higher performance. Here the two versions: http://mattmahoney.net/dc/ -- original zip http://pastebin.com/55x9dT9C -- Original C++ version. http://pastebin.com/TYT7XdwX -- Modified D translation. The problem is that the D version is 50% slower: test.fpaq0 (16562521 bytes) - test.bmp (33159254 bytes) Lang| Comp | Binary size | Time (lower is better) C++ (g++) - 13kb - 2.42s (100%) -O3 -s D(DMD) - 230kb - 4.46s (184%) -O -release -inline D(GDC) -1322kb - 3.69s (152%) -O3 -frelease -s The only diference I could see between the C++ and D versions is that C++ has hints to the compiler about which functions to inline, and I could't find anything similar in D. So I manually inlined the encode and decode functions: http://pastebin.com/N4nuyVMh - Manual inline D(DMD) - 228kb - 3.70s (153%) -O -release -inline D(GDC) -1318kb - 3.50s (144%) -O3 -frelease -s Still, the D version is slower. What makes this speed diference? Is there any way to side-step this? Note that this simple C++ version can be made more than 2 times faster with algoritimical and io optimizations, (ab)using templates, etc. So I'm not asking for generic speed optimizations, but only things that may make the D code more equal to the C++ code. I wrote a version http://codepad.org/phpLP7cx based on the C++ one. My commands used to compile: g++46 -O3 -s fpaq0.cpp -o fpaq0cpp dmd -O -release -inline -noboundscheck fpaq0.d G++ 4.6, dmd 2.059. I did 5 tests for each: test.fpaq0 (34603008 bytes) - test.bmp (34610367 bytes) The C++ average result was 9.99 seconds (varying from 9.98 to 10.01) The D average result was 12.00 seconds (varying from 11.98 to 12.01) That means there is 16.8 percent difference in performance that would be cleared out by usage of gdc (which I don't have around currently). The code is nearly identical (there is a slight difference in update(), where he accesses the array once more than you), but the main difference I see is the -noboundscheck compilation option on DMD. He also uses a class. And -noboundscheck should be automatically induced by -release.
Re: D 50% slower than C++. What I'm doing wrong?
I tested the q66 version in my computer (sandy bridge @ 4.3GHz). Repeating the old timmings here, and the new results are marked as D-v2: test.fpaq0 (16562521 bytes) - test.bmp (33159254 bytes) Lang| Comp | Binary size | Time (lower is better) C++ (g++) - 13kb - 2.42s (100%) -O3 -s D(DMD) - 230kb - 4.46s (184%) -O -release -inline D(GDC) -1322kb - 3.69s (152%) -O3 -frelease -s D-v2 (DMD) - 206kb - 4.50s (186%) -O -release -inline D-v2 (GDC) - 852kb - 3.65s (151%) -O3 -frelease -s So, basically the same thing... Not using clases seems a little slower on DMD, and no difference on GDC. The if (++ct[cxt][y] 65534) made a very small, but measurable difference (those .04s in GDC). The if ((cxt += cxt + y) = 512) only made the code more complicated, with no speed benefit. But the input file is also important. The file you tested seems to be an already compressed one, or something not very compressible. Here a test with an incompressible file: pnad9huff.fpaq0 (43443040 bytes) - test-d.huff (43617049 bytes) C++ (g++) - 13kb - 5.13 (100%) -O3 -s D-v2 (DMD) - 206kb - 8.03 (156%) -O -release -inline D-v2 (GDC) - 852kb - 7.09 (138%) -O3 -frelease -s D-inl(DMD) - 228kb - 6.93 (135%) -O -release -inline D-inl(GDC) -1318kb - 6.86 (134%) -O3 -frelease -s The C++ advantage becomes smaller in this file. D-inl is my manual inline version, with your small optimization on Predictor.Update(). On Saturday, 14 April 2012 at 19:51:21 UTC, Joseph Rushton Wakeling wrote: GDC has all the regular gcc optimization flags available IIRC. The ones on the GDC man page are just the ones specific to GDC. I'm not talking about compiler flags, but the inline keyword in the C++ source code. I saw some discussion about @inline but it seems not implemented (yet?). Well, that is not a priority for D anyway. About compiler optimizations, -finline-functions and -fweb are part of -O3. I tried to compile with -no-bounds-check, but made no diference for DMD and GDC. It probably is part of -release as q66 said.
Re: D 50% slower than C++. What I'm doing wrong?
On Sunday, April 15, 2012 03:51:59 ReneSac wrote: About compiler optimizations, -finline-functions and -fweb are part of -O3. I tried to compile with -no-bounds-check, but made no diference for DMD and GDC. It probably is part of -release as q66 said. Not quite. -noboundscheck turns off _all_ array bounds checking, whereas - release turns it off in @system and @trusted functions, but not in @safe functions. But unless you've marked your code with @safe or it uses templated functions which get inferred as @safe, all of your functions are going to be @system functions anyway, in which case, it makes no difference. - Jonathan M Davis
Re: D 50% slower than C++. What I'm doing wrong?
On 14/04/12 23:03, q66 wrote: He also uses a class. And -noboundscheck should be automatically induced by -release. Ahh, THAT probably explains why some of my numerical code is so markedly different in speed when compiled using DMD with or without the -release switch. It's a MAJOR difference -- between code taking say 5min to run, compared to half an hour or more.
Re: D 50% slower than C++. What I'm doing wrong?
On 14/04/12 23:03, q66 wrote: He also uses a class. And -noboundscheck should be automatically induced by -release. ... but the methods are marked as final -- shouldn't that substantially reduce any speed hit from using class instead of struct?
Re: D 50% slower than C++. What I'm doing wrong?
On Sunday, April 15, 2012 04:21:09 Joseph Rushton Wakeling wrote:
On 14/04/12 23:03, q66 wrote:
He also uses a class. And -noboundscheck should be automatically induced
by
-release.
... but the methods are marked as final -- shouldn't that substantially
reduce any speed hit from using class instead of struct?
In theory. If they don't override anything, then that signals to the compiler
that they don't need to be virtual, in which case, they _shouldn't_ be
virtual, but that's up to the compiler to optimize, and I don't know how good
it is about that right now. Certainly, if you had code like
class C
{
final int foo() { return 42;}
}
and benchmarking showed that it was the same speed as
class C
{
int foo() { return 42;}
}
when compiled with -O and -inline, then I'd submit a bug report (maybe an
enhancement request?) on the compiler failing to make final functions non-
virtual.
Also, if the function is doing enough work, then whether it's virtual or not
really doesn't make any difference, because the function itself costs so much
more than the extra cost of the virtual function call.
- Jonathan M Davis
Re: D 50% slower than C++. What I'm doing wrong?
On Saturday, April 14, 2012 19:31:40 Jonathan M Davis wrote:
On Sunday, April 15, 2012 04:21:09 Joseph Rushton Wakeling wrote:
On 14/04/12 23:03, q66 wrote:
He also uses a class. And -noboundscheck should be automatically induced
by
-release.
... but the methods are marked as final -- shouldn't that substantially
reduce any speed hit from using class instead of struct?
In theory. If they don't override anything, then that signals to the
compiler that they don't need to be virtual, in which case, they
_shouldn't_ be virtual, but that's up to the compiler to optimize, and I
don't know how good it is about that right now. Certainly, if you had code
like
class C
{
final int foo() { return 42;}
}
and benchmarking showed that it was the same speed as
class C
{
int foo() { return 42;}
}
when compiled with -O and -inline, then I'd submit a bug report (maybe an
enhancement request?) on the compiler failing to make final functions non-
virtual.
Actually, if you try and benchmark it, make sure that the code can't know that
the reference is exactly a C. In theory, the compiler could be smart enough to
know in a case such as
auto c = new C;
auto a = c.foo();
that c is exactly a C and that therefore, it can just inline the call to foo
even if it's virtual. If c is set from another function, it can't do that.
e.g.
auto c = bar();
auto a = c.foo();
The compiler _probably_ isn't that smart, but it might be, so you'd have to be
careful about that.
- Jonathan M Davis
Re: D 50% slower than C++. What I'm doing wrong?
On Sunday, 15 April 2012 at 02:20:34 UTC, Joseph Rushton Wakeling wrote: On 14/04/12 23:03, q66 wrote: He also uses a class. And -noboundscheck should be automatically induced by -release. Ahh, THAT probably explains why some of my numerical code is so markedly different in speed when compiled using DMD with or without the -release switch. It's a MAJOR difference -- between code taking say 5min to run, compared to half an hour or more. I know this isn't what your post was about, but you really should compile numerical code with GDC instead of DMD if you care about performance. It generates much faster floating point code.
Re: D 50% slower than C++. What I'm doing wrong?
On 15/04/12 04:37, jerro wrote: I know this isn't what your post was about, but you really should compile numerical code with GDC instead of DMD if you care about performance. It generates much faster floating point code. It's exactly what I do. :-)
Re: D 50% slower than C++. What I'm doing wrong?
On Saturday, 14 April 2012 at 19:51:21 UTC, Joseph Rushton Wakeling wrote: GDC has all the regular gcc optimization flags available IIRC. The ones on the GDC man page are just the ones specific to GDC. I'm not talking about compiler flags, but the inline keyword in the C++ source code. I saw some discussion about @inline but it seems not implemented (yet?). Well, that is not a priority for D anyway. About compiler optimizations, -finline-functions and -fweb are part of -O3. I tried to compile with -no-bounds-check, but made no diference for DMD and GDC. It probably is part of -release as q66 said. Ah yes, you're right. I do wonder if your seeming speed differences are magnified because the whole operation is only 2-4 seconds long: if your algorithm were operating over a longer timeframe I think you'd likely find the relative speed differences decrease. (I have a memory of a program that took ~0.004s with a C/C++ version and 1s with D, and the difference seemed to be just startup time for the D program.) What really amazes me is the difference between g++, DMD and GDC in size of the executable binary. 100 orders of magnitude! 3 remarks about the D code. One is that much of it still seems very C-ish; I'd be interested to see how speed and executable size differ if things like the file opening, or the reading of characters, are done with more idiomatic D code. Sounds stupid as the C stuff should be fastest, but I've been surprised sometimes at how using idiomatic D formulations can improve things. Second remark is more of a query -- can Predictor.p() and .update really be marked as pure? Their result for a given input actually varies depending on the current values of cxt and ct, which are modified outside of function scope. Third remark -- again a query -- why the GC.disable ... ?
Re: D 50% slower than C++. What I'm doing wrong?
(I have a memory of a program that took ~0.004s with a C/C++ version and 1s with D, and the difference seemed to be just startup time for the D program.) I have never seen anything like that. Usually the minimal time to run a D program is something like: j@debian:~$ time ./hello Hello world! real0m0.001s user0m0.000s sys 0m0.000s What really amazes me is the difference between g++, DMD and GDC in size of the executable binary. 100 orders of magnitude! With GDC those flags(for gdmd): -fdata-sections -ffunction-sections -L--gc-sections -L-l help a lot if you want to reduce a size of executable. Besides, this overhead is the standard library and runtime and won't be much larger in larger programs.
Re: D 50% slower than C++. What I'm doing wrong?
On Sunday, 15 April 2012 at 03:41:55 UTC, jerro wrote: (I have a memory of a program that took ~0.004s with a C/C++ version and 1s with D, and the difference seemed to be just startup time for the D program.) I have never seen anything like that. Usually the minimal time to run a D program is something like: j@debian:~$ time ./hello Hello world! real0m0.001s user0m0.000s sys 0m0.000s What really amazes me is the difference between g++, DMD and GDC in size of the executable binary. 100 orders of magnitude! With GDC those flags(for gdmd): -fdata-sections -ffunction-sections -L--gc-sections -L-l help a lot if you want to reduce a size of executable. Besides, this overhead is the standard library and runtime and won't be much larger in larger programs. The last flag should be -L-s
Re: D 50% slower than C++. What I'm doing wrong?
On 15/04/12 05:41, jerro wrote: I have never seen anything like that. Usually the minimal time to run a D program is something like: j@debian:~$ time ./hello Hello world! real 0m0.001s user 0m0.000s sys 0m0.000s Yea, my experience too in general. I can't remember exactly what I was testing but if it's what I think it was (and have just retested:-), the difference may have been less pronounced (maybe 0.080s for D compared to 0.004 for C++) and that would have been due to not enabling optimizations for D. I have another pair of stupid D-vs.-C++ speed-test files where with optimizations engaged, D beats C++: the dominant factor is lots of output to console, so I guess this is D's writeln() beating C++'s cout. What really amazes me is the difference between g++, DMD and GDC in size of the executable binary. 100 orders of magnitude! With GDC those flags(for gdmd): -fdata-sections -ffunction-sections -L--gc-sections -L-l help a lot if you want to reduce a size of executable. Besides, this overhead is the standard library and runtime and won't be much larger in larger programs. Ahh! I hadn't realized that the libphobos package on Ubuntu didn't install a compiled version of the library. (DMD does.)
