D for scientific computing

[John Colvin]

On Friday, 25 January 2013 at 13:38:03 UTC, Iain Buclaw wrote:
> On 25 January 2013 10:27, John Colvin 
> <john.loughran.colvin at gmail.com>wrote:
>
>> On Friday, 25 January 2013 at 01:41:12 UTC, H. S. Teoh wrote:
>>
>>> On Thu, Jan 24, 2013 at 03:18:01PM -0800, Walter Bright wrote:
>>>
>>>> On 1/24/2013 1:13 PM, H. S. Teoh wrote:
>>>> >On Thu, Jan 24, 2013 at 12:15:07PM -0800, Walter Bright 
>>>> >wrote:
>>>> >>On 1/24/2013 8:36 AM, H. S. Teoh wrote:
>>>> >>>Nevertheless, I also have made the same observation that
>>>> >>>>>>code
>>>> >>>produced by gdc consistently outperforms code produced by
>>>> >>>>>>dmd.
>>>> >>>Usually by about 20-30%, sometimes as much as 50-60%, 
>>>> >>>IME. >>>That's a
>>>> >>>pretty big discrepancy for me, esp. when I'm doing
>>>> >>>compute-intensive
>>>> >>>geometric computations.
>>>> >>
>>>> >>Do you mean floating point code? 32 or 64 bit?
>>>> >
>>>> >Floating-point, 64-bit, tested on dmd -O vs. gdc -O3.
>>>>
>>>> Next, are you using floats, doubles, or reals?
>>>>
>>>
>>> Both reals and floats. Well, let's get some real 
>>> measurements. Here's a
>>> quick run-through of various test programs I have lying 
>>> around:
>>>
>>> Test program #1 (iterating 2-variable function over grid), 
>>> uses reals:
>>> - Test case with n=400:
>>>         Using DMD:      ~8 seconds (consistently)
>>>         Using GDC:      ~6 seconds (consistently)
>>>         * So the DMD version is 33% slower than the GDC 
>>> version.
>>>           (That is, 8/6*100 = 133%, so 33% slower.)
>>>
>>> - Test case with n=600:
>>>         Using DMD:      ~27 seconds (consistently)
>>>         Using GDC:      ~19 seconds (consistently)
>>>         * So the DMD version is 42% slower than the GDC 
>>> version.
>>>
>>>
>>> Test program #2 (terrain generation simulator), uses floats:
>>> (The running time of this one depends on the RNG, so I fixed 
>>> the seed
>>> value in order to make a fair comparison.)
>>> - Test case with seed=380170304, n=20 with water & wind 
>>> simulation:
>>>         Using DMD:      ~10 seconds (consistently)
>>>         Using GDC:      ~7 seconds (consistently)
>>>         * So the DMD version is 42% slower than the GDC 
>>> version.
>>>
>>> - Test case with seed=380170304, n=25 with water & wind 
>>> simulation:
>>>         Using DMD:      ~14 seconds (consistently)
>>>         Using GDC:      ~9 seconds (consistently)
>>>         * So the DMD version is 55% slower than the GDC 
>>> version.
>>>
>>>
>>> Test program #3 (enumeration of coordinates of n-dimensional 
>>> polytopes),
>>> uses reals:
>>> - All permutations and changes of sign of <1,2,3,4,5,6,7>:
>>>         Using DMD:      ~4 seconds (consistently)
>>>         Using GDC:      ~3 seconds (consistently)
>>>         * So the DMD version is 33% slower than the GDC 
>>> version.
>>>
>>> - All permutations and changes of sign of <1,2,3,4,5,6,7,7>:
>>>         Using DMD:      ~41 seconds (consistently)
>>>         Using GDC:      ~27 seconds (consistently)
>>>         * So the DMD version is 51% slower than the GDC 
>>> version.
>>>
>>> - Even permutations and all changes of sign of 
>>> <1,2,3,4,5,6,7,8>:
>>>         Using DMD:      ~40 seconds (consistently)
>>>         Using GDC:      ~27 seconds (consistently)
>>>         * So the DMD version is 48% slower than the GDC 
>>> version.
>>>
>>>
>>> All test programs were compiled with dmd -O for the DMD 
>>> version, and gdc
>>> -O3 for the GDC version. The source code is unchanged between 
>>> the two
>>> compilers, and there are no version()'s that depend on a 
>>> particular
>>> compiler. The measurements stated above are averages of about 
>>> 3-4 runs.
>>>
>>> As you can see, the performance difference is between the two 
>>> is pretty
>>> clear.  I'm pretty sure this isn't only because of floating 
>>> point
>>> operations, because the above test programs all use a lot of 
>>> inner
>>> loops, and GDC does some pretty sophisticated loop unrolling 
>>> and other
>>> such optimizations.
>>>
>>>
>>> T
>>>
>>
>> Comparing dmd -O and gdc -O3 is hardly fair. "dmd -release 
>> -inline -O" is
>> more comparable.
>>
>
>
> But then you'd have to do gdc -O3 -frelease. :-)

Ah yes, of course :)