D for scientific computing

[John Colvin]

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.