Why DMD is so slow?

[janderson]

janderson wrote:
> Marco wrote:
>> I have written the code reported below to test execution speed of D in 
>> Windows and I have found that the same code is about 10 times slower 
>> if compiled using DMD w.r.t. GCD: 1.9 minutes in DMD vs 1.84 seconds 
>> in GDC ! Is there perhaps something wrong? why such a difference?
>> Thank you.
>>
>> // begin of file mandel_d1.d
>> /*
>> DMD: dmd -inline -release -O mandel_d1.d
>> GCD: gdc -O3 --fast-math -inline -lgphobos --expensive-optimizations 
>> mandel_d1.d
>> */
>>
>> import std.stdio;
>>
>> int main()
>> {
>>  cdouble a, b, c, z;
>>  double mand_re = 0, mand_im = 0;
>>
>>  for (double y = -2; y < 2; y += 0.01) {
>>   for (double x = -2; x < 2; x += 0.01) {
>>    z = (x + mand_re) + (y + mand_im) * 1i;
>>    c = z;
>>    for (int i = 0; i < 10000; i++) {
>>     z = z * z + c;
>>     if(z.re * z.re + z.im * z.im > 4.0) {
>>      break;
>>     }
>>    }
>>   }
>>  }
>>  return 0;
>> }
>> // end of file mandel_d1.d
>> ------------------
>>
>> H:\Codici\Benchmarks> ..\timethis.exe mandel_d1
>>
>> TimeThis :  Command Line :  mandel_d1
>> TimeThis :    Start Time :  Mon Jun 02 11:28:41 2008
>>
>>
>> TimeThis :  Command Line :  mandel_d1
>> TimeThis :    Start Time :  Mon Jun 02 11:28:41 2008
>> TimeThis :      End Time :  Mon Jun 02 11:30:35 2008
>> TimeThis :  Elapsed Time :  00:01:54.234
>>
>> H:\Codici\Benchmarks> ..\timethis mandel_gdc1
>>
>> TimeThis :  Command Line :  mandel_gdc1
>> TimeThis :    Start Time :  Mon Jun 02 11:42:27 2008
>>
>>
>> TimeThis :  Command Line :  mandel_gdc1
>> TimeThis :    Start Time :  Mon Jun 02 11:42:27 2008
>> TimeThis :      End Time :  Mon Jun 02 11:42:29 2008
>> TimeThis :  Elapsed Time :  00:00:01.843
>>
> 
> It would be interesting to compare the ASM produced.  DMD is not that 
> great at floating point, doesn't unroll so well and has a longer startup 
> time then GDC in my experience.
> 
> -Joel

DMD does seem to beat GDC on some tests.  From memory I think its better 
at integer then GDC.

-Joel