Finding large difference b/w execution time of c++ and D codes for same problem

[Joseph Rushton Wakeling]

On 02/13/2013 03:56 PM, Marco Leise wrote:
> Ok, I get pretty much the same numbers as before with:
>    ldmd2 -O -inline -release
> It's even a bit faster than my loooong command line.

My experience has been that the higher -O values of ldc don't do much, but of 
course, that's going to vary depending on your code.  I think above -O3 it's all 
link-time, no?

> Do these numbers tell us, that there are such huge differences
> in the handling of floating point value between different
> AMD64 CPUs? I can't quite make a rhyme of it yet.

AMD vs Intel might make a difference (my machine is an i7).

> What version of LLVM are you using, mine is 3.1. 3.0 is
> minimum and 3.2 is recommended for LDC2.

LLVM 3.2.

> _THAT_ I can reproduce with GDC! :
>
> D code serial with dimension 32768 ...
>    using floats Total time: 24.415 [sec]
>    using doubles Total time: 23.268 [sec]
>    using reals Total time: 25.168 [sec]
>
> It's the exact same pattern.

I've never, EVER had ldc-compiled code run four times faster than GDC-compiled 
code.  In fact, I don't think I've ever had LDC-compiled code run faster than 
GDC-compiled code at all, except where the choice of optimizations was 
different.  That's what makes me concerned that there's some kind of bug in play 
here ....