Re: GNAT can't vectorize Real_Matrix multiplication from Ada.Numerics.Real_Arrays. What a surprise!

[Bojan Bozovic <bozovic.bojan@gmail.com>]

On Sunday, February 18, 2018 at 2:31:18 PM UTC+1, Jeffrey R. Carter wrote:
> On 02/18/2018 01:05 PM, Bojan Bozovic wrote:
> > Thanks very much for clarification! It's always good to learn something new, I suppose.
> 
> The real optimization in your example seems to be that the compiler optimizes 
> away the 10E6 loop around the in-line code, but not around the call to "*". 
> Removing both loops gives similar times for both multiplications. The call to 
> "*" will never be as fast because it copies its result into your variable. 
> Replacing Ada.Numerics.Real_Arrays with an instantiation of 
> Ada.Numerics.Generic_Real_Arrays gives an additional factor of 2 reduction.
> 
> -- 
> Jeff Carter
> Just as Khan was hindered by two-dimensional thinking in a
> three-dimensional situation, so many developers are hindered
> by sequential thinking in concurrent situations.
> 118

And indeed, now everything is in its place, as I don't see matrix multiplication several times slower than doing things 'by hand'. I have used aggressive optimization because in this day its custom a program to manipulate over gigabytes or even terabytes of data, while being at most megabytes in size - so compiling for various processors of the same family and using launcher program which will query processor capability and run optimally optimized program is nothing new - one might say most computation now is done on GPU but then also exact capabilities of GPU must be known. Thanks for making my Ada learning experience an enjoyment!