Maciej Fijalkowski, 16.10.2011 17:50:
On Sun, Oct 16, 2011 at 2:29 PM, Stefan Behnel wrote
Samuel Vaiter, 14.10.2011 17:59:
The main
reason why Numpy is my main interest is that as Ph.D student in
Applied Mathematics, I really hope one day we will be able to perform
numerical computation without using heavy binding in C/Fortran or
intermediate solution like Cython.
I guess you didn't mean it that way, but "intermediate solution" makes it
sound like you expect any of these to go away one day. They sure won't.
Manually optimised C and Fortran code will always beat JIT compilers,
especially in numerics. It's a game they can't win - whenever JIT compilers
get too close to hand optimised code, someone will come along and write
better code.
I guess what you say is at best [citation needed].
Feel free to quote me. :D
We have proven
already that we can perform several optimizations that are very hard
to perform at the C level. And indeed, while you can always argue
"well, you can just write a better compiler", it's true also for JITs.
I wasn't comparing a JIT to another compiler. I was comparing it to a human
programmer. A JIT, just like any other compiler, will never be able to
*understand* the code it compiles, and it can only apply the optimisations
that it was taught. JITs are nice when you need performance quickly and
don't care about the last few CPU cycles. However, there are cases where
it's not very satisfactory to learn that your JIT compiler, in the current
state that it has, can only get you up to, say, 90%, or even 95% of the
speed that you need for your problem. In those cases where you do care
about the last 5%, and numerics people care about them surprisingly often,
you will eventually end up using a low-level language, usually C or
Fortran, to make sure you get as much out of your code as possible. JIT
compilers are structurally much harder to manually override than static
compilers, and they are certainly not designed to help with the "but I know
what I'm doing" cases.
Mind you, I'm not saying that JIT compilers aren't capable of generating
surprisingly fast code. They certainly are, and what they deliver is often
"good enough". I'm just saying that statically compiled low-level languages
will *always* have a raison d'être, if only to deliver support for the "I
know what I'm doing" cases.
Stefan
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