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Re: FORTH plusminus, was Re: [f-cpu] Winograd DCT on my seul.org account


> hi !

> cedric wrote:
> > > What i need is a DataFlow Graph analysis tool that allows me to
> > > handle large chuncks of code with all the automated tedious tasks
> > > that i usually do by hand (register allocation, reallocation,
> > > interleaving...)
> >
> > What did you mean by reallocation is i memory operation or register
> > reallocation ? If it's the second, the problem is the same as register
> > allocation, and it exist some good algorithm for risc machine (with a lot
> > of registers), that can do that better than a lot of human ;-)
> do you speak about register coloring ? the complexity grows at least O(n^2)
> with the number of registers. the "manual" algo i use (and which can be
> automated) is O(n), or linear complexity. give it more registers and it
> will be even happier (contrarily to register coloring).
Well, a lot of people will be interested by your algorithm I think, you will 
explain it to me "au first jeudi" ?

> >         For interleaving, it's, if I correctly understand what you mean
> > scheduling,
> instruction scheduling, to be exact (look at the end of the DCT paper)

> > the problem is not easy,

> what i do is straight-forward : it's like taking a string aaaaaaaaaaa and
> bbbbbbbbbbb and interleaving it : abababababababababababababababab...
I think that gcc can do that well, it's not very difficult, the solution is 
when you have 2 operations that are dependent, you must maximise the distance 
between them. That's all, I think ? I know that perhaps not always the best 
solution, but it good enough.

> > and need a lot of time to have the right answer.
> at least the time to type it ;-)
So it's not so difficult ;-)

> i know that i am probably the only one who understands myself, and it's
> just of problem of communication from my part. However i wish that
> my knowledge becomes useful to others.

> > But what we can do is detecting where we lost cycle.
> > (It's what I plan to do in my asm).

> it's like calling the doctor who says : "you're sick" and goes away.
Exactly, but actually the human are better than our algorithm, no ?

> writing asm is ok for small code (like the DCT) but not for large code,
> you need to not have to worry about the representation, only about the
> function, and asm programming does not make that possible.
> peephole optimisation might be easier with your tool, but that's all.
> it doesn't solve the "big problems" which often come from superficial
> analysis.
And algorithm, but you know actually developper brain is too expensive, so you 
need a good optimisation but it must be done quickly and without the need of 
learning a new tool or language.

> btw, do you come to the Libre Software Meeting in Bordeaux ?
> will you present some of our work ?
Yes of course, I have some problem with my pop at epita, so if some discussion 
append on it, I can't know them. But we will meet us at the "first jeudi" ?

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