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Subject: Re: [boost] [gsoc] boost.simd news from the front.
From: Ivan Le Lann (ivan.lelann_at_[hidden])
Date: 2011-06-14 06:14:15

----- "David A. Greene" <greened_at_[hidden]> a écrit :

> Mathias Gaunard <mathias.gaunard_at_[hidden]> writes:
> > Making data parallelism simpler is the goal of NT2. And we do that
> by
> > removing loops and pointers entirely.
> First off, I want to apologize for sparking some emotions. That was
> not
> my intent. I am deeply sorry for not expressing myself well.
> NT2 sounds very interesting! Does it generate the loops given calls
> into generic code?
> Let me try to clarify my thinking about boost.simd a bit.
> - There is a place for boost.simd. It's important that I emphasize
> this
> upfront.
> - Here is how I see a typical programmer using it, given a loop nest:
> - Programmer tries to run the compiler on it, examines code
> - Code sometimes (maybe most of the time) executes poorly
> - If not, done
> - Programmer restructures loop nest to expose parallelism
> - Try compiler directives first, if available (tell compiler
> which
> loops to interchange, where to cache block, blocking factors,
> which loops to collapse, etc.)
> - Otherwise, hand-restructure (ouch!)
> - Programmer tries compiler again on restructured loop nest
> - Code may execute poorly
> - If not, done
> - Programmer adds directives to tell the compiler which loops
> to vectorize, which to leave scalar, etc.
> - Code may still execute poorly
> - If not, done
> - Programmer uses boost.simd to write vector code at a higher level
> than provided compiler intrinsics
> Does that seem like a reasonable use case?

I hope I won't disappoint you, but in my case I'd put boost.simd a few ranks up.
Because, from what I've seen in slides, it's a quite easy and really clean way
to do things. I've always been taught to dive into dirty things as a last resort,
so I'd use boost.simd first, and eventually, if performance is still not met,
try hand-written hints.


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