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Subject: Re: [boost] [gsoc] boost.simd news from the front.
From: David A. Greene (greened_at_[hidden])
Date: 2011-06-11 12:17:57

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

- 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?


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