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pcwalton's profile
Patrick Walton
Patrick Walton
Patrick Walton
@pcwalton

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Patrick Walton

@pcwalton

Research engineer at Mozilla

San Francisco, CA
pcwalton.github.io
Joined November 2009

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    Patrick Walton‏ @pcwalton 14 Nov 2019
    • Report Tweet
    • Report NetzDG Violation

    There is no defensible reason why SIMD code should be harder to write than scalar code. GLSL has been around since 2004 and in GLSL it’s easier to write vector code than scalar code.

    11:12 AM - 14 Nov 2019
    • 8 Retweets
    • 66 Likes
    • sirocyl Karan Ganesan Dan Ibanez Yuri S Lefteris Stamatogiannakis 🦀 Pedder 🏸 amit sheokand Daniel Blanco Karanbir Chahal
    9 replies 8 retweets 66 likes
      1. New conversation
      2. Ted Mielczarek‏ @TedMielczarek 14 Nov 2019
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        Replying to @pcwalton

        Is this because of the affordances of the language?

        1 reply 0 retweets 0 likes
      3. Patrick Walton‏ @pcwalton 14 Nov 2019
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        Replying to @TedMielczarek

        It’s because GLSL puts a lot of effort into ergonomics of vector code. The syntactic sugar runs in the right direction: you want to write vector code because it’s easy, not just because it’s fast.

        1 reply 0 retweets 5 likes
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      2. gankra's gay‏ @Gankra_ 14 Nov 2019
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        Replying to @pcwalton

        isn't the pain semi-unavoidable without hardware support to hide the lane width?

        1 reply 0 retweets 3 likes
      3. Patrick Walton‏ @pcwalton 14 Nov 2019
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        Replying to @Gankra_

        I actually mostly think that 128 bits is enough for anyone.

        3 replies 0 retweets 12 likes
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      2. gray‏ @fu5ha 14 Nov 2019
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        Replying to @pcwalton

        I've spent the past 3 weeks or so SIMD-ifying my path tracer, and I feel this. Though I think myself and @Lokathor are helping this situation in Rust somewhat with https://docs.rs/wide  and https://docs.rs/ultraviolet  ;D

        1 reply 0 retweets 1 like
      3. Patrick Walton‏ @pcwalton 14 Nov 2019
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        Replying to @fu5ha @Lokathor

        I’d like to plug pathfinder_simd too :)

        1 reply 0 retweets 1 like
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      1. Sebastian Sylvan‏ @ssylvan 14 Nov 2019
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        Replying to @pcwalton

        It's not. Use ISPC.

        0 replies 2 retweets 15 likes
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      2. Tom Keresztes 🇪🇺‏ @tomcr2100 14 Nov 2019
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        Replying to @pcwalton @vengarioth

        Typically, the inherent issue is that language does not map well to what the hardware actually capable of doing well. Modern C++. Hoping that a compiler that is capable optimising your code will appear in the future is not a paradigm. ISPC is a good example. And its story.

        1 reply 0 retweets 6 likes
      3. Tom Keresztes 🇪🇺‏ @tomcr2100 14 Nov 2019
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        Replying to @tomcr2100 @pcwalton @vengarioth

        https://pharr.org/matt/blog/2018/04/30/ispc-all.html …

        1 reply 0 retweets 2 likes
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      1. Simon Richter‏ @GyrosGeier 14 Nov 2019
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        Replying to @pcwalton

        But GLSL is usually scalarized and then vectorized over the problem space, so the elements of the vector are really four different iterations of the loop over the input vertices or output fragments. Using vector types for SIMD would just be manual loop unrolling.

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