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Replying to @johnregehr @IgorSkochinsky
Isn’t VLIW scheduling pretty tractable in modern compiler architectures though? (Not that I’m saying VLIW is worth it overall, just that the problems aren’t compiler technology)
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Replying to @pcwalton @IgorSkochinsky
I don't even know who's working on this these days, is it a thing outside of some niches?
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I mean, it doesn't *sound* all that hard, but then again it obviously didn't sound that hard back in the day or else Itanium would not have happened
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Replying to @johnregehr @IgorSkochinsky
I mean, GCC wasn’t even SSA back in those days, right?
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I know some older GPUs like VideoCore IV (Raspberry Pi) use VLIW
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I think to some extent it became unclear a sufficiently smart compiler was even possible for several VLIW problems. Like moving branch prediction into the compiler requires fundamentally rethinking some styles of software development.
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I'd read a whole book about this stuff. just spent a few minutes looking for anything at all (survey paper, book, whatever) about this from the last 5 years and came up empty.
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Well, for GPUs it’s easy to see why they moved away from VLIW. Instead of, say, shading 4 pixels at a time with 2 ALUs each, you can see why you can get better utilization by just shading 8 pixels at a time, one pixel per ALU. (Terminology imprecise, but you get the idea)
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Replying to @pcwalton @johnregehr and
Maybe one way to look at the history here is that, for vector processors at least, SIMD beats MIMD (where VLIW is a form of MIMD) in practice.
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Which makes sense—I mean, if you have tons of data parallelism available, why complicate things by adding multiple simultaneous instruction dispatch when you can just decode one instruction and parallelize across lanes
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and in Machine Learning the move has been to make the "software" more embarrassingly parallel
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