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cesarb 5 days ago

> Fewer transistors and pipeline stages required for the decode unit, which is a real but moderate advantage.

Isn't having fixed-size naturally-aligned instructions (like on 64-bit ARM) enough to get that advantage?

ajross 5 days ago | parent [-]

ARM is easier than x86, but not really. VLIW instructions also encode the superscalar pipeline assignments (or a reasonable proxy for them) and are required to be constructed without instruction interdependencies (within the single bundle, anyway), which traditional ISAs need to spend hardware to figure out.

Really VLIW is a fine idea. It's just not that great an idea, and in practice it wasn't enough to save ia64. But it's not what killed it, either.

codedokode 5 days ago | parent [-]

The problem with ia64 was that if you had 1000 legacy applications for x86, written by third-party contractors, for many of which you don't even have the source, then ia64 must be 100x better than standard CPUs to justify rewriting the apps.

And by the way that's why open source makes such migrations much cheaper.