Earlier quoted context omitted.
(disclaimer: current V8 team member replying to senior ex-V8 team member) I'd say there were a lot more things problematic in practice with SoN than not relaxing effect edges enough - I'd argue that the bigger problem was that a single effect chain was not enough to represent the flexibility that SoN promised, while keeping the costs, and getting that flexibility would mean effectively extending the effect chain to o…
Well obviously I don't think that you're a bunch of dummies so please don't throw out strawmen like that. I don't know if Cliff is on the same page w.r.t. how much speculation is necessary (and when) to make JS go fast. In particular, inserting speculative guards has the nice property of improving downstream information for dominated control flow paths. Dominated control flow paths are few and far between when the co…
Re: The acyclic e-graph: Cranelift's mid-end optimizer
#21The dummies phrasing is my own, and I stand by it - I simply find the CFG way of thinking much easier to reason about than the SoN way, and I find myself falling back into it no matter how hard I try to follow what I totally (abstractly) appreciate is a more mathematically beautiful dependency/anti-dependency graph - I think that's a limitation of my ability to maintain that concept in my mind and that other people can do it better than me. I find it far easier to reason on CFG terms most of the time, and to raise the CFG temporarily into some dependency representation for doing eliminations/hoisting/LICM, than I do maintaining that dependency representation across all phases and accurately reasoning in each of those about what concrete dependency I forgot about when writing the reduction (concrete recent example, I tried to make reading from holes segfault by unmapping the hole, to force potential holey field access to always first compare against the sentinel, but I was foiled by TF since the load had no dependency on the hole compare branch and could be hosted above it). Implying that this was simply "some people" insisting on only thinking one way without trying to think the SoN way, or that it was some sort of CFG prejudice, is the actual strawman here.