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565 points zdw | 1 comments | 09 Jul 25 14:40 UTC | HN request time: 0.204s | source
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jcalvinowens ◴[09 Jul 25 18:21 UTC] No.44513250[source]▶
> On the one hand, compilers would like to exploit the strong guarantees of the type system—particularly those pertaining to aliasing of pointers—in order to unlock powerful intraprocedural optimizations.

How true is this really?

Torvalds has argued for a long time that strict aliasing rules in C are more trouble than they're worth, I find his arguments compelling. Here's one of many examples: https://lore.kernel.org/all/CAHk-=wgq1DvgNVoodk7JKc6BuU1m9Un... (the entire thread worth reading if you find this sort of thing interesting)

Is Rust somehow fundamentally different? Based on limited experience, it seems not (at least, when unsafe is involved...).

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1. saghm ◴[10 Jul 25 03:20 UTC] No.44516860[source]▶
When unsafe is involved, sure, but that's a pretty small fraction of Rust code as a whole. As far as I can tell, a lot of his argument seems to be more against needing language changes in C to take advantage of strict aliasing that come at the cost of expanding the circumstances where UB can occur, but I don't really see how those would apply to safe Rust when it already has a perfectly safe way to express a reference guaranteed to not have any alias, i.e. `&mut T`. If the compiler authors came up with better ways to generate optimized code with unaliased pointers, I don't see why Rust would need to make any language changes in order to take advantage of them. That doesn't necessarily mean that there there is any significant untapped potential for these sorts of optmizations of course, or that the amount of effort to identify and implement them would be worthwhile for a toolchain like LLVM that is used for far more than just Rust, but it's not clear to me why the arguments he gives would be relevant to Rust.