Not just all &mut T, but also all &T, where the T does not transitively contain an UnsafeCell<T>. Click "show llvm ir" instead of "build" here: https://play.rust-lang.org/?version=stable&mode=release&edit...

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marcianx 15 hours ago | parent [-]

I was confused by this at first since `&T` clearly allows aliasing (which is what C's `restrict` is about). But I realize that Steve meant just the optimization opportunity: you can be guaranteed that (in the absence of UB), the data behind the `&T` can be known to not change in the absence of a contained `UnsafeCell<T>`, so you don't have to reload it after mutations through other pointers.

	▲	steveklabnik 14 hours ago \| parent \| next [-]
		Yes. It's a bit tricky to think about, because while it is literally called 'noalias', what it actually means is more subtle. I already linked to a version of the C spec below, https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf but if anyone is curious, this part is in "6.7.4.2 Formal definition of restrict" on page 122. In some ways, this is kind of the core observation of Rust: "shared xor mutable". Aliasing is only an issue if the aliasing leads to mutability. You can frame it in terms of aliasing if you have to assume all aliases can mutate, but if they can't, then that changes things.
	▲	salmon640 6 hours ago \| parent \| prev [-]
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