feat(data_structures): introduce PointerExt trait#11095
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Rust v1.87.0 introduced new methods for pointers, notably `offset_from_unsigned` which calculates the distance between 2 pointers. https://doc.rust-lang.org/std/primitive.pointer.html#method.offset_from_unsigned `offset_from_unsigned` is the same as `offset_from`, except it require the source pointer to be before the target, and so returns a `usize` rather than an `isize`. In return for this restriction, the compiler is able to generate more efficient code in some cases. We want to use these methods, but our MSRV won't hit 1.87.0 for 3 months. This PR introduces a `PointerExt` trait which provides similar methods `offset_from_usize` and `byte_offset_from_usize`. On versions of Rust >= 1.87.0, these delegate directly to the native Rust methods `offset_from_unsigned` and `byte_offset_from_unsigned`. On earlier versions of Rust, they use a fallback implementation. This PR replaces all use of `offset_from` with `offset_from_usize` in our crates. This will probably make little difference to perf, as we don't use these methods much, and the perf advantage is small anyway. But reason I'm making this PR now is that allocator will make liberal use of them on very hot paths.
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… comparisons (#11116) Lexer use `offset_from` and `offset_from_unsigned` pointer methods rather than comparing pointers as `usize`s. This utilizes the `PointerExt` trait introduced in #11095. This change tells the compiler "both these pointers are into the same object, and origin pointer is before target pointer", which gives it more information for optimization, and alias analysis. This change also allows simplifying `Source` a little - we now almost entirely now deal in `SourcePosition`s, rather than a mix of `SourcePosition`s, raw pointers, and `ptr as usize`. Tiny improvement on lexer benchmarks. Interestingly, it seems to produce a consistent ~1% speed-up in the byte handler for `/`. It seems to particularly have a positive effect on lexing single-line comments, for some reason.
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Rust v1.87.0 introduced new methods for pointers, notably
offset_from_unsignedwhich calculates the distance between 2 pointers.https://doc.rust-lang.org/std/primitive.pointer.html#method.offset_from_unsigned
offset_from_unsignedis the same asoffset_from, except it require the source pointer to be before the target, and so returns ausizerather than anisize. In return for this restriction, the compiler is able to generate more efficient code in some cases.We want to use these methods, but our MSRV won't hit 1.87.0 for 3 months.
This PR introduces a
PointerExttrait which provides similar methodsoffset_from_usizeandbyte_offset_from_usize.On versions of Rust >= 1.87.0, these delegate directly to the native Rust methods
offset_from_unsignedandbyte_offset_from_unsigned. On earlier versions of Rust, they use a fallback implementation.This PR replaces all use of
offset_fromwithoffset_from_usizein our crates.This will probably make little difference to perf, as we don't use these methods much, and the perf advantage is small anyway. But reason I'm making this PR now is that allocator will make liberal use of them on very hot paths.