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416399dc10
`Decoder` has two impls: - opaque: this impl is already partly infallible, i.e. in some places it currently panics on failure (e.g. if the input is too short, or on a bad `Result` discriminant), and in some places it returns an error (e.g. on a bad `Option` discriminant). The number of places where either happens is surprisingly small, just because the binary representation has very little redundancy and a lot of input reading can occur even on malformed data. - json: this impl is fully fallible, but it's only used (a) for the `.rlink` file production, and there's a `FIXME` comment suggesting it should change to a binary format, and (b) in a few tests in non-fundamental ways. Indeed #85993 is open to remove it entirely. And the top-level places in the compiler that call into decoding just abort on error anyway. So the fallibility is providing little value, and getting rid of it leads to some non-trivial performance improvements. Much of this commit is pretty boring and mechanical. Some notes about a few interesting parts: - The commit removes `Decoder::{Error,error}`. - `InternIteratorElement::intern_with`: the impl for `T` now has the same optimization for small counts that the impl for `Result<T, E>` has, because it's now much hotter. - Decodable impls for SmallVec, LinkedList, VecDeque now all use `collect`, which is nice; the one for `Vec` uses unsafe code, because that gave better perf on some benchmarks.
70 lines
1.7 KiB
Rust
70 lines
1.7 KiB
Rust
//! Calculation and management of a Strict Version Hash for crates
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//!
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//! The SVH is used for incremental compilation to track when HIR
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//! nodes have changed between compilations, and also to detect
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//! mismatches where we have two versions of the same crate that were
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//! compiled from distinct sources.
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use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
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use std::fmt;
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use std::hash::{Hash, Hasher};
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use crate::stable_hasher;
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#[derive(Copy, Clone, PartialEq, Eq, Debug)]
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pub struct Svh {
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hash: u64,
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}
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impl Svh {
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/// Creates a new `Svh` given the hash. If you actually want to
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/// compute the SVH from some HIR, you want the `calculate_svh`
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/// function found in `rustc_incremental`.
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pub fn new(hash: u64) -> Svh {
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Svh { hash }
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}
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pub fn as_u64(&self) -> u64 {
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self.hash
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}
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pub fn to_string(&self) -> String {
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format!("{:016x}", self.hash)
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}
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}
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impl Hash for Svh {
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fn hash<H>(&self, state: &mut H)
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where
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H: Hasher,
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{
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self.hash.to_le().hash(state);
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}
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}
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impl fmt::Display for Svh {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.pad(&self.to_string())
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}
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}
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impl<S: Encoder> Encodable<S> for Svh {
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fn encode(&self, s: &mut S) -> Result<(), S::Error> {
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s.emit_u64(self.as_u64().to_le())
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}
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}
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impl<D: Decoder> Decodable<D> for Svh {
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fn decode(d: &mut D) -> Svh {
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Svh::new(u64::from_le(d.read_u64()))
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}
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}
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impl<T> stable_hasher::HashStable<T> for Svh {
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#[inline]
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fn hash_stable(&self, ctx: &mut T, hasher: &mut stable_hasher::StableHasher) {
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let Svh { hash } = *self;
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hash.hash_stable(ctx, hasher);
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}
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}
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