From 416399dc1028545ea0ac6d68fb0b5cc5fa97d393 Mon Sep 17 00:00:00 2001 From: Nicholas Nethercote Date: Tue, 18 Jan 2022 13:22:50 +1100 Subject: Make `Decodable` and `Decoder` infallible. `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` 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. --- compiler/rustc_incremental/src/persist/load.rs | 15 +++------------ 1 file changed, 3 insertions(+), 12 deletions(-) (limited to 'compiler/rustc_incremental') diff --git a/compiler/rustc_incremental/src/persist/load.rs b/compiler/rustc_incremental/src/persist/load.rs index d563a6ca478..870c3f80682 100644 --- a/compiler/rustc_incremental/src/persist/load.rs +++ b/compiler/rustc_incremental/src/persist/load.rs @@ -158,14 +158,7 @@ pub fn load_dep_graph(sess: &Session) -> DepGraphFuture { // Decode the list of work_products let mut work_product_decoder = Decoder::new(&work_products_data[..], start_pos); let work_products: Vec = - Decodable::decode(&mut work_product_decoder).unwrap_or_else(|e| { - let msg = format!( - "Error decoding `work-products` from incremental \ - compilation session directory: {}", - e - ); - sess.fatal(&msg) - }); + Decodable::decode(&mut work_product_decoder); for swp in work_products { let mut all_files_exist = true; @@ -203,8 +196,7 @@ pub fn load_dep_graph(sess: &Session) -> DepGraphFuture { LoadResult::Error { message } => LoadResult::Error { message }, LoadResult::Ok { data: (bytes, start_pos) } => { let mut decoder = Decoder::new(&bytes, start_pos); - let prev_commandline_args_hash = u64::decode(&mut decoder) - .expect("Error reading commandline arg hash from cached dep-graph"); + let prev_commandline_args_hash = u64::decode(&mut decoder); if prev_commandline_args_hash != expected_hash { if report_incremental_info { @@ -220,8 +212,7 @@ pub fn load_dep_graph(sess: &Session) -> DepGraphFuture { return LoadResult::DataOutOfDate; } - let dep_graph = SerializedDepGraph::decode(&mut decoder) - .expect("Error reading cached dep-graph"); + let dep_graph = SerializedDepGraph::decode(&mut decoder); LoadResult::Ok { data: (dep_graph, prev_work_products) } } -- cgit 1.4.1-3-g733a5