diff options
| -rw-r--r-- | compiler/rustc_mir_build/src/thir/pattern/_match.rs | 179 | ||||
| -rw-r--r-- | compiler/rustc_mir_build/src/thir/pattern/mod.rs | 8 |
2 files changed, 165 insertions, 22 deletions
diff --git a/compiler/rustc_mir_build/src/thir/pattern/_match.rs b/compiler/rustc_mir_build/src/thir/pattern/_match.rs index eddd2882406..904524e13ae 100644 --- a/compiler/rustc_mir_build/src/thir/pattern/_match.rs +++ b/compiler/rustc_mir_build/src/thir/pattern/_match.rs @@ -139,10 +139,10 @@ //! //! It is computed as follows. We look at the pattern `p_1` on top of the stack, //! and we have three cases: -//! 1.1. `p_1 = c(r_1, .., r_a)`. We discard the current stack and return nothing. -//! 1.2. `p_1 = _`. We return the rest of the stack: +//! 2.1. `p_1 = c(r_1, .., r_a)`. We discard the current stack and return nothing. +//! 2.2. `p_1 = _`. We return the rest of the stack: //! p_2, .., p_n -//! 1.3. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting +//! 2.3. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting //! stack. //! D((r_1, p_2, .., p_n)) //! D((r_2, p_2, .., p_n)) @@ -276,7 +276,7 @@ use self::Usefulness::*; use self::WitnessPreference::*; use rustc_data_structures::captures::Captures; -use rustc_data_structures::fx::FxHashSet; +use rustc_data_structures::fx::{FxHashMap, FxHashSet}; use rustc_index::vec::Idx; use super::{compare_const_vals, PatternFoldable, PatternFolder}; @@ -416,7 +416,7 @@ impl<'tcx> Pat<'tcx> { /// A row of a matrix. Rows of len 1 are very common, which is why `SmallVec[_; 2]` /// works well. -#[derive(Debug, Clone)] +#[derive(Debug, Clone, PartialEq)] crate struct PatStack<'p, 'tcx>(SmallVec<[&'p Pat<'tcx>; 2]>); impl<'p, 'tcx> PatStack<'p, 'tcx> { @@ -504,13 +504,36 @@ impl<'p, 'tcx> FromIterator<&'p Pat<'tcx>> for PatStack<'p, 'tcx> { } } +/// Depending on the match patterns, the specialization process might be able to use a fast path. +/// Tracks whether we can use the fast path and the lookup table needed in those cases. +#[derive(Clone, Debug, PartialEq)] +enum SpecializationCache { + /// Patterns consist of only enum variants. + /// Variant patterns does not intersect with each other (in contrast to range patterns), + /// so it is possible to precompute the result of `Matrix::specialize_constructor` at a + /// lower computational complexity. + /// `lookup` is responsible for holding the precomputed result of + /// `Matrix::specialize_constructor`, while `wilds` is used for two purposes: the first one is + /// the precomputed result of `Matrix::specialize_wildcard`, and the second is to be used as a + /// fallback for `Matrix::specialize_constructor` when it tries to apply a constructor that + /// has not been seen in the `Matrix`. See `update_cache` for further explanations. + Variants { lookup: FxHashMap<DefId, SmallVec<[usize; 1]>>, wilds: SmallVec<[usize; 1]> }, + /// Does not belong to the cases above, use the slow path. + Incompatible, +} + /// A 2D matrix. -#[derive(Clone)] -crate struct Matrix<'p, 'tcx>(Vec<PatStack<'p, 'tcx>>); +#[derive(Clone, PartialEq)] +crate struct Matrix<'p, 'tcx> { + patterns: Vec<PatStack<'p, 'tcx>>, + cache: SpecializationCache, +} impl<'p, 'tcx> Matrix<'p, 'tcx> { crate fn empty() -> Self { - Matrix(vec![]) + // Use `SpecializationCache::Incompatible` as a placeholder; we will initialize it on the + // first call to `push`. See the first half of `update_cache`. + Matrix { patterns: vec![], cache: SpecializationCache::Incompatible } } /// Pushes a new row to the matrix. If the row starts with an or-pattern, this expands it. @@ -522,18 +545,101 @@ impl<'p, 'tcx> Matrix<'p, 'tcx> { self.push(row) } } else { - self.0.push(row); + self.patterns.push(row); + self.update_cache(self.patterns.len() - 1); + } + } + + fn update_cache(&mut self, idx: usize) { + let row = &self.patterns[idx]; + // We don't know which kind of cache could be used until we see the first row; therefore an + // empty `Matrix` is initialized with `SpecializationCache::Empty`, then the cache is + // assigned the appropriate variant below on the first call to `push`. + if self.patterns.is_empty() { + self.cache = if row.is_empty() { + SpecializationCache::Incompatible + } else { + match *row.head().kind { + PatKind::Variant { .. } => SpecializationCache::Variants { + lookup: FxHashMap::default(), + wilds: SmallVec::new(), + }, + // Note: If the first pattern is a wildcard, then all patterns after that is not + // useful. The check is simple enough so we treat it as the same as unsupported + // patterns. + _ => SpecializationCache::Incompatible, + } + }; + } + // Update the cache. + match &mut self.cache { + SpecializationCache::Variants { ref mut lookup, ref mut wilds } => { + let head = row.head(); + match *head.kind { + _ if head.is_wildcard() => { + // Per rule 1.3 in the top-level comments, a wildcard pattern is included in + // the result of `specialize_constructor` for *any* `Constructor`. + // We push the wildcard pattern to the precomputed result for constructors + // that we have seen before; results for constructors we have not yet seen + // defaults to `wilds`, which is updated right below. + for (_, v) in lookup.iter_mut() { + v.push(idx); + } + // Per rule 2.1 and 2.2 in the top-level comments, only wildcard patterns + // are included in the result of `specialize_wildcard`. + // What we do here is to track the wildcards we have seen; so in addition to + // acting as the precomputed result of `specialize_wildcard`, `wilds` also + // serves as the default value of `specialize_constructor` for constructors + // that are not in `lookup`. + wilds.push(idx); + } + PatKind::Variant { adt_def, variant_index, .. } => { + // Handle the cases of rule 1.1 and 1.2 in the top-level comments. + // A variant pattern can only be included in the results of + // `specialize_constructor` for a particular constructor, therefore we are + // using a HashMap to track that. + lookup + .entry(adt_def.variants[variant_index].def_id) + // Default to `wilds` for absent keys. See above for an explanation. + .or_insert_with(|| wilds.clone()) + .push(idx); + } + _ => { + self.cache = SpecializationCache::Incompatible; + } + } + } + SpecializationCache::Incompatible => {} } } /// Iterate over the first component of each row fn heads<'a>(&'a self) -> impl Iterator<Item = &'a Pat<'tcx>> + Captures<'p> { - self.0.iter().map(|r| r.head()) + self.patterns.iter().map(|r| r.head()) } /// This computes `D(self)`. See top of the file for explanations. fn specialize_wildcard(&self) -> Self { - self.0.iter().filter_map(|r| r.specialize_wildcard()).collect() + match &self.cache { + SpecializationCache::Variants { wilds, .. } => { + let result = + wilds.iter().filter_map(|&i| self.patterns[i].specialize_wildcard()).collect(); + // When debug assertions are enabled, check the results against the "slow path" + // result. + debug_assert_eq!( + result, + Self { + patterns: self.patterns.clone(), + cache: SpecializationCache::Incompatible + } + .specialize_wildcard() + ); + result + } + SpecializationCache::Incompatible => { + self.patterns.iter().filter_map(|r| r.specialize_wildcard()).collect() + } + } } /// This computes `S(constructor, self)`. See top of the file for explanations. @@ -543,10 +649,47 @@ impl<'p, 'tcx> Matrix<'p, 'tcx> { constructor: &Constructor<'tcx>, ctor_wild_subpatterns: &Fields<'p, 'tcx>, ) -> Matrix<'p, 'tcx> { - self.0 - .iter() - .filter_map(|r| r.specialize_constructor(cx, constructor, ctor_wild_subpatterns)) - .collect() + match &self.cache { + SpecializationCache::Variants { lookup, wilds } => { + let result: Self = if let Constructor::Variant(id) = constructor { + lookup + .get(id) + // Default to `wilds` for absent keys. See `update_cache` for an explanation. + .unwrap_or(&wilds) + .iter() + .filter_map(|&i| { + self.patterns[i].specialize_constructor( + cx, + constructor, + ctor_wild_subpatterns, + ) + }) + .collect() + } else { + unreachable!() + }; + // When debug assertions are enabled, check the results against the "slow path" + // result. + debug_assert_eq!( + result, + Matrix { + patterns: self.patterns.clone(), + cache: SpecializationCache::Incompatible + } + .specialize_constructor( + cx, + constructor, + ctor_wild_subpatterns + ) + ); + result + } + SpecializationCache::Incompatible => self + .patterns + .iter() + .filter_map(|r| r.specialize_constructor(cx, constructor, ctor_wild_subpatterns)) + .collect(), + } } } @@ -568,7 +711,7 @@ impl<'p, 'tcx> fmt::Debug for Matrix<'p, 'tcx> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "\n")?; - let &Matrix(ref m) = self; + let Matrix { patterns: m, .. } = self; let pretty_printed_matrix: Vec<Vec<String>> = m.iter().map(|row| row.iter().map(|pat| format!("{:?}", pat)).collect()).collect(); @@ -1824,7 +1967,7 @@ crate fn is_useful<'p, 'tcx>( is_under_guard: bool, is_top_level: bool, ) -> Usefulness<'tcx> { - let &Matrix(ref rows) = matrix; + let Matrix { patterns: rows, .. } = matrix; debug!("is_useful({:#?}, {:#?})", matrix, v); // The base case. We are pattern-matching on () and the return value is @@ -2266,7 +2409,7 @@ fn split_grouped_constructors<'p, 'tcx>( // `borders` is the set of borders between equivalence classes: each equivalence // class lies between 2 borders. let row_borders = matrix - .0 + .patterns .iter() .flat_map(|row| { IntRange::from_pat(tcx, param_env, row.head()).map(|r| (r, row.len())) diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs index d617f4a6aa6..718ed78889f 100644 --- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs +++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs @@ -39,19 +39,19 @@ crate enum PatternError { NonConstPath(Span), } -#[derive(Copy, Clone, Debug)] +#[derive(Copy, Clone, Debug, PartialEq)] crate enum BindingMode { ByValue, ByRef(BorrowKind), } -#[derive(Clone, Debug)] +#[derive(Clone, Debug, PartialEq)] crate struct FieldPat<'tcx> { crate field: Field, crate pattern: Pat<'tcx>, } -#[derive(Clone, Debug)] +#[derive(Clone, Debug, PartialEq)] crate struct Pat<'tcx> { crate ty: Ty<'tcx>, crate span: Span, @@ -116,7 +116,7 @@ crate struct Ascription<'tcx> { crate user_ty_span: Span, } -#[derive(Clone, Debug)] +#[derive(Clone, Debug, PartialEq)] crate enum PatKind<'tcx> { Wild, |