diff options
Diffstat (limited to 'compiler/rustc_pattern_analysis/src/usefulness.rs')
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/usefulness.rs | 102 |
1 files changed, 47 insertions, 55 deletions
diff --git a/compiler/rustc_pattern_analysis/src/usefulness.rs b/compiler/rustc_pattern_analysis/src/usefulness.rs index 0834d08106f..3760db8b688 100644 --- a/compiler/rustc_pattern_analysis/src/usefulness.rs +++ b/compiler/rustc_pattern_analysis/src/usefulness.rs @@ -242,7 +242,7 @@ //! Therefore `usefulness(tp_1, tp_2, tq)` returns the single witness-tuple `[Variant2(Some(true), 0)]`. //! //! -//! Computing the set of constructors for a type is done in [`TypeCx::ctors_for_ty`]. See +//! Computing the set of constructors for a type is done in [`PatCx::ctors_for_ty`]. See //! the following sections for more accurate versions of the algorithm and corresponding links. //! //! @@ -540,8 +540,8 @@ //! We track in the algorithm whether a given place is known to contain valid data. This is done //! first by inspecting the scrutinee syntactically (which gives us `cx.known_valid_scrutinee`), and //! then by tracking validity of each column of the matrix (which correspond to places) as we -//! recurse into subpatterns. That second part is done through [`ValidityConstraint`], most notably -//! [`ValidityConstraint::specialize`]. +//! recurse into subpatterns. That second part is done through [`PlaceValidity`], most notably +//! [`PlaceValidity::specialize`]. //! //! Having said all that, in practice we don't fully follow what's been presented in this section. //! Let's call "toplevel exception" the case where the match scrutinee itself has type `!` or @@ -716,9 +716,9 @@ use std::fmt; use crate::constructor::{Constructor, ConstructorSet, IntRange}; use crate::pat::{DeconstructedPat, PatId, PatOrWild, WitnessPat}; -use crate::{Captures, MatchArm, PrivateUninhabitedField, TypeCx}; +use crate::{Captures, MatchArm, PatCx, PrivateUninhabitedField}; -use self::ValidityConstraint::*; +use self::PlaceValidity::*; #[cfg(feature = "rustc")] use rustc_data_structures::stack::ensure_sufficient_stack; @@ -728,7 +728,7 @@ pub fn ensure_sufficient_stack<R>(f: impl FnOnce() -> R) -> R { } /// Context that provides information for usefulness checking. -struct UsefulnessCtxt<'a, Cx: TypeCx> { +struct UsefulnessCtxt<'a, Cx: PatCx> { /// The context for type information. tycx: &'a Cx, /// Collect the patterns found useful during usefulness checking. This is used to lint @@ -738,7 +738,7 @@ struct UsefulnessCtxt<'a, Cx: TypeCx> { complexity_level: usize, } -impl<'a, Cx: TypeCx> UsefulnessCtxt<'a, Cx> { +impl<'a, Cx: PatCx> UsefulnessCtxt<'a, Cx> { fn increase_complexity_level(&mut self, complexity_add: usize) -> Result<(), Cx::Error> { self.complexity_level += complexity_add; if self @@ -752,26 +752,26 @@ impl<'a, Cx: TypeCx> UsefulnessCtxt<'a, Cx> { } /// Context that provides information local to a place under investigation. -struct PlaceCtxt<'a, Cx: TypeCx> { +struct PlaceCtxt<'a, Cx: PatCx> { cx: &'a Cx, /// Type of the place under investigation. ty: &'a Cx::Ty, } -impl<'a, Cx: TypeCx> Copy for PlaceCtxt<'a, Cx> {} -impl<'a, Cx: TypeCx> Clone for PlaceCtxt<'a, Cx> { +impl<'a, Cx: PatCx> Copy for PlaceCtxt<'a, Cx> {} +impl<'a, Cx: PatCx> Clone for PlaceCtxt<'a, Cx> { fn clone(&self) -> Self { Self { cx: self.cx, ty: self.ty } } } -impl<'a, Cx: TypeCx> fmt::Debug for PlaceCtxt<'a, Cx> { +impl<'a, Cx: PatCx> fmt::Debug for PlaceCtxt<'a, Cx> { fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { fmt.debug_struct("PlaceCtxt").field("ty", self.ty).finish() } } -impl<'a, Cx: TypeCx> PlaceCtxt<'a, Cx> { +impl<'a, Cx: PatCx> PlaceCtxt<'a, Cx> { fn ctor_arity(&self, ctor: &Constructor<Cx>) -> usize { self.cx.ctor_arity(ctor, self.ty) } @@ -780,18 +780,14 @@ impl<'a, Cx: TypeCx> PlaceCtxt<'a, Cx> { } } -/// Serves two purposes: -/// - in a wildcard, tracks whether the wildcard matches only valid values (i.e. is a binding `_a`) -/// or also invalid values (i.e. is a true `_` pattern). -/// - in the matrix, track whether a given place (aka column) is known to contain a valid value or -/// not. +/// Track whether a given place (aka column) is known to contain a valid value or not. #[derive(Debug, Copy, Clone, PartialEq, Eq)] -pub enum ValidityConstraint { +pub enum PlaceValidity { ValidOnly, MaybeInvalid, } -impl ValidityConstraint { +impl PlaceValidity { pub fn from_bool(is_valid_only: bool) -> Self { if is_valid_only { ValidOnly } else { MaybeInvalid } } @@ -806,7 +802,7 @@ impl ValidityConstraint { /// /// Pending further opsem decisions, the current behavior is: validity is preserved, except /// inside `&` and union fields where validity is reset to `MaybeInvalid`. - fn specialize<Cx: TypeCx>(self, ctor: &Constructor<Cx>) -> Self { + fn specialize<Cx: PatCx>(self, ctor: &Constructor<Cx>) -> Self { // We preserve validity except when we go inside a reference or a union field. if matches!(ctor, Constructor::Ref | Constructor::UnionField) { // Validity of `x: &T` does not imply validity of `*x: T`. @@ -817,7 +813,7 @@ impl ValidityConstraint { } } -impl fmt::Display for ValidityConstraint { +impl fmt::Display for PlaceValidity { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { let s = match self { ValidOnly => "✓", @@ -829,19 +825,19 @@ impl fmt::Display for ValidityConstraint { /// Data about a place under investigation. Its methods contain a lot of the logic used to analyze /// the constructors in the matrix. -struct PlaceInfo<Cx: TypeCx> { +struct PlaceInfo<Cx: PatCx> { /// The type of the place. ty: Cx::Ty, /// Whether the place is a private uninhabited field. If so we skip this field during analysis /// so that we don't observe its emptiness. private_uninhabited: bool, /// Whether the place is known to contain valid data. - validity: ValidityConstraint, + validity: PlaceValidity, /// Whether the place is the scrutinee itself or a subplace of it. is_scrutinee: bool, } -impl<Cx: TypeCx> PlaceInfo<Cx> { +impl<Cx: PatCx> PlaceInfo<Cx> { /// Given a constructor for the current place, we return one `PlaceInfo` for each field of the /// constructor. fn specialize<'a>( @@ -936,7 +932,7 @@ impl<Cx: TypeCx> PlaceInfo<Cx> { } } -impl<Cx: TypeCx> Clone for PlaceInfo<Cx> { +impl<Cx: PatCx> Clone for PlaceInfo<Cx> { fn clone(&self) -> Self { Self { ty: self.ty.clone(), @@ -951,7 +947,7 @@ impl<Cx: TypeCx> Clone for PlaceInfo<Cx> { // The three lifetimes are: // - 'p coming from the input // - Cx global compilation context -struct PatStack<'p, Cx: TypeCx> { +struct PatStack<'p, Cx: PatCx> { // Rows of len 1 are very common, which is why `SmallVec[_; 2]` works well. pats: SmallVec<[PatOrWild<'p, Cx>; 2]>, /// Sometimes we know that as far as this row is concerned, the current case is already handled @@ -960,13 +956,13 @@ struct PatStack<'p, Cx: TypeCx> { relevant: bool, } -impl<'p, Cx: TypeCx> Clone for PatStack<'p, Cx> { +impl<'p, Cx: PatCx> Clone for PatStack<'p, Cx> { fn clone(&self) -> Self { Self { pats: self.pats.clone(), relevant: self.relevant } } } -impl<'p, Cx: TypeCx> PatStack<'p, Cx> { +impl<'p, Cx: PatCx> PatStack<'p, Cx> { fn from_pattern(pat: &'p DeconstructedPat<Cx>) -> Self { PatStack { pats: smallvec![PatOrWild::Pat(pat)], relevant: true } } @@ -1026,7 +1022,7 @@ impl<'p, Cx: TypeCx> PatStack<'p, Cx> { } } -impl<'p, Cx: TypeCx> fmt::Debug for PatStack<'p, Cx> { +impl<'p, Cx: PatCx> fmt::Debug for PatStack<'p, Cx> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { // We pretty-print similarly to the `Debug` impl of `Matrix`. write!(f, "+")?; @@ -1039,7 +1035,7 @@ impl<'p, Cx: TypeCx> fmt::Debug for PatStack<'p, Cx> { /// A row of the matrix. #[derive(Clone)] -struct MatrixRow<'p, Cx: TypeCx> { +struct MatrixRow<'p, Cx: PatCx> { // The patterns in the row. pats: PatStack<'p, Cx>, /// Whether the original arm had a guard. This is inherited when specializing. @@ -1059,7 +1055,7 @@ struct MatrixRow<'p, Cx: TypeCx> { intersects: BitSet<usize>, } -impl<'p, Cx: TypeCx> MatrixRow<'p, Cx> { +impl<'p, Cx: PatCx> MatrixRow<'p, Cx> { fn is_empty(&self) -> bool { self.pats.is_empty() } @@ -1108,7 +1104,7 @@ impl<'p, Cx: TypeCx> MatrixRow<'p, Cx> { } } -impl<'p, Cx: TypeCx> fmt::Debug for MatrixRow<'p, Cx> { +impl<'p, Cx: PatCx> fmt::Debug for MatrixRow<'p, Cx> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { self.pats.fmt(f) } @@ -1125,7 +1121,7 @@ impl<'p, Cx: TypeCx> fmt::Debug for MatrixRow<'p, Cx> { /// specializing `(,)` and `Some` on a pattern of type `(Option<u32>, bool)`, the first column of /// the matrix will correspond to `scrutinee.0.Some.0` and the second column to `scrutinee.1`. #[derive(Clone)] -struct Matrix<'p, Cx: TypeCx> { +struct Matrix<'p, Cx: PatCx> { /// Vector of rows. The rows must form a rectangular 2D array. Moreover, all the patterns of /// each column must have the same type. Each column corresponds to a place within the /// scrutinee. @@ -1138,7 +1134,7 @@ struct Matrix<'p, Cx: TypeCx> { wildcard_row_is_relevant: bool, } -impl<'p, Cx: TypeCx> Matrix<'p, Cx> { +impl<'p, Cx: PatCx> Matrix<'p, Cx> { /// Pushes a new row to the matrix. If the row starts with an or-pattern, this recursively /// expands it. Internal method, prefer [`Matrix::new`]. fn expand_and_push(&mut self, mut row: MatrixRow<'p, Cx>) { @@ -1155,11 +1151,7 @@ impl<'p, Cx: TypeCx> Matrix<'p, Cx> { } /// Build a new matrix from an iterator of `MatchArm`s. - fn new( - arms: &[MatchArm<'p, Cx>], - scrut_ty: Cx::Ty, - scrut_validity: ValidityConstraint, - ) -> Self { + fn new(arms: &[MatchArm<'p, Cx>], scrut_ty: Cx::Ty, scrut_validity: PlaceValidity) -> Self { let place_info = PlaceInfo { ty: scrut_ty, private_uninhabited: false, @@ -1264,7 +1256,7 @@ impl<'p, Cx: TypeCx> Matrix<'p, Cx> { /// + _ + [_, _, tail @ ..] + /// | ✓ | ? | // column validity /// ``` -impl<'p, Cx: TypeCx> fmt::Debug for Matrix<'p, Cx> { +impl<'p, Cx: PatCx> fmt::Debug for Matrix<'p, Cx> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "\n")?; @@ -1355,15 +1347,15 @@ impl<'p, Cx: TypeCx> fmt::Debug for Matrix<'p, Cx> { /// /// See the top of the file for more detailed explanations and examples. #[derive(Debug)] -struct WitnessStack<Cx: TypeCx>(Vec<WitnessPat<Cx>>); +struct WitnessStack<Cx: PatCx>(Vec<WitnessPat<Cx>>); -impl<Cx: TypeCx> Clone for WitnessStack<Cx> { +impl<Cx: PatCx> Clone for WitnessStack<Cx> { fn clone(&self) -> Self { Self(self.0.clone()) } } -impl<Cx: TypeCx> WitnessStack<Cx> { +impl<Cx: PatCx> WitnessStack<Cx> { /// Asserts that the witness contains a single pattern, and returns it. fn single_pattern(self) -> WitnessPat<Cx> { assert_eq!(self.0.len(), 1); @@ -1408,15 +1400,15 @@ impl<Cx: TypeCx> WitnessStack<Cx> { /// Just as the `Matrix` starts with a single column, by the end of the algorithm, this has a single /// column, which contains the patterns that are missing for the match to be exhaustive. #[derive(Debug)] -struct WitnessMatrix<Cx: TypeCx>(Vec<WitnessStack<Cx>>); +struct WitnessMatrix<Cx: PatCx>(Vec<WitnessStack<Cx>>); -impl<Cx: TypeCx> Clone for WitnessMatrix<Cx> { +impl<Cx: PatCx> Clone for WitnessMatrix<Cx> { fn clone(&self) -> Self { Self(self.0.clone()) } } -impl<Cx: TypeCx> WitnessMatrix<Cx> { +impl<Cx: PatCx> WitnessMatrix<Cx> { /// New matrix with no witnesses. fn empty() -> Self { WitnessMatrix(Vec::new()) @@ -1490,7 +1482,7 @@ impl<Cx: TypeCx> WitnessMatrix<Cx> { /// /// We can however get false negatives because exhaustiveness does not explore all cases. See the /// section on relevancy at the top of the file. -fn collect_overlapping_range_endpoints<'p, Cx: TypeCx>( +fn collect_overlapping_range_endpoints<'p, Cx: PatCx>( cx: &Cx, overlap_range: IntRange, matrix: &Matrix<'p, Cx>, @@ -1549,7 +1541,7 @@ fn collect_overlapping_range_endpoints<'p, Cx: TypeCx>( } /// Collect ranges that have a singleton gap between them. -fn collect_non_contiguous_range_endpoints<'p, Cx: TypeCx>( +fn collect_non_contiguous_range_endpoints<'p, Cx: PatCx>( cx: &Cx, gap_range: &IntRange, matrix: &Matrix<'p, Cx>, @@ -1590,7 +1582,7 @@ fn collect_non_contiguous_range_endpoints<'p, Cx: TypeCx>( /// (using `apply_constructor` and by updating `row.useful` for each parent row). /// This is all explained at the top of the file. #[instrument(level = "debug", skip(mcx), ret)] -fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>( +fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: PatCx>( mcx: &mut UsefulnessCtxt<'a, Cx>, matrix: &mut Matrix<'p, Cx>, ) -> Result<WitnessMatrix<Cx>, Cx::Error> { @@ -1687,7 +1679,7 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>( /// Indicates whether or not a given arm is useful. #[derive(Clone, Debug)] -pub enum Usefulness<'p, Cx: TypeCx> { +pub enum Usefulness<'p, Cx: PatCx> { /// The arm is useful. This additionally carries a set of or-pattern branches that have been /// found to be redundant despite the overall arm being useful. Used only in the presence of /// or-patterns, otherwise it stays empty. @@ -1698,11 +1690,11 @@ pub enum Usefulness<'p, Cx: TypeCx> { } /// Report whether this pattern was found useful, and its subpatterns that were not useful if any. -fn collect_pattern_usefulness<'p, Cx: TypeCx>( +fn collect_pattern_usefulness<'p, Cx: PatCx>( useful_subpatterns: &FxHashSet<PatId>, pat: &'p DeconstructedPat<Cx>, ) -> Usefulness<'p, Cx> { - fn pat_is_useful<'p, Cx: TypeCx>( + fn pat_is_useful<'p, Cx: PatCx>( useful_subpatterns: &FxHashSet<PatId>, pat: &'p DeconstructedPat<Cx>, ) -> bool { @@ -1740,7 +1732,7 @@ fn collect_pattern_usefulness<'p, Cx: TypeCx>( } /// The output of checking a match for exhaustiveness and arm usefulness. -pub struct UsefulnessReport<'p, Cx: TypeCx> { +pub struct UsefulnessReport<'p, Cx: PatCx> { /// For each arm of the input, whether that arm is useful after the arms above it. pub arm_usefulness: Vec<(MatchArm<'p, Cx>, Usefulness<'p, Cx>)>, /// If the match is exhaustive, this is empty. If not, this contains witnesses for the lack of @@ -1750,11 +1742,11 @@ pub struct UsefulnessReport<'p, Cx: TypeCx> { /// Computes whether a match is exhaustive and which of its arms are useful. #[instrument(skip(tycx, arms), level = "debug")] -pub fn compute_match_usefulness<'p, Cx: TypeCx>( +pub fn compute_match_usefulness<'p, Cx: PatCx>( tycx: &Cx, arms: &[MatchArm<'p, Cx>], scrut_ty: Cx::Ty, - scrut_validity: ValidityConstraint, + scrut_validity: PlaceValidity, complexity_limit: Option<usize>, ) -> Result<UsefulnessReport<'p, Cx>, Cx::Error> { let mut cx = UsefulnessCtxt { |