diff options
Diffstat (limited to 'compiler/rustc_pattern_analysis/src')
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/constructor.rs | 29 | ||||
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/rustc.rs | 3 | ||||
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/usefulness.rs | 49 |
3 files changed, 68 insertions, 13 deletions
diff --git a/compiler/rustc_pattern_analysis/src/constructor.rs b/compiler/rustc_pattern_analysis/src/constructor.rs index 1c9a9ab0f72..44f09b66bf6 100644 --- a/compiler/rustc_pattern_analysis/src/constructor.rs +++ b/compiler/rustc_pattern_analysis/src/constructor.rs @@ -140,6 +140,34 @@ //! [`ConstructorSet::split`]. The invariants of [`SplitConstructorSet`] are also of interest. //! //! +//! ## Unions +//! +//! Unions allow us to match a value via several overlapping representations at the same time. For +//! example, the following is exhaustive because when seeing the value as a boolean we handled all +//! possible cases (other cases such as `n == 3` would trigger UB). +//! +//! ```rust +//! # fn main() { +//! union U8AsBool { +//! n: u8, +//! b: bool, +//! } +//! let x = U8AsBool { n: 1 }; +//! unsafe { +//! match x { +//! U8AsBool { n: 2 } => {} +//! U8AsBool { b: true } => {} +//! U8AsBool { b: false } => {} +//! } +//! } +//! # } +//! ``` +//! +//! Pattern-matching has no knowledge that e.g. `false as u8 == 0`, so the values we consider in the +//! algorithm look like `U8AsBool { b: true, n: 2 }`. In other words, for the most part a union is +//! treated like a struct with the same fields. The difference lies in how we construct witnesses of +//! non-exhaustiveness. +//! //! //! ## Opaque patterns //! @@ -974,7 +1002,6 @@ impl<Cx: PatCx> ConstructorSet<Cx> { /// any) are missing; 2/ split constructors to handle non-trivial intersections e.g. on ranges /// or slices. This can get subtle; see [`SplitConstructorSet`] for details of this operation /// and its invariants. - #[instrument(level = "debug", skip(self, ctors), ret)] pub fn split<'a>( &self, ctors: impl Iterator<Item = &'a Constructor<Cx>> + Clone, diff --git a/compiler/rustc_pattern_analysis/src/rustc.rs b/compiler/rustc_pattern_analysis/src/rustc.rs index b0f506c3651..548a7b43005 100644 --- a/compiler/rustc_pattern_analysis/src/rustc.rs +++ b/compiler/rustc_pattern_analysis/src/rustc.rs @@ -186,7 +186,6 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> { /// Returns the types of the fields for a given constructor. The result must have a length of /// `ctor.arity()`. - #[instrument(level = "trace", skip(self))] pub(crate) fn ctor_sub_tys<'a>( &'a self, ctor: &'a Constructor<'p, 'tcx>, @@ -283,7 +282,6 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> { /// Creates a set that represents all the constructors of `ty`. /// /// See [`crate::constructor`] for considerations of emptiness. - #[instrument(level = "debug", skip(self), ret)] pub fn ctors_for_ty( &self, ty: RevealedTy<'tcx>, @@ -401,6 +399,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> { | ty::RawPtr(_, _) | ty::FnDef(_, _) | ty::FnPtr(_) + | ty::Pat(_, _) | ty::Dynamic(_, _, _) | ty::Closure(..) | ty::CoroutineClosure(..) diff --git a/compiler/rustc_pattern_analysis/src/usefulness.rs b/compiler/rustc_pattern_analysis/src/usefulness.rs index cdc03eaeb37..7246039174a 100644 --- a/compiler/rustc_pattern_analysis/src/usefulness.rs +++ b/compiler/rustc_pattern_analysis/src/usefulness.rs @@ -871,12 +871,14 @@ impl<Cx: PatCx> PlaceInfo<Cx> { where Cx: 'a, { + debug!(?self.ty); if self.private_uninhabited { // Skip the whole column return Ok((smallvec![Constructor::PrivateUninhabited], vec![])); } let ctors_for_ty = cx.ctors_for_ty(&self.ty)?; + debug!(?ctors_for_ty); // We treat match scrutinees of type `!` or `EmptyEnum` differently. let is_toplevel_exception = @@ -895,6 +897,7 @@ impl<Cx: PatCx> PlaceInfo<Cx> { // Analyze the constructors present in this column. let mut split_set = ctors_for_ty.split(ctors); + debug!(?split_set); let all_missing = split_set.present.is_empty(); // Build the set of constructors we will specialize with. It must cover the whole type, so @@ -1254,7 +1257,7 @@ impl<'p, Cx: PatCx> Matrix<'p, Cx> { /// + true + [Second(true)] + /// + false + [_] + /// + _ + [_, _, tail @ ..] + -/// | ✓ | ? | // column validity +/// | ✓ | ? | // validity /// ``` impl<'p, Cx: PatCx> fmt::Debug for Matrix<'p, Cx> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { @@ -1285,7 +1288,7 @@ impl<'p, Cx: PatCx> fmt::Debug for Matrix<'p, Cx> { write!(f, " {sep}")?; } if is_validity_row { - write!(f, " // column validity")?; + write!(f, " // validity")?; } write!(f, "\n")?; } @@ -1381,12 +1384,35 @@ impl<Cx: PatCx> WitnessStack<Cx> { /// pats: [(false, "foo"), _, true] /// result: [Enum::Variant { a: (false, "foo"), b: _ }, true] /// ``` - fn apply_constructor(&mut self, pcx: &PlaceCtxt<'_, Cx>, ctor: &Constructor<Cx>) { + fn apply_constructor( + mut self, + pcx: &PlaceCtxt<'_, Cx>, + ctor: &Constructor<Cx>, + ) -> SmallVec<[Self; 1]> { let len = self.0.len(); let arity = pcx.ctor_arity(ctor); - let fields = self.0.drain((len - arity)..).rev().collect(); - let pat = WitnessPat::new(ctor.clone(), fields, pcx.ty.clone()); - self.0.push(pat); + let fields: Vec<_> = self.0.drain((len - arity)..).rev().collect(); + if matches!(ctor, Constructor::UnionField) + && fields.iter().filter(|p| !matches!(p.ctor(), Constructor::Wildcard)).count() >= 2 + { + // Convert a `Union { a: p, b: q }` witness into `Union { a: p }` and `Union { b: q }`. + // First add `Union { .. }` to `self`. + self.0.push(WitnessPat::wild_from_ctor(pcx.cx, ctor.clone(), pcx.ty.clone())); + fields + .into_iter() + .enumerate() + .filter(|(_, p)| !matches!(p.ctor(), Constructor::Wildcard)) + .map(|(i, p)| { + let mut ret = self.clone(); + // Fill the `i`th field of the union with `p`. + ret.0.last_mut().unwrap().fields[i] = p; + ret + }) + .collect() + } else { + self.0.push(WitnessPat::new(ctor.clone(), fields, pcx.ty.clone())); + smallvec![self] + } } } @@ -1459,8 +1485,8 @@ impl<Cx: PatCx> WitnessMatrix<Cx> { *self = ret; } else { // Any other constructor we unspecialize as expected. - for witness in self.0.iter_mut() { - witness.apply_constructor(pcx, ctor) + for witness in std::mem::take(&mut self.0) { + self.0.extend(witness.apply_constructor(pcx, ctor)); } } } @@ -1617,7 +1643,6 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: PatCx>( }; // Analyze the constructors present in this column. - debug!("ty: {:?}", place.ty); let ctors = matrix.heads().map(|p| p.ctor()); let (split_ctors, missing_ctors) = place.split_column_ctors(mcx.tycx, ctors)?; @@ -1669,7 +1694,10 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: PatCx>( for row in matrix.rows() { if row.useful { if let PatOrWild::Pat(pat) = row.head() { - mcx.useful_subpatterns.insert(pat.uid); + let newly_useful = mcx.useful_subpatterns.insert(pat.uid); + if newly_useful { + debug!("newly useful: {pat:?}"); + } } } } @@ -1768,6 +1796,7 @@ pub fn compute_match_usefulness<'p, Cx: PatCx>( .map(|arm| { debug!(?arm); let usefulness = collect_pattern_usefulness(&cx.useful_subpatterns, arm.pat); + debug!(?usefulness); (arm, usefulness) }) .collect(); |