From 8f9cd3d1e820eb114c32627cc34f3897cda7903e Mon Sep 17 00:00:00 2001 From: Nadrieril Date: Tue, 3 Oct 2023 15:17:52 +0200 Subject: [PATCH] Rework range splitting api --- .../src/thir/pattern/deconstruct_pat.rs | 202 ++++++++---------- 1 file changed, 90 insertions(+), 112 deletions(-) diff --git a/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs index 3ee4befa121..d63190985a3 100644 --- a/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs +++ b/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs @@ -39,7 +39,7 @@ //! //! Splitting is implemented in the [`Constructor::split`] function. We don't do splitting for //! or-patterns; instead we just try the alternatives one-by-one. For details on splitting -//! wildcards, see [`SplitWildcard`]; for integer ranges, see [`SplitIntRange`]; for slices, see +//! wildcards, see [`SplitWildcard`]; for integer ranges, see [`IntRange::split`]; for slices, see //! [`SplitVarLenSlice`]. use std::cell::Cell; @@ -186,6 +186,93 @@ impl IntRange { (lo == other_hi || hi == other_lo) && !self.is_singleton() && !other.is_singleton() } + /// See `Constructor::is_covered_by` + fn is_covered_by(&self, other: &Self) -> bool { + if self.intersection(other).is_some() { + // Constructor splitting should ensure that all intersections we encounter are actually + // inclusions. + assert!(self.is_subrange(other)); + true + } else { + false + } + } + + /// Partition a range of integers into disjoint subranges. This does constructor splitting for + /// integer ranges as explained at the top of the file. + /// + /// This returns an output that covers `self`. The output is split so that the only + /// intersections between an output range and a column range are inclusions. No output range + /// straddles the boundary of one of the inputs. + /// + /// The following input: + /// ```text + /// |-------------------------| // `self` + /// |------| |----------| |----| + /// |-------| |-------| + /// ``` + /// would be iterated over as follows: + /// ```text + /// ||---|--||-|---|---|---|--| + /// ``` + fn split( + &self, + column_ranges: impl Iterator, + ) -> impl Iterator { + /// Represents a boundary between 2 integers. Because the intervals spanning boundaries must be + /// able to cover every integer, we need to be able to represent 2^128 + 1 such boundaries. + #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)] + enum IntBoundary { + JustBefore(u128), + AfterMax, + } + + fn unpack_intrange(range: IntRange) -> [IntBoundary; 2] { + use IntBoundary::*; + let (lo, hi) = range.boundaries(); + let lo = JustBefore(lo); + let hi = match hi.checked_add(1) { + Some(m) => JustBefore(m), + None => AfterMax, + }; + [lo, hi] + } + + // The boundaries of ranges in `column_ranges` intersected with `self`. + let mut boundaries: Vec = column_ranges + .filter_map(|r| self.intersection(&r)) + .map(unpack_intrange) + .flat_map(|[lo, hi]| [lo, hi]) + .collect(); + boundaries.sort_unstable(); + + let [self_start, self_end] = unpack_intrange(self.clone()); + // Gather pairs of adjacent boundaries. + let mut prev_bdy = self_start; + boundaries + .into_iter() + // End with the end of the range. + .chain(once(self_end)) + // List pairs of adjacent boundaries. + .map(move |bdy| { + let ret = (prev_bdy, bdy); + prev_bdy = bdy; + ret + }) + // Skip duplicates. + .filter(|&(prev_bdy, bdy)| prev_bdy != bdy) + // Convert back to ranges. + .map(move |(prev_bdy, bdy)| { + use IntBoundary::*; + let range = match (prev_bdy, bdy) { + (JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1), + (JustBefore(n), AfterMax) => n..=u128::MAX, + _ => unreachable!(), // Ruled out by the sorting and filtering we did + }; + IntRange { range } + }) + } + /// Only used for displaying the range properly. fn to_pat<'tcx>(&self, tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Pat<'tcx> { let (lo, hi) = self.boundaries(); @@ -254,18 +341,6 @@ impl IntRange { ); } } - - /// See `Constructor::is_covered_by` - fn is_covered_by(&self, other: &Self) -> bool { - if self.intersection(other).is_some() { - // Constructor splitting should ensure that all intersections we encounter are actually - // inclusions. - assert!(self.is_subrange(other)); - true - } else { - false - } - } } /// Note: this is often not what we want: e.g. `false` is converted into the range `0..=0` and @@ -279,101 +354,6 @@ impl fmt::Debug for IntRange { } } -/// Represents a border between 2 integers. Because the intervals spanning borders must be able to -/// cover every integer, we need to be able to represent 2^128 + 1 such borders. -#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)] -enum IntBorder { - JustBefore(u128), - AfterMax, -} - -/// A range of integers that is partitioned into disjoint subranges. This does constructor -/// splitting for integer ranges as explained at the top of the file. -/// -/// This is fed multiple ranges, and returns an output that covers the input, but is split so that -/// the only intersections between an output range and a seen range are inclusions. No output range -/// straddles the boundary of one of the inputs. -/// -/// The following input: -/// ```text -/// |-------------------------| // `self` -/// |------| |----------| |----| -/// |-------| |-------| -/// ``` -/// would be iterated over as follows: -/// ```text -/// ||---|--||-|---|---|---|--| -/// ``` -#[derive(Debug, Clone)] -struct SplitIntRange { - /// The range we are splitting - range: IntRange, - /// The borders of ranges we have seen. They are all contained within `range`. This is kept - /// sorted. - borders: Vec, -} - -impl SplitIntRange { - fn new(range: IntRange) -> Self { - SplitIntRange { range, borders: Vec::new() } - } - - /// Internal use - fn to_borders(r: IntRange) -> [IntBorder; 2] { - use IntBorder::*; - let (lo, hi) = r.boundaries(); - let lo = JustBefore(lo); - let hi = match hi.checked_add(1) { - Some(m) => JustBefore(m), - None => AfterMax, - }; - [lo, hi] - } - - /// Add ranges relative to which we split. - fn split(&mut self, ranges: impl Iterator) { - let this_range = &self.range; - let included_ranges = ranges.filter_map(|r| this_range.intersection(&r)); - let included_borders = included_ranges.flat_map(|r| { - let borders = Self::to_borders(r); - once(borders[0]).chain(once(borders[1])) - }); - self.borders.extend(included_borders); - self.borders.sort_unstable(); - } - - /// Iterate over the contained ranges. - fn iter(&self) -> impl Iterator + Captures<'_> { - use IntBorder::*; - - let self_range = Self::to_borders(self.range.clone()); - // Start with the start of the range. - let mut prev_border = self_range[0]; - self.borders - .iter() - .copied() - // End with the end of the range. - .chain(once(self_range[1])) - // List pairs of adjacent borders. - .map(move |border| { - let ret = (prev_border, border); - prev_border = border; - ret - }) - // Skip duplicates. - .filter(|(prev_border, border)| prev_border != border) - // Finally, convert to ranges. - .map(move |(prev_border, border)| { - let range = match (prev_border, border) { - (JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1), - (JustBefore(n), AfterMax) => n..=u128::MAX, - _ => unreachable!(), // Ruled out by the sorting and filtering we did - }; - IntRange { range } - }) - } -} - #[derive(Copy, Clone, Debug, PartialEq, Eq)] enum SliceKind { /// Patterns of length `n` (`[x, y]`). @@ -733,10 +713,8 @@ impl<'tcx> Constructor<'tcx> { // Fast-track if the range is trivial. In particular, we don't do the overlapping // ranges check. IntRange(ctor_range) if !ctor_range.is_singleton() => { - let mut split_range = SplitIntRange::new(ctor_range.clone()); - let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range()); - split_range.split(int_ranges.cloned()); - split_range.iter().map(IntRange).collect() + let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range()).cloned(); + ctor_range.split(int_ranges).map(IntRange).collect() } &Slice(Slice { kind: VarLen(self_prefix, self_suffix), array_len }) => { let mut split_self = SplitVarLenSlice::new(self_prefix, self_suffix, array_len);