points.rs

use rustc_index::bit_set::BitSet;
use rustc_index::interval::SparseIntervalMatrix;
use rustc_index::{Idx, IndexVec};
use rustc_middle::mir::{self, BasicBlock, Body, Location};

use crate::framework::{visit_results, ResultsVisitable, ResultsVisitor};

/// Maps between a `Location` and a `PointIndex` (and vice versa).
pub struct DenseLocationMap {
    /// For each basic block, how many points are contained within?
    statements_before_block: IndexVec<BasicBlock, usize>,

    /// Map backward from each point to the basic block that it
    /// belongs to.
    basic_blocks: IndexVec<PointIndex, BasicBlock>,

    num_points: usize,
}

impl DenseLocationMap {
    #[inline]
    pub fn new(body: &Body<'_>) -> Self {
        let mut num_points = 0;
        let statements_before_block: IndexVec<BasicBlock, usize> = body
            .basic_blocks
            .iter()
            .map(|block_data| {
                let v = num_points;
                num_points += block_data.statements.len() + 1;
                v
            })
            .collect();

        let mut basic_blocks = IndexVec::with_capacity(num_points);
        for (bb, bb_data) in body.basic_blocks.iter_enumerated() {
            basic_blocks.extend((0..=bb_data.statements.len()).map(|_| bb));
        }

        Self { statements_before_block, basic_blocks, num_points }
    }

    /// Total number of point indices
    #[inline]
    pub fn num_points(&self) -> usize {
        self.num_points
    }

    /// Converts a `Location` into a `PointIndex`. O(1).
    #[inline]
    pub fn point_from_location(&self, location: Location) -> PointIndex {
        let Location { block, statement_index } = location;
        let start_index = self.statements_before_block[block];
        PointIndex::new(start_index + statement_index)
    }

    /// Returns the `PointIndex` for the first statement in the given `BasicBlock`. O(1).
    #[inline]
    pub fn entry_point(&self, block: BasicBlock) -> PointIndex {
        let start_index = self.statements_before_block[block];
        PointIndex::new(start_index)
    }

    /// Return the PointIndex for the block start of this index.
    #[inline]
    pub fn to_block_start(&self, index: PointIndex) -> PointIndex {
        PointIndex::new(self.statements_before_block[self.basic_blocks[index]])
    }

    /// Converts a `PointIndex` back to a location. O(1).
    #[inline]
    pub fn to_location(&self, index: PointIndex) -> Location {
        assert!(index.index() < self.num_points);
        let block = self.basic_blocks[index];
        let start_index = self.statements_before_block[block];
        let statement_index = index.index() - start_index;
        Location { block, statement_index }
    }

    /// Sometimes we get point-indices back from bitsets that may be
    /// out of range (because they round up to the nearest 2^N number
    /// of bits). Use this function to filter such points out if you
    /// like.
    #[inline]
    pub fn point_in_range(&self, index: PointIndex) -> bool {
        index.index() < self.num_points
    }
}

rustc_index::newtype_index! {
    /// A single integer representing a `Location` in the MIR control-flow
    /// graph. Constructed efficiently from `DenseLocationMap`.
    #[orderable]
    #[debug_format = "PointIndex({})"]
    pub struct PointIndex {}
}

/// Add points depending on the result of the given dataflow analysis.
pub fn save_as_intervals<'tcx, N, R>(
    elements: &DenseLocationMap,
    body: &mir::Body<'tcx>,
    mut results: R,
) -> SparseIntervalMatrix<N, PointIndex>
where
    N: Idx,
    R: ResultsVisitable<'tcx, FlowState = BitSet<N>>,
{
    let values = SparseIntervalMatrix::new(elements.num_points());
    let mut visitor = Visitor { elements, values };
    visit_results(
        body,
        body.basic_blocks.reverse_postorder().iter().copied(),
        &mut results,
        &mut visitor,
    );
    visitor.values
}

struct Visitor<'a, N: Idx> {
    elements: &'a DenseLocationMap,
    values: SparseIntervalMatrix<N, PointIndex>,
}

impl<'mir, 'tcx, R, N> ResultsVisitor<'mir, 'tcx, R> for Visitor<'_, N>
where
    N: Idx,
{
    type FlowState = BitSet<N>;

    fn visit_statement_after_primary_effect(
        &mut self,
        _results: &mut R,
        state: &Self::FlowState,
        _statement: &'mir mir::Statement<'tcx>,
        location: Location,
    ) {
        let point = self.elements.point_from_location(location);
        // Use internal iterator manually as it is much more efficient.
        state.iter().for_each(|node| {
            self.values.insert(node, point);
        });
    }

    fn visit_terminator_after_primary_effect(
        &mut self,
        _results: &mut R,
        state: &Self::FlowState,
        _terminator: &'mir mir::Terminator<'tcx>,
        location: Location,
    ) {
        let point = self.elements.point_from_location(location);
        // Use internal iterator manually as it is much more efficient.
        state.iter().for_each(|node| {
            self.values.insert(node, point);
        });
    }
}