109 lines
3.8 KiB
Rust
109 lines
3.8 KiB
Rust
#![deny(rustc::untranslatable_diagnostic)]
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#![deny(rustc::diagnostic_outside_of_impl)]
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use rustc_index::vec::{Idx, IndexVec};
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use rustc_middle::mir::{BasicBlock, Body, Location};
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/// Maps between a MIR Location, which identifies a particular
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/// statement within a basic block, to a "rich location", which
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/// identifies at a finer granularity. In particular, we distinguish
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/// the *start* of a statement and the *mid-point*. The mid-point is
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/// the point *just* before the statement takes effect; in particular,
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/// for an assignment `A = B`, it is the point where B is about to be
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/// written into A. This mid-point is a kind of hack to work around
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/// our inability to track the position information at sufficient
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/// granularity through outlives relations; however, the rich location
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/// table serves another purpose: it compresses locations from
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/// multiple words into a single u32.
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pub struct LocationTable {
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num_points: usize,
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statements_before_block: IndexVec<BasicBlock, usize>,
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}
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rustc_index::newtype_index! {
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pub struct LocationIndex {
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DEBUG_FORMAT = "LocationIndex({})"
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}
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}
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#[derive(Copy, Clone, Debug)]
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pub enum RichLocation {
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Start(Location),
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Mid(Location),
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}
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impl LocationTable {
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pub(crate) fn new(body: &Body<'_>) -> Self {
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let mut num_points = 0;
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let statements_before_block = body
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.basic_blocks
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.iter()
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.map(|block_data| {
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let v = num_points;
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num_points += (block_data.statements.len() + 1) * 2;
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v
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})
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.collect();
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debug!("LocationTable(statements_before_block={:#?})", statements_before_block);
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debug!("LocationTable: num_points={:#?}", num_points);
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Self { num_points, statements_before_block }
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}
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pub fn all_points(&self) -> impl Iterator<Item = LocationIndex> {
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(0..self.num_points).map(LocationIndex::new)
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}
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pub fn start_index(&self, location: Location) -> LocationIndex {
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let Location { block, statement_index } = location;
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let start_index = self.statements_before_block[block];
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LocationIndex::new(start_index + statement_index * 2)
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}
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pub fn mid_index(&self, location: Location) -> LocationIndex {
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let Location { block, statement_index } = location;
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let start_index = self.statements_before_block[block];
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LocationIndex::new(start_index + statement_index * 2 + 1)
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}
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pub fn to_location(&self, index: LocationIndex) -> RichLocation {
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let point_index = index.index();
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// Find the basic block. We have a vector with the
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// starting index of the statement in each block. Imagine
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// we have statement #22, and we have a vector like:
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//
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// [0, 10, 20]
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//
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// In that case, this represents point_index 2 of
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// basic block BB2. We know this because BB0 accounts for
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// 0..10, BB1 accounts for 11..20, and BB2 accounts for
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// 20...
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//
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// To compute this, we could do a binary search, but
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// because I am lazy we instead iterate through to find
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// the last point where the "first index" (0, 10, or 20)
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// was less than the statement index (22). In our case, this will
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// be (BB2, 20).
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let (block, &first_index) = self
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.statements_before_block
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.iter_enumerated()
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.rfind(|&(_, &first_index)| first_index <= point_index)
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.unwrap();
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let statement_index = (point_index - first_index) / 2;
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if index.is_start() {
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RichLocation::Start(Location { block, statement_index })
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} else {
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RichLocation::Mid(Location { block, statement_index })
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}
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}
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}
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impl LocationIndex {
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fn is_start(self) -> bool {
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// even indices are start points; odd indices are mid points
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(self.index() % 2) == 0
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}
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}
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