1 use rustc::mir::{BasicBlock, Location, Mir};
2 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
4 /// Maps between a MIR Location, which identifies a particular
5 /// statement within a basic block, to a "rich location", which
6 /// identifies at a finer granularity. In particular, we distinguish
7 /// the *start* of a statement and the *mid-point*. The mid-point is
8 /// the point *just* before the statement takes effect; in particular,
9 /// for an assignment `A = B`, it is the point where B is about to be
10 /// written into A. This mid-point is a kind of hack to work around
11 /// our inability to track the position information at sufficient
12 /// granularity through outlives relations; however, the rich location
13 /// table serves another purpose: it compresses locations from
14 /// multiple words into a single u32.
15 crate struct LocationTable {
17 statements_before_block: IndexVec<BasicBlock, usize>,
21 pub struct LocationIndex {
22 DEBUG_FORMAT = "LocationIndex({})"
26 #[derive(Copy, Clone, Debug)]
27 crate enum RichLocation {
33 crate fn new(mir: &Mir<'_>) -> Self {
34 let mut num_points = 0;
35 let statements_before_block = mir.basic_blocks()
39 num_points += (block_data.statements.len() + 1) * 2;
45 "LocationTable(statements_before_block={:#?})",
46 statements_before_block
48 debug!("LocationTable: num_points={:#?}", num_points);
52 statements_before_block,
56 crate fn all_points(&self) -> impl Iterator<Item = LocationIndex> {
57 (0..self.num_points).map(LocationIndex::new)
60 crate fn start_index(&self, location: Location) -> LocationIndex {
65 let start_index = self.statements_before_block[block];
66 LocationIndex::new(start_index + statement_index * 2)
69 crate fn mid_index(&self, location: Location) -> LocationIndex {
74 let start_index = self.statements_before_block[block];
75 LocationIndex::new(start_index + statement_index * 2 + 1)
78 crate fn to_location(&self, index: LocationIndex) -> RichLocation {
79 let point_index = index.index();
81 // Find the basic block. We have a vector with the
82 // starting index of the statement in each block. Imagine
83 // we have statement #22, and we have a vector like:
87 // In that case, this represents point_index 2 of
88 // basic block BB2. We know this because BB0 accounts for
89 // 0..10, BB1 accounts for 11..20, and BB2 accounts for
92 // To compute this, we could do a binary search, but
93 // because I am lazy we instead iterate through to find
94 // the last point where the "first index" (0, 10, or 20)
95 // was less than the statement index (22). In our case, this will
97 let (block, &first_index) = self.statements_before_block
99 .filter(|(_, first_index)| **first_index <= point_index)
103 let statement_index = (point_index - first_index) / 2;
104 if index.is_start() {
105 RichLocation::Start(Location { block, statement_index })
107 RichLocation::Mid(Location { block, statement_index })
113 fn is_start(&self) -> bool {
114 // even indices are start points; odd indices are mid points
115 (self.index() % 2) == 0