compiler/rustc_mir/src/transform/coverage/query.rs

   1 use super::*;
   2
   3 use rustc_middle::mir::coverage::*;
   4 use rustc_middle::mir::visit::Visitor;
   5 use rustc_middle::mir::{self, Coverage, CoverageInfo, Location};
   6 use rustc_middle::ty::query::Providers;
   7 use rustc_middle::ty::TyCtxt;
   8 use rustc_span::def_id::DefId;
   9
  10 /// The `query` provider for `CoverageInfo`, requested by `codegen_coverage()` (to inject each
  11 /// counter) and `FunctionCoverage::new()` (to extract the coverage map metadata from the MIR).
  12 pub(crate) fn provide(providers: &mut Providers) {
  13     providers.coverageinfo = |tcx, def_id| coverageinfo_from_mir(tcx, def_id);
  14     providers.covered_file_name = |tcx, def_id| covered_file_name(tcx, def_id);
  15     providers.covered_code_regions = |tcx, def_id| covered_code_regions(tcx, def_id);
  16 }
  17
  18 /// The `num_counters` argument to `llvm.instrprof.increment` is the max counter_id + 1, or in
  19 /// other words, the number of counter value references injected into the MIR (plus 1 for the
  20 /// reserved `ZERO` counter, which uses counter ID `0` when included in an expression). Injected
  21 /// counters have a counter ID from `1..num_counters-1`.
  22 ///
  23 /// `num_expressions` is the number of counter expressions added to the MIR body.
  24 ///
  25 /// Both `num_counters` and `num_expressions` are used to initialize new vectors, during backend
  26 /// code generate, to lookup counters and expressions by simple u32 indexes.
  27 ///
  28 /// MIR optimization may split and duplicate some BasicBlock sequences, or optimize out some code
  29 /// including injected counters. (It is OK if some counters are optimized out, but those counters
  30 /// are still included in the total `num_counters` or `num_expressions`.) Simply counting the
  31 /// calls may not work; but computing the number of counters or expressions by adding `1` to the
  32 /// highest ID (for a given instrumented function) is valid.
  33 ///
  34 /// This visitor runs twice, first with `add_missing_operands` set to `false`, to find the maximum
  35 /// counter ID and maximum expression ID based on their enum variant `id` fields; then, as a
  36 /// safeguard, with `add_missing_operands` set to `true`, to find any other counter or expression
  37 /// IDs referenced by expression operands, if not already seen.
  38 ///
  39 /// Ideally, each operand ID in a MIR `CoverageKind::Expression` will have a separate MIR `Coverage`
  40 /// statement for the `Counter` or `Expression` with the referenced ID. but since current or future
  41 /// MIR optimizations can theoretically optimize out segments of a MIR, it may not be possible to
  42 /// guarantee this, so the second pass ensures the `CoverageInfo` counts include all referenced IDs.
  43 struct CoverageVisitor {
  44     info: CoverageInfo,
  45     add_missing_operands: bool,
  46 }
  47
  48 impl CoverageVisitor {
  49     /// Updates `num_counters` to the maximum encountered zero-based counter_id plus 1. Note the
  50     /// final computed number of counters should be the number of all `CoverageKind::Counter`
  51     /// statements in the MIR *plus one* for the implicit `ZERO` counter.
  52     #[inline(always)]
  53     fn update_num_counters(&mut self, counter_id: u32) {
  54         self.info.num_counters = std::cmp::max(self.info.num_counters, counter_id + 1);
  55     }
  56
  57     /// Computes an expression index for each expression ID, and updates `num_expressions` to the
  58     /// maximum encountered index plus 1.
  59     #[inline(always)]
  60     fn update_num_expressions(&mut self, expression_id: u32) {
  61         let expression_index = u32::MAX - expression_id;
  62         self.info.num_expressions = std::cmp::max(self.info.num_expressions, expression_index + 1);
  63     }
  64
  65     fn update_from_expression_operand(&mut self, operand_id: u32) {
  66         if operand_id >= self.info.num_counters {
  67             let operand_as_expression_index = u32::MAX - operand_id;
  68             if operand_as_expression_index >= self.info.num_expressions {
  69                 // The operand ID is outside the known range of counter IDs and also outside the
  70                 // known range of expression IDs. In either case, the result of a missing operand
  71                 // (if and when used in an expression) will be zero, so from a computation
  72                 // perspective, it doesn't matter whether it is interepretted as a counter or an
  73                 // expression.
  74                 //
  75                 // However, the `num_counters` and `num_expressions` query results are used to
  76                 // allocate arrays when generating the coverage map (during codegen), so choose
  77                 // the type that grows either `num_counters` or `num_expressions` the least.
  78                 if operand_id - self.info.num_counters
  79                     < operand_as_expression_index - self.info.num_expressions
  80                 {
  81                     self.update_num_counters(operand_id)
  82                 } else {
  83                     self.update_num_expressions(operand_id)
  84                 }
  85             }
  86         }
  87     }
  88 }
  89
  90 impl Visitor<'_> for CoverageVisitor {
  91     fn visit_coverage(&mut self, coverage: &Coverage, _location: Location) {
  92         if self.add_missing_operands {
  93             match coverage.kind {
  94                 CoverageKind::Expression { lhs, rhs, .. } => {
  95                     self.update_from_expression_operand(u32::from(lhs));
  96                     self.update_from_expression_operand(u32::from(rhs));
  97                 }
  98                 _ => {}
  99             }
 100         } else {
 101             match coverage.kind {
 102                 CoverageKind::Counter { id, .. } => {
 103                     self.update_num_counters(u32::from(id));
 104                 }
 105                 CoverageKind::Expression { id, .. } => {
 106                     self.update_num_expressions(u32::from(id));
 107                 }
 108                 _ => {}
 109             }
 110         }
 111     }
 112 }
 113
 114 fn coverageinfo_from_mir<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> CoverageInfo {
 115     let mir_body = tcx.optimized_mir(def_id);
 116
 117     let mut coverage_visitor = CoverageVisitor {
 118         // num_counters always has at least the `ZERO` counter.
 119         info: CoverageInfo { num_counters: 1, num_expressions: 0 },
 120         add_missing_operands: false,
 121     };
 122
 123     coverage_visitor.visit_body(mir_body);
 124
 125     coverage_visitor.add_missing_operands = true;
 126     coverage_visitor.visit_body(mir_body);
 127
 128     coverage_visitor.info
 129 }
 130
 131 fn covered_file_name<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Option<Symbol> {
 132     let mir_body = tcx.optimized_mir(def_id);
 133     for bb_data in mir_body.basic_blocks().iter() {
 134         for statement in bb_data.statements.iter() {
 135             if let StatementKind::Coverage(box ref coverage) = statement.kind {
 136                 if let Some(code_region) = coverage.code_region.as_ref() {
 137                     return Some(code_region.file_name);
 138                 }
 139             }
 140         }
 141     }
 142     None
 143 }
 144
 145 fn covered_code_regions<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Vec<&'tcx CodeRegion> {
 146     let mir_body: &'tcx mir::Body<'tcx> = tcx.optimized_mir(def_id);
 147     mir_body
 148         .basic_blocks()
 149         .iter()
 150         .map(|data| {
 151             data.statements.iter().filter_map(|statement| match statement.kind {
 152                 StatementKind::Coverage(box ref coverage) => {
 153                     coverage.code_region.as_ref() // may be None
 154                 }
 155                 _ => None,
 156             })
 157         })
 158         .flatten()
 159         .collect()
 160 }