1 files changed, 170 insertions, 0 deletions
diff --git a/compiler/rustc_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
new file mode 100644
index 000000000..9d02f58ae
--- /dev/null
+++ b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -0,0 +1,170 @@
+use super::*;
+
+use rustc_middle::mir::coverage::*;
+use rustc_middle::mir::{self, Body, Coverage, CoverageInfo};
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::{self, TyCtxt};
+use rustc_span::def_id::DefId;
+
+/// A `query` provider for retrieving coverage information injected into MIR.
+pub(crate) fn provide(providers: &mut Providers) {
+    providers.coverageinfo = |tcx, def_id| coverageinfo(tcx, def_id);
+    providers.covered_code_regions = |tcx, def_id| covered_code_regions(tcx, def_id);
+}
+
+/// The `num_counters` argument to `llvm.instrprof.increment` is the max counter_id + 1, or in
+/// other words, the number of counter value references injected into the MIR (plus 1 for the
+/// reserved `ZERO` counter, which uses counter ID `0` when included in an expression). Injected
+/// counters have a counter ID from `1..num_counters-1`.
+///
+/// `num_expressions` is the number of counter expressions added to the MIR body.
+///
+/// Both `num_counters` and `num_expressions` are used to initialize new vectors, during backend
+/// code generate, to lookup counters and expressions by simple u32 indexes.
+///
+/// MIR optimization may split and duplicate some BasicBlock sequences, or optimize out some code
+/// including injected counters. (It is OK if some counters are optimized out, but those counters
+/// are still included in the total `num_counters` or `num_expressions`.) Simply counting the
+/// calls may not work; but computing the number of counters or expressions by adding `1` to the
+/// highest ID (for a given instrumented function) is valid.
+///
+/// This visitor runs twice, first with `add_missing_operands` set to `false`, to find the maximum
+/// counter ID and maximum expression ID based on their enum variant `id` fields; then, as a
+/// safeguard, with `add_missing_operands` set to `true`, to find any other counter or expression
+/// IDs referenced by expression operands, if not already seen.
+///
+/// Ideally, each operand ID in a MIR `CoverageKind::Expression` will have a separate MIR `Coverage`
+/// statement for the `Counter` or `Expression` with the referenced ID. but since current or future
+/// MIR optimizations can theoretically optimize out segments of a MIR, it may not be possible to
+/// guarantee this, so the second pass ensures the `CoverageInfo` counts include all referenced IDs.
+struct CoverageVisitor {
+    info: CoverageInfo,
+    add_missing_operands: bool,
+}
+
+impl CoverageVisitor {
+    /// Updates `num_counters` to the maximum encountered zero-based counter_id plus 1. Note the
+    /// final computed number of counters should be the number of all `CoverageKind::Counter`
+    /// statements in the MIR *plus one* for the implicit `ZERO` counter.
+    #[inline(always)]
+    fn update_num_counters(&mut self, counter_id: u32) {
+        self.info.num_counters = std::cmp::max(self.info.num_counters, counter_id + 1);
+    }
+
+    /// Computes an expression index for each expression ID, and updates `num_expressions` to the
+    /// maximum encountered index plus 1.
+    #[inline(always)]
+    fn update_num_expressions(&mut self, expression_id: u32) {
+        let expression_index = u32::MAX - expression_id;
+        self.info.num_expressions = std::cmp::max(self.info.num_expressions, expression_index + 1);
+    }
+
+    fn update_from_expression_operand(&mut self, operand_id: u32) {
+        if operand_id >= self.info.num_counters {
+            let operand_as_expression_index = u32::MAX - operand_id;
+            if operand_as_expression_index >= self.info.num_expressions {
+                // The operand ID is outside the known range of counter IDs and also outside the
+                // known range of expression IDs. In either case, the result of a missing operand
+                // (if and when used in an expression) will be zero, so from a computation
+                // perspective, it doesn't matter whether it is interpreted as a counter or an
+                // expression.
+                //
+                // However, the `num_counters` and `num_expressions` query results are used to
+                // allocate arrays when generating the coverage map (during codegen), so choose
+                // the type that grows either `num_counters` or `num_expressions` the least.
+                if operand_id - self.info.num_counters
+                    < operand_as_expression_index - self.info.num_expressions
+                {
+                    self.update_num_counters(operand_id)
+                } else {
+                    self.update_num_expressions(operand_id)
+                }
+            }
+        }
+    }
+
+    fn visit_body(&mut self, body: &Body<'_>) {
+        for bb_data in body.basic_blocks().iter() {
+            for statement in bb_data.statements.iter() {
+                if let StatementKind::Coverage(box ref coverage) = statement.kind {
+                    if is_inlined(body, statement) {
+                        continue;
+                    }
+                    self.visit_coverage(coverage);
+                }
+            }
+        }
+    }
+
+    fn visit_coverage(&mut self, coverage: &Coverage) {
+        if self.add_missing_operands {
+            match coverage.kind {
+                CoverageKind::Expression { lhs, rhs, .. } => {
+                    self.update_from_expression_operand(u32::from(lhs));
+                    self.update_from_expression_operand(u32::from(rhs));
+                }
+                _ => {}
+            }
+        } else {
+            match coverage.kind {
+                CoverageKind::Counter { id, .. } => {
+                    self.update_num_counters(u32::from(id));
+                }
+                CoverageKind::Expression { id, .. } => {
+                    self.update_num_expressions(u32::from(id));
+                }
+                _ => {}
+            }
+        }
+    }
+}
+
+fn coverageinfo<'tcx>(tcx: TyCtxt<'tcx>, instance_def: ty::InstanceDef<'tcx>) -> CoverageInfo {
+    let mir_body = tcx.instance_mir(instance_def);
+
+    let mut coverage_visitor = CoverageVisitor {
+        // num_counters always has at least the `ZERO` counter.
+        info: CoverageInfo { num_counters: 1, num_expressions: 0 },
+        add_missing_operands: false,
+    };
+
+    coverage_visitor.visit_body(mir_body);
+
+    coverage_visitor.add_missing_operands = true;
+    coverage_visitor.visit_body(mir_body);
+
+    coverage_visitor.info
+}
+
+fn covered_code_regions<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Vec<&'tcx CodeRegion> {
+    let body = mir_body(tcx, def_id);
+    body.basic_blocks()
+        .iter()
+        .flat_map(|data| {
+            data.statements.iter().filter_map(|statement| match statement.kind {
+                StatementKind::Coverage(box ref coverage) => {
+                    if is_inlined(body, statement) {
+                        None
+                    } else {
+                        coverage.code_region.as_ref() // may be None
+                    }
+                }
+                _ => None,
+            })
+        })
+        .collect()
+}
+
+fn is_inlined(body: &Body<'_>, statement: &Statement<'_>) -> bool {
+    let scope_data = &body.source_scopes[statement.source_info.scope];
+    scope_data.inlined.is_some() || scope_data.inlined_parent_scope.is_some()
+}
+
+/// This function ensures we obtain the correct MIR for the given item irrespective of
+/// whether that means const mir or runtime mir. For `const fn` this opts for runtime
+/// mir.
+fn mir_body<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx mir::Body<'tcx> {
+    let id = ty::WithOptConstParam::unknown(def_id);
+    let def = ty::InstanceDef::Item(id);
+    tcx.instance_mir(def)
+}