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use rustc_middle::mir::coverage::*;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::{Coverage, CoverageInfo, Location};
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::TyCtxt;
use rustc_span::def_id::DefId;
/// The `query` provider for `CoverageInfo`, requested by `codegen_coverage()` (to inject each
/// counter) and `FunctionCoverage::new()` (to extract the coverage map metadata from the MIR).
pub(crate) fn provide(providers: &mut Providers) {
providers.coverageinfo = |tcx, def_id| coverageinfo_from_mir(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 interepretted 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)
}
}
}
}
}
impl Visitor<'_> for CoverageVisitor {
fn visit_coverage(&mut self, coverage: &Coverage, _location: Location) {
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_from_mir<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> CoverageInfo {
let mir_body = tcx.optimized_mir(def_id);
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
}
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