768 lines
31 KiB
Rust
768 lines
31 KiB
Rust
use super::Error;
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use rustc_data_structures::fx::FxHashMap;
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use rustc_data_structures::graph::dominators::{self, Dominators};
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use rustc_data_structures::graph::{self, GraphSuccessors, WithNumNodes, WithStartNode};
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use rustc_index::bit_set::BitSet;
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use rustc_index::vec::IndexVec;
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use rustc_middle::mir::coverage::*;
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use rustc_middle::mir::{self, BasicBlock, BasicBlockData, Terminator, TerminatorKind};
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use std::ops::{Index, IndexMut};
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const ID_SEPARATOR: &str = ",";
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/// A coverage-specific simplification of the MIR control flow graph (CFG). The `CoverageGraph`s
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/// nodes are `BasicCoverageBlock`s, which encompass one or more MIR `BasicBlock`s, plus a
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/// `CoverageKind` counter (to be added by `CoverageCounters::make_bcb_counters`), and an optional
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/// set of additional counters--if needed--to count incoming edges, if there are more than one.
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/// (These "edge counters" are eventually converted into new MIR `BasicBlock`s.)
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#[derive(Debug)]
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pub(super) struct CoverageGraph {
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bcbs: IndexVec<BasicCoverageBlock, BasicCoverageBlockData>,
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bb_to_bcb: IndexVec<BasicBlock, Option<BasicCoverageBlock>>,
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pub successors: IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>>,
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pub predecessors: IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>>,
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dominators: Option<Dominators<BasicCoverageBlock>>,
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}
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impl CoverageGraph {
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pub fn from_mir(mir_body: &mir::Body<'tcx>) -> Self {
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let (bcbs, bb_to_bcb) = Self::compute_basic_coverage_blocks(mir_body);
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// Pre-transform MIR `BasicBlock` successors and predecessors into the BasicCoverageBlock
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// equivalents. Note that since the BasicCoverageBlock graph has been fully simplified, the
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// each predecessor of a BCB leader_bb should be in a unique BCB. It is possible for a
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// `SwitchInt` to have multiple targets to the same destination `BasicBlock`, so
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// de-duplication is required. This is done without reordering the successors.
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let bcbs_len = bcbs.len();
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let mut seen = IndexVec::from_elem_n(false, bcbs_len);
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let successors = IndexVec::from_fn_n(
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|bcb| {
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for b in seen.iter_mut() {
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*b = false;
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}
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let bcb_data = &bcbs[bcb];
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let mut bcb_successors = Vec::new();
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for successor in
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bcb_filtered_successors(&mir_body, &bcb_data.terminator(mir_body).kind)
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.filter_map(|&successor_bb| bb_to_bcb[successor_bb])
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{
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if !seen[successor] {
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seen[successor] = true;
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bcb_successors.push(successor);
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}
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}
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bcb_successors
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},
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bcbs.len(),
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);
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let mut predecessors = IndexVec::from_elem_n(Vec::new(), bcbs.len());
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for (bcb, bcb_successors) in successors.iter_enumerated() {
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for &successor in bcb_successors {
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predecessors[successor].push(bcb);
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}
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}
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let mut basic_coverage_blocks =
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Self { bcbs, bb_to_bcb, successors, predecessors, dominators: None };
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let dominators = dominators::dominators(&basic_coverage_blocks);
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basic_coverage_blocks.dominators = Some(dominators);
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basic_coverage_blocks
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}
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fn compute_basic_coverage_blocks(
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mir_body: &mir::Body<'tcx>,
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) -> (
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IndexVec<BasicCoverageBlock, BasicCoverageBlockData>,
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IndexVec<BasicBlock, Option<BasicCoverageBlock>>,
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) {
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let num_basic_blocks = mir_body.num_nodes();
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let mut bcbs = IndexVec::with_capacity(num_basic_blocks);
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let mut bb_to_bcb = IndexVec::from_elem_n(None, num_basic_blocks);
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// Walk the MIR CFG using a Preorder traversal, which starts from `START_BLOCK` and follows
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// each block terminator's `successors()`. Coverage spans must map to actual source code,
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// so compiler generated blocks and paths can be ignored. To that end, the CFG traversal
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// intentionally omits unwind paths.
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// FIXME(#78544): MIR InstrumentCoverage: Improve coverage of `#[should_panic]` tests and
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// `catch_unwind()` handlers.
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let mir_cfg_without_unwind = ShortCircuitPreorder::new(&mir_body, bcb_filtered_successors);
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let mut basic_blocks = Vec::new();
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for (bb, data) in mir_cfg_without_unwind {
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if let Some(last) = basic_blocks.last() {
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let predecessors = &mir_body.predecessors()[bb];
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if predecessors.len() > 1 || !predecessors.contains(last) {
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// The `bb` has more than one _incoming_ edge, and should start its own
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// `BasicCoverageBlockData`. (Note, the `basic_blocks` vector does not yet
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// include `bb`; it contains a sequence of one or more sequential basic_blocks
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// with no intermediate branches in or out. Save these as a new
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// `BasicCoverageBlockData` before starting the new one.)
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Self::add_basic_coverage_block(
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&mut bcbs,
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&mut bb_to_bcb,
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basic_blocks.split_off(0),
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);
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debug!(
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" because {}",
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if predecessors.len() > 1 {
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"predecessors.len() > 1".to_owned()
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} else {
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format!("bb {} is not in precessors: {:?}", bb.index(), predecessors)
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}
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);
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}
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}
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basic_blocks.push(bb);
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let term = data.terminator();
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match term.kind {
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TerminatorKind::Return { .. }
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| TerminatorKind::Abort
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| TerminatorKind::Yield { .. }
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| TerminatorKind::SwitchInt { .. } => {
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// The `bb` has more than one _outgoing_ edge, or exits the function. Save the
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// current sequence of `basic_blocks` gathered to this point, as a new
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// `BasicCoverageBlockData`.
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Self::add_basic_coverage_block(
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&mut bcbs,
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&mut bb_to_bcb,
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basic_blocks.split_off(0),
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);
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debug!(" because term.kind = {:?}", term.kind);
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// Note that this condition is based on `TerminatorKind`, even though it
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// theoretically boils down to `successors().len() != 1`; that is, either zero
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// (e.g., `Return`, `Abort`) or multiple successors (e.g., `SwitchInt`), but
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// since the BCB CFG ignores things like unwind branches (which exist in the
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// `Terminator`s `successors()` list) checking the number of successors won't
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// work.
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}
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// The following `TerminatorKind`s are either not expected outside an unwind branch,
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// or they should not (under normal circumstances) branch. Coverage graphs are
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// simplified by assuring coverage results are accurate for program executions that
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// don't panic.
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//
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// Programs that panic and unwind may record slightly inaccurate coverage results
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// for a coverage region containing the `Terminator` that began the panic. This
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// is as intended. (See Issue #78544 for a possible future option to support
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// coverage in test programs that panic.)
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TerminatorKind::Goto { .. }
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| TerminatorKind::Resume
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| TerminatorKind::Unreachable
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| TerminatorKind::Drop { .. }
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| TerminatorKind::DropAndReplace { .. }
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| TerminatorKind::Call { .. }
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| TerminatorKind::GeneratorDrop
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| TerminatorKind::Assert { .. }
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| TerminatorKind::FalseEdge { .. }
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| TerminatorKind::FalseUnwind { .. }
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| TerminatorKind::InlineAsm { .. } => {}
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}
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}
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if !basic_blocks.is_empty() {
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// process any remaining basic_blocks into a final `BasicCoverageBlockData`
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Self::add_basic_coverage_block(&mut bcbs, &mut bb_to_bcb, basic_blocks.split_off(0));
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debug!(" because the end of the MIR CFG was reached while traversing");
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}
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(bcbs, bb_to_bcb)
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}
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fn add_basic_coverage_block(
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bcbs: &mut IndexVec<BasicCoverageBlock, BasicCoverageBlockData>,
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bb_to_bcb: &mut IndexVec<BasicBlock, Option<BasicCoverageBlock>>,
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basic_blocks: Vec<BasicBlock>,
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) {
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let bcb = BasicCoverageBlock::from_usize(bcbs.len());
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for &bb in basic_blocks.iter() {
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bb_to_bcb[bb] = Some(bcb);
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}
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let bcb_data = BasicCoverageBlockData::from(basic_blocks);
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debug!("adding bcb{}: {:?}", bcb.index(), bcb_data);
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bcbs.push(bcb_data);
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}
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#[inline(always)]
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pub fn iter_enumerated(
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&self,
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) -> impl Iterator<Item = (BasicCoverageBlock, &BasicCoverageBlockData)> {
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self.bcbs.iter_enumerated()
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}
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#[inline(always)]
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pub fn iter_enumerated_mut(
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&mut self,
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) -> impl Iterator<Item = (BasicCoverageBlock, &mut BasicCoverageBlockData)> {
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self.bcbs.iter_enumerated_mut()
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}
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#[inline(always)]
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pub fn bcb_from_bb(&self, bb: BasicBlock) -> Option<BasicCoverageBlock> {
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if bb.index() < self.bb_to_bcb.len() { self.bb_to_bcb[bb] } else { None }
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}
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#[inline(always)]
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pub fn is_dominated_by(&self, node: BasicCoverageBlock, dom: BasicCoverageBlock) -> bool {
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self.dominators.as_ref().unwrap().is_dominated_by(node, dom)
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}
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#[inline(always)]
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pub fn dominators(&self) -> &Dominators<BasicCoverageBlock> {
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self.dominators.as_ref().unwrap()
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}
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}
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impl Index<BasicCoverageBlock> for CoverageGraph {
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type Output = BasicCoverageBlockData;
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#[inline]
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fn index(&self, index: BasicCoverageBlock) -> &BasicCoverageBlockData {
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&self.bcbs[index]
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}
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}
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impl IndexMut<BasicCoverageBlock> for CoverageGraph {
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#[inline]
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fn index_mut(&mut self, index: BasicCoverageBlock) -> &mut BasicCoverageBlockData {
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&mut self.bcbs[index]
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}
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}
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impl graph::DirectedGraph for CoverageGraph {
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type Node = BasicCoverageBlock;
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}
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impl graph::WithNumNodes for CoverageGraph {
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#[inline]
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fn num_nodes(&self) -> usize {
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self.bcbs.len()
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}
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}
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impl graph::WithStartNode for CoverageGraph {
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#[inline]
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fn start_node(&self) -> Self::Node {
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self.bcb_from_bb(mir::START_BLOCK)
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.expect("mir::START_BLOCK should be in a BasicCoverageBlock")
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}
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}
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type BcbSuccessors<'graph> = std::slice::Iter<'graph, BasicCoverageBlock>;
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impl<'graph> graph::GraphSuccessors<'graph> for CoverageGraph {
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type Item = BasicCoverageBlock;
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type Iter = std::iter::Cloned<BcbSuccessors<'graph>>;
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}
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impl graph::WithSuccessors for CoverageGraph {
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#[inline]
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fn successors(&self, node: Self::Node) -> <Self as GraphSuccessors<'_>>::Iter {
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self.successors[node].iter().cloned()
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}
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}
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impl graph::GraphPredecessors<'graph> for CoverageGraph {
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type Item = BasicCoverageBlock;
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type Iter = std::vec::IntoIter<BasicCoverageBlock>;
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}
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impl graph::WithPredecessors for CoverageGraph {
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#[inline]
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fn predecessors(&self, node: Self::Node) -> <Self as graph::GraphPredecessors<'_>>::Iter {
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self.predecessors[node].clone().into_iter()
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}
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}
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rustc_index::newtype_index! {
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/// A node in the [control-flow graph][CFG] of CoverageGraph.
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pub(super) struct BasicCoverageBlock {
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DEBUG_FORMAT = "bcb{}",
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const START_BCB = 0,
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}
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}
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/// `BasicCoverageBlockData` holds the data indexed by a `BasicCoverageBlock`.
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///
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/// A `BasicCoverageBlock` (BCB) represents the maximal-length sequence of MIR `BasicBlock`s without
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/// conditional branches, and form a new, simplified, coverage-specific Control Flow Graph, without
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/// altering the original MIR CFG.
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///
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/// Note that running the MIR `SimplifyCfg` transform is not sufficient (and therefore not
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/// necessary). The BCB-based CFG is a more aggressive simplification. For example:
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///
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/// * The BCB CFG ignores (trims) branches not relevant to coverage, such as unwind-related code,
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/// that is injected by the Rust compiler but has no physical source code to count. This also
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/// means a BasicBlock with a `Call` terminator can be merged into its primary successor target
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/// block, in the same BCB. (But, note: Issue #78544: "MIR InstrumentCoverage: Improve coverage
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/// of `#[should_panic]` tests and `catch_unwind()` handlers")
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/// * Some BasicBlock terminators support Rust-specific concerns--like borrow-checking--that are
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/// not relevant to coverage analysis. `FalseUnwind`, for example, can be treated the same as
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/// a `Goto`, and merged with its successor into the same BCB.
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///
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/// Each BCB with at least one computed `CoverageSpan` will have no more than one `Counter`.
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/// In some cases, a BCB's execution count can be computed by `Expression`. Additional
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/// disjoint `CoverageSpan`s in a BCB can also be counted by `Expression` (by adding `ZERO`
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/// to the BCB's primary counter or expression).
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///
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/// The BCB CFG is critical to simplifying the coverage analysis by ensuring graph path-based
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/// queries (`is_dominated_by()`, `predecessors`, `successors`, etc.) have branch (control flow)
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/// significance.
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#[derive(Debug, Clone)]
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pub(super) struct BasicCoverageBlockData {
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pub basic_blocks: Vec<BasicBlock>,
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pub counter_kind: Option<CoverageKind>,
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edge_from_bcbs: Option<FxHashMap<BasicCoverageBlock, CoverageKind>>,
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}
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impl BasicCoverageBlockData {
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pub fn from(basic_blocks: Vec<BasicBlock>) -> Self {
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assert!(basic_blocks.len() > 0);
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Self { basic_blocks, counter_kind: None, edge_from_bcbs: None }
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}
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#[inline(always)]
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pub fn leader_bb(&self) -> BasicBlock {
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self.basic_blocks[0]
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}
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#[inline(always)]
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pub fn last_bb(&self) -> BasicBlock {
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*self.basic_blocks.last().unwrap()
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}
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#[inline(always)]
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pub fn terminator<'a, 'tcx>(&self, mir_body: &'a mir::Body<'tcx>) -> &'a Terminator<'tcx> {
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&mir_body[self.last_bb()].terminator()
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}
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pub fn set_counter(
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&mut self,
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counter_kind: CoverageKind,
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) -> Result<ExpressionOperandId, Error> {
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debug_assert!(
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// If the BCB has an edge counter (to be injected into a new `BasicBlock`), it can also
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// have an expression (to be injected into an existing `BasicBlock` represented by this
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// `BasicCoverageBlock`).
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self.edge_from_bcbs.is_none() || counter_kind.is_expression(),
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"attempt to add a `Counter` to a BCB target with existing incoming edge counters"
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);
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let operand = counter_kind.as_operand_id();
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if let Some(replaced) = self.counter_kind.replace(counter_kind) {
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Error::from_string(format!(
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"attempt to set a BasicCoverageBlock coverage counter more than once; \
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{:?} already had counter {:?}",
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self, replaced,
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))
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} else {
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Ok(operand)
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}
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}
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#[inline(always)]
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pub fn counter(&self) -> Option<&CoverageKind> {
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self.counter_kind.as_ref()
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}
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#[inline(always)]
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pub fn take_counter(&mut self) -> Option<CoverageKind> {
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self.counter_kind.take()
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}
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pub fn set_edge_counter_from(
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&mut self,
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from_bcb: BasicCoverageBlock,
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counter_kind: CoverageKind,
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) -> Result<ExpressionOperandId, Error> {
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if level_enabled!(tracing::Level::DEBUG) {
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// If the BCB has an edge counter (to be injected into a new `BasicBlock`), it can also
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// have an expression (to be injected into an existing `BasicBlock` represented by this
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// `BasicCoverageBlock`).
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if !self.counter_kind.as_ref().map_or(true, |c| c.is_expression()) {
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return Error::from_string(format!(
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"attempt to add an incoming edge counter from {:?} when the target BCB already \
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has a `Counter`",
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from_bcb
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));
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}
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}
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let operand = counter_kind.as_operand_id();
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if let Some(replaced) = self
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.edge_from_bcbs
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.get_or_insert_with(FxHashMap::default)
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.insert(from_bcb, counter_kind)
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{
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Error::from_string(format!(
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"attempt to set an edge counter more than once; from_bcb: \
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{:?} already had counter {:?}",
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from_bcb, replaced,
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))
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} else {
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Ok(operand)
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}
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}
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#[inline]
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pub fn edge_counter_from(&self, from_bcb: BasicCoverageBlock) -> Option<&CoverageKind> {
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if let Some(edge_from_bcbs) = &self.edge_from_bcbs {
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edge_from_bcbs.get(&from_bcb)
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} else {
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None
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}
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}
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#[inline]
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pub fn take_edge_counters(
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&mut self,
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) -> Option<impl Iterator<Item = (BasicCoverageBlock, CoverageKind)>> {
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self.edge_from_bcbs.take().map_or(None, |m| Some(m.into_iter()))
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}
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pub fn id(&self) -> String {
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format!(
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"@{}",
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self.basic_blocks
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.iter()
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.map(|bb| bb.index().to_string())
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.collect::<Vec<_>>()
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.join(ID_SEPARATOR)
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)
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}
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}
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/// Represents a successor from a branching BasicCoverageBlock (such as the arms of a `SwitchInt`)
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/// as either the successor BCB itself, if it has only one incoming edge, or the successor _plus_
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/// the specific branching BCB, representing the edge between the two. The latter case
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/// distinguishes this incoming edge from other incoming edges to the same `target_bcb`.
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#[derive(Clone, Copy, PartialEq, Eq)]
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pub(super) struct BcbBranch {
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pub edge_from_bcb: Option<BasicCoverageBlock>,
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pub target_bcb: BasicCoverageBlock,
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}
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impl BcbBranch {
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pub fn from_to(
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from_bcb: BasicCoverageBlock,
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to_bcb: BasicCoverageBlock,
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basic_coverage_blocks: &CoverageGraph,
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) -> Self {
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let edge_from_bcb = if basic_coverage_blocks.predecessors[to_bcb].len() > 1 {
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Some(from_bcb)
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} else {
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None
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};
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Self { edge_from_bcb, target_bcb: to_bcb }
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}
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pub fn counter<'a>(
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&self,
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basic_coverage_blocks: &'a CoverageGraph,
|
|
) -> Option<&'a CoverageKind> {
|
|
if let Some(from_bcb) = self.edge_from_bcb {
|
|
basic_coverage_blocks[self.target_bcb].edge_counter_from(from_bcb)
|
|
} else {
|
|
basic_coverage_blocks[self.target_bcb].counter()
|
|
}
|
|
}
|
|
|
|
pub fn is_only_path_to_target(&self) -> bool {
|
|
self.edge_from_bcb.is_none()
|
|
}
|
|
}
|
|
|
|
impl std::fmt::Debug for BcbBranch {
|
|
fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
|
|
if let Some(from_bcb) = self.edge_from_bcb {
|
|
write!(fmt, "{:?}->{:?}", from_bcb, self.target_bcb)
|
|
} else {
|
|
write!(fmt, "{:?}", self.target_bcb)
|
|
}
|
|
}
|
|
}
|
|
|
|
// Returns the `Terminator`s non-unwind successors.
|
|
// FIXME(#78544): MIR InstrumentCoverage: Improve coverage of `#[should_panic]` tests and
|
|
// `catch_unwind()` handlers.
|
|
fn bcb_filtered_successors<'a, 'tcx>(
|
|
body: &'tcx &'a mir::Body<'tcx>,
|
|
term_kind: &'tcx TerminatorKind<'tcx>,
|
|
) -> Box<dyn Iterator<Item = &'a BasicBlock> + 'a> {
|
|
let mut successors = term_kind.successors();
|
|
box match &term_kind {
|
|
// SwitchInt successors are never unwind, and all of them should be traversed.
|
|
TerminatorKind::SwitchInt { .. } => successors,
|
|
// For all other kinds, return only the first successor, if any, and ignore unwinds.
|
|
// NOTE: `chain(&[])` is required to coerce the `option::iter` (from
|
|
// `next().into_iter()`) into the `mir::Successors` aliased type.
|
|
_ => successors.next().into_iter().chain(&[]),
|
|
}
|
|
.filter(move |&&successor| body[successor].terminator().kind != TerminatorKind::Unreachable)
|
|
}
|
|
|
|
/// Maintains separate worklists for each loop in the BasicCoverageBlock CFG, plus one for the
|
|
/// CoverageGraph outside all loops. This supports traversing the BCB CFG in a way that
|
|
/// ensures a loop is completely traversed before processing Blocks after the end of the loop.
|
|
#[derive(Debug)]
|
|
pub(super) struct TraversalContext {
|
|
/// From one or more backedges returning to a loop header.
|
|
pub loop_backedges: Option<(Vec<BasicCoverageBlock>, BasicCoverageBlock)>,
|
|
|
|
/// worklist, to be traversed, of CoverageGraph in the loop with the given loop
|
|
/// backedges, such that the loop is the inner inner-most loop containing these
|
|
/// CoverageGraph
|
|
pub worklist: Vec<BasicCoverageBlock>,
|
|
}
|
|
|
|
pub(super) struct TraverseCoverageGraphWithLoops {
|
|
pub backedges: IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>>,
|
|
pub context_stack: Vec<TraversalContext>,
|
|
visited: BitSet<BasicCoverageBlock>,
|
|
}
|
|
|
|
impl TraverseCoverageGraphWithLoops {
|
|
pub fn new(basic_coverage_blocks: &CoverageGraph) -> Self {
|
|
let start_bcb = basic_coverage_blocks.start_node();
|
|
let backedges = find_loop_backedges(basic_coverage_blocks);
|
|
let mut context_stack = Vec::new();
|
|
context_stack.push(TraversalContext { loop_backedges: None, worklist: vec![start_bcb] });
|
|
// `context_stack` starts with a `TraversalContext` for the main function context (beginning
|
|
// with the `start` BasicCoverageBlock of the function). New worklists are pushed to the top
|
|
// of the stack as loops are entered, and popped off of the stack when a loop's worklist is
|
|
// exhausted.
|
|
let visited = BitSet::new_empty(basic_coverage_blocks.num_nodes());
|
|
Self { backedges, context_stack, visited }
|
|
}
|
|
|
|
pub fn next(&mut self, basic_coverage_blocks: &CoverageGraph) -> Option<BasicCoverageBlock> {
|
|
debug!(
|
|
"TraverseCoverageGraphWithLoops::next - context_stack: {:?}",
|
|
self.context_stack.iter().rev().collect::<Vec<_>>()
|
|
);
|
|
while let Some(next_bcb) = {
|
|
// Strip contexts with empty worklists from the top of the stack
|
|
while self.context_stack.last().map_or(false, |context| context.worklist.is_empty()) {
|
|
self.context_stack.pop();
|
|
}
|
|
// Pop the next bcb off of the current context_stack. If none, all BCBs were visited.
|
|
self.context_stack.last_mut().map_or(None, |context| context.worklist.pop())
|
|
} {
|
|
if !self.visited.insert(next_bcb) {
|
|
debug!("Already visited: {:?}", next_bcb);
|
|
continue;
|
|
}
|
|
debug!("Visiting {:?}", next_bcb);
|
|
if self.backedges[next_bcb].len() > 0 {
|
|
debug!("{:?} is a loop header! Start a new TraversalContext...", next_bcb);
|
|
self.context_stack.push(TraversalContext {
|
|
loop_backedges: Some((self.backedges[next_bcb].clone(), next_bcb)),
|
|
worklist: Vec::new(),
|
|
});
|
|
}
|
|
self.extend_worklist(basic_coverage_blocks, next_bcb);
|
|
return Some(next_bcb);
|
|
}
|
|
None
|
|
}
|
|
|
|
pub fn extend_worklist(
|
|
&mut self,
|
|
basic_coverage_blocks: &CoverageGraph,
|
|
bcb: BasicCoverageBlock,
|
|
) {
|
|
let successors = &basic_coverage_blocks.successors[bcb];
|
|
debug!("{:?} has {} successors:", bcb, successors.len());
|
|
for &successor in successors {
|
|
if successor == bcb {
|
|
debug!(
|
|
"{:?} has itself as its own successor. (Note, the compiled code will \
|
|
generate an infinite loop.)",
|
|
bcb
|
|
);
|
|
// Don't re-add this successor to the worklist. We are already processing it.
|
|
break;
|
|
}
|
|
for context in self.context_stack.iter_mut().rev() {
|
|
// Add successors of the current BCB to the appropriate context. Successors that
|
|
// stay within a loop are added to the BCBs context worklist. Successors that
|
|
// exit the loop (they are not dominated by the loop header) must be reachable
|
|
// from other BCBs outside the loop, and they will be added to a different
|
|
// worklist.
|
|
//
|
|
// Branching blocks (with more than one successor) must be processed before
|
|
// blocks with only one successor, to prevent unnecessarily complicating
|
|
// `Expression`s by creating a Counter in a `BasicCoverageBlock` that the
|
|
// branching block would have given an `Expression` (or vice versa).
|
|
let (some_successor_to_add, some_loop_header) =
|
|
if let Some((_, loop_header)) = context.loop_backedges {
|
|
if basic_coverage_blocks.is_dominated_by(successor, loop_header) {
|
|
(Some(successor), Some(loop_header))
|
|
} else {
|
|
(None, None)
|
|
}
|
|
} else {
|
|
(Some(successor), None)
|
|
};
|
|
if let Some(successor_to_add) = some_successor_to_add {
|
|
if basic_coverage_blocks.successors[successor_to_add].len() > 1 {
|
|
debug!(
|
|
"{:?} successor is branching. Prioritize it at the beginning of \
|
|
the {}",
|
|
successor_to_add,
|
|
if let Some(loop_header) = some_loop_header {
|
|
format!("worklist for the loop headed by {:?}", loop_header)
|
|
} else {
|
|
String::from("non-loop worklist")
|
|
},
|
|
);
|
|
context.worklist.insert(0, successor_to_add);
|
|
} else {
|
|
debug!(
|
|
"{:?} successor is non-branching. Defer it to the end of the {}",
|
|
successor_to_add,
|
|
if let Some(loop_header) = some_loop_header {
|
|
format!("worklist for the loop headed by {:?}", loop_header)
|
|
} else {
|
|
String::from("non-loop worklist")
|
|
},
|
|
);
|
|
context.worklist.push(successor_to_add);
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
pub fn is_complete(&self) -> bool {
|
|
self.visited.count() == self.visited.domain_size()
|
|
}
|
|
|
|
pub fn unvisited(&self) -> Vec<BasicCoverageBlock> {
|
|
let mut unvisited_set: BitSet<BasicCoverageBlock> =
|
|
BitSet::new_filled(self.visited.domain_size());
|
|
unvisited_set.subtract(&self.visited);
|
|
unvisited_set.iter().collect::<Vec<_>>()
|
|
}
|
|
}
|
|
|
|
pub(super) fn find_loop_backedges(
|
|
basic_coverage_blocks: &CoverageGraph,
|
|
) -> IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>> {
|
|
let num_bcbs = basic_coverage_blocks.num_nodes();
|
|
let mut backedges = IndexVec::from_elem_n(Vec::<BasicCoverageBlock>::new(), num_bcbs);
|
|
|
|
// Identify loops by their backedges.
|
|
//
|
|
// The computational complexity is bounded by: n(s) x d where `n` is the number of
|
|
// `BasicCoverageBlock` nodes (the simplified/reduced representation of the CFG derived from the
|
|
// MIR); `s` is the average number of successors per node (which is most likely less than 2, and
|
|
// independent of the size of the function, so it can be treated as a constant);
|
|
// and `d` is the average number of dominators per node.
|
|
//
|
|
// The average number of dominators depends on the size and complexity of the function, and
|
|
// nodes near the start of the function's control flow graph typically have less dominators
|
|
// than nodes near the end of the CFG. Without doing a detailed mathematical analysis, I
|
|
// think the resulting complexity has the characteristics of O(n log n).
|
|
//
|
|
// The overall complexity appears to be comparable to many other MIR transform algorithms, and I
|
|
// don't expect that this function is creating a performance hot spot, but if this becomes an
|
|
// issue, there may be ways to optimize the `is_dominated_by` algorithm (as indicated by an
|
|
// existing `FIXME` comment in that code), or possibly ways to optimize it's usage here, perhaps
|
|
// by keeping track of results for visited `BasicCoverageBlock`s if they can be used to short
|
|
// circuit downstream `is_dominated_by` checks.
|
|
//
|
|
// For now, that kind of optimization seems unnecessarily complicated.
|
|
for (bcb, _) in basic_coverage_blocks.iter_enumerated() {
|
|
for &successor in &basic_coverage_blocks.successors[bcb] {
|
|
if basic_coverage_blocks.is_dominated_by(bcb, successor) {
|
|
let loop_header = successor;
|
|
let backedge_from_bcb = bcb;
|
|
debug!(
|
|
"Found BCB backedge: {:?} -> loop_header: {:?}",
|
|
backedge_from_bcb, loop_header
|
|
);
|
|
backedges[loop_header].push(backedge_from_bcb);
|
|
}
|
|
}
|
|
}
|
|
backedges
|
|
}
|
|
|
|
pub struct ShortCircuitPreorder<
|
|
'a,
|
|
'tcx,
|
|
F: Fn(
|
|
&'tcx &'a mir::Body<'tcx>,
|
|
&'tcx TerminatorKind<'tcx>,
|
|
) -> Box<dyn Iterator<Item = &'a BasicBlock> + 'a>,
|
|
> {
|
|
body: &'tcx &'a mir::Body<'tcx>,
|
|
visited: BitSet<BasicBlock>,
|
|
worklist: Vec<BasicBlock>,
|
|
filtered_successors: F,
|
|
}
|
|
|
|
impl<
|
|
'a,
|
|
'tcx,
|
|
F: Fn(
|
|
&'tcx &'a mir::Body<'tcx>,
|
|
&'tcx TerminatorKind<'tcx>,
|
|
) -> Box<dyn Iterator<Item = &'a BasicBlock> + 'a>,
|
|
> ShortCircuitPreorder<'a, 'tcx, F>
|
|
{
|
|
pub fn new(
|
|
body: &'tcx &'a mir::Body<'tcx>,
|
|
filtered_successors: F,
|
|
) -> ShortCircuitPreorder<'a, 'tcx, F> {
|
|
let worklist = vec![mir::START_BLOCK];
|
|
|
|
ShortCircuitPreorder {
|
|
body,
|
|
visited: BitSet::new_empty(body.basic_blocks().len()),
|
|
worklist,
|
|
filtered_successors,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<
|
|
'a: 'tcx,
|
|
'tcx,
|
|
F: Fn(
|
|
&'tcx &'a mir::Body<'tcx>,
|
|
&'tcx TerminatorKind<'tcx>,
|
|
) -> Box<dyn Iterator<Item = &'a BasicBlock> + 'a>,
|
|
> Iterator for ShortCircuitPreorder<'a, 'tcx, F>
|
|
{
|
|
type Item = (BasicBlock, &'a BasicBlockData<'tcx>);
|
|
|
|
fn next(&mut self) -> Option<(BasicBlock, &'a BasicBlockData<'tcx>)> {
|
|
while let Some(idx) = self.worklist.pop() {
|
|
if !self.visited.insert(idx) {
|
|
continue;
|
|
}
|
|
|
|
let data = &self.body[idx];
|
|
|
|
if let Some(ref term) = data.terminator {
|
|
self.worklist.extend((self.filtered_successors)(&self.body, &term.kind));
|
|
}
|
|
|
|
return Some((idx, data));
|
|
}
|
|
|
|
None
|
|
}
|
|
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
let size = self.body.basic_blocks().len() - self.visited.count();
|
|
(size, Some(size))
|
|
}
|
|
}
|