diff options
Diffstat (limited to 'compiler/rustc_mir/src/transform/coverage/counters.rs')
| -rw-r--r-- | compiler/rustc_mir/src/transform/coverage/counters.rs | 524 |
1 files changed, 521 insertions, 3 deletions
diff --git a/compiler/rustc_mir/src/transform/coverage/counters.rs b/compiler/rustc_mir/src/transform/coverage/counters.rs index c31f401780e..a3ae3021524 100644 --- a/compiler/rustc_mir/src/transform/coverage/counters.rs +++ b/compiler/rustc_mir/src/transform/coverage/counters.rs @@ -1,7 +1,15 @@ +use super::Error; + use super::debug; +use super::graph; +use super::spans; -use debug::DebugCounters; +use debug::{DebugCounters, NESTED_INDENT}; +use graph::{BasicCoverageBlock, BcbBranch, CoverageGraph, TraverseCoverageGraphWithLoops}; +use spans::CoverageSpan; +use rustc_data_structures::graph::WithNumNodes; +use rustc_index::bit_set::BitSet; use rustc_middle::mir::coverage::*; /// Manages the counter and expression indexes/IDs to generate `CoverageKind` components for MIR @@ -29,7 +37,19 @@ impl CoverageCounters { self.debug_counters.enable(); } - pub fn make_counter<F>(&mut self, debug_block_label_fn: F) -> CoverageKind + /// Makes `CoverageKind` `Counter`s and `Expressions` for the `BasicCoverageBlocks` directly or + /// indirectly associated with `CoverageSpans`, and returns additional `Expression`s + /// representing intermediate values. + pub fn make_bcb_counters( + &mut self, + basic_coverage_blocks: &mut CoverageGraph, + coverage_spans: &Vec<CoverageSpan>, + ) -> Result<Vec<CoverageKind>, Error> { + let mut bcb_counters = BcbCounters::new(self, basic_coverage_blocks); + bcb_counters.make_bcb_counters(coverage_spans) + } + + fn make_counter<F>(&mut self, debug_block_label_fn: F) -> CoverageKind where F: Fn() -> Option<String>, { @@ -43,7 +63,7 @@ impl CoverageCounters { counter } - pub fn make_expression<F>( + fn make_expression<F>( &mut self, lhs: ExpressionOperandId, op: Op, @@ -61,6 +81,17 @@ impl CoverageCounters { expression } + pub fn make_identity_counter(&mut self, counter_operand: ExpressionOperandId) -> CoverageKind { + let some_debug_block_label = if self.debug_counters.is_enabled() { + self.debug_counters.some_block_label(counter_operand).cloned() + } else { + None + }; + self.make_expression(counter_operand, Op::Add, ExpressionOperandId::ZERO, || { + some_debug_block_label.clone() + }) + } + /// Counter IDs start from one and go up. fn next_counter(&mut self) -> CounterValueReference { assert!(self.next_counter_id < u32::MAX - self.num_expressions); @@ -79,3 +110,490 @@ impl CoverageCounters { InjectedExpressionId::from(next) } } + +/// Traverse the `CoverageGraph` and add either a `Counter` or `Expression` to every BCB, to be +/// injected with `CoverageSpan`s. `Expressions` have no runtime overhead, so if a viable expression +/// (adding or subtracting two other counters or expressions) can compute the same result as an +/// embedded counter, an `Expression` should be used. +struct BcbCounters<'a> { + coverage_counters: &'a mut CoverageCounters, + basic_coverage_blocks: &'a mut CoverageGraph, +} + +impl<'a> BcbCounters<'a> { + fn new( + coverage_counters: &'a mut CoverageCounters, + basic_coverage_blocks: &'a mut CoverageGraph, + ) -> Self { + Self { coverage_counters, basic_coverage_blocks } + } + + /// If two `CoverageGraph` branch from another `BasicCoverageBlock`, one of the branches + /// can be counted by `Expression` by subtracting the other branch from the branching + /// block. Otherwise, the `BasicCoverageBlock` executed the least should have the `Counter`. + /// One way to predict which branch executes the least is by considering loops. A loop is exited + /// at a branch, so the branch that jumps to a `BasicCoverageBlock` outside the loop is almost + /// always executed less than the branch that does not exit the loop. + /// + /// Returns any non-code-span expressions created to represent intermediate values (such as to + /// add two counters so the result can be subtracted from another counter), or an Error with + /// message for subsequent debugging. + fn make_bcb_counters( + &mut self, + coverage_spans: &Vec<CoverageSpan>, + ) -> Result<Vec<CoverageKind>, Error> { + debug!("make_bcb_counters(): adding a counter or expression to each BasicCoverageBlock"); + let num_bcbs = self.basic_coverage_blocks.num_nodes(); + let mut collect_intermediate_expressions = Vec::with_capacity(num_bcbs); + + let mut bcbs_with_coverage = BitSet::new_empty(num_bcbs); + for covspan in coverage_spans { + bcbs_with_coverage.insert(covspan.bcb); + } + + // FIXME(richkadel): Add more comments to explain the logic here and in the rest of this + // function, and refactor this function to break it up into smaller functions that are + // easier to understand. + + let mut traversal = TraverseCoverageGraphWithLoops::new(&self.basic_coverage_blocks); + while let Some(bcb) = traversal.next(self.basic_coverage_blocks) { + if bcbs_with_coverage.contains(bcb) { + debug!("{:?} has at least one `CoverageSpan`. Get or make its counter", bcb); + let branching_counter_operand = + self.get_or_make_counter_operand(bcb, &mut collect_intermediate_expressions)?; + + if self.bcb_needs_branch_counters(bcb) { + self.make_branch_counters( + &mut traversal, + bcb, + branching_counter_operand, + &mut collect_intermediate_expressions, + )?; + } + } else { + debug!( + "{:?} does not have any `CoverageSpan`s. A counter will only be added if \ + and when a covered BCB has an expression dependency.", + bcb, + ); + } + } + + if traversal.is_complete() { + Ok(collect_intermediate_expressions) + } else { + Error::from_string(format!( + "`TraverseCoverageGraphWithLoops` missed some `BasicCoverageBlock`s: {:?}", + traversal.unvisited(), + )) + } + } + + fn make_branch_counters( + &mut self, + traversal: &mut TraverseCoverageGraphWithLoops, + branching_bcb: BasicCoverageBlock, + branching_counter_operand: ExpressionOperandId, + collect_intermediate_expressions: &mut Vec<CoverageKind>, + ) -> Result<(), Error> { + let branches = self.bcb_branches(branching_bcb); + debug!( + "{:?} has some branch(es) without counters:\n {}", + branching_bcb, + branches + .iter() + .map(|branch| { + format!("{:?}: {:?}", branch, branch.counter(&self.basic_coverage_blocks)) + }) + .collect::<Vec<_>>() + .join("\n "), + ); + + let expression_branch = self.choose_preferred_expression_branch(traversal, &branches); + // Assign a Counter or Expression to each branch, plus additional + // `Expression`s, as needed, to sum up intermediate results. + let mut some_sumup_counter_operand = None; + for branch in branches { + if branch != expression_branch { + let branch_counter_operand = if branch.is_only_path_to_target() { + debug!( + " {:?} has only one incoming edge (from {:?}), so adding a \ + counter", + branch, branching_bcb + ); + self.get_or_make_counter_operand( + branch.target_bcb, + collect_intermediate_expressions, + )? + } else { + debug!(" {:?} has multiple incoming edges, so adding an edge counter", branch); + self.get_or_make_edge_counter_operand( + branching_bcb, + branch.target_bcb, + collect_intermediate_expressions, + )? + }; + if let Some(sumup_counter_operand) = + some_sumup_counter_operand.replace(branch_counter_operand) + { + let intermediate_expression = self.coverage_counters.make_expression( + branch_counter_operand, + Op::Add, + sumup_counter_operand, + || None, + ); + debug!( + " [new intermediate expression: {}]", + self.format_counter(&intermediate_expression) + ); + let intermediate_expression_operand = intermediate_expression.as_operand_id(); + collect_intermediate_expressions.push(intermediate_expression); + some_sumup_counter_operand.replace(intermediate_expression_operand); + } + } + } + let sumup_counter_operand = + some_sumup_counter_operand.expect("sumup_counter_operand should have a value"); + debug!( + "Making an expression for the selected expression_branch: {:?} \ + (expression_branch predecessors: {:?})", + expression_branch, + self.bcb_predecessors(expression_branch.target_bcb), + ); + let expression = self.coverage_counters.make_expression( + branching_counter_operand, + Op::Subtract, + sumup_counter_operand, + || Some(format!("{:?}", expression_branch)), + ); + debug!("{:?} gets an expression: {}", expression_branch, self.format_counter(&expression)); + let bcb = expression_branch.target_bcb; + if expression_branch.is_only_path_to_target() { + self.basic_coverage_blocks[bcb].set_counter(expression)?; + } else { + self.basic_coverage_blocks[bcb].set_edge_counter_from(branching_bcb, expression)?; + } + Ok(()) + } + + fn get_or_make_counter_operand( + &mut self, + bcb: BasicCoverageBlock, + collect_intermediate_expressions: &mut Vec<CoverageKind>, + ) -> Result<ExpressionOperandId, Error> { + self.recursive_get_or_make_counter_operand(bcb, collect_intermediate_expressions, 1) + } + + fn recursive_get_or_make_counter_operand( + &mut self, + bcb: BasicCoverageBlock, + collect_intermediate_expressions: &mut Vec<CoverageKind>, + debug_indent_level: usize, + ) -> Result<ExpressionOperandId, Error> { + Ok({ + if let Some(counter_kind) = self.basic_coverage_blocks[bcb].counter() { + debug!( + "{}{:?} already has a counter: {}", + NESTED_INDENT.repeat(debug_indent_level), + bcb, + self.format_counter(counter_kind), + ); + counter_kind.as_operand_id() + } else { + let one_path_to_target = self.bcb_has_one_path_to_target(bcb); + if one_path_to_target || self.bcb_predecessors(bcb).contains(&bcb) { + let counter_kind = + self.coverage_counters.make_counter(|| Some(format!("{:?}", bcb))); + if one_path_to_target { + debug!( + "{}{:?} gets a new counter: {}", + NESTED_INDENT.repeat(debug_indent_level), + bcb, + self.format_counter(&counter_kind), + ); + } else { + debug!( + "{}{:?} has itself as its own predecessor. It can't be part of its own \ + Expression sum, so it will get its own new counter: {}. (Note, the \ + compiled code will generate an infinite loop.)", + NESTED_INDENT.repeat(debug_indent_level), + bcb, + self.format_counter(&counter_kind), + ); + } + self.basic_coverage_blocks[bcb].set_counter(counter_kind)? + } else { + let mut predecessors = self.bcb_predecessors(bcb).clone().into_iter(); + debug!( + "{}{:?} has multiple incoming edges and will get an expression that sums \ + them up...", + NESTED_INDENT.repeat(debug_indent_level), + bcb, + ); + let first_edge_counter_operand = self + .recursive_get_or_make_edge_counter_operand( + predecessors.next().unwrap(), + bcb, + collect_intermediate_expressions, + debug_indent_level + 1, + )?; + let mut some_sumup_edge_counter_operand = None; + for predecessor in predecessors { + let edge_counter_operand = self + .recursive_get_or_make_edge_counter_operand( + predecessor, + bcb, + collect_intermediate_expressions, + debug_indent_level + 1, + )?; + if let Some(sumup_edge_counter_operand) = + some_sumup_edge_counter_operand.replace(edge_counter_operand) + { + let intermediate_expression = self.coverage_counters.make_expression( + sumup_edge_counter_operand, + Op::Add, + edge_counter_operand, + || None, + ); + debug!( + "{}new intermediate expression: {}", + NESTED_INDENT.repeat(debug_indent_level), + self.format_counter(&intermediate_expression) + ); + let intermediate_expression_operand = + intermediate_expression.as_operand_id(); + collect_intermediate_expressions.push(intermediate_expression); + some_sumup_edge_counter_operand + .replace(intermediate_expression_operand); + } + } + let counter_kind = self.coverage_counters.make_expression( + first_edge_counter_operand, + Op::Add, + some_sumup_edge_counter_operand.unwrap(), + || Some(format!("{:?}", bcb)), + ); + debug!( + "{}{:?} gets a new counter (sum of predecessor counters): {}", + NESTED_INDENT.repeat(debug_indent_level), + bcb, + self.format_counter(&counter_kind) + ); + self.basic_coverage_blocks[bcb].set_counter(counter_kind)? + } + } + }) + } + + fn get_or_make_edge_counter_operand( + &mut self, + from_bcb: BasicCoverageBlock, + to_bcb: BasicCoverageBlock, + collect_intermediate_expressions: &mut Vec<CoverageKind>, + ) -> Result<ExpressionOperandId, Error> { + self.recursive_get_or_make_edge_counter_operand( + from_bcb, + to_bcb, + collect_intermediate_expressions, + 1, + ) + } + + fn recursive_get_or_make_edge_counter_operand( + &mut self, + from_bcb: BasicCoverageBlock, + to_bcb: BasicCoverageBlock, + collect_intermediate_expressions: &mut Vec<CoverageKind>, + debug_indent_level: usize, + ) -> Result<ExpressionOperandId, Error> { + Ok({ + let successors = self.bcb_successors(from_bcb).iter(); + if successors.len() > 1 { + if let Some(counter_kind) = + self.basic_coverage_blocks[to_bcb].edge_counter_from(from_bcb) + { + debug!( + "{}Edge {:?}->{:?} already has a counter: {}", + NESTED_INDENT.repeat(debug_indent_level), + from_bcb, + to_bcb, + self.format_counter(counter_kind) + ); + counter_kind.as_operand_id() + } else { + let counter_kind = self + .coverage_counters + .make_counter(|| Some(format!("{:?}->{:?}", from_bcb, to_bcb))); + debug!( + "{}Edge {:?}->{:?} gets a new counter: {}", + NESTED_INDENT.repeat(debug_indent_level), + from_bcb, + to_bcb, + self.format_counter(&counter_kind) + ); + self.basic_coverage_blocks[to_bcb] + .set_edge_counter_from(from_bcb, counter_kind)? + } + } else { + self.recursive_get_or_make_counter_operand( + from_bcb, + collect_intermediate_expressions, + debug_indent_level + 1, + )? + } + }) + } + + /// Select a branch for the expression, either the recommended `reloop_branch`, or + /// if none was found, select any branch. + fn choose_preferred_expression_branch( + &self, + traversal: &TraverseCoverageGraphWithLoops, + branches: &Vec<BcbBranch>, + ) -> BcbBranch { + let branch_needs_a_counter = + |branch: &BcbBranch| branch.counter(&self.basic_coverage_blocks).is_none(); + + let some_reloop_branch = self.find_some_reloop_branch(traversal, &branches); + if let Some(reloop_branch_without_counter) = + some_reloop_branch.filter(branch_needs_a_counter) + { + debug!( + "Selecting reloop_branch={:?} that still needs a counter, to get the \ + `Expression`", + reloop_branch_without_counter + ); + reloop_branch_without_counter + } else { + let &branch_without_counter = branches + .iter() + .find(|&&branch| branch.counter(&self.basic_coverage_blocks).is_none()) + .expect( + "needs_branch_counters was `true` so there should be at least one \ + branch", + ); + debug!( + "Selecting any branch={:?} that still needs a counter, to get the \ + `Expression` because there was no `reloop_branch`, or it already had a \ + counter", + branch_without_counter + ); + branch_without_counter + } + } + + /// At most one of the branches (or its edge, from the branching_bcb, + /// if the branch has multiple incoming edges) can have a counter computed by + /// expression. + /// + /// If at least one of the branches leads outside of a loop (`found_loop_exit` is + /// true), and at least one other branch does not exit the loop (the first of which + /// is captured in `some_reloop_branch`), it's likely any reloop branch will be + /// executed far more often than loop exit branch, making the reloop branch a better + /// candidate for an expression. + fn find_some_reloop_branch( + &self, + traversal: &TraverseCoverageGraphWithLoops, + branches: &Vec<BcbBranch>, + ) -> Option<BcbBranch> { + let branch_needs_a_counter = + |branch: &BcbBranch| branch.counter(&self.basic_coverage_blocks).is_none(); + + let mut some_reloop_branch: Option<BcbBranch> = None; + for context in traversal.context_stack.iter().rev() { + if let Some((backedge_from_bcbs, _)) = &context.loop_backedges { + let mut found_loop_exit = false; + for &branch in branches.iter() { + if backedge_from_bcbs.iter().any(|&backedge_from_bcb| { + self.bcb_is_dominated_by(backedge_from_bcb, branch.target_bcb) + }) { + if let Some(reloop_branch) = some_reloop_branch { + if reloop_branch.counter(&self.basic_coverage_blocks).is_none() { + // we already found a candidate reloop_branch that still + // needs a counter + continue; + } + } + // The path from branch leads back to the top of the loop. Set this + // branch as the `reloop_branch`. If this branch already has a + // counter, and we find another reloop branch that doesn't have a + // counter yet, that branch will be selected as the `reloop_branch` + // instead. + some_reloop_branch = Some(branch); + } else { + // The path from branch leads outside this loop + found_loop_exit = true; + } + if found_loop_exit + && some_reloop_branch.filter(branch_needs_a_counter).is_some() + { + // Found both a branch that exits the loop and a branch that returns + // to the top of the loop (`reloop_branch`), and the `reloop_branch` + // doesn't already have a counter. + break; + } + } + if !found_loop_exit { + debug!( + "No branches exit the loop, so any branch without an existing \ + counter can have the `Expression`." + ); + break; + } + if some_reloop_branch.is_some() { + debug!( + "Found a branch that exits the loop and a branch the loops back to \ + the top of the loop (`reloop_branch`). The `reloop_branch` will \ + get the `Expression`, as long as it still needs a counter." + ); + break; + } + // else all branches exited this loop context, so run the same checks with + // the outer loop(s) + } + } + some_reloop_branch + } + + #[inline] + fn bcb_predecessors(&self, bcb: BasicCoverageBlock) -> &Vec<BasicCoverageBlock> { + &self.basic_coverage_blocks.predecessors[bcb] + } + + #[inline] + fn bcb_successors(&self, bcb: BasicCoverageBlock) -> &Vec<BasicCoverageBlock> { + &self.basic_coverage_blocks.successors[bcb] + } + + #[inline] + fn bcb_branches(&self, from_bcb: BasicCoverageBlock) -> Vec<BcbBranch> { + self.bcb_successors(from_bcb) + .iter() + .map(|&to_bcb| BcbBranch::from_to(from_bcb, to_bcb, &self.basic_coverage_blocks)) + .collect::<Vec<_>>() + } + + fn bcb_needs_branch_counters(&self, bcb: BasicCoverageBlock) -> bool { + let branch_needs_a_counter = + |branch: &BcbBranch| branch.counter(&self.basic_coverage_blocks).is_none(); + let branches = self.bcb_branches(bcb); + branches.len() > 1 && branches.iter().any(branch_needs_a_counter) + } + + /// Returns true if the BasicCoverageBlock has zero or one incoming edge. (If zero, it should be + /// the entry point for the function.) + #[inline] + fn bcb_has_one_path_to_target(&self, bcb: BasicCoverageBlock) -> bool { + self.bcb_predecessors(bcb).len() <= 1 + } + + #[inline] + fn bcb_is_dominated_by(&self, node: BasicCoverageBlock, dom: BasicCoverageBlock) -> bool { + self.basic_coverage_blocks.is_dominated_by(node, dom) + } + + #[inline] + fn format_counter(&self, counter_kind: &CoverageKind) -> String { + self.coverage_counters.debug_counters.format_counter(counter_kind) + } +} |