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coverage. Split mcdc code into a sub module of coverageingo
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@ZhuUx
ZhuUx committed Apr 26, 2024
1 parent e59f2c5 commit a3d737a
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Showing 2 changed files with 288 additions and 247 deletions.
304 changes: 57 additions & 247 deletions compiler/rustc_mir_build/src/build/coverageinfo.rs
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Original file line number Diff line number Diff line change
@@ -1,31 +1,24 @@
mod mcdc;
use mcdc::MCDCInfoBuilder;
use std::assert_matches::assert_matches;
use std::collections::hash_map::Entry;
use std::collections::VecDeque;

use rustc_data_structures::fx::FxHashMap;
use rustc_middle::mir::coverage::{
BlockMarkerId, BranchSpan, ConditionId, ConditionInfo, CoverageKind, MCDCBranchSpan,
MCDCDecisionSpan,
};
use rustc_middle::mir::coverage::{BlockMarkerId, BranchSpan, CoverageKind};
use rustc_middle::mir::{self, BasicBlock, SourceInfo, UnOp};
use rustc_middle::thir::{ExprId, ExprKind, LogicalOp, Thir};
use rustc_middle::thir::{ExprId, ExprKind, Thir};
use rustc_middle::ty::TyCtxt;
use rustc_span::def_id::LocalDefId;
use rustc_span::Span;

use crate::build::{Builder, CFG};
use crate::errors::MCDCExceedsConditionNumLimit;

pub(crate) struct BranchInfoBuilder {
/// Maps condition expressions to their enclosing `!`, for better instrumentation.
nots: FxHashMap<ExprId, NotInfo>,

num_block_markers: usize,
block_marker_generator: BlockMarkerGenerator,
branch_spans: Vec<BranchSpan>,

mcdc_branch_spans: Vec<MCDCBranchSpan>,
mcdc_decision_spans: Vec<MCDCDecisionSpan>,
mcdc_state: Option<MCDCState>,
mcdc_builder: Option<MCDCInfoBuilder>,
}

#[derive(Clone, Copy)]
Expand All @@ -38,18 +31,46 @@ struct NotInfo {
is_flipped: bool,
}

#[derive(Default)]
struct BlockMarkerGenerator {
num_block_markers: usize,
}

impl BlockMarkerGenerator {
fn next_block_marker_id(&mut self) -> BlockMarkerId {
let id = BlockMarkerId::from_usize(self.num_block_markers);
self.num_block_markers += 1;
id
}

fn inject_block_marker(
&mut self,
cfg: &mut CFG<'_>,
source_info: SourceInfo,
block: BasicBlock,
) -> BlockMarkerId {
let id = self.next_block_marker_id();

let marker_statement = mir::Statement {
source_info,
kind: mir::StatementKind::Coverage(CoverageKind::BlockMarker { id }),
};
cfg.push(block, marker_statement);

id
}
}

impl BranchInfoBuilder {
/// Creates a new branch info builder, but only if branch coverage instrumentation
/// is enabled and `def_id` represents a function that is eligible for coverage.
pub(crate) fn new_if_enabled(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<Self> {
if tcx.sess.instrument_coverage_branch() && tcx.is_eligible_for_coverage(def_id) {
Some(Self {
nots: FxHashMap::default(),
num_block_markers: 0,
block_marker_generator: BlockMarkerGenerator::default(),
branch_spans: vec![],
mcdc_branch_spans: vec![],
mcdc_decision_spans: vec![],
mcdc_state: MCDCState::new_if_enabled(tcx),
mcdc_builder: tcx.sess.instrument_coverage_mcdc().then(MCDCInfoBuilder::new),
})
} else {
None
Expand Down Expand Up @@ -96,245 +117,46 @@ impl BranchInfoBuilder {
}
}

fn fetch_mcdc_condition_info(
&mut self,
tcx: TyCtxt<'_>,
true_marker: BlockMarkerId,
false_marker: BlockMarkerId,
) -> Option<ConditionInfo> {
let mcdc_state = self.mcdc_state.as_mut()?;
let (mut condition_info, decision_result) =
mcdc_state.take_condition(true_marker, false_marker);
if let Some(decision) = decision_result {
match decision.conditions_num {
0 => {
unreachable!("Decision with no condition is not expected");
}
1..=MAX_CONDITIONS_NUM_IN_DECISION => {
self.mcdc_decision_spans.push(decision);
}
_ => {
// Do not generate mcdc mappings and statements for decisions with too many conditions.
let rebase_idx = self.mcdc_branch_spans.len() - decision.conditions_num + 1;
for branch in &mut self.mcdc_branch_spans[rebase_idx..] {
branch.condition_info = None;
}

// ConditionInfo of this branch shall also be reset.
condition_info = None;

tcx.dcx().emit_warn(MCDCExceedsConditionNumLimit {
span: decision.span,
conditions_num: decision.conditions_num,
max_conditions_num: MAX_CONDITIONS_NUM_IN_DECISION,
});
}
}
}
condition_info
}

fn add_two_way_branch<'tcx>(
&mut self,
cfg: &mut CFG<'tcx>,
source_info: SourceInfo,
true_block: BasicBlock,
false_block: BasicBlock,
) {
let true_marker = self.inject_block_marker(cfg, source_info, true_block);
let false_marker = self.inject_block_marker(cfg, source_info, false_block);
let true_marker =
self.block_marker_generator.inject_block_marker(cfg, source_info, true_block);
let false_marker =
self.block_marker_generator.inject_block_marker(cfg, source_info, false_block);

self.branch_spans.push(BranchSpan { span: source_info.span, true_marker, false_marker });
}

fn next_block_marker_id(&mut self) -> BlockMarkerId {
let id = BlockMarkerId::from_usize(self.num_block_markers);
self.num_block_markers += 1;
id
}

fn inject_block_marker(
&mut self,
cfg: &mut CFG<'_>,
source_info: SourceInfo,
block: BasicBlock,
) -> BlockMarkerId {
let id = self.next_block_marker_id();

let marker_statement = mir::Statement {
source_info,
kind: mir::StatementKind::Coverage(CoverageKind::BlockMarker { id }),
};
cfg.push(block, marker_statement);

id
}

pub(crate) fn into_done(self) -> Option<Box<mir::coverage::BranchInfo>> {
let Self {
nots: _,
num_block_markers,
block_marker_generator: BlockMarkerGenerator { num_block_markers },
branch_spans,
mcdc_branch_spans,
mcdc_decision_spans,
mcdc_state: _,
mcdc_builder,
} = self;

if num_block_markers == 0 {
assert!(branch_spans.is_empty());
return None;
}

let (mcdc_decision_spans, mcdc_branch_spans) =
mcdc_builder.map(MCDCInfoBuilder::into_done).unwrap_or_default();

Some(Box::new(mir::coverage::BranchInfo {
num_block_markers,
branch_spans,
mcdc_branch_spans,
mcdc_decision_spans,
mcdc_branch_spans,
}))
}
}

/// The MCDC bitmap scales exponentially (2^n) based on the number of conditions seen,
/// So llvm sets a maximum value prevents the bitmap footprint from growing too large without the user's knowledge.
/// This limit may be relaxed if the [upstream change](https://github.com/llvm/llvm-project/pull/82448) is merged.
const MAX_CONDITIONS_NUM_IN_DECISION: usize = 6;

struct MCDCState {
/// To construct condition evaluation tree.
decision_stack: VecDeque<ConditionInfo>,
processing_decision: Option<MCDCDecisionSpan>,
}

impl MCDCState {
fn new_if_enabled(tcx: TyCtxt<'_>) -> Option<Self> {
tcx.sess
.instrument_coverage_mcdc()
.then(|| Self { decision_stack: VecDeque::new(), processing_decision: None })
}

// At first we assign ConditionIds for each sub expression.
// If the sub expression is composite, re-assign its ConditionId to its LHS and generate a new ConditionId for its RHS.
//
// Example: "x = (A && B) || (C && D) || (D && F)"
//
// Visit Depth1:
// (A && B) || (C && D) || (D && F)
// ^-------LHS--------^ ^-RHS--^
// ID=1 ID=2
//
// Visit LHS-Depth2:
// (A && B) || (C && D)
// ^-LHS--^ ^-RHS--^
// ID=1 ID=3
//
// Visit LHS-Depth3:
// (A && B)
// LHS RHS
// ID=1 ID=4
//
// Visit RHS-Depth3:
// (C && D)
// LHS RHS
// ID=3 ID=5
//
// Visit RHS-Depth2: (D && F)
// LHS RHS
// ID=2 ID=6
//
// Visit Depth1:
// (A && B) || (C && D) || (D && F)
// ID=1 ID=4 ID=3 ID=5 ID=2 ID=6
//
// A node ID of '0' always means MC/DC isn't being tracked.
//
// If a "next" node ID is '0', it means it's the end of the test vector.
//
// As the compiler tracks expression in pre-order, we can ensure that condition info of parents are always properly assigned when their children are visited.
// - If the op is AND, the "false_next" of LHS and RHS should be the parent's "false_next". While "true_next" of the LHS is the RHS, the "true next" of RHS is the parent's "true_next".
// - If the op is OR, the "true_next" of LHS and RHS should be the parent's "true_next". While "false_next" of the LHS is the RHS, the "false next" of RHS is the parent's "false_next".
fn record_conditions(&mut self, op: LogicalOp, span: Span) {
let decision = match self.processing_decision.as_mut() {
Some(decision) => {
decision.span = decision.span.to(span);
decision
}
None => self.processing_decision.insert(MCDCDecisionSpan {
span,
conditions_num: 0,
end_markers: vec![],
}),
};

let parent_condition = self.decision_stack.pop_back().unwrap_or_default();
let lhs_id = if parent_condition.condition_id == ConditionId::NONE {
decision.conditions_num += 1;
ConditionId::from(decision.conditions_num)
} else {
parent_condition.condition_id
};

decision.conditions_num += 1;
let rhs_condition_id = ConditionId::from(decision.conditions_num);

let (lhs, rhs) = match op {
LogicalOp::And => {
let lhs = ConditionInfo {
condition_id: lhs_id,
true_next_id: rhs_condition_id,
false_next_id: parent_condition.false_next_id,
};
let rhs = ConditionInfo {
condition_id: rhs_condition_id,
true_next_id: parent_condition.true_next_id,
false_next_id: parent_condition.false_next_id,
};
(lhs, rhs)
}
LogicalOp::Or => {
let lhs = ConditionInfo {
condition_id: lhs_id,
true_next_id: parent_condition.true_next_id,
false_next_id: rhs_condition_id,
};
let rhs = ConditionInfo {
condition_id: rhs_condition_id,
true_next_id: parent_condition.true_next_id,
false_next_id: parent_condition.false_next_id,
};
(lhs, rhs)
}
};
// We visit expressions tree in pre-order, so place the left-hand side on the top.
self.decision_stack.push_back(rhs);
self.decision_stack.push_back(lhs);
}

fn take_condition(
&mut self,
true_marker: BlockMarkerId,
false_marker: BlockMarkerId,
) -> (Option<ConditionInfo>, Option<MCDCDecisionSpan>) {
let Some(condition_info) = self.decision_stack.pop_back() else {
return (None, None);
};
let Some(decision) = self.processing_decision.as_mut() else {
bug!("Processing decision should have been created before any conditions are taken");
};
if condition_info.true_next_id == ConditionId::NONE {
decision.end_markers.push(true_marker);
}
if condition_info.false_next_id == ConditionId::NONE {
decision.end_markers.push(false_marker);
}

if self.decision_stack.is_empty() {
(Some(condition_info), self.processing_decision.take())
} else {
(Some(condition_info), None)
}
}
}

impl Builder<'_, '_> {
/// If branch coverage is enabled, inject marker statements into `then_block`
/// and `else_block`, and record their IDs in the table of branch spans.
Expand All @@ -359,30 +181,18 @@ impl Builder<'_, '_> {
let source_info = SourceInfo { span: self.thir[expr_id].span, scope: self.source_scope };

// Separate path for handling branches when MC/DC is enabled.
if branch_info.mcdc_state.is_some() {
let mut inject_block_marker =
|block| branch_info.inject_block_marker(&mut self.cfg, source_info, block);
let true_marker = inject_block_marker(then_block);
let false_marker = inject_block_marker(else_block);
let condition_info =
branch_info.fetch_mcdc_condition_info(self.tcx, true_marker, false_marker);
branch_info.mcdc_branch_spans.push(MCDCBranchSpan {
span: source_info.span,
condition_info,
true_marker,
false_marker,
});
if let Some(mcdc_builder) = branch_info.mcdc_builder.as_mut() {
mcdc_builder.visit_evaluated_condition(
self.tcx,
&mut self.cfg,
source_info,
then_block,
else_block,
&mut branch_info.block_marker_generator,
);
return;
}

branch_info.add_two_way_branch(&mut self.cfg, source_info, then_block, else_block);
}

pub(crate) fn visit_coverage_branch_operation(&mut self, logical_op: LogicalOp, span: Span) {
if let Some(branch_info) = self.coverage_branch_info.as_mut()
&& let Some(mcdc_state) = branch_info.mcdc_state.as_mut()
{
mcdc_state.record_conditions(logical_op, span);
}
}
}
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