Skip to content

Commit

Permalink
coverage. Split mcdc builder to a sub module of coverageinfo
Browse files Browse the repository at this point in the history
  • Loading branch information
@ZhuUx
ZhuUx committed Apr 30, 2024
1 parent e198c51 commit 6c8b492
Show file tree
Hide file tree
Showing 2 changed files with 279 additions and 269 deletions.
273 changes: 4 additions & 269 deletions compiler/rustc_mir_build/src/build/coverageinfo.rs
View file
Original file line number Diff line number Diff line change
@@ -1,20 +1,16 @@
mod mcdc;
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::coverageinfo::mcdc::MCDCInfoBuilder;
use crate::build::{Builder, CFG};
use crate::errors::MCDCExceedsConditionNumLimit;

pub(crate) struct BranchInfoBuilder {
/// Maps condition expressions to their enclosing `!`, for better instrumentation.
Expand Down Expand Up @@ -159,241 +155,6 @@ impl BranchInfoBuilder {
}
}

/// 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;

#[derive(Default)]
struct MCDCDecisionCtx {
/// To construct condition evaluation tree.
decision_stack: VecDeque<ConditionInfo>,
processing_decision: Option<MCDCDecisionSpan>,
}

struct MCDCState {
decision_ctx_stack: Vec<MCDCDecisionCtx>,
}

impl MCDCState {
fn new() -> Self {
Self { decision_ctx_stack: vec![MCDCDecisionCtx::default()] }
}

/// Decision depth is given as a u16 to reduce the size of the `CoverageKind`,
/// as it is very unlikely that the depth ever reaches 2^16.
#[inline]
fn decision_depth(&self) -> u16 {
match u16::try_from(self.decision_ctx_stack.len())
.expect(
"decision depth did not fit in u16, this is likely to be an instrumentation error",
)
.checked_sub(1)
{
Some(d) => d,
None => bug!("Unexpected empty decision stack"),
}
}

// 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_depth = self.decision_depth();
let Some(decision_ctx) = self.decision_ctx_stack.last_mut() else {
bug!("Unexpected empty decision_ctx_stack")
};
let decision = match decision_ctx.processing_decision.as_mut() {
Some(decision) => {
decision.span = decision.span.to(span);
decision
}
None => decision_ctx.processing_decision.insert(MCDCDecisionSpan {
span,
conditions_num: 0,
end_markers: vec![],
decision_depth,
}),
};

let parent_condition = decision_ctx.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.
decision_ctx.decision_stack.push_back(rhs);
decision_ctx.decision_stack.push_back(lhs);
}

fn take_condition(
&mut self,
true_marker: BlockMarkerId,
false_marker: BlockMarkerId,
) -> (Option<ConditionInfo>, Option<MCDCDecisionSpan>) {
let Some(decision_ctx) = self.decision_ctx_stack.last_mut() else {
bug!("Unexpected empty decision_ctx_stack")
};
let Some(condition_info) = decision_ctx.decision_stack.pop_back() else {
return (None, None);
};
let Some(decision) = decision_ctx.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 decision_ctx.decision_stack.is_empty() {
(Some(condition_info), decision_ctx.processing_decision.take())
} else {
(Some(condition_info), None)
}
}
}

struct MCDCInfoBuilder {
branch_spans: Vec<MCDCBranchSpan>,
decision_spans: Vec<MCDCDecisionSpan>,
state: MCDCState,
}

impl MCDCInfoBuilder {
fn new() -> Self {
Self { branch_spans: vec![], decision_spans: vec![], state: MCDCState::new() }
}

fn visit_evaluated_condition(
&mut self,
tcx: TyCtxt<'_>,
source_info: SourceInfo,
true_block: BasicBlock,
false_block: BasicBlock,
mut inject_block_marker: impl FnMut(SourceInfo, BasicBlock) -> BlockMarkerId,
) {
let true_marker = inject_block_marker(source_info, true_block);
let false_marker = inject_block_marker(source_info, false_block);

let decision_depth = self.state.decision_depth();
let (mut condition_info, decision_result) =
self.state.take_condition(true_marker, false_marker);
// take_condition() returns Some for decision_result when the decision stack
// is empty, i.e. when all the conditions of the decision were instrumented,
// and the decision is "complete".
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.decision_spans.push(decision);
}
_ => {
// Do not generate mcdc mappings and statements for decisions with too many conditions.
let rebase_idx = self.branch_spans.len() - decision.conditions_num + 1;
for branch in &mut self.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,
});
}
}
}
self.branch_spans.push(MCDCBranchSpan {
span: source_info.span,
condition_info,
true_marker,
false_marker,
decision_depth,
});
}

fn into_done(self) -> (Vec<MCDCDecisionSpan>, Vec<MCDCBranchSpan>) {
(self.decision_spans, self.branch_spans)
}
}

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 Down Expand Up @@ -434,30 +195,4 @@ impl Builder<'_, '_> {

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_info) = branch_info.mcdc_info.as_mut()
{
mcdc_info.state.record_conditions(logical_op, span);
}
}

pub(crate) fn mcdc_increment_depth_if_enabled(&mut self) {
if let Some(branch_info) = self.coverage_branch_info.as_mut()
&& let Some(mcdc_info) = branch_info.mcdc_info.as_mut()
{
mcdc_info.state.decision_ctx_stack.push(MCDCDecisionCtx::default());
};
}

pub(crate) fn mcdc_decrement_depth_if_enabled(&mut self) {
if let Some(branch_info) = self.coverage_branch_info.as_mut()
&& let Some(mcdc_info) = branch_info.mcdc_info.as_mut()
{
if mcdc_info.state.decision_ctx_stack.pop().is_none() {
bug!("Unexpected empty decision stack");
}
};
}
}
Loading

0 comments on commit 6c8b492

Please sign in to comment.