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Rollup merge of #134029 - Zalathar:zero, r=oli-obk

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coverage: Use a query to find counters/expressions that must be zero

As of #133446, this query (`coverage_ids_info`) determines which counter/expression IDs are unused. So with only a little extra work, we can take the code that was using that information to determine which coverage counters/expressions must be zero, and move that inside the query as well.

There should be no change in compiler output.
This commit is contained in:
León Orell Valerian Liehr 2024-12-10 08:55:59 +01:00 committed by GitHub
commit bb8a20678c
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7 changed files with 173 additions and 227 deletions
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190
compiler/rustc_codegen_llvm/src/coverageinfo/map_data.rs
View File

@ -1,159 +1,38 @@
use rustc_data_structures::captures::Captures;
use rustc_data_structures::fx::FxIndexSet;
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::CoverageIdsInfo;
use rustc_middle::mir::coverage::{
CounterId, CovTerm, Expression, ExpressionId, FunctionCoverageInfo, Mapping, MappingKind, Op,
CovTerm, CoverageIdsInfo, Expression, FunctionCoverageInfo, Mapping, MappingKind, Op,
SourceRegion,
};
use rustc_middle::ty::Instance;
use tracing::debug;
use crate::coverageinfo::ffi::{Counter, CounterExpression, ExprKind};
/// Holds all of the coverage mapping data associated with a function instance,
/// collected during traversal of `Coverage` statements in the function's MIR.
#[derive(Debug)]
pub(crate) struct FunctionCoverageCollector<'tcx> {
/// Coverage info that was attached to this function by the instrumentor.
function_coverage_info: &'tcx FunctionCoverageInfo,
ids_info: &'tcx CoverageIdsInfo,
is_used: bool,
}
impl<'tcx> FunctionCoverageCollector<'tcx> {
/// Creates a new set of coverage data for a used (called) function.
pub(crate) fn new(
instance: Instance<'tcx>,
function_coverage_info: &'tcx FunctionCoverageInfo,
ids_info: &'tcx CoverageIdsInfo,
) -> Self {
Self::create(instance, function_coverage_info, ids_info, true)
}
/// Creates a new set of coverage data for an unused (never called) function.
pub(crate) fn unused(
instance: Instance<'tcx>,
function_coverage_info: &'tcx FunctionCoverageInfo,
ids_info: &'tcx CoverageIdsInfo,
) -> Self {
Self::create(instance, function_coverage_info, ids_info, false)
}
fn create(
instance: Instance<'tcx>,
function_coverage_info: &'tcx FunctionCoverageInfo,
ids_info: &'tcx CoverageIdsInfo,
is_used: bool,
) -> Self {
let num_counters = function_coverage_info.num_counters;
let num_expressions = function_coverage_info.expressions.len();
debug!(
"FunctionCoverage::create(instance={instance:?}) has \
num_counters={num_counters}, num_expressions={num_expressions}, is_used={is_used}"
);
Self { function_coverage_info, ids_info, is_used }
}
/// Identify expressions that will always have a value of zero, and note
/// their IDs in [`ZeroExpressions`]. Mappings that refer to a zero expression
/// can instead become mappings to a constant zero value.
///
/// This method mainly exists to preserve the simplifications that were
/// already being performed by the Rust-side expression renumbering, so that
/// the resulting coverage mappings don't get worse.
fn identify_zero_expressions(&self) -> ZeroExpressions {
// The set of expressions that either were optimized out entirely, or
// have zero as both of their operands, and will therefore always have
// a value of zero. Other expressions that refer to these as operands
// can have those operands replaced with `CovTerm::Zero`.
let mut zero_expressions = ZeroExpressions::default();
// Simplify a copy of each expression based on lower-numbered expressions,
// and then update the set of always-zero expressions if necessary.
// (By construction, expressions can only refer to other expressions
// that have lower IDs, so one pass is sufficient.)
for (id, expression) in self.function_coverage_info.expressions.iter_enumerated() {
if !self.is_used || !self.ids_info.expressions_seen.contains(id) {
// If an expression was not seen, it must have been optimized away,
// so any operand that refers to it can be replaced with zero.
zero_expressions.insert(id);
continue;
}
// We don't need to simplify the actual expression data in the
// expressions list; we can just simplify a temporary copy and then
// use that to update the set of always-zero expressions.
let Expression { mut lhs, op, mut rhs } = *expression;
// If an expression has an operand that is also an expression, the
// operand's ID must be strictly lower. This is what lets us find
// all zero expressions in one pass.
let assert_operand_expression_is_lower = |operand_id: ExpressionId| {
assert!(
operand_id < id,
"Operand {operand_id:?} should be less than {id:?} in {expression:?}",
)
};
// If an operand refers to a counter or expression that is always
// zero, then that operand can be replaced with `CovTerm::Zero`.
let maybe_set_operand_to_zero = |operand: &mut CovTerm| {
if let CovTerm::Expression(id) = *operand {
assert_operand_expression_is_lower(id);
}
if is_zero_term(&self.ids_info.counters_seen, &zero_expressions, *operand) {
*operand = CovTerm::Zero;
}
};
maybe_set_operand_to_zero(&mut lhs);
maybe_set_operand_to_zero(&mut rhs);
// Coverage counter values cannot be negative, so if an expression
// involves subtraction from zero, assume that its RHS must also be zero.
// (Do this after simplifications that could set the LHS to zero.)
if lhs == CovTerm::Zero && op == Op::Subtract {
rhs = CovTerm::Zero;
}
// After the above simplifications, if both operands are zero, then
// we know that this expression is always zero too.
if lhs == CovTerm::Zero && rhs == CovTerm::Zero {
zero_expressions.insert(id);
}
}
zero_expressions
}
pub(crate) fn into_finished(self) -> FunctionCoverage<'tcx> {
let zero_expressions = self.identify_zero_expressions();
let FunctionCoverageCollector { function_coverage_info, ids_info, is_used, .. } = self;
FunctionCoverage { function_coverage_info, ids_info, is_used, zero_expressions }
}
}
pub(crate) struct FunctionCoverage<'tcx> {
pub(crate) function_coverage_info: &'tcx FunctionCoverageInfo,
ids_info: &'tcx CoverageIdsInfo,
is_used: bool,
zero_expressions: ZeroExpressions,
/// If `None`, the corresponding function is unused.
ids_info: Option<&'tcx CoverageIdsInfo>,
}
impl<'tcx> FunctionCoverage<'tcx> {
pub(crate) fn new_used(
function_coverage_info: &'tcx FunctionCoverageInfo,
ids_info: &'tcx CoverageIdsInfo,
) -> Self {
Self { function_coverage_info, ids_info: Some(ids_info) }
}
pub(crate) fn new_unused(function_coverage_info: &'tcx FunctionCoverageInfo) -> Self {
Self { function_coverage_info, ids_info: None }
}
/// Returns true for a used (called) function, and false for an unused function.
pub(crate) fn is_used(&self) -> bool {
self.is_used
self.ids_info.is_some()
}
/// Return the source hash, generated from the HIR node structure, and used to indicate whether
/// or not the source code structure changed between different compilations.
pub(crate) fn source_hash(&self) -> u64 {
if self.is_used { self.function_coverage_info.function_source_hash } else { 0 }
if self.is_used() { self.function_coverage_info.function_source_hash } else { 0 }
}
/// Convert this function's coverage expression data into a form that can be
@ -196,37 +75,10 @@ impl<'tcx> FunctionCoverage<'tcx> {
}
fn is_zero_term(&self, term: CovTerm) -> bool {
!self.is_used || is_zero_term(&self.ids_info.counters_seen, &self.zero_expressions, term)
}
}
/// Set of expression IDs that are known to always evaluate to zero.
/// Any mapping or expression operand that refers to these expressions can have
/// that reference replaced with a constant zero value.
#[derive(Default)]
struct ZeroExpressions(FxIndexSet<ExpressionId>);
impl ZeroExpressions {
fn insert(&mut self, id: ExpressionId) {
self.0.insert(id);
}
fn contains(&self, id: ExpressionId) -> bool {
self.0.contains(&id)
}
}
/// Returns `true` if the given term is known to have a value of zero, taking
/// into account knowledge of which counters are unused and which expressions
/// are always zero.
fn is_zero_term(
counters_seen: &BitSet<CounterId>,
zero_expressions: &ZeroExpressions,
term: CovTerm,
) -> bool {
match term {
CovTerm::Zero => true,
CovTerm::Counter(id) => !counters_seen.contains(id),
CovTerm::Expression(id) => zero_expressions.contains(id),
match self.ids_info {
Some(ids_info) => ids_info.is_zero_term(term),
// This function is unused, so all coverage counters/expressions are zero.
None => true,
}
}
}

20
compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
View File

@ -20,7 +20,7 @@ use rustc_target::spec::HasTargetSpec;
use tracing::debug;
use crate::common::CodegenCx;
use crate::coverageinfo::map_data::{FunctionCoverage, FunctionCoverageCollector};
use crate::coverageinfo::map_data::FunctionCoverage;
use crate::coverageinfo::{ffi, llvm_cov};
use crate::llvm;
@ -63,16 +63,11 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
None => return,
};
if function_coverage_map.is_empty() {
// This module has no functions with coverage instrumentation
// This CGU has no functions with coverage instrumentation.
return;
}
let function_coverage_entries = function_coverage_map
.into_iter()
.map(|(instance, function_coverage)| (instance, function_coverage.into_finished()))
.collect::<Vec<_>>();
let all_file_names = function_coverage_entries
let all_file_names = function_coverage_map
.iter()
.map(|(_, fn_cov)| fn_cov.function_coverage_info.body_span)
.map(|span| span_file_name(tcx, span));
@ -92,7 +87,7 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
let mut unused_function_names = Vec::new();
// Encode coverage mappings and generate function records
for (instance, function_coverage) in function_coverage_entries {
for (instance, function_coverage) in function_coverage_map {
debug!("Generate function coverage for {}, {:?}", cx.codegen_unit.name(), instance);
let mangled_function_name = tcx.symbol_name(instance).name;
@ -536,11 +531,6 @@ fn add_unused_function_coverage<'tcx>(
);
// An unused function's mappings will all be rewritten to map to zero.
let function_coverage = FunctionCoverageCollector::unused(
instance,
function_coverage_info,
tcx.coverage_ids_info(instance.def),
);
let function_coverage = FunctionCoverage::new_unused(function_coverage_info);
cx.coverage_cx().function_coverage_map.borrow_mut().insert(instance, function_coverage);
}

12
compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
View File

@ -13,7 +13,7 @@ use tracing::{debug, instrument};
use crate::builder::Builder;
use crate::common::CodegenCx;
use crate::coverageinfo::map_data::FunctionCoverageCollector;
use crate::coverageinfo::map_data::FunctionCoverage;
use crate::llvm;
pub(crate) mod ffi;
@ -24,8 +24,7 @@ mod mapgen;
/// Extra per-CGU context/state needed for coverage instrumentation.
pub(crate) struct CguCoverageContext<'ll, 'tcx> {
/// Coverage data for each instrumented function identified by DefId.
pub(crate) function_coverage_map:
RefCell<FxIndexMap<Instance<'tcx>, FunctionCoverageCollector<'tcx>>>,
pub(crate) function_coverage_map: RefCell<FxIndexMap<Instance<'tcx>, FunctionCoverage<'tcx>>>,
pub(crate) pgo_func_name_var_map: RefCell<FxHashMap<Instance<'tcx>, &'ll llvm::Value>>,
pub(crate) mcdc_condition_bitmap_map: RefCell<FxHashMap<Instance<'tcx>, Vec<&'ll llvm::Value>>>,
@ -42,9 +41,7 @@ impl<'ll, 'tcx> CguCoverageContext<'ll, 'tcx> {
}
}
fn take_function_coverage_map(
&self,
) -> FxIndexMap<Instance<'tcx>, FunctionCoverageCollector<'tcx>> {
fn take_function_coverage_map(&self) -> FxIndexMap<Instance<'tcx>, FunctionCoverage<'tcx>> {
self.function_coverage_map.replace(FxIndexMap::default())
}
@ -161,8 +158,7 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
// This includes functions that were not partitioned into this CGU,
// but were MIR-inlined into one of this CGU's functions.
coverage_cx.function_coverage_map.borrow_mut().entry(instance).or_insert_with(|| {
FunctionCoverageCollector::new(
instance,
FunctionCoverage::new_used(
function_coverage_info,
bx.tcx.coverage_ids_info(instance.def),
)

39
compiler/rustc_middle/src/mir/coverage.rs
View File

@ -3,6 +3,7 @@
use std::fmt::{self, Debug, Formatter};
use rustc_index::IndexVec;
use rustc_index::bit_set::BitSet;
use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
use rustc_span::Span;
@ -310,3 +311,41 @@ pub struct MCDCDecisionSpan {
pub decision_depth: u16,
pub num_conditions: usize,
}
/// Summarizes coverage IDs inserted by the `InstrumentCoverage` MIR pass
/// (for compiler option `-Cinstrument-coverage`), after MIR optimizations
/// have had a chance to potentially remove some of them.
///
/// Used by the `coverage_ids_info` query.
#[derive(Clone, TyEncodable, TyDecodable, Debug, HashStable)]
pub struct CoverageIdsInfo {
pub counters_seen: BitSet<CounterId>,
pub zero_expressions: BitSet<ExpressionId>,
}
impl CoverageIdsInfo {
/// Coverage codegen needs to know how many coverage counters are ever
/// incremented within a function, so that it can set the `num-counters`
/// argument of the `llvm.instrprof.increment` intrinsic.
///
/// This may be less than the highest counter ID emitted by the
/// InstrumentCoverage MIR pass, if the highest-numbered counter increments
/// were removed by MIR optimizations.
pub fn num_counters_after_mir_opts(&self) -> u32 {
// FIXME(Zalathar): Currently this treats an unused counter as "used"
// if its ID is less than that of the highest counter that really is
// used. Fixing this would require adding a renumbering step somewhere.
self.counters_seen.last_set_in(..).map_or(0, |max| max.as_u32() + 1)
}
/// Returns `true` if the given term is known to have a value of zero, taking
/// into account knowledge of which counters are unused and which expressions
/// are always zero.
pub fn is_zero_term(&self, term: CovTerm) -> bool {
match term {
CovTerm::Zero => true,
CovTerm::Counter(id) => !self.counters_seen.contains(id),
CovTerm::Expression(id) => self.zero_expressions.contains(id),
}
}
}

30
compiler/rustc_middle/src/mir/query.rs
View File

@ -8,7 +8,7 @@ use rustc_abi::{FieldIdx, VariantIdx};
use rustc_data_structures::fx::FxIndexMap;
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def_id::LocalDefId;
use rustc_index::bit_set::{BitMatrix, BitSet};
use rustc_index::bit_set::BitMatrix;
use rustc_index::{Idx, IndexVec};
use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
use rustc_span::Span;
@ -16,7 +16,6 @@ use rustc_span::symbol::Symbol;
use smallvec::SmallVec;
use super::{ConstValue, SourceInfo};
use crate::mir;
use crate::ty::fold::fold_regions;
use crate::ty::{self, CoroutineArgsExt, OpaqueHiddenType, Ty, TyCtxt};
@ -351,30 +350,3 @@ pub struct DestructuredConstant<'tcx> {
pub variant: Option<VariantIdx>,
pub fields: &'tcx [(ConstValue<'tcx>, Ty<'tcx>)],
}
/// Summarizes coverage IDs inserted by the `InstrumentCoverage` MIR pass
/// (for compiler option `-Cinstrument-coverage`), after MIR optimizations
/// have had a chance to potentially remove some of them.
///
/// Used by the `coverage_ids_info` query.
#[derive(Clone, TyEncodable, TyDecodable, Debug, HashStable)]
pub struct CoverageIdsInfo {
pub counters_seen: BitSet<mir::coverage::CounterId>,
pub expressions_seen: BitSet<mir::coverage::ExpressionId>,
}
impl CoverageIdsInfo {
/// Coverage codegen needs to know how many coverage counters are ever
/// incremented within a function, so that it can set the `num-counters`
/// argument of the `llvm.instrprof.increment` intrinsic.
///
/// This may be less than the highest counter ID emitted by the
/// InstrumentCoverage MIR pass, if the highest-numbered counter increments
/// were removed by MIR optimizations.
pub fn num_counters_after_mir_opts(&self) -> u32 {
// FIXME(Zalathar): Currently this treats an unused counter as "used"
// if its ID is less than that of the highest counter that really is
// used. Fixing this would require adding a renumbering step somewhere.
self.counters_seen.last_set_in(..).map_or(0, |max| max.as_u32() + 1)
}
}

2
compiler/rustc_middle/src/query/mod.rs
View File

@ -581,7 +581,7 @@ rustc_queries! {
/// Summarizes coverage IDs inserted by the `InstrumentCoverage` MIR pass
/// (for compiler option `-Cinstrument-coverage`), after MIR optimizations
/// have had a chance to potentially remove some of them.
query coverage_ids_info(key: ty::InstanceKind<'tcx>) -> &'tcx mir::CoverageIdsInfo {
query coverage_ids_info(key: ty::InstanceKind<'tcx>) -> &'tcx mir::coverage::CoverageIdsInfo {
desc { |tcx| "retrieving coverage IDs info from MIR for `{}`", tcx.def_path_str(key.def_id()) }
arena_cache
}

107
compiler/rustc_mir_transform/src/coverage/query.rs
View File

@ -1,8 +1,11 @@
use rustc_data_structures::captures::Captures;
use rustc_index::bit_set::BitSet;
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
use rustc_middle::mir::coverage::{CovTerm, CoverageKind, MappingKind};
use rustc_middle::mir::{Body, CoverageIdsInfo, Statement, StatementKind};
use rustc_middle::mir::coverage::{
CounterId, CovTerm, CoverageIdsInfo, CoverageKind, Expression, ExpressionId,
FunctionCoverageInfo, MappingKind, Op,
};
use rustc_middle::mir::{Body, Statement, StatementKind};
use rustc_middle::query::TyCtxtAt;
use rustc_middle::ty::{self, TyCtxt};
use rustc_middle::util::Providers;
@ -87,10 +90,10 @@ fn coverage_ids_info<'tcx>(
) -> CoverageIdsInfo {
let mir_body = tcx.instance_mir(instance_def);
let Some(fn_cov_info) = mir_body.function_coverage_info.as_ref() else {
let Some(fn_cov_info) = mir_body.function_coverage_info.as_deref() else {
return CoverageIdsInfo {
counters_seen: BitSet::new_empty(0),
expressions_seen: BitSet::new_empty(0),
zero_expressions: BitSet::new_empty(0),
};
};
@ -123,7 +126,10 @@ fn coverage_ids_info<'tcx>(
}
}
CoverageIdsInfo { counters_seen, expressions_seen }
let zero_expressions =
identify_zero_expressions(fn_cov_info, &counters_seen, &expressions_seen);
CoverageIdsInfo { counters_seen, zero_expressions }
}
fn all_coverage_in_mir_body<'a, 'tcx>(
@ -141,3 +147,94 @@ fn is_inlined(body: &Body<'_>, statement: &Statement<'_>) -> bool {
let scope_data = &body.source_scopes[statement.source_info.scope];
scope_data.inlined.is_some() || scope_data.inlined_parent_scope.is_some()
}
/// Identify expressions that will always have a value of zero, and note
/// their IDs in a `BitSet`. Mappings that refer to a zero expression
/// can instead become mappings to a constant zero value.
///
/// This function mainly exists to preserve the simplifications that were
/// already being performed by the Rust-side expression renumbering, so that
/// the resulting coverage mappings don't get worse.
fn identify_zero_expressions(
fn_cov_info: &FunctionCoverageInfo,
counters_seen: &BitSet<CounterId>,
expressions_seen: &BitSet<ExpressionId>,
) -> BitSet<ExpressionId> {
// The set of expressions that either were optimized out entirely, or
// have zero as both of their operands, and will therefore always have
// a value of zero. Other expressions that refer to these as operands
// can have those operands replaced with `CovTerm::Zero`.
let mut zero_expressions = BitSet::new_empty(fn_cov_info.expressions.len());
// Simplify a copy of each expression based on lower-numbered expressions,
// and then update the set of always-zero expressions if necessary.
// (By construction, expressions can only refer to other expressions
// that have lower IDs, so one pass is sufficient.)
for (id, expression) in fn_cov_info.expressions.iter_enumerated() {
if !expressions_seen.contains(id) {
// If an expression was not seen, it must have been optimized away,
// so any operand that refers to it can be replaced with zero.
zero_expressions.insert(id);
continue;
}
// We don't need to simplify the actual expression data in the
// expressions list; we can just simplify a temporary copy and then
// use that to update the set of always-zero expressions.
let Expression { mut lhs, op, mut rhs } = *expression;
// If an expression has an operand that is also an expression, the
// operand's ID must be strictly lower. This is what lets us find
// all zero expressions in one pass.
let assert_operand_expression_is_lower = |operand_id: ExpressionId| {
assert!(
operand_id < id,
"Operand {operand_id:?} should be less than {id:?} in {expression:?}",
)
};
// If an operand refers to a counter or expression that is always
// zero, then that operand can be replaced with `CovTerm::Zero`.
let maybe_set_operand_to_zero = |operand: &mut CovTerm| {
if let CovTerm::Expression(id) = *operand {
assert_operand_expression_is_lower(id);
}
if is_zero_term(&counters_seen, &zero_expressions, *operand) {
*operand = CovTerm::Zero;
}
};
maybe_set_operand_to_zero(&mut lhs);
maybe_set_operand_to_zero(&mut rhs);
// Coverage counter values cannot be negative, so if an expression
// involves subtraction from zero, assume that its RHS must also be zero.
// (Do this after simplifications that could set the LHS to zero.)
if lhs == CovTerm::Zero && op == Op::Subtract {
rhs = CovTerm::Zero;
}
// After the above simplifications, if both operands are zero, then
// we know that this expression is always zero too.
if lhs == CovTerm::Zero && rhs == CovTerm::Zero {
zero_expressions.insert(id);
}
}
zero_expressions
}
/// Returns `true` if the given term is known to have a value of zero, taking
/// into account knowledge of which counters are unused and which expressions
/// are always zero.
fn is_zero_term(
counters_seen: &BitSet<CounterId>,
zero_expressions: &BitSet<ExpressionId>,
term: CovTerm,
) -> bool {
match term {
CovTerm::Zero => true,
CovTerm::Counter(id) => !counters_seen.contains(id),
CovTerm::Expression(id) => zero_expressions.contains(id),
}
}