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coverage: Clean up marker statements that aren't needed later

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Some of the marker statements used by coverage are added during MIR building
for use by the InstrumentCoverage pass (during analysis), and are not needed
afterwards.
This commit is contained in:
Zalathar 2024-03-15 22:27:30 +11:00
parent cdb683f6e4
commit 91aae58568
8 changed files with 159 additions and 14 deletions
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10
compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
View File

@ -85,14 +85,6 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
let bx = self;
match coverage.kind {
// Marker statements have no effect during codegen,
// so return early and don't create `func_coverage`.
CoverageKind::SpanMarker | CoverageKind::BlockMarker { .. } => return,
// Match exhaustively to ensure that newly-added kinds are classified correctly.
CoverageKind::CounterIncrement { .. } | CoverageKind::ExpressionUsed { .. } => {}
}
let Some(function_coverage_info) =
bx.tcx.instance_mir(instance.def).function_coverage_info.as_deref()
else {
@ -109,7 +101,7 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
let Coverage { kind } = coverage;
match *kind {
CoverageKind::SpanMarker | CoverageKind::BlockMarker { .. } => unreachable!(
"unexpected marker statement {kind:?} should have caused an early return"
"marker statement {kind:?} should have been removed by CleanupPostBorrowck"
),
CoverageKind::CounterIncrement { id } => {
func_coverage.mark_counter_id_seen(id);

13
compiler/rustc_const_eval/src/transform/validate.rs
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@ -4,6 +4,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_index::bit_set::BitSet;
use rustc_index::IndexVec;
use rustc_infer::traits::Reveal;
use rustc_middle::mir::coverage::CoverageKind;
use rustc_middle::mir::interpret::Scalar;
use rustc_middle::mir::visit::{NonUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
@ -345,11 +346,21 @@ impl<'a, 'tcx> Visitor<'tcx> for CfgChecker<'a, 'tcx> {
self.fail(location, format!("explicit `{kind:?}` is forbidden"));
}
}
StatementKind::Coverage(coverage) => {
let kind = &coverage.kind;
if self.mir_phase >= MirPhase::Analysis(AnalysisPhase::PostCleanup)
&& let CoverageKind::BlockMarker { .. } | CoverageKind::SpanMarker { .. } = kind
{
self.fail(
location,
format!("{kind:?} should have been removed after analysis"),
);
}
}
StatementKind::Assign(..)
| StatementKind::StorageLive(_)
| StatementKind::StorageDead(_)
| StatementKind::Intrinsic(_)
| StatementKind::Coverage(_)
| StatementKind::ConstEvalCounter
| StatementKind::PlaceMention(..)
| StatementKind::Nop => {}

5
compiler/rustc_middle/src/mir/coverage.rs
View File

@ -88,14 +88,13 @@ pub enum CoverageKind {
/// Marks a span that might otherwise not be represented in MIR, so that
/// coverage instrumentation can associate it with its enclosing block/BCB.
///
/// Only used by the `InstrumentCoverage` pass, and has no effect during
/// codegen.
/// Should be erased before codegen (at some point after `InstrumentCoverage`).
SpanMarker,
/// Marks its enclosing basic block with an ID that can be referred to by
/// side data in [`BranchInfo`].
///
/// Has no effect during codegen.
/// Should be erased before codegen (at some point after `InstrumentCoverage`).
BlockMarker { id: BlockMarkerId },
/// Marks the point in MIR control flow represented by a coverage counter.

1
compiler/rustc_middle/src/mir/syntax.rs
View File

@ -124,6 +124,7 @@ pub enum AnalysisPhase {
/// * [`TerminatorKind::FalseEdge`]
/// * [`StatementKind::FakeRead`]
/// * [`StatementKind::AscribeUserType`]
/// * [`StatementKind::Coverage`] with [`CoverageKind::BlockMarker`] or [`CoverageKind::SpanMarker`]
/// * [`Rvalue::Ref`] with `BorrowKind::Fake`
///
/// Furthermore, `Deref` projections must be the first projection within any place (if they

13
compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
View File

@ -5,15 +5,20 @@
//! - [`AscribeUserType`]
//! - [`FakeRead`]
//! - [`Assign`] statements with a [`Fake`] borrow
//! - [`Coverage`] statements of kind [`BlockMarker`] or [`SpanMarker`]
//!
//! [`AscribeUserType`]: rustc_middle::mir::StatementKind::AscribeUserType
//! [`Assign`]: rustc_middle::mir::StatementKind::Assign
//! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
//! [`Nop`]: rustc_middle::mir::StatementKind::Nop
//! [`Fake`]: rustc_middle::mir::BorrowKind::Fake
//! [`Coverage`]: rustc_middle::mir::StatementKind::Coverage
//! [`BlockMarker`]: rustc_middle::mir::coverage::CoverageKind::BlockMarker
//! [`SpanMarker`]: rustc_middle::mir::coverage::CoverageKind::SpanMarker
use crate::MirPass;
use rustc_middle::mir::{Body, BorrowKind, Rvalue, StatementKind, TerminatorKind};
use rustc_middle::mir::coverage::CoverageKind;
use rustc_middle::mir::{Body, BorrowKind, Coverage, Rvalue, StatementKind, TerminatorKind};
use rustc_middle::ty::TyCtxt;
pub struct CleanupPostBorrowck;
@ -25,6 +30,12 @@ impl<'tcx> MirPass<'tcx> for CleanupPostBorrowck {
match statement.kind {
StatementKind::AscribeUserType(..)
| StatementKind::Assign(box (_, Rvalue::Ref(_, BorrowKind::Fake, _)))
| StatementKind::Coverage(box Coverage {
// These kinds of coverage statements are markers inserted during
// MIR building, and are not needed after InstrumentCoverage.
kind: CoverageKind::BlockMarker { .. } | CoverageKind::SpanMarker { .. },
..
})
| StatementKind::FakeRead(..) => statement.make_nop(),
_ => (),
}

56
tests/mir-opt/instrument_coverage_cleanup.main.CleanupPostBorrowck.diff Normal file
View File

@ -0,0 +1,56 @@
- // MIR for `main` before CleanupPostBorrowck
+ // MIR for `main` after CleanupPostBorrowck
fn main() -> () {
let mut _0: ();
let mut _1: bool;
coverage branch { true: BlockMarkerId(0), false: BlockMarkerId(1) } => /the/src/instrument_coverage_cleanup.rs:15:8: 15:36 (#0)
coverage ExpressionId(0) => Expression { lhs: Counter(0), op: Subtract, rhs: Counter(1) };
coverage ExpressionId(1) => Expression { lhs: Counter(1), op: Add, rhs: Expression(0) };
coverage Code(Counter(0)) => /the/src/instrument_coverage_cleanup.rs:14:1 - 15:36;
coverage Code(Expression(0)) => /the/src/instrument_coverage_cleanup.rs:15:37 - 15:39;
coverage Code(Counter(1)) => /the/src/instrument_coverage_cleanup.rs:15:39 - 15:40;
coverage Code(Expression(1)) => /the/src/instrument_coverage_cleanup.rs:16:1 - 16:2;
coverage Branch { true_term: Expression(0), false_term: Counter(1) } => /the/src/instrument_coverage_cleanup.rs:15:8 - 15:36;
bb0: {
Coverage::CounterIncrement(0);
- Coverage::SpanMarker;
+ nop;
StorageLive(_1);
_1 = std::hint::black_box::<bool>(const true) -> [return: bb1, unwind: bb5];
}
bb1: {
switchInt(move _1) -> [0: bb3, otherwise: bb2];
}
bb2: {
Coverage::CounterIncrement(1);
- Coverage::BlockMarker(1);
+ nop;
_0 = const ();
goto -> bb4;
}
bb3: {
Coverage::ExpressionUsed(0);
- Coverage::BlockMarker(0);
+ nop;
_0 = const ();
goto -> bb4;
}
bb4: {
Coverage::ExpressionUsed(1);
StorageDead(_1);
return;
}
bb5 (cleanup): {
resume;
}
}

53
tests/mir-opt/instrument_coverage_cleanup.main.InstrumentCoverage.diff Normal file
View File

@ -0,0 +1,53 @@
- // MIR for `main` before InstrumentCoverage
+ // MIR for `main` after InstrumentCoverage
fn main() -> () {
let mut _0: ();
let mut _1: bool;
coverage branch { true: BlockMarkerId(0), false: BlockMarkerId(1) } => /the/src/instrument_coverage_cleanup.rs:15:8: 15:36 (#0)
+ coverage ExpressionId(0) => Expression { lhs: Counter(0), op: Subtract, rhs: Counter(1) };
+ coverage ExpressionId(1) => Expression { lhs: Counter(1), op: Add, rhs: Expression(0) };
+ coverage Code(Counter(0)) => /the/src/instrument_coverage_cleanup.rs:14:1 - 15:36;
+ coverage Code(Expression(0)) => /the/src/instrument_coverage_cleanup.rs:15:37 - 15:39;
+ coverage Code(Counter(1)) => /the/src/instrument_coverage_cleanup.rs:15:39 - 15:40;
+ coverage Code(Expression(1)) => /the/src/instrument_coverage_cleanup.rs:16:1 - 16:2;
+ coverage Branch { true_term: Expression(0), false_term: Counter(1) } => /the/src/instrument_coverage_cleanup.rs:15:8 - 15:36;
+
bb0: {
+ Coverage::CounterIncrement(0);
Coverage::SpanMarker;
StorageLive(_1);
_1 = std::hint::black_box::<bool>(const true) -> [return: bb1, unwind: bb5];
}
bb1: {
switchInt(move _1) -> [0: bb3, otherwise: bb2];
}
bb2: {
+ Coverage::CounterIncrement(1);
Coverage::BlockMarker(1);
_0 = const ();
goto -> bb4;
}
bb3: {
+ Coverage::ExpressionUsed(0);
Coverage::BlockMarker(0);
_0 = const ();
goto -> bb4;
}
bb4: {
+ Coverage::ExpressionUsed(1);
StorageDead(_1);
return;
}
bb5 (cleanup): {
resume;
}
}

22
tests/mir-opt/instrument_coverage_cleanup.rs Normal file
View File

@ -0,0 +1,22 @@
// Test that CleanupPostBorrowck cleans up the marker statements that are
// inserted during MIR building (after InstrumentCoverage is done with them),
// but leaves the statements that were added by InstrumentCoverage.
//
// Removed statement kinds: BlockMarker, SpanMarker
// Retained statement kinds: CounterIncrement, ExpressionUsed
//@ unit-test: InstrumentCoverage
//@ compile-flags: -Cinstrument-coverage -Zcoverage-options=branch -Zno-profiler-runtime
//@ compile-flags: --remap-path-prefix={{src-base}}=/the/src
// EMIT_MIR instrument_coverage_cleanup.main.InstrumentCoverage.diff
// EMIT_MIR instrument_coverage_cleanup.main.CleanupPostBorrowck.diff
fn main() {
if !core::hint::black_box(true) {}
}
// CHECK-NOT: Coverage::BlockMarker
// CHECK-NOT: Coverage::SpanMarker
// CHECK: Coverage::CounterIncrement
// CHECK-NOT: Coverage::BlockMarker
// CHECK-NOT: Coverage::SpanMarker