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Rollup merge of rust-lang#125756 - Zalathar:branch-on-bool, r=oli-obk
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coverage: Optionally instrument the RHS of lazy logical operators

(This is an updated version of rust-lang#124644 and rust-lang#124402. Fixes rust-lang#124120.)

When `||` or `&&` is used outside of a branching context (such as the condition of an `if`), the rightmost value does not directly influence any branching decision, so branch coverage instrumentation does not treat it as its own true-or-false branch.

That is a correct and useful interpretation of “branch coverage”, but might be undesirable in some contexts, as described at rust-lang#124120. This PR therefore adds a new coverage level `-Zcoverage-options=condition` that behaves like branch coverage, but also adds additional branch instrumentation to the right-hand-side of lazy boolean operators.

---

As discussed at rust-lang#124120 (comment), this is mainly intended as an intermediate step towards fully-featured MC/DC instrumentation. It's likely that we'll eventually want to remove this coverage level (rather than stabilize it), either because it has been incorporated into MC/DC instrumentation, or because it's getting in the way of future MC/DC work. The main appeal of landing it now is so that work on tracking conditions can proceed concurrently with other MC/DC-related work.

```@rustbot``` label +A-code-coverage
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jieyouxu authored May 31, 2024
2 parents fe6ecc2 + 35a8746 commit 45147ef
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Showing 11 changed files with 411 additions and 8 deletions.
57 changes: 57 additions & 0 deletions compiler/rustc_mir_build/src/build/coverageinfo.rs
Original file line number Diff line number Diff line change
Expand Up @@ -157,6 +157,63 @@ impl BranchInfoBuilder {
}

impl<'tcx> Builder<'_, 'tcx> {
/// If condition coverage is enabled, inject extra blocks and marker statements
/// that will let us track the value of the condition in `place`.
pub(crate) fn visit_coverage_standalone_condition(
&mut self,
mut expr_id: ExprId, // Expression giving the span of the condition
place: mir::Place<'tcx>, // Already holds the boolean condition value
block: &mut BasicBlock,
) {
// Bail out if condition coverage is not enabled for this function.
let Some(branch_info) = self.coverage_branch_info.as_mut() else { return };
if !self.tcx.sess.instrument_coverage_condition() {
return;
};

// Remove any wrappers, so that we can inspect the real underlying expression.
while let ExprKind::Use { source: inner } | ExprKind::Scope { value: inner, .. } =
self.thir[expr_id].kind
{
expr_id = inner;
}
// If the expression is a lazy logical op, it will naturally get branch
// coverage as part of its normal lowering, so we can disregard it here.
if let ExprKind::LogicalOp { .. } = self.thir[expr_id].kind {
return;
}

let source_info = SourceInfo { span: self.thir[expr_id].span, scope: self.source_scope };

// Using the boolean value that has already been stored in `place`, set up
// control flow in the shape of a diamond, so that we can place separate
// marker statements in the true and false blocks. The coverage MIR pass
// will use those markers to inject coverage counters as appropriate.
//
// block
// / \
// true_block false_block
// (marker) (marker)
// \ /
// join_block

let true_block = self.cfg.start_new_block();
let false_block = self.cfg.start_new_block();
self.cfg.terminate(
*block,
source_info,
mir::TerminatorKind::if_(mir::Operand::Copy(place), true_block, false_block),
);

branch_info.add_two_way_branch(&mut self.cfg, source_info, true_block, false_block);

let join_block = self.cfg.start_new_block();
self.cfg.goto(true_block, source_info, join_block);
self.cfg.goto(false_block, source_info, join_block);
// Any subsequent codegen in the caller should use the new join block.
*block = join_block;
}

/// If branch coverage is enabled, inject marker statements into `then_block`
/// and `else_block`, and record their IDs in the table of branch spans.
pub(crate) fn visit_coverage_branch_condition(
Expand Down
8 changes: 6 additions & 2 deletions compiler/rustc_mir_build/src/build/expr/into.rs
Original file line number Diff line number Diff line change
Expand Up @@ -183,9 +183,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
const_: Const::from_bool(this.tcx, constant),
},
);
let rhs = unpack!(this.expr_into_dest(destination, continuation, rhs));
let mut rhs_block = unpack!(this.expr_into_dest(destination, continuation, rhs));
// Instrument the lowered RHS's value for condition coverage.
// (Does nothing if condition coverage is not enabled.)
this.visit_coverage_standalone_condition(rhs, destination, &mut rhs_block);

let target = this.cfg.start_new_block();
this.cfg.goto(rhs, source_info, target);
this.cfg.goto(rhs_block, source_info, target);
this.cfg.goto(short_circuit, source_info, target);
target.unit()
}
Expand Down
18 changes: 17 additions & 1 deletion compiler/rustc_session/src/config.rs
Original file line number Diff line number Diff line change
Expand Up @@ -159,7 +159,23 @@ pub enum CoverageLevel {
Block,
/// Also instrument branch points (includes block coverage).
Branch,
/// Instrument for MC/DC. Mostly a superset of branch coverage, but might
/// Same as branch coverage, but also adds branch instrumentation for
/// certain boolean expressions that are not directly used for branching.
///
/// For example, in the following code, `b` does not directly participate
/// in a branch, but condition coverage will instrument it as its own
/// artificial branch:
/// ```
/// # let (a, b) = (false, true);
/// let x = a && b;
/// // ^ last operand
/// ```
///
/// This level is mainly intended to be a stepping-stone towards full MC/DC
/// instrumentation, so it might be removed in the future when MC/DC is
/// sufficiently complete, or if it is making MC/DC changes difficult.
Condition,
/// Instrument for MC/DC. Mostly a superset of condition coverage, but might
/// differ in some corner cases.
Mcdc,
}
Expand Down
3 changes: 2 additions & 1 deletion compiler/rustc_session/src/options.rs
Original file line number Diff line number Diff line change
Expand Up @@ -395,7 +395,7 @@ mod desc {
pub const parse_optimization_fuel: &str = "crate=integer";
pub const parse_dump_mono_stats: &str = "`markdown` (default) or `json`";
pub const parse_instrument_coverage: &str = parse_bool;
pub const parse_coverage_options: &str = "`block` | `branch` | `mcdc`";
pub const parse_coverage_options: &str = "`block` | `branch` | `condition` | `mcdc`";
pub const parse_instrument_xray: &str = "either a boolean (`yes`, `no`, `on`, `off`, etc), or a comma separated list of settings: `always` or `never` (mutually exclusive), `ignore-loops`, `instruction-threshold=N`, `skip-entry`, `skip-exit`";
pub const parse_unpretty: &str = "`string` or `string=string`";
pub const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
Expand Down Expand Up @@ -961,6 +961,7 @@ mod parse {
match option {
"block" => slot.level = CoverageLevel::Block,
"branch" => slot.level = CoverageLevel::Branch,
"condition" => slot.level = CoverageLevel::Condition,
"mcdc" => slot.level = CoverageLevel::Mcdc,
_ => return false,
}
Expand Down
5 changes: 5 additions & 0 deletions compiler/rustc_session/src/session.rs
Original file line number Diff line number Diff line change
Expand Up @@ -353,6 +353,11 @@ impl Session {
&& self.opts.unstable_opts.coverage_options.level >= CoverageLevel::Branch
}

pub fn instrument_coverage_condition(&self) -> bool {
self.instrument_coverage()
&& self.opts.unstable_opts.coverage_options.level >= CoverageLevel::Condition
}

pub fn instrument_coverage_mcdc(&self) -> bool {
self.instrument_coverage()
&& self.opts.unstable_opts.coverage_options.level >= CoverageLevel::Mcdc
Expand Down
7 changes: 5 additions & 2 deletions src/doc/unstable-book/src/compiler-flags/coverage-options.md
Original file line number Diff line number Diff line change
Expand Up @@ -5,13 +5,16 @@ This option controls details of the coverage instrumentation performed by

Multiple options can be passed, separated by commas. Valid options are:

- `block`, `branch`, `mcdc`:
- `block`, `branch`, `condition`, `mcdc`:
Sets the level of coverage instrumentation.
Setting the level will override any previously-specified level.
- `block` (default):
Blocks in the control-flow graph will be instrumented for coverage.
- `branch`:
In addition to block coverage, also enables branch coverage instrumentation.
- `condition`:
In addition to branch coverage, also instruments some boolean expressions
as branches, even if they are not directly used as branch conditions.
- `mcdc`:
In addition to block and branch coverage, also enables MC/DC instrumentation.
In addition to condition coverage, also enables MC/DC instrumentation.
(Branch coverage instrumentation may differ in some cases.)
152 changes: 152 additions & 0 deletions tests/coverage/condition/conditions.cov-map
Original file line number Diff line number Diff line change
@@ -0,0 +1,152 @@
Function name: conditions::assign_3_and_or
Raw bytes (69): 0x[01, 01, 07, 07, 11, 09, 0d, 01, 05, 05, 09, 16, 1a, 05, 09, 01, 05, 09, 01, 1c, 01, 00, 2f, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 1a, 00, 0d, 00, 0e, 05, 00, 12, 00, 13, 20, 09, 16, 00, 12, 00, 13, 13, 00, 17, 00, 18, 20, 0d, 11, 00, 17, 00, 18, 03, 01, 05, 01, 02]
Number of files: 1
- file 0 => global file 1
Number of expressions: 7
- expression 0 operands: lhs = Expression(1, Add), rhs = Counter(4)
- expression 1 operands: lhs = Counter(2), rhs = Counter(3)
- expression 2 operands: lhs = Counter(0), rhs = Counter(1)
- expression 3 operands: lhs = Counter(1), rhs = Counter(2)
- expression 4 operands: lhs = Expression(5, Sub), rhs = Expression(6, Sub)
- expression 5 operands: lhs = Counter(1), rhs = Counter(2)
- expression 6 operands: lhs = Counter(0), rhs = Counter(1)
Number of file 0 mappings: 9
- Code(Counter(0)) at (prev + 28, 1) to (start + 0, 47)
- Code(Expression(0, Add)) at (prev + 1, 9) to (start + 0, 10)
= ((c2 + c3) + c4)
- Code(Counter(0)) at (prev + 0, 13) to (start + 0, 14)
- Branch { true: Counter(1), false: Expression(6, Sub) } at (prev + 0, 13) to (start + 0, 14)
true = c1
false = (c0 - c1)
- Code(Counter(1)) at (prev + 0, 18) to (start + 0, 19)
- Branch { true: Counter(2), false: Expression(5, Sub) } at (prev + 0, 18) to (start + 0, 19)
true = c2
false = (c1 - c2)
- Code(Expression(4, Add)) at (prev + 0, 23) to (start + 0, 24)
= ((c1 - c2) + (c0 - c1))
- Branch { true: Counter(3), false: Counter(4) } at (prev + 0, 23) to (start + 0, 24)
true = c3
false = c4
- Code(Expression(0, Add)) at (prev + 1, 5) to (start + 1, 2)
= ((c2 + c3) + c4)

Function name: conditions::assign_3_or_and
Raw bytes (73): 0x[01, 01, 09, 05, 07, 0b, 11, 09, 0d, 01, 05, 01, 05, 22, 11, 01, 05, 22, 11, 01, 05, 09, 01, 17, 01, 00, 2f, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 22, 00, 0d, 00, 0e, 22, 00, 12, 00, 13, 20, 1e, 11, 00, 12, 00, 13, 1e, 00, 17, 00, 18, 20, 09, 0d, 00, 17, 00, 18, 03, 01, 05, 01, 02]
Number of files: 1
- file 0 => global file 1
Number of expressions: 9
- expression 0 operands: lhs = Counter(1), rhs = Expression(1, Add)
- expression 1 operands: lhs = Expression(2, Add), rhs = Counter(4)
- expression 2 operands: lhs = Counter(2), rhs = Counter(3)
- expression 3 operands: lhs = Counter(0), rhs = Counter(1)
- expression 4 operands: lhs = Counter(0), rhs = Counter(1)
- expression 5 operands: lhs = Expression(8, Sub), rhs = Counter(4)
- expression 6 operands: lhs = Counter(0), rhs = Counter(1)
- expression 7 operands: lhs = Expression(8, Sub), rhs = Counter(4)
- expression 8 operands: lhs = Counter(0), rhs = Counter(1)
Number of file 0 mappings: 9
- Code(Counter(0)) at (prev + 23, 1) to (start + 0, 47)
- Code(Expression(0, Add)) at (prev + 1, 9) to (start + 0, 10)
= (c1 + ((c2 + c3) + c4))
- Code(Counter(0)) at (prev + 0, 13) to (start + 0, 14)
- Branch { true: Counter(1), false: Expression(8, Sub) } at (prev + 0, 13) to (start + 0, 14)
true = c1
false = (c0 - c1)
- Code(Expression(8, Sub)) at (prev + 0, 18) to (start + 0, 19)
= (c0 - c1)
- Branch { true: Expression(7, Sub), false: Counter(4) } at (prev + 0, 18) to (start + 0, 19)
true = ((c0 - c1) - c4)
false = c4
- Code(Expression(7, Sub)) at (prev + 0, 23) to (start + 0, 24)
= ((c0 - c1) - c4)
- Branch { true: Counter(2), false: Counter(3) } at (prev + 0, 23) to (start + 0, 24)
true = c2
false = c3
- Code(Expression(0, Add)) at (prev + 1, 5) to (start + 1, 2)
= (c1 + ((c2 + c3) + c4))

Function name: conditions::assign_and
Raw bytes (51): 0x[01, 01, 04, 07, 0e, 09, 0d, 01, 05, 01, 05, 07, 01, 0d, 01, 00, 21, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 0e, 00, 0d, 00, 0e, 05, 00, 12, 00, 13, 20, 09, 0d, 00, 12, 00, 13, 03, 01, 05, 01, 02]
Number of files: 1
- file 0 => global file 1
Number of expressions: 4
- expression 0 operands: lhs = Expression(1, Add), rhs = Expression(3, Sub)
- expression 1 operands: lhs = Counter(2), rhs = Counter(3)
- expression 2 operands: lhs = Counter(0), rhs = Counter(1)
- expression 3 operands: lhs = Counter(0), rhs = Counter(1)
Number of file 0 mappings: 7
- Code(Counter(0)) at (prev + 13, 1) to (start + 0, 33)
- Code(Expression(0, Add)) at (prev + 1, 9) to (start + 0, 10)
= ((c2 + c3) + (c0 - c1))
- Code(Counter(0)) at (prev + 0, 13) to (start + 0, 14)
- Branch { true: Counter(1), false: Expression(3, Sub) } at (prev + 0, 13) to (start + 0, 14)
true = c1
false = (c0 - c1)
- Code(Counter(1)) at (prev + 0, 18) to (start + 0, 19)
- Branch { true: Counter(2), false: Counter(3) } at (prev + 0, 18) to (start + 0, 19)
true = c2
false = c3
- Code(Expression(0, Add)) at (prev + 1, 5) to (start + 1, 2)
= ((c2 + c3) + (c0 - c1))

Function name: conditions::assign_or
Raw bytes (51): 0x[01, 01, 04, 07, 0d, 05, 09, 01, 05, 01, 05, 07, 01, 12, 01, 00, 20, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 0e, 00, 0d, 00, 0e, 0e, 00, 12, 00, 13, 20, 09, 0d, 00, 12, 00, 13, 03, 01, 05, 01, 02]
Number of files: 1
- file 0 => global file 1
Number of expressions: 4
- expression 0 operands: lhs = Expression(1, Add), rhs = Counter(3)
- expression 1 operands: lhs = Counter(1), rhs = Counter(2)
- expression 2 operands: lhs = Counter(0), rhs = Counter(1)
- expression 3 operands: lhs = Counter(0), rhs = Counter(1)
Number of file 0 mappings: 7
- Code(Counter(0)) at (prev + 18, 1) to (start + 0, 32)
- Code(Expression(0, Add)) at (prev + 1, 9) to (start + 0, 10)
= ((c1 + c2) + c3)
- Code(Counter(0)) at (prev + 0, 13) to (start + 0, 14)
- Branch { true: Counter(1), false: Expression(3, Sub) } at (prev + 0, 13) to (start + 0, 14)
true = c1
false = (c0 - c1)
- Code(Expression(3, Sub)) at (prev + 0, 18) to (start + 0, 19)
= (c0 - c1)
- Branch { true: Counter(2), false: Counter(3) } at (prev + 0, 18) to (start + 0, 19)
true = c2
false = c3
- Code(Expression(0, Add)) at (prev + 1, 5) to (start + 1, 2)
= ((c1 + c2) + c3)

Function name: conditions::foo
Raw bytes (9): 0x[01, 01, 00, 01, 01, 21, 01, 02, 02]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 33, 1) to (start + 2, 2)

Function name: conditions::func_call
Raw bytes (39): 0x[01, 01, 03, 01, 05, 0b, 02, 09, 0d, 05, 01, 25, 01, 01, 0a, 20, 05, 02, 01, 09, 00, 0a, 05, 00, 0e, 00, 0f, 20, 09, 0d, 00, 0e, 00, 0f, 07, 01, 01, 00, 02]
Number of files: 1
- file 0 => global file 1
Number of expressions: 3
- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
- expression 1 operands: lhs = Expression(2, Add), rhs = Expression(0, Sub)
- expression 2 operands: lhs = Counter(2), rhs = Counter(3)
Number of file 0 mappings: 5
- Code(Counter(0)) at (prev + 37, 1) to (start + 1, 10)
- Branch { true: Counter(1), false: Expression(0, Sub) } at (prev + 1, 9) to (start + 0, 10)
true = c1
false = (c0 - c1)
- Code(Counter(1)) at (prev + 0, 14) to (start + 0, 15)
- Branch { true: Counter(2), false: Counter(3) } at (prev + 0, 14) to (start + 0, 15)
true = c2
false = c3
- Code(Expression(1, Add)) at (prev + 1, 1) to (start + 0, 2)
= ((c2 + c3) + (c0 - c1))

Function name: conditions::simple_assign
Raw bytes (9): 0x[01, 01, 00, 01, 01, 08, 01, 03, 02]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 8, 1) to (start + 3, 2)

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