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coverage: Simplify counter expressions using simple algebra

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Some of these cases currently don't occur in practice, but are included for
completeness, and to avoid having to add them later as branch coverage and
MC/DC coverage start building more complex expressions.
This commit is contained in:
Zalathar 2024-05-14 13:51:24 +10:00
parent a68bb5e176
commit d01df6f9aa
43 changed files with 845 additions and 1315 deletions
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37
compiler/rustc_mir_transform/src/coverage/counters.rs
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@ -115,6 +115,43 @@ impl CoverageCounters {
expressions: &mut IndexVec<ExpressionId, BcbExpression>,
new_expr: BcbExpression,
) -> BcbCounter {
// Simplify expressions using basic algebra.
//
// Some of these cases might not actually occur in practice, depending
// on the details of how the instrumentor builds expressions.
let BcbExpression { lhs, op, rhs } = new_expr;
if let BcbCounter::Expression { id } = lhs {
let lhs_expr = &expressions[id];
// Simplify `(a - b) + b` to `a`.
if lhs_expr.op == Op::Subtract && op == Op::Add && lhs_expr.rhs == rhs {
return lhs_expr.lhs;
}
// Simplify `(a + b) - b` to `a`.
if lhs_expr.op == Op::Add && op == Op::Subtract && lhs_expr.rhs == rhs {
return lhs_expr.lhs;
}
// Simplify `(a + b) - a` to `b`.
if lhs_expr.op == Op::Add && op == Op::Subtract && lhs_expr.lhs == rhs {
return lhs_expr.rhs;
}
}
if let BcbCounter::Expression { id } = rhs {
let rhs_expr = &expressions[id];
// Simplify `a + (b - a)` to `b`.
if op == Op::Add && rhs_expr.op == Op::Subtract && lhs == rhs_expr.rhs {
return rhs_expr.lhs;
}
// Simplify `a - (a - b)` to `b`.
if op == Op::Subtract && rhs_expr.op == Op::Subtract && lhs == rhs_expr.lhs {
return rhs_expr.rhs;
}
}
// Simplification failed, so actually create the new expression.
let id = expressions.push(new_expr);
BcbCounter::Expression { id }
}