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Fix divmul peeling

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This commit is contained in:
teor 2024-01-17 12:22:23 +10:00
parent d109e68178
commit 1cbb58bd06
1 changed files with 11 additions and 4 deletions
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15
clippy_lints/src/casts/cast_sign_loss.rs
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@ -229,23 +229,30 @@ fn exprs_with_muldiv_binop_peeled<'e>(expr: &'e Expr<'_>) -> Vec<&'e Expr<'e>> {
// For binary operators which both contribute to the sign of the result,
// collect all their operands, recursively. This ignores overflow.
ControlFlow::Continue(Descend::Yes)
} else if matches!(op.node, BinOpKind::Rem) {
} else if matches!(op.node, BinOpKind::Rem | BinOpKind::Shr) {
// For binary operators where the left hand side determines the sign of the result,
// only collect that side, recursively. Overflow panics, so this always holds.
//
// Large left shifts turn negatives into zeroes, so we can't use it here.
//
// > Given remainder = dividend % divisor, the remainder will have the same sign as the dividend
// > ...
// > Arithmetic right shift on signed integer types
// https://doc.rust-lang.org/reference/expressions/operator-expr.html#arithmetic-and-logical-binary-operators
// We want to descend into the lhs, but skip the rhs.
// That's tricky to do using for_each_expr(), so we just keep the lhs intact.
res.push(lhs);
ControlFlow::Break(())
ControlFlow::Continue(Descend::No)
} else {
// The sign of the result of other binary operators depends on the values of the operands,
// so try to evaluate the expression.
res.push(expr);
res.push(sub_expr);
ControlFlow::Continue(Descend::No)
}
} else {
// For other expressions, including unary operators and constants, try to evaluate the expression.
res.push(expr);
res.push(sub_expr);
ControlFlow::Continue(Descend::No)
}
});