rust-clippy/clippy_lints/src/floating_point_arithmetic.rs
2020-09-04 18:27:33 +02:00

721 lines
24 KiB
Rust

use crate::consts::{
constant, constant_simple, Constant,
Constant::{Int, F32, F64},
};
use crate::utils::{eq_expr_value, get_parent_expr, higher, numeric_literal, span_lint_and_sugg, sugg};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind, PathSegment, UnOp};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Spanned;
use rustc_ast::ast;
use std::f32::consts as f32_consts;
use std::f64::consts as f64_consts;
use sugg::Sugg;
declare_clippy_lint! {
/// **What it does:** Looks for floating-point expressions that
/// can be expressed using built-in methods to improve accuracy
/// at the cost of performance.
///
/// **Why is this bad?** Negatively impacts accuracy.
///
/// **Known problems:** None
///
/// **Example:**
///
/// ```rust
/// let a = 3f32;
/// let _ = a.powf(1.0 / 3.0);
/// let _ = (1.0 + a).ln();
/// let _ = a.exp() - 1.0;
/// ```
///
/// is better expressed as
///
/// ```rust
/// let a = 3f32;
/// let _ = a.cbrt();
/// let _ = a.ln_1p();
/// let _ = a.exp_m1();
/// ```
pub IMPRECISE_FLOPS,
nursery,
"usage of imprecise floating point operations"
}
declare_clippy_lint! {
/// **What it does:** Looks for floating-point expressions that
/// can be expressed using built-in methods to improve both
/// accuracy and performance.
///
/// **Why is this bad?** Negatively impacts accuracy and performance.
///
/// **Known problems:** None
///
/// **Example:**
///
/// ```rust
/// use std::f32::consts::E;
///
/// let a = 3f32;
/// let _ = (2f32).powf(a);
/// let _ = E.powf(a);
/// let _ = a.powf(1.0 / 2.0);
/// let _ = a.log(2.0);
/// let _ = a.log(10.0);
/// let _ = a.log(E);
/// let _ = a.powf(2.0);
/// let _ = a * 2.0 + 4.0;
/// let _ = if a < 0.0 {
/// -a
/// } else {
/// a
/// };
/// let _ = if a < 0.0 {
/// a
/// } else {
/// -a
/// };
/// ```
///
/// is better expressed as
///
/// ```rust
/// use std::f32::consts::E;
///
/// let a = 3f32;
/// let _ = a.exp2();
/// let _ = a.exp();
/// let _ = a.sqrt();
/// let _ = a.log2();
/// let _ = a.log10();
/// let _ = a.ln();
/// let _ = a.powi(2);
/// let _ = a.mul_add(2.0, 4.0);
/// let _ = a.abs();
/// let _ = -a.abs();
/// ```
pub SUBOPTIMAL_FLOPS,
nursery,
"usage of sub-optimal floating point operations"
}
declare_lint_pass!(FloatingPointArithmetic => [
IMPRECISE_FLOPS,
SUBOPTIMAL_FLOPS
]);
// Returns the specialized log method for a given base if base is constant
// and is one of 2, 10 and e
fn get_specialized_log_method(cx: &LateContext<'_>, base: &Expr<'_>) -> Option<&'static str> {
if let Some((value, _)) = constant(cx, cx.typeck_results(), base) {
if F32(2.0) == value || F64(2.0) == value {
return Some("log2");
} else if F32(10.0) == value || F64(10.0) == value {
return Some("log10");
} else if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
return Some("ln");
}
}
None
}
// Adds type suffixes and parenthesis to method receivers if necessary
fn prepare_receiver_sugg<'a>(cx: &LateContext<'_>, mut expr: &'a Expr<'a>) -> Sugg<'a> {
let mut suggestion = Sugg::hir(cx, expr, "..");
if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
expr = &inner_expr;
}
if_chain! {
// if the expression is a float literal and it is unsuffixed then
// add a suffix so the suggestion is valid and unambiguous
if let ty::Float(float_ty) = cx.typeck_results().expr_ty(expr).kind();
if let ExprKind::Lit(lit) = &expr.kind;
if let ast::LitKind::Float(sym, ast::LitFloatType::Unsuffixed) = lit.node;
then {
let op = format!(
"{}{}{}",
suggestion,
// Check for float literals without numbers following the decimal
// separator such as `2.` and adds a trailing zero
if sym.as_str().ends_with('.') {
"0"
} else {
""
},
float_ty.name_str()
).into();
suggestion = match suggestion {
Sugg::MaybeParen(_) => Sugg::MaybeParen(op),
_ => Sugg::NonParen(op)
};
}
}
suggestion.maybe_par()
}
fn check_log_base(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
if let Some(method) = get_specialized_log_method(cx, &args[1]) {
span_lint_and_sugg(
cx,
SUBOPTIMAL_FLOPS,
expr.span,
"logarithm for bases 2, 10 and e can be computed more accurately",
"consider using",
format!("{}.{}()", Sugg::hir(cx, &args[0], ".."), method),
Applicability::MachineApplicable,
);
}
}
// TODO: Lint expressions of the form `(x + y).ln()` where y > 1 and
// suggest usage of `(x + (y - 1)).ln_1p()` instead
fn check_ln1p(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Add, ..
},
lhs,
rhs,
) = &args[0].kind
{
let recv = match (
constant(cx, cx.typeck_results(), lhs),
constant(cx, cx.typeck_results(), rhs),
) {
(Some((value, _)), _) if F32(1.0) == value || F64(1.0) == value => rhs,
(_, Some((value, _))) if F32(1.0) == value || F64(1.0) == value => lhs,
_ => return,
};
span_lint_and_sugg(
cx,
IMPRECISE_FLOPS,
expr.span,
"ln(1 + x) can be computed more accurately",
"consider using",
format!("{}.ln_1p()", prepare_receiver_sugg(cx, recv)),
Applicability::MachineApplicable,
);
}
}
// Returns an integer if the float constant is a whole number and it can be
// converted to an integer without loss of precision. For now we only check
// ranges [-16777215, 16777216) for type f32 as whole number floats outside
// this range are lossy and ambiguous.
#[allow(clippy::cast_possible_truncation)]
fn get_integer_from_float_constant(value: &Constant) -> Option<i32> {
match value {
F32(num) if num.fract() == 0.0 => {
if (-16_777_215.0..16_777_216.0).contains(num) {
Some(num.round() as i32)
} else {
None
}
},
F64(num) if num.fract() == 0.0 => {
if (-2_147_483_648.0..2_147_483_648.0).contains(num) {
Some(num.round() as i32)
} else {
None
}
},
_ => None,
}
}
fn check_powf(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
// Check receiver
if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
let method = if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
"exp"
} else if F32(2.0) == value || F64(2.0) == value {
"exp2"
} else {
return;
};
span_lint_and_sugg(
cx,
SUBOPTIMAL_FLOPS,
expr.span,
"exponent for bases 2 and e can be computed more accurately",
"consider using",
format!("{}.{}()", prepare_receiver_sugg(cx, &args[1]), method),
Applicability::MachineApplicable,
);
}
// Check argument
if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[1]) {
let (lint, help, suggestion) = if F32(1.0 / 2.0) == value || F64(1.0 / 2.0) == value {
(
SUBOPTIMAL_FLOPS,
"square-root of a number can be computed more efficiently and accurately",
format!("{}.sqrt()", Sugg::hir(cx, &args[0], "..")),
)
} else if F32(1.0 / 3.0) == value || F64(1.0 / 3.0) == value {
(
IMPRECISE_FLOPS,
"cube-root of a number can be computed more accurately",
format!("{}.cbrt()", Sugg::hir(cx, &args[0], "..")),
)
} else if let Some(exponent) = get_integer_from_float_constant(&value) {
(
SUBOPTIMAL_FLOPS,
"exponentiation with integer powers can be computed more efficiently",
format!(
"{}.powi({})",
Sugg::hir(cx, &args[0], ".."),
numeric_literal::format(&exponent.to_string(), None, false)
),
)
} else {
return;
};
span_lint_and_sugg(
cx,
lint,
expr.span,
help,
"consider using",
suggestion,
Applicability::MachineApplicable,
);
}
}
fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[1]) {
if value == Int(2) {
if let Some(parent) = get_parent_expr(cx, expr) {
if let Some(grandparent) = get_parent_expr(cx, parent) {
if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, _, args, _) = grandparent.kind {
if method_name.as_str() == "sqrt" && detect_hypot(cx, args).is_some() {
return;
}
}
}
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Add, ..
},
ref lhs,
ref rhs,
) = parent.kind
{
let other_addend = if lhs.hir_id == expr.hir_id { rhs } else { lhs };
span_lint_and_sugg(
cx,
SUBOPTIMAL_FLOPS,
parent.span,
"square can be computed more efficiently",
"consider using",
format!(
"{}.mul_add({}, {})",
Sugg::hir(cx, &args[0], ".."),
Sugg::hir(cx, &args[0], ".."),
Sugg::hir(cx, &other_addend, ".."),
),
Applicability::MachineApplicable,
);
return;
}
}
span_lint_and_sugg(
cx,
SUBOPTIMAL_FLOPS,
expr.span,
"square can be computed more efficiently",
"consider using",
format!("{} * {}", Sugg::hir(cx, &args[0], ".."), Sugg::hir(cx, &args[0], "..")),
Applicability::MachineApplicable,
);
}
}
}
fn detect_hypot(cx: &LateContext<'_>, args: &[Expr<'_>]) -> Option<String> {
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Add, ..
},
ref add_lhs,
ref add_rhs,
) = args[0].kind
{
// check if expression of the form x * x + y * y
if_chain! {
if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, ref lmul_lhs, ref lmul_rhs) = add_lhs.kind;
if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, ref rmul_lhs, ref rmul_rhs) = add_rhs.kind;
if eq_expr_value(cx, lmul_lhs, lmul_rhs);
if eq_expr_value(cx, rmul_lhs, rmul_rhs);
then {
return Some(format!("{}.hypot({})", Sugg::hir(cx, &lmul_lhs, ".."), Sugg::hir(cx, &rmul_lhs, "..")));
}
}
// check if expression of the form x.powi(2) + y.powi(2)
if_chain! {
if let ExprKind::MethodCall(
PathSegment { ident: lmethod_name, .. },
ref _lspan,
ref largs,
_
) = add_lhs.kind;
if let ExprKind::MethodCall(
PathSegment { ident: rmethod_name, .. },
ref _rspan,
ref rargs,
_
) = add_rhs.kind;
if lmethod_name.as_str() == "powi" && rmethod_name.as_str() == "powi";
if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), &largs[1]);
if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), &rargs[1]);
if Int(2) == lvalue && Int(2) == rvalue;
then {
return Some(format!("{}.hypot({})", Sugg::hir(cx, &largs[0], ".."), Sugg::hir(cx, &rargs[0], "..")));
}
}
}
None
}
fn check_hypot(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
if let Some(message) = detect_hypot(cx, args) {
span_lint_and_sugg(
cx,
IMPRECISE_FLOPS,
expr.span,
"hypotenuse can be computed more accurately",
"consider using",
message,
Applicability::MachineApplicable,
);
}
}
// TODO: Lint expressions of the form `x.exp() - y` where y > 1
// and suggest usage of `x.exp_m1() - (y - 1)` instead
fn check_expm1(cx: &LateContext<'_>, expr: &Expr<'_>) {
if_chain! {
if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, ref lhs, ref rhs) = expr.kind;
if cx.typeck_results().expr_ty(lhs).is_floating_point();
if let Some((value, _)) = constant(cx, cx.typeck_results(), rhs);
if F32(1.0) == value || F64(1.0) == value;
if let ExprKind::MethodCall(ref path, _, ref method_args, _) = lhs.kind;
if cx.typeck_results().expr_ty(&method_args[0]).is_floating_point();
if path.ident.name.as_str() == "exp";
then {
span_lint_and_sugg(
cx,
IMPRECISE_FLOPS,
expr.span,
"(e.pow(x) - 1) can be computed more accurately",
"consider using",
format!(
"{}.exp_m1()",
Sugg::hir(cx, &method_args[0], "..")
),
Applicability::MachineApplicable,
);
}
}
}
fn is_float_mul_expr<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
if_chain! {
if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, ref lhs, ref rhs) = &expr.kind;
if cx.typeck_results().expr_ty(lhs).is_floating_point();
if cx.typeck_results().expr_ty(rhs).is_floating_point();
then {
return Some((lhs, rhs));
}
}
None
}
// TODO: Fix rust-lang/rust-clippy#4735
fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Add, ..
},
lhs,
rhs,
) = &expr.kind
{
if let Some(parent) = get_parent_expr(cx, expr) {
if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, _, args, _) = parent.kind {
if method_name.as_str() == "sqrt" && detect_hypot(cx, args).is_some() {
return;
}
}
}
let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
(inner_lhs, inner_rhs, rhs)
} else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
(inner_lhs, inner_rhs, lhs)
} else {
return;
};
span_lint_and_sugg(
cx,
SUBOPTIMAL_FLOPS,
expr.span,
"multiply and add expressions can be calculated more efficiently and accurately",
"consider using",
format!(
"{}.mul_add({}, {})",
prepare_receiver_sugg(cx, recv),
Sugg::hir(cx, arg1, ".."),
Sugg::hir(cx, arg2, ".."),
),
Applicability::MachineApplicable,
);
}
}
/// Returns true iff expr is an expression which tests whether or not
/// test is positive or an expression which tests whether or not test
/// is nonnegative.
/// Used for check-custom-abs function below
fn is_testing_positive(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
match op {
BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, right) && eq_expr_value(cx, left, test),
BinOpKind::Lt | BinOpKind::Le => is_zero(cx, left) && eq_expr_value(cx, right, test),
_ => false,
}
} else {
false
}
}
/// See [`is_testing_positive`]
fn is_testing_negative(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
match op {
BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, left) && eq_expr_value(cx, right, test),
BinOpKind::Lt | BinOpKind::Le => is_zero(cx, right) && eq_expr_value(cx, left, test),
_ => false,
}
} else {
false
}
}
/// Returns true iff expr is some zero literal
fn is_zero(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
match constant_simple(cx, cx.typeck_results(), expr) {
Some(Constant::Int(i)) => i == 0,
Some(Constant::F32(f)) => f == 0.0,
Some(Constant::F64(f)) => f == 0.0,
_ => false,
}
}
/// If the two expressions are negations of each other, then it returns
/// a tuple, in which the first element is true iff expr1 is the
/// positive expressions, and the second element is the positive
/// one of the two expressions
/// If the two expressions are not negations of each other, then it
/// returns None.
fn are_negated<'a>(cx: &LateContext<'_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a>) -> Option<(bool, &'a Expr<'a>)> {
if let ExprKind::Unary(UnOp::UnNeg, expr1_negated) = &expr1.kind {
if eq_expr_value(cx, expr1_negated, expr2) {
return Some((false, expr2));
}
}
if let ExprKind::Unary(UnOp::UnNeg, expr2_negated) = &expr2.kind {
if eq_expr_value(cx, expr1, expr2_negated) {
return Some((true, expr1));
}
}
None
}
fn check_custom_abs(cx: &LateContext<'_>, expr: &Expr<'_>) {
if_chain! {
if let Some((cond, body, Some(else_body))) = higher::if_block(&expr);
if let ExprKind::Block(block, _) = body.kind;
if block.stmts.is_empty();
if let Some(if_body_expr) = block.expr;
if let ExprKind::Block(else_block, _) = else_body.kind;
if else_block.stmts.is_empty();
if let Some(else_body_expr) = else_block.expr;
if let Some((if_expr_positive, body)) = are_negated(cx, if_body_expr, else_body_expr);
then {
let positive_abs_sugg = (
"manual implementation of `abs` method",
format!("{}.abs()", Sugg::hir(cx, body, "..")),
);
let negative_abs_sugg = (
"manual implementation of negation of `abs` method",
format!("-{}.abs()", Sugg::hir(cx, body, "..")),
);
let sugg = if is_testing_positive(cx, cond, body) {
if if_expr_positive {
positive_abs_sugg
} else {
negative_abs_sugg
}
} else if is_testing_negative(cx, cond, body) {
if if_expr_positive {
negative_abs_sugg
} else {
positive_abs_sugg
}
} else {
return;
};
span_lint_and_sugg(
cx,
SUBOPTIMAL_FLOPS,
expr.span,
sugg.0,
"try",
sugg.1,
Applicability::MachineApplicable,
);
}
}
}
fn are_same_base_logs(cx: &LateContext<'_>, expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
if_chain! {
if let ExprKind::MethodCall(PathSegment { ident: method_name_a, .. }, _, ref args_a, _) = expr_a.kind;
if let ExprKind::MethodCall(PathSegment { ident: method_name_b, .. }, _, ref args_b, _) = expr_b.kind;
then {
return method_name_a.as_str() == method_name_b.as_str() &&
args_a.len() == args_b.len() &&
(
["ln", "log2", "log10"].contains(&&*method_name_a.as_str()) ||
method_name_a.as_str() == "log" && args_a.len() == 2 && eq_expr_value(cx, &args_a[1], &args_b[1])
);
}
}
false
}
fn check_log_division(cx: &LateContext<'_>, expr: &Expr<'_>) {
// check if expression of the form x.logN() / y.logN()
if_chain! {
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Div, ..
},
lhs,
rhs,
) = &expr.kind;
if are_same_base_logs(cx, lhs, rhs);
if let ExprKind::MethodCall(_, _, ref largs, _) = lhs.kind;
if let ExprKind::MethodCall(_, _, ref rargs, _) = rhs.kind;
then {
span_lint_and_sugg(
cx,
SUBOPTIMAL_FLOPS,
expr.span,
"log base can be expressed more clearly",
"consider using",
format!("{}.log({})", Sugg::hir(cx, &largs[0], ".."), Sugg::hir(cx, &rargs[0], ".."),),
Applicability::MachineApplicable,
);
}
}
}
fn check_radians(cx: &LateContext<'_>, expr: &Expr<'_>) {
if_chain! {
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Div, ..
},
div_lhs,
div_rhs,
) = &expr.kind;
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Mul, ..
},
mul_lhs,
mul_rhs,
) = &div_lhs.kind;
if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), div_rhs);
if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), mul_rhs);
then {
// TODO: also check for constant values near PI/180 or 180/PI
if (F32(f32_consts::PI) == rvalue || F64(f64_consts::PI) == rvalue) &&
(F32(180_f32) == lvalue || F64(180_f64) == lvalue)
{
span_lint_and_sugg(
cx,
SUBOPTIMAL_FLOPS,
expr.span,
"conversion to degrees can be done more accurately",
"consider using",
format!("{}.to_degrees()", Sugg::hir(cx, &mul_lhs, "..")),
Applicability::MachineApplicable,
);
} else if
(F32(180_f32) == rvalue || F64(180_f64) == rvalue) &&
(F32(f32_consts::PI) == lvalue || F64(f64_consts::PI) == lvalue)
{
span_lint_and_sugg(
cx,
SUBOPTIMAL_FLOPS,
expr.span,
"conversion to radians can be done more accurately",
"consider using",
format!("{}.to_radians()", Sugg::hir(cx, &mul_lhs, "..")),
Applicability::MachineApplicable,
);
}
}
}
}
impl<'tcx> LateLintPass<'tcx> for FloatingPointArithmetic {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let ExprKind::MethodCall(ref path, _, args, _) = &expr.kind {
let recv_ty = cx.typeck_results().expr_ty(&args[0]);
if recv_ty.is_floating_point() {
match &*path.ident.name.as_str() {
"ln" => check_ln1p(cx, expr, args),
"log" => check_log_base(cx, expr, args),
"powf" => check_powf(cx, expr, args),
"powi" => check_powi(cx, expr, args),
"sqrt" => check_hypot(cx, expr, args),
_ => {},
}
}
} else {
check_expm1(cx, expr);
check_mul_add(cx, expr);
check_custom_abs(cx, expr);
check_log_division(cx, expr);
check_radians(cx, expr);
}
}
}