1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution.
4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
7 // option. This file may not be copied, modified, or distributed
8 // except according to those terms.
10 use crate::consts::{constant, Constant};
11 use crate::rustc::hir::*;
12 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
13 use crate::rustc::{declare_tool_lint, lint_array};
14 use crate::rustc_errors::Applicability;
15 use crate::syntax::ast::LitKind;
16 use crate::syntax::source_map::Span;
17 use crate::utils::sugg::Sugg;
18 use crate::utils::{span_lint, span_lint_and_then};
19 use if_chain::if_chain;
21 /// **What it does:** Checks for incompatible bit masks in comparisons.
23 /// The formula for detecting if an expression of the type `_ <bit_op> m
24 /// <cmp_op> c` (where `<bit_op>` is one of {`&`, `|`} and `<cmp_op>` is one of
25 /// {`!=`, `>=`, `>`, `!=`, `>=`, `>`}) can be determined from the following
28 /// |Comparison |Bit Op|Example |is always|Formula |
29 /// |------------|------|------------|---------|----------------------|
30 /// |`==` or `!=`| `&` |`x & 2 == 3`|`false` |`c & m != c` |
31 /// |`<` or `>=`| `&` |`x & 2 < 3` |`true` |`m < c` |
32 /// |`>` or `<=`| `&` |`x & 1 > 1` |`false` |`m <= c` |
33 /// |`==` or `!=`| `|` |`x | 1 == 0`|`false` |`c | m != c` |
34 /// |`<` or `>=`| `|` |`x | 1 < 1` |`false` |`m >= c` |
35 /// |`<=` or `>` | `|` |`x | 1 > 0` |`true` |`m > c` |
37 /// **Why is this bad?** If the bits that the comparison cares about are always
38 /// set to zero or one by the bit mask, the comparison is constant `true` or
39 /// `false` (depending on mask, compared value, and operators).
41 /// So the code is actively misleading, and the only reason someone would write
42 /// this intentionally is to win an underhanded Rust contest or create a
43 /// test-case for this lint.
45 /// **Known problems:** None.
49 /// if (x & 1 == 2) { … }
51 declare_clippy_lint! {
54 "expressions of the form `_ & mask == select` that will only ever return `true` or `false`"
57 /// **What it does:** Checks for bit masks in comparisons which can be removed
58 /// without changing the outcome. The basic structure can be seen in the
61 /// |Comparison| Bit Op |Example |equals |
62 /// |----------|---------|-----------|-------|
63 /// |`>` / `<=`|`|` / `^`|`x | 2 > 3`|`x > 3`|
64 /// |`<` / `>=`|`|` / `^`|`x ^ 1 < 4`|`x < 4`|
66 /// **Why is this bad?** Not equally evil as [`bad_bit_mask`](#bad_bit_mask),
67 /// but still a bit misleading, because the bit mask is ineffective.
69 /// **Known problems:** False negatives: This lint will only match instances
70 /// where we have figured out the math (which is for a power-of-two compared
71 /// value). This means things like `x | 1 >= 7` (which would be better written
72 /// as `x >= 6`) will not be reported (but bit masks like this are fairly
77 /// if (x | 1 > 3) { … }
79 declare_clippy_lint! {
80 pub INEFFECTIVE_BIT_MASK,
82 "expressions where a bit mask will be rendered useless by a comparison, e.g. `(x | 1) > 2`"
85 /// **What it does:** Checks for bit masks that can be replaced by a call
86 /// to `trailing_zeros`
88 /// **Why is this bad?** `x.trailing_zeros() > 4` is much clearer than `x & 15
91 /// **Known problems:** llvm generates better code for `x & 15 == 0` on x86
97 declare_clippy_lint! {
100 "expressions where a bit mask is less readable than the corresponding method call"
103 #[derive(Copy, Clone)]
105 verbose_bit_mask_threshold: u64,
109 pub fn new(verbose_bit_mask_threshold: u64) -> Self {
111 verbose_bit_mask_threshold,
116 impl LintPass for BitMask {
117 fn get_lints(&self) -> LintArray {
118 lint_array!(BAD_BIT_MASK, INEFFECTIVE_BIT_MASK, VERBOSE_BIT_MASK)
122 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BitMask {
123 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
124 if let ExprKind::Binary(ref cmp, ref left, ref right) = e.node {
125 if cmp.node.is_comparison() {
126 if let Some(cmp_opt) = fetch_int_literal(cx, right) {
127 check_compare(cx, left, cmp.node, cmp_opt, e.span)
128 } else if let Some(cmp_val) = fetch_int_literal(cx, left) {
129 check_compare(cx, right, invert_cmp(cmp.node), cmp_val, e.span)
134 if let ExprKind::Binary(ref op, ref left, ref right) = e.node;
135 if BinOpKind::Eq == op.node;
136 if let ExprKind::Binary(ref op1, ref left1, ref right1) = left.node;
137 if BinOpKind::BitAnd == op1.node;
138 if let ExprKind::Lit(ref lit) = right1.node;
139 if let LitKind::Int(n, _) = lit.node;
140 if let ExprKind::Lit(ref lit1) = right.node;
141 if let LitKind::Int(0, _) = lit1.node;
142 if n.leading_zeros() == n.count_zeros();
143 if n > u128::from(self.verbose_bit_mask_threshold);
145 span_lint_and_then(cx,
148 "bit mask could be simplified with a call to `trailing_zeros`",
150 let sugg = Sugg::hir(cx, left1, "...").maybe_par();
151 db.span_suggestion_with_applicability(
154 format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()),
155 Applicability::MaybeIncorrect,
163 fn invert_cmp(cmp: BinOpKind) -> BinOpKind {
165 BinOpKind::Eq => BinOpKind::Eq,
166 BinOpKind::Ne => BinOpKind::Ne,
167 BinOpKind::Lt => BinOpKind::Gt,
168 BinOpKind::Gt => BinOpKind::Lt,
169 BinOpKind::Le => BinOpKind::Ge,
170 BinOpKind::Ge => BinOpKind::Le,
171 _ => BinOpKind::Or, // Dummy
175 fn check_compare(cx: &LateContext<'_, '_>, bit_op: &Expr, cmp_op: BinOpKind, cmp_value: u128, span: Span) {
176 if let ExprKind::Binary(ref op, ref left, ref right) = bit_op.node {
177 if op.node != BinOpKind::BitAnd && op.node != BinOpKind::BitOr {
180 fetch_int_literal(cx, right)
181 .or_else(|| fetch_int_literal(cx, left))
182 .map_or((), |mask| check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span))
187 cx: &LateContext<'_, '_>,
195 BinOpKind::Eq | BinOpKind::Ne => match bit_op {
196 BinOpKind::BitAnd => {
197 if mask_value & cmp_value != cmp_value {
204 "incompatible bit mask: `_ & {}` can never be equal to `{}`",
205 mask_value, cmp_value
209 } else if mask_value == 0 {
210 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
213 BinOpKind::BitOr => {
214 if mask_value | cmp_value != cmp_value {
220 "incompatible bit mask: `_ | {}` can never be equal to `{}`",
221 mask_value, cmp_value
228 BinOpKind::Lt | BinOpKind::Ge => match bit_op {
229 BinOpKind::BitAnd => {
230 if mask_value < cmp_value {
236 "incompatible bit mask: `_ & {}` will always be lower than `{}`",
237 mask_value, cmp_value
240 } else if mask_value == 0 {
241 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
244 BinOpKind::BitOr => {
245 if mask_value >= cmp_value {
251 "incompatible bit mask: `_ | {}` will never be lower than `{}`",
252 mask_value, cmp_value
256 check_ineffective_lt(cx, span, mask_value, cmp_value, "|");
259 BinOpKind::BitXor => check_ineffective_lt(cx, span, mask_value, cmp_value, "^"),
262 BinOpKind::Le | BinOpKind::Gt => match bit_op {
263 BinOpKind::BitAnd => {
264 if mask_value <= cmp_value {
270 "incompatible bit mask: `_ & {}` will never be higher than `{}`",
271 mask_value, cmp_value
274 } else if mask_value == 0 {
275 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
278 BinOpKind::BitOr => {
279 if mask_value > cmp_value {
285 "incompatible bit mask: `_ | {}` will always be higher than `{}`",
286 mask_value, cmp_value
290 check_ineffective_gt(cx, span, mask_value, cmp_value, "|");
293 BinOpKind::BitXor => check_ineffective_gt(cx, span, mask_value, cmp_value, "^"),
300 fn check_ineffective_lt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
301 if c.is_power_of_two() && m < c {
304 INEFFECTIVE_BIT_MASK,
307 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
314 fn check_ineffective_gt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
315 if (c + 1).is_power_of_two() && m <= c {
318 INEFFECTIVE_BIT_MASK,
321 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
328 fn fetch_int_literal(cx: &LateContext<'_, '_>, lit: &Expr) -> Option<u128> {
329 match constant(cx, cx.tables, lit)?.0 {
330 Constant::Int(n) => Some(n),