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.
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 if_chain::if_chain;
15 use crate::syntax::ast::LitKind;
16 use crate::syntax::source_map::Span;
17 use crate::utils::{span_lint, span_lint_and_then};
18 use crate::utils::sugg::Sugg;
19 use crate::consts::{constant, Constant};
20 use crate::rustc_errors::Applicability;
22 /// **What it does:** Checks for incompatible bit masks in comparisons.
24 /// The formula for detecting if an expression of the type `_ <bit_op> m
25 /// <cmp_op> c` (where `<bit_op>` is one of {`&`, `|`} and `<cmp_op>` is one of
26 /// {`!=`, `>=`, `>`, `!=`, `>=`, `>`}) can be determined from the following
29 /// |Comparison |Bit Op|Example |is always|Formula |
30 /// |------------|------|------------|---------|----------------------|
31 /// |`==` or `!=`| `&` |`x & 2 == 3`|`false` |`c & m != c` |
32 /// |`<` or `>=`| `&` |`x & 2 < 3` |`true` |`m < c` |
33 /// |`>` or `<=`| `&` |`x & 1 > 1` |`false` |`m <= c` |
34 /// |`==` or `!=`| `|` |`x | 1 == 0`|`false` |`c | m != c` |
35 /// |`<` or `>=`| `|` |`x | 1 < 1` |`false` |`m >= c` |
36 /// |`<=` or `>` | `|` |`x | 1 > 0` |`true` |`m > c` |
38 /// **Why is this bad?** If the bits that the comparison cares about are always
39 /// set to zero or one by the bit mask, the comparison is constant `true` or
40 /// `false` (depending on mask, compared value, and operators).
42 /// So the code is actively misleading, and the only reason someone would write
43 /// this intentionally is to win an underhanded Rust contest or create a
44 /// test-case for this lint.
46 /// **Known problems:** None.
50 /// if (x & 1 == 2) { … }
52 declare_clippy_lint! {
55 "expressions of the form `_ & mask == select` that will only ever return `true` or `false`"
58 /// **What it does:** Checks for bit masks in comparisons which can be removed
59 /// without changing the outcome. The basic structure can be seen in the
62 /// |Comparison| Bit Op |Example |equals |
63 /// |----------|---------|-----------|-------|
64 /// |`>` / `<=`|`|` / `^`|`x | 2 > 3`|`x > 3`|
65 /// |`<` / `>=`|`|` / `^`|`x ^ 1 < 4`|`x < 4`|
67 /// **Why is this bad?** Not equally evil as [`bad_bit_mask`](#bad_bit_mask),
68 /// but still a bit misleading, because the bit mask is ineffective.
70 /// **Known problems:** False negatives: This lint will only match instances
71 /// where we have figured out the math (which is for a power-of-two compared
72 /// value). This means things like `x | 1 >= 7` (which would be better written
73 /// as `x >= 6`) will not be reported (but bit masks like this are fairly
78 /// if (x | 1 > 3) { … }
80 declare_clippy_lint! {
81 pub INEFFECTIVE_BIT_MASK,
83 "expressions where a bit mask will be rendered useless by a comparison, e.g. `(x | 1) > 2`"
86 /// **What it does:** Checks for bit masks that can be replaced by a call
87 /// to `trailing_zeros`
89 /// **Why is this bad?** `x.trailing_zeros() > 4` is much clearer than `x & 15
92 /// **Known problems:** llvm generates better code for `x & 15 == 0` on x86
98 declare_clippy_lint! {
101 "expressions where a bit mask is less readable than the corresponding method call"
104 #[derive(Copy, Clone)]
106 verbose_bit_mask_threshold: u64,
110 pub fn new(verbose_bit_mask_threshold: u64) -> Self {
112 verbose_bit_mask_threshold,
117 impl LintPass for BitMask {
118 fn get_lints(&self) -> LintArray {
119 lint_array!(BAD_BIT_MASK, INEFFECTIVE_BIT_MASK, VERBOSE_BIT_MASK)
123 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BitMask {
124 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
125 if let ExprKind::Binary(ref cmp, ref left, ref right) = e.node {
126 if cmp.node.is_comparison() {
127 if let Some(cmp_opt) = fetch_int_literal(cx, right) {
128 check_compare(cx, left, cmp.node, cmp_opt, e.span)
129 } else if let Some(cmp_val) = fetch_int_literal(cx, left) {
130 check_compare(cx, right, invert_cmp(cmp.node), cmp_val, e.span)
135 if let ExprKind::Binary(ref op, ref left, ref right) = e.node;
136 if BinOpKind::Eq == op.node;
137 if let ExprKind::Binary(ref op1, ref left1, ref right1) = left.node;
138 if BinOpKind::BitAnd == op1.node;
139 if let ExprKind::Lit(ref lit) = right1.node;
140 if let LitKind::Int(n, _) = lit.node;
141 if let ExprKind::Lit(ref lit1) = right.node;
142 if let LitKind::Int(0, _) = lit1.node;
143 if n.leading_zeros() == n.count_zeros();
144 if n > u128::from(self.verbose_bit_mask_threshold);
146 span_lint_and_then(cx,
149 "bit mask could be simplified with a call to `trailing_zeros`",
151 let sugg = Sugg::hir(cx, left1, "...").maybe_par();
152 db.span_suggestion_with_applicability(
155 format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()),
156 Applicability::MaybeIncorrect,
164 fn invert_cmp(cmp: BinOpKind) -> BinOpKind {
166 BinOpKind::Eq => BinOpKind::Eq,
167 BinOpKind::Ne => BinOpKind::Ne,
168 BinOpKind::Lt => BinOpKind::Gt,
169 BinOpKind::Gt => BinOpKind::Lt,
170 BinOpKind::Le => BinOpKind::Ge,
171 BinOpKind::Ge => BinOpKind::Le,
172 _ => BinOpKind::Or, // Dummy
177 fn check_compare(cx: &LateContext<'_, '_>, bit_op: &Expr, cmp_op: BinOpKind, cmp_value: u128, span: Span) {
178 if let ExprKind::Binary(ref op, ref left, ref right) = bit_op.node {
179 if op.node != BinOpKind::BitAnd && op.node != BinOpKind::BitOr {
182 fetch_int_literal(cx, right)
183 .or_else(|| fetch_int_literal(cx, left))
184 .map_or((), |mask| check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span))
188 fn check_bit_mask(cx: &LateContext<'_, '_>, bit_op: BinOpKind, cmp_op: BinOpKind, mask_value: u128, cmp_value: u128, span: Span) {
190 BinOpKind::Eq | BinOpKind::Ne => match bit_op {
191 BinOpKind::BitAnd => if mask_value & cmp_value != cmp_value {
198 "incompatible bit mask: `_ & {}` can never be equal to `{}`",
204 } else if mask_value == 0 {
205 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
207 BinOpKind::BitOr => if mask_value | cmp_value != cmp_value {
213 "incompatible bit mask: `_ | {}` can never be equal to `{}`",
221 BinOpKind::Lt | BinOpKind::Ge => match bit_op {
222 BinOpKind::BitAnd => if mask_value < cmp_value {
228 "incompatible bit mask: `_ & {}` will always be lower than `{}`",
233 } else if mask_value == 0 {
234 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
236 BinOpKind::BitOr => if mask_value >= cmp_value {
242 "incompatible bit mask: `_ | {}` will never be lower than `{}`",
248 check_ineffective_lt(cx, span, mask_value, cmp_value, "|");
250 BinOpKind::BitXor => check_ineffective_lt(cx, span, mask_value, cmp_value, "^"),
253 BinOpKind::Le | BinOpKind::Gt => match bit_op {
254 BinOpKind::BitAnd => if mask_value <= cmp_value {
260 "incompatible bit mask: `_ & {}` will never be higher than `{}`",
265 } else if mask_value == 0 {
266 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
268 BinOpKind::BitOr => if mask_value > cmp_value {
274 "incompatible bit mask: `_ | {}` will always be higher than `{}`",
280 check_ineffective_gt(cx, span, mask_value, cmp_value, "|");
282 BinOpKind::BitXor => check_ineffective_gt(cx, span, mask_value, cmp_value, "^"),
289 fn check_ineffective_lt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
290 if c.is_power_of_two() && m < c {
293 INEFFECTIVE_BIT_MASK,
296 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
305 fn check_ineffective_gt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
306 if (c + 1).is_power_of_two() && m <= c {
309 INEFFECTIVE_BIT_MASK,
312 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
321 fn fetch_int_literal(cx: &LateContext<'_, '_>, lit: &Expr) -> Option<u128> {
322 match constant(cx, cx.tables, lit)?.0 {
323 Constant::Int(n) => Some(n),