1 use crate::rustc::hir::*;
2 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
3 use crate::rustc::{declare_tool_lint, lint_array};
4 use if_chain::if_chain;
5 use crate::syntax::ast::LitKind;
6 use crate::syntax::source_map::Span;
7 use crate::utils::{span_lint, span_lint_and_then};
8 use crate::utils::sugg::Sugg;
9 use crate::consts::{constant, Constant};
10 use crate::rustc_errors::Applicability;
12 /// **What it does:** Checks for incompatible bit masks in comparisons.
14 /// The formula for detecting if an expression of the type `_ <bit_op> m
15 /// <cmp_op> c` (where `<bit_op>` is one of {`&`, `|`} and `<cmp_op>` is one of
16 /// {`!=`, `>=`, `>`, `!=`, `>=`, `>`}) can be determined from the following
19 /// |Comparison |Bit Op|Example |is always|Formula |
20 /// |------------|------|------------|---------|----------------------|
21 /// |`==` or `!=`| `&` |`x & 2 == 3`|`false` |`c & m != c` |
22 /// |`<` or `>=`| `&` |`x & 2 < 3` |`true` |`m < c` |
23 /// |`>` or `<=`| `&` |`x & 1 > 1` |`false` |`m <= c` |
24 /// |`==` or `!=`| `|` |`x | 1 == 0`|`false` |`c | m != c` |
25 /// |`<` or `>=`| `|` |`x | 1 < 1` |`false` |`m >= c` |
26 /// |`<=` or `>` | `|` |`x | 1 > 0` |`true` |`m > c` |
28 /// **Why is this bad?** If the bits that the comparison cares about are always
29 /// set to zero or one by the bit mask, the comparison is constant `true` or
30 /// `false` (depending on mask, compared value, and operators).
32 /// So the code is actively misleading, and the only reason someone would write
33 /// this intentionally is to win an underhanded Rust contest or create a
34 /// test-case for this lint.
36 /// **Known problems:** None.
40 /// if (x & 1 == 2) { … }
42 declare_clippy_lint! {
45 "expressions of the form `_ & mask == select` that will only ever return `true` or `false`"
48 /// **What it does:** Checks for bit masks in comparisons which can be removed
49 /// without changing the outcome. The basic structure can be seen in the
52 /// |Comparison| Bit Op |Example |equals |
53 /// |----------|---------|-----------|-------|
54 /// |`>` / `<=`|`|` / `^`|`x | 2 > 3`|`x > 3`|
55 /// |`<` / `>=`|`|` / `^`|`x ^ 1 < 4`|`x < 4`|
57 /// **Why is this bad?** Not equally evil as [`bad_bit_mask`](#bad_bit_mask),
58 /// but still a bit misleading, because the bit mask is ineffective.
60 /// **Known problems:** False negatives: This lint will only match instances
61 /// where we have figured out the math (which is for a power-of-two compared
62 /// value). This means things like `x | 1 >= 7` (which would be better written
63 /// as `x >= 6`) will not be reported (but bit masks like this are fairly
68 /// if (x | 1 > 3) { … }
70 declare_clippy_lint! {
71 pub INEFFECTIVE_BIT_MASK,
73 "expressions where a bit mask will be rendered useless by a comparison, e.g. `(x | 1) > 2`"
76 /// **What it does:** Checks for bit masks that can be replaced by a call
77 /// to `trailing_zeros`
79 /// **Why is this bad?** `x.trailing_zeros() > 4` is much clearer than `x & 15
82 /// **Known problems:** llvm generates better code for `x & 15 == 0` on x86
88 declare_clippy_lint! {
91 "expressions where a bit mask is less readable than the corresponding method call"
94 #[derive(Copy, Clone)]
96 verbose_bit_mask_threshold: u64,
100 pub fn new(verbose_bit_mask_threshold: u64) -> Self {
102 verbose_bit_mask_threshold,
107 impl LintPass for BitMask {
108 fn get_lints(&self) -> LintArray {
109 lint_array!(BAD_BIT_MASK, INEFFECTIVE_BIT_MASK, VERBOSE_BIT_MASK)
113 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BitMask {
114 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
115 if let ExprKind::Binary(ref cmp, ref left, ref right) = e.node {
116 if cmp.node.is_comparison() {
117 if let Some(cmp_opt) = fetch_int_literal(cx, right) {
118 check_compare(cx, left, cmp.node, cmp_opt, e.span)
119 } else if let Some(cmp_val) = fetch_int_literal(cx, left) {
120 check_compare(cx, right, invert_cmp(cmp.node), cmp_val, e.span)
125 if let ExprKind::Binary(ref op, ref left, ref right) = e.node;
126 if BinOpKind::Eq == op.node;
127 if let ExprKind::Binary(ref op1, ref left1, ref right1) = left.node;
128 if BinOpKind::BitAnd == op1.node;
129 if let ExprKind::Lit(ref lit) = right1.node;
130 if let LitKind::Int(n, _) = lit.node;
131 if let ExprKind::Lit(ref lit1) = right.node;
132 if let LitKind::Int(0, _) = lit1.node;
133 if n.leading_zeros() == n.count_zeros();
134 if n > u128::from(self.verbose_bit_mask_threshold);
136 span_lint_and_then(cx,
139 "bit mask could be simplified with a call to `trailing_zeros`",
141 let sugg = Sugg::hir(cx, left1, "...").maybe_par();
142 db.span_suggestion_with_applicability(
145 format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()),
146 Applicability::MaybeIncorrect,
154 fn invert_cmp(cmp: BinOpKind) -> BinOpKind {
156 BinOpKind::Eq => BinOpKind::Eq,
157 BinOpKind::Ne => BinOpKind::Ne,
158 BinOpKind::Lt => BinOpKind::Gt,
159 BinOpKind::Gt => BinOpKind::Lt,
160 BinOpKind::Le => BinOpKind::Ge,
161 BinOpKind::Ge => BinOpKind::Le,
162 _ => BinOpKind::Or, // Dummy
167 fn check_compare(cx: &LateContext<'_, '_>, bit_op: &Expr, cmp_op: BinOpKind, cmp_value: u128, span: Span) {
168 if let ExprKind::Binary(ref op, ref left, ref right) = bit_op.node {
169 if op.node != BinOpKind::BitAnd && op.node != BinOpKind::BitOr {
172 fetch_int_literal(cx, right)
173 .or_else(|| fetch_int_literal(cx, left))
174 .map_or((), |mask| check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span))
178 fn check_bit_mask(cx: &LateContext<'_, '_>, bit_op: BinOpKind, cmp_op: BinOpKind, mask_value: u128, cmp_value: u128, span: Span) {
180 BinOpKind::Eq | BinOpKind::Ne => match bit_op {
181 BinOpKind::BitAnd => if mask_value & cmp_value != cmp_value {
188 "incompatible bit mask: `_ & {}` can never be equal to `{}`",
194 } else if mask_value == 0 {
195 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
197 BinOpKind::BitOr => if mask_value | cmp_value != cmp_value {
203 "incompatible bit mask: `_ | {}` can never be equal to `{}`",
211 BinOpKind::Lt | BinOpKind::Ge => match bit_op {
212 BinOpKind::BitAnd => if mask_value < cmp_value {
218 "incompatible bit mask: `_ & {}` will always be lower than `{}`",
223 } else if mask_value == 0 {
224 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
226 BinOpKind::BitOr => if mask_value >= cmp_value {
232 "incompatible bit mask: `_ | {}` will never be lower than `{}`",
238 check_ineffective_lt(cx, span, mask_value, cmp_value, "|");
240 BinOpKind::BitXor => check_ineffective_lt(cx, span, mask_value, cmp_value, "^"),
243 BinOpKind::Le | BinOpKind::Gt => match bit_op {
244 BinOpKind::BitAnd => if mask_value <= cmp_value {
250 "incompatible bit mask: `_ & {}` will never be higher than `{}`",
255 } else if mask_value == 0 {
256 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
258 BinOpKind::BitOr => if mask_value > cmp_value {
264 "incompatible bit mask: `_ | {}` will always be higher than `{}`",
270 check_ineffective_gt(cx, span, mask_value, cmp_value, "|");
272 BinOpKind::BitXor => check_ineffective_gt(cx, span, mask_value, cmp_value, "^"),
279 fn check_ineffective_lt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
280 if c.is_power_of_two() && m < c {
283 INEFFECTIVE_BIT_MASK,
286 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
295 fn check_ineffective_gt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
296 if (c + 1).is_power_of_two() && m <= c {
299 INEFFECTIVE_BIT_MASK,
302 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
311 fn fetch_int_literal(cx: &LateContext<'_, '_>, lit: &Expr) -> Option<u128> {
312 match constant(cx, cx.tables, lit)?.0 {
313 Constant::Int(n) => Some(n),