1 use crate::consts::{constant, Constant};
2 use crate::utils::sugg::Sugg;
3 use crate::utils::{span_lint, span_lint_and_then};
4 use if_chain::if_chain;
6 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
7 use rustc::{declare_tool_lint, lint_array};
8 use rustc_errors::Applicability;
9 use syntax::ast::LitKind;
10 use syntax::source_map::Span;
12 declare_clippy_lint! {
13 /// **What it does:** Checks for incompatible bit masks in comparisons.
15 /// The formula for detecting if an expression of the type `_ <bit_op> m
16 /// <cmp_op> c` (where `<bit_op>` is one of {`&`, `|`} and `<cmp_op>` is one of
17 /// {`!=`, `>=`, `>`, `!=`, `>=`, `>`}) can be determined from the following
20 /// |Comparison |Bit Op|Example |is always|Formula |
21 /// |------------|------|------------|---------|----------------------|
22 /// |`==` or `!=`| `&` |`x & 2 == 3`|`false` |`c & m != c` |
23 /// |`<` or `>=`| `&` |`x & 2 < 3` |`true` |`m < c` |
24 /// |`>` or `<=`| `&` |`x & 1 > 1` |`false` |`m <= c` |
25 /// |`==` or `!=`| `|` |`x | 1 == 0`|`false` |`c | m != c` |
26 /// |`<` or `>=`| `|` |`x | 1 < 1` |`false` |`m >= c` |
27 /// |`<=` or `>` | `|` |`x | 1 > 0` |`true` |`m > c` |
29 /// **Why is this bad?** If the bits that the comparison cares about are always
30 /// set to zero or one by the bit mask, the comparison is constant `true` or
31 /// `false` (depending on mask, compared value, and operators).
33 /// So the code is actively misleading, and the only reason someone would write
34 /// this intentionally is to win an underhanded Rust contest or create a
35 /// test-case for this lint.
37 /// **Known problems:** None.
42 /// if (x & 1 == 2) { }
46 "expressions of the form `_ & mask == select` that will only ever return `true` or `false`"
49 declare_clippy_lint! {
50 /// **What it does:** Checks for bit masks in comparisons which can be removed
51 /// without changing the outcome. The basic structure can be seen in the
54 /// |Comparison| Bit Op |Example |equals |
55 /// |----------|---------|-----------|-------|
56 /// |`>` / `<=`|`|` / `^`|`x | 2 > 3`|`x > 3`|
57 /// |`<` / `>=`|`|` / `^`|`x ^ 1 < 4`|`x < 4`|
59 /// **Why is this bad?** Not equally evil as [`bad_bit_mask`](#bad_bit_mask),
60 /// but still a bit misleading, because the bit mask is ineffective.
62 /// **Known problems:** False negatives: This lint will only match instances
63 /// where we have figured out the math (which is for a power-of-two compared
64 /// value). This means things like `x | 1 >= 7` (which would be better written
65 /// as `x >= 6`) will not be reported (but bit masks like this are fairly
71 /// if (x | 1 > 3) { }
73 pub INEFFECTIVE_BIT_MASK,
75 "expressions where a bit mask will be rendered useless by a comparison, e.g., `(x | 1) > 2`"
78 declare_clippy_lint! {
79 /// **What it does:** Checks for bit masks that can be replaced by a call
80 /// to `trailing_zeros`
82 /// **Why is this bad?** `x.trailing_zeros() > 4` is much clearer than `x & 15
85 /// **Known problems:** llvm generates better code for `x & 15 == 0` on x86
90 /// if x & 0x1111 == 0 { }
94 "expressions where a bit mask is less readable than the corresponding method call"
97 #[derive(Copy, Clone)]
99 verbose_bit_mask_threshold: u64,
103 pub fn new(verbose_bit_mask_threshold: u64) -> Self {
105 verbose_bit_mask_threshold,
110 impl LintPass for BitMask {
111 fn get_lints(&self) -> LintArray {
112 lint_array!(BAD_BIT_MASK, INEFFECTIVE_BIT_MASK, VERBOSE_BIT_MASK)
114 fn name(&self) -> &'static str {
119 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BitMask {
120 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
121 if let ExprKind::Binary(cmp, left, right) = &e.node {
122 if cmp.node.is_comparison() {
123 if let Some(cmp_opt) = fetch_int_literal(cx, right) {
124 check_compare(cx, left, cmp.node, cmp_opt, e.span)
125 } else if let Some(cmp_val) = fetch_int_literal(cx, left) {
126 check_compare(cx, right, invert_cmp(cmp.node), cmp_val, e.span)
131 if let ExprKind::Binary(op, left, right) = &e.node;
132 if BinOpKind::Eq == op.node;
133 if let ExprKind::Binary(op1, left1, right1) = &left.node;
134 if BinOpKind::BitAnd == op1.node;
135 if let ExprKind::Lit(lit) = &right1.node;
136 if let LitKind::Int(n, _) = lit.node;
137 if let ExprKind::Lit(lit1) = &right.node;
138 if let LitKind::Int(0, _) = lit1.node;
139 if n.leading_zeros() == n.count_zeros();
140 if n > u128::from(self.verbose_bit_mask_threshold);
142 span_lint_and_then(cx,
145 "bit mask could be simplified with a call to `trailing_zeros`",
147 let sugg = Sugg::hir(cx, left1, "...").maybe_par();
151 format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()),
152 Applicability::MaybeIncorrect,
160 fn invert_cmp(cmp: BinOpKind) -> BinOpKind {
162 BinOpKind::Eq => BinOpKind::Eq,
163 BinOpKind::Ne => BinOpKind::Ne,
164 BinOpKind::Lt => BinOpKind::Gt,
165 BinOpKind::Gt => BinOpKind::Lt,
166 BinOpKind::Le => BinOpKind::Ge,
167 BinOpKind::Ge => BinOpKind::Le,
168 _ => BinOpKind::Or, // Dummy
172 fn check_compare(cx: &LateContext<'_, '_>, bit_op: &Expr, cmp_op: BinOpKind, cmp_value: u128, span: Span) {
173 if let ExprKind::Binary(op, left, right) = &bit_op.node {
174 if op.node != BinOpKind::BitAnd && op.node != BinOpKind::BitOr {
177 fetch_int_literal(cx, right)
178 .or_else(|| fetch_int_literal(cx, left))
179 .map_or((), |mask| check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span))
183 #[allow(clippy::too_many_lines)]
185 cx: &LateContext<'_, '_>,
193 BinOpKind::Eq | BinOpKind::Ne => match bit_op {
194 BinOpKind::BitAnd => {
195 if mask_value & cmp_value != cmp_value {
202 "incompatible bit mask: `_ & {}` can never be equal to `{}`",
203 mask_value, cmp_value
207 } else if mask_value == 0 {
208 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
211 BinOpKind::BitOr => {
212 if mask_value | cmp_value != cmp_value {
218 "incompatible bit mask: `_ | {}` can never be equal to `{}`",
219 mask_value, cmp_value
226 BinOpKind::Lt | BinOpKind::Ge => match bit_op {
227 BinOpKind::BitAnd => {
228 if mask_value < cmp_value {
234 "incompatible bit mask: `_ & {}` will always be lower than `{}`",
235 mask_value, cmp_value
238 } else if mask_value == 0 {
239 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
242 BinOpKind::BitOr => {
243 if mask_value >= cmp_value {
249 "incompatible bit mask: `_ | {}` will never be lower than `{}`",
250 mask_value, cmp_value
254 check_ineffective_lt(cx, span, mask_value, cmp_value, "|");
257 BinOpKind::BitXor => check_ineffective_lt(cx, span, mask_value, cmp_value, "^"),
260 BinOpKind::Le | BinOpKind::Gt => match bit_op {
261 BinOpKind::BitAnd => {
262 if mask_value <= cmp_value {
268 "incompatible bit mask: `_ & {}` will never be higher than `{}`",
269 mask_value, cmp_value
272 } else if mask_value == 0 {
273 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
276 BinOpKind::BitOr => {
277 if mask_value > cmp_value {
283 "incompatible bit mask: `_ | {}` will always be higher than `{}`",
284 mask_value, cmp_value
288 check_ineffective_gt(cx, span, mask_value, cmp_value, "|");
291 BinOpKind::BitXor => check_ineffective_gt(cx, span, mask_value, cmp_value, "^"),
298 fn check_ineffective_lt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
299 if c.is_power_of_two() && m < c {
302 INEFFECTIVE_BIT_MASK,
305 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
312 fn check_ineffective_gt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
313 if (c + 1).is_power_of_two() && m <= c {
316 INEFFECTIVE_BIT_MASK,
319 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
326 fn fetch_int_literal(cx: &LateContext<'_, '_>, lit: &Expr) -> Option<u128> {
327 match constant(cx, cx.tables, lit)?.0 {
328 Constant::Int(n) => Some(n),