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;
5 use rustc::impl_lint_pass;
6 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
7 use rustc_errors::Applicability;
9 use rustc_session::declare_tool_lint;
10 use rustc_span::source_map::Span;
11 use syntax::ast::LitKind;
13 declare_clippy_lint! {
14 /// **What it does:** Checks for incompatible bit masks in comparisons.
16 /// The formula for detecting if an expression of the type `_ <bit_op> m
17 /// <cmp_op> c` (where `<bit_op>` is one of {`&`, `|`} and `<cmp_op>` is one of
18 /// {`!=`, `>=`, `>`, `!=`, `>=`, `>`}) can be determined from the following
21 /// |Comparison |Bit Op|Example |is always|Formula |
22 /// |------------|------|------------|---------|----------------------|
23 /// |`==` or `!=`| `&` |`x & 2 == 3`|`false` |`c & m != c` |
24 /// |`<` or `>=`| `&` |`x & 2 < 3` |`true` |`m < c` |
25 /// |`>` or `<=`| `&` |`x & 1 > 1` |`false` |`m <= c` |
26 /// |`==` or `!=`| `|` |`x | 1 == 0`|`false` |`c | m != c` |
27 /// |`<` or `>=`| `|` |`x | 1 < 1` |`false` |`m >= c` |
28 /// |`<=` or `>` | `|` |`x | 1 > 0` |`true` |`m > c` |
30 /// **Why is this bad?** If the bits that the comparison cares about are always
31 /// set to zero or one by the bit mask, the comparison is constant `true` or
32 /// `false` (depending on mask, compared value, and operators).
34 /// So the code is actively misleading, and the only reason someone would write
35 /// this intentionally is to win an underhanded Rust contest or create a
36 /// test-case for this lint.
38 /// **Known problems:** None.
43 /// if (x & 1 == 2) { }
47 "expressions of the form `_ & mask == select` that will only ever return `true` or `false`"
50 declare_clippy_lint! {
51 /// **What it does:** Checks for bit masks in comparisons which can be removed
52 /// without changing the outcome. The basic structure can be seen in the
55 /// |Comparison| Bit Op |Example |equals |
56 /// |----------|---------|-----------|-------|
57 /// |`>` / `<=`|`|` / `^`|`x | 2 > 3`|`x > 3`|
58 /// |`<` / `>=`|`|` / `^`|`x ^ 1 < 4`|`x < 4`|
60 /// **Why is this bad?** Not equally evil as [`bad_bit_mask`](#bad_bit_mask),
61 /// but still a bit misleading, because the bit mask is ineffective.
63 /// **Known problems:** False negatives: This lint will only match instances
64 /// where we have figured out the math (which is for a power-of-two compared
65 /// value). This means things like `x | 1 >= 7` (which would be better written
66 /// as `x >= 6`) will not be reported (but bit masks like this are fairly
72 /// if (x | 1 > 3) { }
74 pub INEFFECTIVE_BIT_MASK,
76 "expressions where a bit mask will be rendered useless by a comparison, e.g., `(x | 1) > 2`"
79 declare_clippy_lint! {
80 /// **What it does:** Checks for bit masks that can be replaced by a call
81 /// to `trailing_zeros`
83 /// **Why is this bad?** `x.trailing_zeros() > 4` is much clearer than `x & 15
86 /// **Known problems:** llvm generates better code for `x & 15 == 0` on x86
91 /// if x & 0x1111 == 0 { }
95 "expressions where a bit mask is less readable than the corresponding method call"
98 #[derive(Copy, Clone)]
100 verbose_bit_mask_threshold: u64,
105 pub fn new(verbose_bit_mask_threshold: u64) -> Self {
107 verbose_bit_mask_threshold,
112 impl_lint_pass!(BitMask => [BAD_BIT_MASK, INEFFECTIVE_BIT_MASK, VERBOSE_BIT_MASK]);
114 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BitMask {
115 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
116 if let ExprKind::Binary(cmp, left, right) = &e.kind {
117 if cmp.node.is_comparison() {
118 if let Some(cmp_opt) = fetch_int_literal(cx, right) {
119 check_compare(cx, left, cmp.node, cmp_opt, e.span)
120 } else if let Some(cmp_val) = fetch_int_literal(cx, left) {
121 check_compare(cx, right, invert_cmp(cmp.node), cmp_val, e.span)
126 if let ExprKind::Binary(op, left, right) = &e.kind;
127 if BinOpKind::Eq == op.node;
128 if let ExprKind::Binary(op1, left1, right1) = &left.kind;
129 if BinOpKind::BitAnd == op1.node;
130 if let ExprKind::Lit(lit) = &right1.kind;
131 if let LitKind::Int(n, _) = lit.node;
132 if let ExprKind::Lit(lit1) = &right.kind;
133 if let LitKind::Int(0, _) = lit1.node;
134 if n.leading_zeros() == n.count_zeros();
135 if n > u128::from(self.verbose_bit_mask_threshold);
137 span_lint_and_then(cx,
140 "bit mask could be simplified with a call to `trailing_zeros`",
142 let sugg = Sugg::hir(cx, left1, "...").maybe_par();
146 format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()),
147 Applicability::MaybeIncorrect,
156 fn invert_cmp(cmp: BinOpKind) -> BinOpKind {
158 BinOpKind::Eq => BinOpKind::Eq,
159 BinOpKind::Ne => BinOpKind::Ne,
160 BinOpKind::Lt => BinOpKind::Gt,
161 BinOpKind::Gt => BinOpKind::Lt,
162 BinOpKind::Le => BinOpKind::Ge,
163 BinOpKind::Ge => BinOpKind::Le,
164 _ => BinOpKind::Or, // Dummy
168 fn check_compare(cx: &LateContext<'_, '_>, bit_op: &Expr<'_>, cmp_op: BinOpKind, cmp_value: u128, span: Span) {
169 if let ExprKind::Binary(op, left, right) = &bit_op.kind {
170 if op.node != BinOpKind::BitAnd && op.node != BinOpKind::BitOr {
173 fetch_int_literal(cx, right)
174 .or_else(|| fetch_int_literal(cx, left))
175 .map_or((), |mask| check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span))
179 #[allow(clippy::too_many_lines)]
181 cx: &LateContext<'_, '_>,
189 BinOpKind::Eq | BinOpKind::Ne => match bit_op {
190 BinOpKind::BitAnd => {
191 if mask_value & cmp_value != cmp_value {
198 "incompatible bit mask: `_ & {}` can never be equal to `{}`",
199 mask_value, cmp_value
203 } else if mask_value == 0 {
204 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
207 BinOpKind::BitOr => {
208 if mask_value | cmp_value != cmp_value {
214 "incompatible bit mask: `_ | {}` can never be equal to `{}`",
215 mask_value, cmp_value
222 BinOpKind::Lt | BinOpKind::Ge => match bit_op {
223 BinOpKind::BitAnd => {
224 if mask_value < cmp_value {
230 "incompatible bit mask: `_ & {}` will always be lower than `{}`",
231 mask_value, cmp_value
234 } else if mask_value == 0 {
235 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
238 BinOpKind::BitOr => {
239 if mask_value >= cmp_value {
245 "incompatible bit mask: `_ | {}` will never be lower than `{}`",
246 mask_value, cmp_value
250 check_ineffective_lt(cx, span, mask_value, cmp_value, "|");
253 BinOpKind::BitXor => check_ineffective_lt(cx, span, mask_value, cmp_value, "^"),
256 BinOpKind::Le | BinOpKind::Gt => match bit_op {
257 BinOpKind::BitAnd => {
258 if mask_value <= cmp_value {
264 "incompatible bit mask: `_ & {}` will never be higher than `{}`",
265 mask_value, cmp_value
268 } else if mask_value == 0 {
269 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
272 BinOpKind::BitOr => {
273 if mask_value > cmp_value {
279 "incompatible bit mask: `_ | {}` will always be higher than `{}`",
280 mask_value, cmp_value
284 check_ineffective_gt(cx, span, mask_value, cmp_value, "|");
287 BinOpKind::BitXor => check_ineffective_gt(cx, span, mask_value, cmp_value, "^"),
294 fn check_ineffective_lt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
295 if c.is_power_of_two() && m < c {
298 INEFFECTIVE_BIT_MASK,
301 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
308 fn check_ineffective_gt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
309 if (c + 1).is_power_of_two() && m <= c {
312 INEFFECTIVE_BIT_MASK,
315 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
322 fn fetch_int_literal(cx: &LateContext<'_, '_>, lit: &Expr<'_>) -> Option<u128> {
323 match constant(cx, cx.tables, lit)?.0 {
324 Constant::Int(n) => Some(n),