1 use crate::consts::{constant, Constant};
2 use crate::utils::sugg::Sugg;
3 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
4 use if_chain::if_chain;
5 use rustc_ast::ast::LitKind;
6 use rustc_errors::Applicability;
7 use rustc_hir::{BinOpKind, Expr, ExprKind};
8 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_session::{declare_tool_lint, impl_lint_pass};
10 use rustc_span::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 & 0b1111 == 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,
104 pub fn new(verbose_bit_mask_threshold: u64) -> Self {
106 verbose_bit_mask_threshold,
111 impl_lint_pass!(BitMask => [BAD_BIT_MASK, INEFFECTIVE_BIT_MASK, VERBOSE_BIT_MASK]);
113 impl<'tcx> LateLintPass<'tcx> for BitMask {
114 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
115 if let ExprKind::Binary(cmp, left, right) = &e.kind {
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(op, left, right) = &e.kind;
126 if BinOpKind::Eq == op.node;
127 if let ExprKind::Binary(op1, left1, right1) = &left.kind;
128 if BinOpKind::BitAnd == op1.node;
129 if let ExprKind::Lit(lit) = &right1.kind;
130 if let LitKind::Int(n, _) = lit.node;
131 if let ExprKind::Lit(lit1) = &right.kind;
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 diag.span_suggestion(
145 format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()),
146 Applicability::MaybeIncorrect,
155 fn invert_cmp(cmp: BinOpKind) -> BinOpKind {
157 BinOpKind::Eq => BinOpKind::Eq,
158 BinOpKind::Ne => BinOpKind::Ne,
159 BinOpKind::Lt => BinOpKind::Gt,
160 BinOpKind::Gt => BinOpKind::Lt,
161 BinOpKind::Le => BinOpKind::Ge,
162 BinOpKind::Ge => BinOpKind::Le,
163 _ => 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(op, left, right) = &bit_op.kind {
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 #[allow(clippy::too_many_lines)]
180 cx: &LateContext<'_>,
188 BinOpKind::Eq | BinOpKind::Ne => match bit_op {
189 BinOpKind::BitAnd => {
190 if mask_value & cmp_value != cmp_value {
197 "incompatible bit mask: `_ & {}` can never be equal to `{}`",
198 mask_value, cmp_value
202 } else if mask_value == 0 {
203 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
206 BinOpKind::BitOr => {
207 if mask_value | cmp_value != cmp_value {
213 "incompatible bit mask: `_ | {}` can never be equal to `{}`",
214 mask_value, cmp_value
221 BinOpKind::Lt | BinOpKind::Ge => match bit_op {
222 BinOpKind::BitAnd => {
223 if mask_value < cmp_value {
229 "incompatible bit mask: `_ & {}` will always be lower than `{}`",
230 mask_value, cmp_value
233 } else if mask_value == 0 {
234 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
237 BinOpKind::BitOr => {
238 if mask_value >= cmp_value {
244 "incompatible bit mask: `_ | {}` will never be lower than `{}`",
245 mask_value, cmp_value
249 check_ineffective_lt(cx, span, mask_value, cmp_value, "|");
252 BinOpKind::BitXor => check_ineffective_lt(cx, span, mask_value, cmp_value, "^"),
255 BinOpKind::Le | BinOpKind::Gt => match bit_op {
256 BinOpKind::BitAnd => {
257 if mask_value <= cmp_value {
263 "incompatible bit mask: `_ & {}` will never be higher than `{}`",
264 mask_value, cmp_value
267 } else if mask_value == 0 {
268 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
271 BinOpKind::BitOr => {
272 if mask_value > cmp_value {
278 "incompatible bit mask: `_ | {}` will always be higher than `{}`",
279 mask_value, cmp_value
283 check_ineffective_gt(cx, span, mask_value, cmp_value, "|");
286 BinOpKind::BitXor => check_ineffective_gt(cx, span, mask_value, cmp_value, "^"),
293 fn check_ineffective_lt(cx: &LateContext<'_>, span: Span, m: u128, c: u128, op: &str) {
294 if c.is_power_of_two() && m < c {
297 INEFFECTIVE_BIT_MASK,
300 "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
307 fn check_ineffective_gt(cx: &LateContext<'_>, span: Span, m: u128, c: u128, op: &str) {
308 if (c + 1).is_power_of_two() && m <= c {
311 INEFFECTIVE_BIT_MASK,
314 "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.typeck_results(), lit)?.0 {
323 Constant::Int(n) => Some(n),