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, impl_lint_pass};
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_lint_pass!(BitMask => [BAD_BIT_MASK, INEFFECTIVE_BIT_MASK, VERBOSE_BIT_MASK]);
112 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BitMask {
113 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
114 if let ExprKind::Binary(cmp, left, right) = &e.node {
115 if cmp.node.is_comparison() {
116 if let Some(cmp_opt) = fetch_int_literal(cx, right) {
117 check_compare(cx, left, cmp.node, cmp_opt, e.span)
118 } else if let Some(cmp_val) = fetch_int_literal(cx, left) {
119 check_compare(cx, right, invert_cmp(cmp.node), cmp_val, e.span)
124 if let ExprKind::Binary(op, left, right) = &e.node;
125 if BinOpKind::Eq == op.node;
126 if let ExprKind::Binary(op1, left1, right1) = &left.node;
127 if BinOpKind::BitAnd == op1.node;
128 if let ExprKind::Lit(lit) = &right1.node;
129 if let LitKind::Int(n, _) = lit.node;
130 if let ExprKind::Lit(lit1) = &right.node;
131 if let LitKind::Int(0, _) = lit1.node;
132 if n.leading_zeros() == n.count_zeros();
133 if n > u128::from(self.verbose_bit_mask_threshold);
135 span_lint_and_then(cx,
138 "bit mask could be simplified with a call to `trailing_zeros`",
140 let sugg = Sugg::hir(cx, left1, "...").maybe_par();
144 format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()),
145 Applicability::MaybeIncorrect,
153 fn invert_cmp(cmp: BinOpKind) -> BinOpKind {
155 BinOpKind::Eq => BinOpKind::Eq,
156 BinOpKind::Ne => BinOpKind::Ne,
157 BinOpKind::Lt => BinOpKind::Gt,
158 BinOpKind::Gt => BinOpKind::Lt,
159 BinOpKind::Le => BinOpKind::Ge,
160 BinOpKind::Ge => BinOpKind::Le,
161 _ => BinOpKind::Or, // Dummy
165 fn check_compare(cx: &LateContext<'_, '_>, bit_op: &Expr, cmp_op: BinOpKind, cmp_value: u128, span: Span) {
166 if let ExprKind::Binary(op, left, right) = &bit_op.node {
167 if op.node != BinOpKind::BitAnd && op.node != BinOpKind::BitOr {
170 fetch_int_literal(cx, right)
171 .or_else(|| fetch_int_literal(cx, left))
172 .map_or((), |mask| check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span))
176 #[allow(clippy::too_many_lines)]
178 cx: &LateContext<'_, '_>,
186 BinOpKind::Eq | BinOpKind::Ne => match bit_op {
187 BinOpKind::BitAnd => {
188 if mask_value & cmp_value != cmp_value {
195 "incompatible bit mask: `_ & {}` can never be equal to `{}`",
196 mask_value, cmp_value
200 } else if mask_value == 0 {
201 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
204 BinOpKind::BitOr => {
205 if mask_value | cmp_value != cmp_value {
211 "incompatible bit mask: `_ | {}` can never be equal to `{}`",
212 mask_value, cmp_value
219 BinOpKind::Lt | BinOpKind::Ge => match bit_op {
220 BinOpKind::BitAnd => {
221 if mask_value < cmp_value {
227 "incompatible bit mask: `_ & {}` will always be lower than `{}`",
228 mask_value, cmp_value
231 } else if mask_value == 0 {
232 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
235 BinOpKind::BitOr => {
236 if mask_value >= cmp_value {
242 "incompatible bit mask: `_ | {}` will never be lower than `{}`",
243 mask_value, cmp_value
247 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 => {
255 if mask_value <= cmp_value {
261 "incompatible bit mask: `_ & {}` will never be higher than `{}`",
262 mask_value, cmp_value
265 } else if mask_value == 0 {
266 span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero");
269 BinOpKind::BitOr => {
270 if mask_value > cmp_value {
276 "incompatible bit mask: `_ | {}` will always be higher than `{}`",
277 mask_value, cmp_value
281 check_ineffective_gt(cx, span, mask_value, cmp_value, "|");
284 BinOpKind::BitXor => check_ineffective_gt(cx, span, mask_value, cmp_value, "^"),
291 fn check_ineffective_lt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) {
292 if c.is_power_of_two() && m < c {
295 INEFFECTIVE_BIT_MASK,
298 "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",
319 fn fetch_int_literal(cx: &LateContext<'_, '_>, lit: &Expr) -> Option<u128> {
320 match constant(cx, cx.tables, lit)?.0 {
321 Constant::Int(n) => Some(n),