2015-04-30 09:48:43 +00:00
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use rustc::plugin::Registry;
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use rustc::lint::*;
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2015-04-30 13:17:06 +00:00
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use rustc::middle::const_eval::lookup_const_by_id;
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use rustc::middle::def::*;
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2015-04-30 09:48:43 +00:00
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use syntax::ast::*;
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use syntax::ast_util::{is_comparison_binop, binop_to_string};
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use syntax::ptr::P;
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use syntax::codemap::Span;
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2015-07-26 14:53:11 +00:00
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use utils::span_lint;
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2015-04-30 09:48:43 +00:00
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declare_lint! {
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pub BAD_BIT_MASK,
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Deny,
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2015-05-22 22:49:13 +00:00
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"Deny the use of incompatible bit masks in comparisons, e.g. \
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'(a & 1) == 2'"
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2015-04-30 09:48:43 +00:00
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}
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2015-05-15 12:09:29 +00:00
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declare_lint! {
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pub INEFFECTIVE_BIT_MASK,
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Warn,
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2015-05-22 22:49:13 +00:00
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"Warn on the use of an ineffective bit mask in comparisons, e.g. \
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'(a & 1) > 2'"
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2015-05-15 12:09:29 +00:00
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}
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2015-05-22 22:49:13 +00:00
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/// Checks for incompatible bit masks in comparisons, e.g. `x & 1 == 2`.
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/// This cannot work because the bit that makes up the value two was
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/// zeroed out by the bit-and with 1. So the formula for detecting if an
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/// expression of the type `_ <bit_op> m <cmp_op> c` (where `<bit_op>`
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/// is one of {`&`, '|'} and `<cmp_op>` is one of {`!=`, `>=`, `>` ,
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/// `!=`, `>=`, `>`}) can be determined from the following table:
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///
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/// |Comparison |Bit-Op|Example |is always|Formula |
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/// |------------|------|------------|---------|----------------------|
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/// |`==` or `!=`| `&` |`x & 2 == 3`|`false` |`c & m != c` |
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/// |`<` or `>=`| `&` |`x & 2 < 3` |`true` |`m < c` |
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/// |`>` or `<=`| `&` |`x & 1 > 1` |`false` |`m <= c` |
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/// |`==` or `!=`| `|` |`x | 1 == 0`|`false` |`c | m != c` |
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2015-05-23 10:32:29 +00:00
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/// |`<` or `>=`| `|` |`x | 1 < 1` |`false` |`m >= c` |
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2015-05-22 22:49:13 +00:00
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/// |`<=` or `>` | `|` |`x | 1 > 0` |`true` |`m > c` |
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///
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/// This lint is **deny** by default
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///
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/// There is also a lint that warns on ineffective masks that is *warn*
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/// by default
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2015-04-30 09:48:43 +00:00
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#[derive(Copy,Clone)]
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pub struct BitMask;
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impl LintPass for BitMask {
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fn get_lints(&self) -> LintArray {
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2015-05-15 12:09:29 +00:00
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lint_array!(BAD_BIT_MASK, INEFFECTIVE_BIT_MASK)
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2015-04-30 09:48:43 +00:00
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}
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fn check_expr(&mut self, cx: &Context, e: &Expr) {
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if let ExprBinary(ref cmp, ref left, ref right) = e.node {
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if is_comparison_binop(cmp.node) {
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2015-05-22 22:49:13 +00:00
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fetch_int_literal(cx, right).map_or_else(||
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fetch_int_literal(cx, left).map_or((), |cmp_val|
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check_compare(cx, right, invert_cmp(cmp.node),
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cmp_val, &e.span)),
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|cmp_opt| check_compare(cx, left, cmp.node, cmp_opt,
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&e.span))
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2015-04-30 09:48:43 +00:00
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}
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}
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}
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}
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2015-05-04 05:17:15 +00:00
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fn invert_cmp(cmp : BinOp_) -> BinOp_ {
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match cmp {
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BiEq => BiEq,
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BiNe => BiNe,
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BiLt => BiGt,
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BiGt => BiLt,
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BiLe => BiGe,
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BiGe => BiLe,
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_ => BiOr // Dummy
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}
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}
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2015-04-30 09:48:43 +00:00
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fn check_compare(cx: &Context, bit_op: &Expr, cmp_op: BinOp_, cmp_value: u64, span: &Span) {
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match &bit_op.node {
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&ExprParen(ref subexp) => check_compare(cx, subexp, cmp_op, cmp_value, span),
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&ExprBinary(ref op, ref left, ref right) => {
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if op.node != BiBitAnd && op.node != BiBitOr { return; }
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2015-05-22 22:49:13 +00:00
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fetch_int_literal(cx, right).or_else(|| fetch_int_literal(
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cx, left)).map_or((), |mask| check_bit_mask(cx, op.node,
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cmp_op, mask, cmp_value, span))
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2015-04-30 09:48:43 +00:00
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},
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_ => ()
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}
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}
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2015-06-06 00:27:48 +00:00
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fn check_bit_mask(cx: &Context, bit_op: BinOp_, cmp_op: BinOp_,
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mask_value: u64, cmp_value: u64, span: &Span) {
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2015-04-30 09:48:43 +00:00
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match cmp_op {
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BiEq | BiNe => match bit_op {
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BiBitAnd => if mask_value & cmp_value != mask_value {
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2015-06-06 00:27:48 +00:00
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if cmp_value != 0 {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, BAD_BIT_MASK, *span, &format!(
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2015-06-06 00:27:48 +00:00
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"incompatible bit mask: _ & {} can never be equal to {}",
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mask_value, cmp_value));
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}
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2015-05-04 05:17:15 +00:00
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} else {
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if mask_value == 0 {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, BAD_BIT_MASK, *span,
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2015-06-06 00:27:48 +00:00
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&format!("&-masking with zero"));
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2015-05-04 05:17:15 +00:00
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}
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2015-04-30 09:48:43 +00:00
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},
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BiBitOr => if mask_value | cmp_value != cmp_value {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, BAD_BIT_MASK, *span, &format!(
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2015-06-06 00:27:48 +00:00
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"incompatible bit mask: _ | {} can never be equal to {}",
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mask_value, cmp_value));
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2015-04-30 09:48:43 +00:00
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},
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_ => ()
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},
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BiLt | BiGe => match bit_op {
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BiBitAnd => if mask_value < cmp_value {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, BAD_BIT_MASK, *span, &format!(
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2015-05-15 12:09:29 +00:00
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"incompatible bit mask: _ & {} will always be lower than {}",
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mask_value, cmp_value));
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2015-05-04 05:17:15 +00:00
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} else {
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if mask_value == 0 {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, BAD_BIT_MASK, *span,
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2015-06-06 00:27:48 +00:00
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&format!("&-masking with zero"));
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2015-05-04 05:17:15 +00:00
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}
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2015-04-30 09:48:43 +00:00
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},
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BiBitOr => if mask_value >= cmp_value {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, BAD_BIT_MASK, *span, &format!(
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2015-05-15 12:09:29 +00:00
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"incompatible bit mask: _ | {} will never be lower than {}",
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mask_value, cmp_value));
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} else {
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if mask_value < cmp_value {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, INEFFECTIVE_BIT_MASK, *span, &format!(
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2015-05-15 12:09:29 +00:00
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"ineffective bit mask: x | {} compared to {} is the same as x compared directly",
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mask_value, cmp_value));
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}
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2015-04-30 09:48:43 +00:00
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},
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_ => ()
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},
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BiLe | BiGt => match bit_op {
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BiBitAnd => if mask_value <= cmp_value {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, BAD_BIT_MASK, *span, &format!(
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2015-05-15 12:09:29 +00:00
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"incompatible bit mask: _ & {} will never be higher than {}",
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mask_value, cmp_value));
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2015-05-04 05:17:15 +00:00
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} else {
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if mask_value == 0 {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, BAD_BIT_MASK, *span,
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2015-06-06 00:27:48 +00:00
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&format!("&-masking with zero"));
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2015-05-04 05:17:15 +00:00
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}
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2015-04-30 09:48:43 +00:00
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},
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BiBitOr => if mask_value > cmp_value {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, BAD_BIT_MASK, *span, &format!(
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2015-05-15 12:09:29 +00:00
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"incompatible bit mask: _ | {} will always be higher than {}",
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mask_value, cmp_value));
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} else {
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if mask_value < cmp_value {
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2015-07-26 14:53:11 +00:00
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span_lint(cx, INEFFECTIVE_BIT_MASK, *span, &format!(
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2015-05-15 12:09:29 +00:00
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"ineffective bit mask: x | {} compared to {} is the same as x compared directly",
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mask_value, cmp_value));
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}
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2015-04-30 09:48:43 +00:00
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},
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_ => ()
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},
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_ => ()
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}
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}
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2015-04-30 13:17:06 +00:00
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fn fetch_int_literal(cx: &Context, lit : &Expr) -> Option<u64> {
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match &lit.node {
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&ExprLit(ref lit_ptr) => {
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if let &LitInt(value, _) = &lit_ptr.node {
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Option::Some(value) //TODO: Handle sign
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} else { Option::None }
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},
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&ExprPath(_, _) => {
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2015-05-07 04:41:54 +00:00
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// Important to let the borrow expire before the const lookup to avoid double
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// borrowing.
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let def_map = cx.tcx.def_map.borrow();
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match def_map.get(&lit.id) {
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Some(&PathResolution { base_def: DefConst(def_id), ..}) => Some(def_id),
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_ => None
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}
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}
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.and_then(|def_id| lookup_const_by_id(cx.tcx, def_id, Option::None))
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.and_then(|l| fetch_int_literal(cx, l)),
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2015-04-30 13:17:06 +00:00
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_ => Option::None
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2015-04-30 09:48:43 +00:00
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}
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}
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