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use rustc::hir::*;
use rustc::hir::def::Def;
use rustc::lint::*;
use rustc_const_eval::lookup_const_by_id;
use syntax::ast::LitKind;
use syntax::codemap::Span;
use utils::span_lint;
declare_lint! {
pub BAD_BIT_MASK,
Warn,
"expressions of the form `_ & mask == select` that will only ever return `true` or `false`"
}
declare_lint! {
pub INEFFECTIVE_BIT_MASK,
Warn,
"expressions where a bit mask will be rendered useless by a comparison, e.g. `(x | 1) > 2`"
}
#[derive(Copy,Clone)]
pub struct BitMask;
impl LintPass for BitMask {
fn get_lints(&self) -> LintArray {
lint_array!(BAD_BIT_MASK, INEFFECTIVE_BIT_MASK)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BitMask {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
if let ExprBinary(ref cmp, ref left, ref right) = e.node {
if cmp.node.is_comparison() {
if let Some(cmp_opt) = fetch_int_literal(cx, right) {
check_compare(cx, left, cmp.node, cmp_opt, &e.span)
} else if let Some(cmp_val) = fetch_int_literal(cx, left) {
check_compare(cx, right, invert_cmp(cmp.node), cmp_val, &e.span)
}
}
}
}
}
fn invert_cmp(cmp: BinOp_) -> BinOp_ {
match cmp {
BiEq => BiEq,
BiNe => BiNe,
BiLt => BiGt,
BiGt => BiLt,
BiLe => BiGe,
BiGe => BiLe,
_ => BiOr,
}
}
fn check_compare(cx: &LateContext, bit_op: &Expr, cmp_op: BinOp_, cmp_value: u128, span: &Span) {
if let ExprBinary(ref op, ref left, ref right) = bit_op.node {
if op.node != BiBitAnd && op.node != BiBitOr {
return;
}
fetch_int_literal(cx, right)
.or_else(|| fetch_int_literal(cx, left))
.map_or((), |mask| check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span))
}
}
fn check_bit_mask(cx: &LateContext, bit_op: BinOp_, cmp_op: BinOp_, mask_value: u128, cmp_value: u128, span: &Span) {
match cmp_op {
BiEq | BiNe => {
match bit_op {
BiBitAnd => {
if mask_value & cmp_value != cmp_value {
if cmp_value != 0 {
span_lint(cx,
BAD_BIT_MASK,
*span,
&format!("incompatible bit mask: `_ & {}` can never be equal to `{}`",
mask_value,
cmp_value));
}
} else if mask_value == 0 {
span_lint(cx, BAD_BIT_MASK, *span, "&-masking with zero");
}
},
BiBitOr => {
if mask_value | cmp_value != cmp_value {
span_lint(cx,
BAD_BIT_MASK,
*span,
&format!("incompatible bit mask: `_ | {}` can never be equal to `{}`",
mask_value,
cmp_value));
}
},
_ => (),
}
},
BiLt | BiGe => {
match bit_op {
BiBitAnd => {
if mask_value < cmp_value {
span_lint(cx,
BAD_BIT_MASK,
*span,
&format!("incompatible bit mask: `_ & {}` will always be lower than `{}`",
mask_value,
cmp_value));
} else if mask_value == 0 {
span_lint(cx, BAD_BIT_MASK, *span, "&-masking with zero");
}
},
BiBitOr => {
if mask_value >= cmp_value {
span_lint(cx,
BAD_BIT_MASK,
*span,
&format!("incompatible bit mask: `_ | {}` will never be lower than `{}`",
mask_value,
cmp_value));
} else {
check_ineffective_lt(cx, *span, mask_value, cmp_value, "|");
}
},
BiBitXor => check_ineffective_lt(cx, *span, mask_value, cmp_value, "^"),
_ => (),
}
},
BiLe | BiGt => {
match bit_op {
BiBitAnd => {
if mask_value <= cmp_value {
span_lint(cx,
BAD_BIT_MASK,
*span,
&format!("incompatible bit mask: `_ & {}` will never be higher than `{}`",
mask_value,
cmp_value));
} else if mask_value == 0 {
span_lint(cx, BAD_BIT_MASK, *span, "&-masking with zero");
}
},
BiBitOr => {
if mask_value > cmp_value {
span_lint(cx,
BAD_BIT_MASK,
*span,
&format!("incompatible bit mask: `_ | {}` will always be higher than `{}`",
mask_value,
cmp_value));
} else {
check_ineffective_gt(cx, *span, mask_value, cmp_value, "|");
}
},
BiBitXor => check_ineffective_gt(cx, *span, mask_value, cmp_value, "^"),
_ => (),
}
},
_ => (),
}
}
fn check_ineffective_lt(cx: &LateContext, span: Span, m: u128, c: u128, op: &str) {
if c.is_power_of_two() && m < c {
span_lint(cx,
INEFFECTIVE_BIT_MASK,
span,
&format!("ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
op,
m,
c));
}
}
fn check_ineffective_gt(cx: &LateContext, span: Span, m: u128, c: u128, op: &str) {
if (c + 1).is_power_of_two() && m <= c {
span_lint(cx,
INEFFECTIVE_BIT_MASK,
span,
&format!("ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly",
op,
m,
c));
}
}
fn fetch_int_literal(cx: &LateContext, lit: &Expr) -> Option<u128> {
match lit.node {
ExprLit(ref lit_ptr) => {
if let LitKind::Int(value, _) = lit_ptr.node {
Some(value)
} else {
None
}
},
ExprPath(ref qpath) => {
let def = cx.tcx.tables().qpath_def(qpath, lit.id);
if let Def::Const(def_id) = def {
lookup_const_by_id(cx.tcx, def_id, None).and_then(|(l, _ty)| fetch_int_literal(cx, l))
} else {
None
}
},
_ => None,
}
}