use rustc::lint::*;
use rustc::middle::const_eval::lookup_const_by_id;
use rustc::middle::def::*;
use rustc_front::hir::*;
use rustc_front::util::is_comparison_binop;
use syntax::codemap::Span;
use syntax::ast::Lit_::*;
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` \
(because in the example `select` containing bits that `mask` doesn't have)"
}
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 LateLintPass for BitMask {
fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
if let ExprBinary(ref cmp, ref left, ref right) = e.node {
if is_comparison_binop(cmp.node) {
fetch_int_literal(cx, right).map_or_else(||
fetch_int_literal(cx, left).map_or((), |cmp_val|
check_compare(cx, right, invert_cmp(cmp.node),
cmp_val, &e.span)),
|cmp_opt| check_compare(cx, left, cmp.node, cmp_opt,
&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: u64, span: &Span) {
match bit_op.node {
ExprBinary(ref op, ref left, ref right) => {
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: u64, cmp_value: u64, 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: u64, c: u64, 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: u64, c: u64, 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<u64> {
match lit.node {
ExprLit(ref lit_ptr) => {
if let &LitInt(value, _) = &lit_ptr.node {
Option::Some(value) } else { Option::None }
},
ExprPath(_, _) => {
let def_map = cx.tcx.def_map.borrow();
match def_map.get(&lit.id) {
Some(&PathResolution { base_def: DefConst(def_id), ..}) => Some(def_id),
_ => None
}
}
.and_then(|def_id| lookup_const_by_id(cx.tcx, def_id, Option::None))
.and_then(|l| fetch_int_literal(cx, l)),
_ => Option::None
}
}