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Auto merge of #57978 - varkor:fix-irrefutable-integer-range-match, r=oli-obk

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Fix bug in integer range matching

Fixes #57894.
This commit is contained in:
bors 2019-02-01 20:57:36 +00:00
commit 852701ad6d
2 changed files with 21 additions and 7 deletions
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21
src/librustc_mir/build/matches/simplify.rs
View file

@ -106,27 +106,34 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
}
PatternKind::Range(PatternRange { lo, hi, ty, end }) => {
let range = match ty.sty {
let (range, bias) = match ty.sty {
ty::Char => {
Some(('\u{0000}' as u128, '\u{10FFFF}' as u128, Size::from_bits(32)))
(Some(('\u{0000}' as u128, '\u{10FFFF}' as u128, Size::from_bits(32))), 0)
}
ty::Int(ity) => {
// FIXME(49937): refactor these bit manipulations into interpret.
let size = Integer::from_attr(&tcx, SignedInt(ity)).size();
let min = 1u128 << (size.bits() - 1);
let max = (1u128 << (size.bits() - 1)) - 1;
Some((min, max, size))
let max = !0u128 >> (128 - size.bits());
let bias = 1u128 << (size.bits() - 1);
(Some((0, max, size)), bias)
}
ty::Uint(uty) => {
// FIXME(49937): refactor these bit manipulations into interpret.
let size = Integer::from_attr(&tcx, UnsignedInt(uty)).size();
let max = !0u128 >> (128 - size.bits());
Some((0, max, size))
(Some((0, max, size)), 0)
}
_ => None,
_ => (None, 0),
};
if let Some((min, max, sz)) = range {
if let (Some(lo), Some(hi)) = (lo.val.try_to_bits(sz), hi.val.try_to_bits(sz)) {
// We want to compare ranges numerically, but the order of the bitwise
// representation of signed integers does not match their numeric order.
// Thus, to correct the ordering, we need to shift the range of signed
// integers to correct the comparison. This is achieved by XORing with a
// bias (see pattern/_match.rs for another pertinent example of this
// pattern).
let (lo, hi) = (lo ^ bias, hi ^ bias);
if lo <= min && (hi > max || hi == max && end == RangeEnd::Included) {
// Irrefutable pattern match.
return Ok(());

7
src/test/ui/match-on-negative-integer-ranges.rs Normal file
View file

@ -0,0 +1,7 @@
// run-pass
fn main() {
assert_eq!(false, match -50_i8 { -128i8..=-101i8 => true, _ => false, });
assert_eq!(false, if let -128i8..=-101i8 = -50_i8 { true } else { false });
}