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Tweak VarLenSlice subtraction

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This commit is contained in:
Nadrieril 2019-11-06 16:52:37 +00:00
parent 9b0214d9c5
commit 143fb4357f
1 changed files with 34 additions and 33 deletions
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67
src/librustc_mir/hair/pattern/_match.rs
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@ -655,44 +655,45 @@ impl<'tcx> Constructor<'tcx> {
.into_iter()
.flat_map(|pos_ctor| -> SmallVec<[Constructor<'tcx>; 1]> {
// Compute `pos_ctor \ neg_ctor`.
match (&pos_ctor, neg_ctor) {
(&FixedLenSlice(pos_len), &VarLenSlice(neg_prefix, neg_suffix)) => {
let neg_len = neg_prefix + neg_suffix;
if neg_len <= pos_len {
match pos_ctor {
FixedLenSlice(pos_len) => match *neg_ctor {
FixedLenSlice(neg_len) if neg_len == pos_len => smallvec![],
VarLenSlice(neg_prefix, neg_suffix)
if neg_prefix + neg_suffix <= pos_len =>
{
smallvec![]
} else {
smallvec![pos_ctor]
}
}
(
&VarLenSlice(pos_prefix, pos_suffix),
&VarLenSlice(neg_prefix, neg_suffix),
) => {
let neg_len = neg_prefix + neg_suffix;
_ => smallvec![pos_ctor],
},
VarLenSlice(pos_prefix, pos_suffix) => {
let pos_len = pos_prefix + pos_suffix;
if neg_len <= pos_len {
smallvec![]
} else {
(pos_len..neg_len).map(FixedLenSlice).collect()
match *neg_ctor {
FixedLenSlice(neg_len) if neg_len >= pos_len => {
(pos_len..neg_len)
.map(FixedLenSlice)
// We know that `neg_len + 1 >= pos_len >=
// pos_suffix`.
.chain(Some(VarLenSlice(
neg_len + 1 - pos_suffix,
pos_suffix,
)))
.collect()
}
VarLenSlice(neg_prefix, neg_suffix) => {
let neg_len = neg_prefix + neg_suffix;
if neg_len <= pos_len {
smallvec![]
} else {
(pos_len..neg_len).map(FixedLenSlice).collect()
}
}
_ => smallvec![pos_ctor],
}
}
(&VarLenSlice(pos_prefix, pos_suffix), &FixedLenSlice(neg_len)) => {
let pos_len = pos_prefix + pos_suffix;
if neg_len < pos_len {
smallvec![pos_ctor]
} else {
(pos_len..neg_len)
.map(FixedLenSlice)
// We know that `neg_len + 1 >= pos_len >= pos_suffix`.
.chain(Some(VarLenSlice(
neg_len + 1 - pos_suffix,
pos_suffix,
)))
.collect()
}
}
_ if pos_ctor == *neg_ctor => smallvec![],
_ => smallvec![pos_ctor],
_ => bug!(
"unexpected ctor while subtracting from VarLenSlice: {:?}",
pos_ctor
),
}
})
.collect();