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Rollup merge of #53019 - ljedrz:bad_collects, r=estebank

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Don't collect() when size_hint is useless

This adjusts PRs #52738 and #52697 by falling back to calculating capacity and extending or pushing in a loop where `collect()` can't be trusted to calculate the right capacity.

It is a performance win.
This commit is contained in:
Guillaume Gomez 2018-08-12 23:26:49 +02:00 committed by GitHub
commit 7d3864954e
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3 changed files with 18 additions and 7 deletions
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12
src/librustc/infer/outlives/obligations.rs
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@ -151,12 +151,14 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
debug!("process_registered_region_obligations()");
// pull out the region obligations with the given `body_id` (leaving the rest)
let my_region_obligations = {
let mut my_region_obligations = Vec::with_capacity(self.region_obligations.borrow().len());
{
let mut r_o = self.region_obligations.borrow_mut();
let my_r_o = r_o.drain_filter(|(ro_body_id, _)| *ro_body_id == body_id)
.map(|(_, obligation)| obligation).collect::<Vec<_>>();
my_r_o
};
my_region_obligations.extend(
r_o.drain_filter(|(ro_body_id, _)| *ro_body_id == body_id)
.map(|(_, obligation)| obligation)
);
}
let outlives = &mut TypeOutlives::new(
self,

7
src/librustc_data_structures/small_vec.rs
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@ -210,7 +210,12 @@ impl<A> Decodable for SmallVec<A>
A::Element: Decodable {
fn decode<D: Decoder>(d: &mut D) -> Result<SmallVec<A>, D::Error> {
d.read_seq(|d, len| {
(0..len).map(|i| d.read_seq_elt(i, |d| Decodable::decode(d))).collect()
let mut vec = SmallVec::with_capacity(len);
// FIXME(#48994) - could just be collected into a Result<SmallVec, D::Error>
for i in 0..len {
vec.push(d.read_seq_elt(i, |d| Decodable::decode(d))?);
}
Ok(vec)
})
}
}

6
src/libsyntax/ast.rs
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@ -501,7 +501,11 @@ impl Pat {
PatKind::Slice(pats, None, _) if pats.len() == 1 =>
pats[0].to_ty().map(TyKind::Slice)?,
PatKind::Tuple(pats, None) => {
let tys = pats.iter().map(|pat| pat.to_ty()).collect::<Option<Vec<_>>>()?;
let mut tys = Vec::with_capacity(pats.len());
// FIXME(#48994) - could just be collected into an Option<Vec>
for pat in pats {
tys.push(pat.to_ty()?);
}
TyKind::Tup(tys)
}
_ => return None,