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Rollup merge of #50963 - nnethercote:coercion-VecDeque1, r=petrochenkov

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Right-size the `VecDeque` in `coerce_unsized`.

The default capacity of a VecDeque is 8, which is excessive here. In a
"base incremental" check build of rustc-perf's tuple-stress benchmark,
this decreases total heap allocation by 26%. I couldn't see a clear
speedup, but it can't hurt.
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kennytm 2018-05-23 00:26:23 +08:00 committed by GitHub
parent 28e43582a3 a86544b799
commit 0c4d337c3c
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1 changed files with 3 additions and 2 deletions
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5
src/librustc_typeck/check/coercion.rs
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@ -537,8 +537,9 @@ impl<'f, 'gcx, 'tcx> Coerce<'f, 'gcx, 'tcx> {
let mut selcx = traits::SelectionContext::new(self);
// Use a FIFO queue for this custom fulfillment procedure.
let mut queue = VecDeque::new();
// Use a FIFO queue for this custom fulfillment procedure. (The maximum
// length is almost always 1.)
let mut queue = VecDeque::with_capacity(1);
// Create an obligation for `Source: CoerceUnsized<Target>`.
let cause = ObligationCause::misc(self.cause.span, self.body_id);