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Optimize slightly by avoiding to call Niche::reserve when not needed

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This commit is contained in:
Olivier Goffart 2020-03-25 23:05:47 +01:00
parent 4d77d01096
commit 81006f644d
1 changed files with 18 additions and 7 deletions
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25
src/librustc/ty/layout.rs
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@ -907,14 +907,25 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
let count = (niche_variants.end().as_u32()
- niche_variants.start().as_u32()
+ 1) as u128;
if let Some((field_index, niche, (niche_start, niche_scalar))) = variants[i]
.iter()
.enumerate()
.filter_map(|(i, &field)| {
let niche = field.largest_niche.as_ref()?;
Some((i, niche, niche.reserve(self, count)?))
let mut niche_size = 0;
if let Some((field_index, niche, niche_start, niche_scalar)) =
variants[i].iter().enumerate().fold(None, |acc, (j, &field)| {
let niche = match &field.largest_niche {
Some(niche) => niche,
_ => return acc,
};
let ns = niche.available(dl);
if ns <= niche_size {
return acc;
}
match niche.reserve(self, count) {
Some(pair) => {
niche_size = ns;
Some((j, niche, pair.0, pair.1))
}
None => acc,
}
})
.max_by_key(|(_, niche, _)| niche.available(dl))
{
let mut align = dl.aggregate_align;
let st = variants