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Small allocation improvement

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This commit is contained in:
Nadrieril 2020-05-09 13:49:04 +01:00
parent 59fa40a5a0
commit 8f08b16c03
1 changed files with 16 additions and 13 deletions
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29
src/librustc_mir_build/hair/pattern/_match.rs
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@ -990,8 +990,8 @@ impl<'p, 'tcx> Fields<'p, 'tcx> {
/// Construct a new `Fields` from the given patterns. You must be sure those patterns can't
/// contain fields that need to be filtered out. When in doubt, prefer `replace_fields`.
fn from_vec_unfiltered(pats: SmallVec<[&'p Pat<'tcx>; 2]>) -> Self {
Fields::Vec(pats)
fn from_slice_unfiltered(pats: &'p [Pat<'tcx>]) -> Self {
Fields::Slice(pats)
}
/// Convenience; internal use.
@ -2537,20 +2537,23 @@ fn specialize_one_pattern<'p, 'tcx>(
if ctor_wild_subpatterns.len() as u64 != n {
return None;
}
// Convert a constant slice/array pattern to a list of patterns.
let layout = cx.tcx.layout_of(cx.param_env.and(ty)).ok()?;
let ptr = Pointer::new(AllocId(0), offset);
let pats = (0..n)
.map(|i| {
let ptr = ptr.offset(layout.size * i, &cx.tcx).ok()?;
let scalar = alloc.read_scalar(&cx.tcx, ptr, layout.size).ok()?;
let scalar = scalar.not_undef().ok()?;
let value = ty::Const::from_scalar(cx.tcx, scalar, ty);
let pattern = Pat { ty, span: pat.span, kind: box PatKind::Constant { value } };
Some(&*cx.pattern_arena.alloc(pattern))
})
.collect::<Option<_>>()?;
Some(Fields::from_vec_unfiltered(pats))
let pats = cx.pattern_arena.alloc_from_iter((0..n).filter_map(|i| {
let ptr = ptr.offset(layout.size * i, &cx.tcx).ok()?;
let scalar = alloc.read_scalar(&cx.tcx, ptr, layout.size).ok()?;
let scalar = scalar.not_undef().ok()?;
let value = ty::Const::from_scalar(cx.tcx, scalar, ty);
let pattern = Pat { ty, span: pat.span, kind: box PatKind::Constant { value } };
Some(pattern)
}));
// Ensure none of the dereferences failed.
if pats.len() as u64 != n {
return None;
}
Some(Fields::from_slice_unfiltered(pats))
}
PatKind::Constant { .. } | PatKind::Range { .. } => {