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Don't optimize pairs

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This commit is contained in:
Austin Hicks 2016-11-21 20:38:47 -05:00
parent 1af8e146f1
commit cb21cc5607
1 changed files with 7 additions and 2 deletions
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9
src/librustc/ty/layout.rs
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@ -549,9 +549,14 @@ impl<'a, 'gcx, 'tcx> Struct {
min_size: Size::from_bytes(0),
};
// 1-member and 2-member structs don't optimize.
// In addition, large bodies of code in trans assume that 2-element structs can become pairs.
// It's easier to just short-circuit here.
let can_optimize_struct = fields.len() > 2;
let (optimize, sort_ascending) = match (repr, kind) {
(attr::ReprAny, StructKind::AlwaysSizedUnivariant) => (true, false),
(attr::ReprAny, StructKind::MaybeUnsizedUnivariant) => (true, true),
(attr::ReprAny, StructKind::AlwaysSizedUnivariant) => (can_optimize_struct, false),
(attr::ReprAny, StructKind::MaybeUnsizedUnivariant) => (can_optimize_struct, true),
(attr::ReprAny, StructKind::EnumVariant) => {
assert!(fields.len() >= 1, "Enum variants must have discriminants.");
(true, fields[0].size(dl).bytes() == 1)