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First attempt at detecting if structs can ever be unsized

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This commit is contained in:
Austin Hicks 2016-11-21 19:26:56 -05:00
parent e7c3540706
commit 1af8e146f1
1 changed files with 14 additions and 2 deletions
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16
src/librustc/ty/layout.rs
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@ -566,7 +566,7 @@ impl<'a, 'gcx, 'tcx> Struct {
if optimize {
let start = if let StructKind::EnumVariant = kind {1} else {0};
let end = if let StructKind::MaybeUnsizedUnivariant = kind { fields.len()-1 } else { 0 };
let end = if let StructKind::MaybeUnsizedUnivariant = kind { fields.len()-1 } else { fields.len() };
if end > start {
let optimizing = &mut inverse_memory_index[start..end];
if sort_ascending {
@ -1155,6 +1155,18 @@ impl<'a, 'gcx, 'tcx> Layout {
// Struct, or union, or univariant enum equivalent to a struct.
// (Typechecking will reject discriminant-sizing attrs.)
let kind = if def.is_enum() || def.variants[0].fields.len() == 0{
StructKind::AlwaysSizedUnivariant
} else {
use middle::region::ROOT_CODE_EXTENT;
let param_env = tcx.construct_parameter_environment(DUMMY_SP, def.did, ROOT_CODE_EXTENT);
let fields = &def.variants[0].fields;
let last_field = &fields[fields.len()-1];
let always_sized = last_field.unsubst_ty().is_sized(tcx, &param_env, DUMMY_SP);
if !always_sized { StructKind::MaybeUnsizedUnivariant }
else { StructKind::AlwaysSizedUnivariant }
};
let fields = def.variants[0].fields.iter().map(|field| {
field.ty(tcx, substs).layout(infcx)
}).collect::<Result<Vec<_>, _>>()?;
@ -1165,7 +1177,7 @@ impl<'a, 'gcx, 'tcx> Layout {
UntaggedUnion { variants: un }
} else {
let st = Struct::new(dl, &fields, hint,
StructKind::MaybeUnsizedUnivariant, ty)?;
kind, ty)?;
let non_zero = Some(def.did) == tcx.lang_items.non_zero();
Univariant { variant: st, non_zero: non_zero }
};