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Early abort instead of building up zero sized values

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This commit is contained in:
Oliver Scherer 2019-12-22 20:39:35 +01:00
parent 95205518dd
commit 1acbf4b802
2 changed files with 11 additions and 13 deletions
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4
src/librustc/mir/interpret/allocation.rs
View File

@ -127,10 +127,6 @@ impl<Tag> Allocation<Tag> {
extra: (),
}
}
pub fn zst(align: Align) -> Self {
Self::undef(Size::ZERO, align)
}
}
impl Allocation<(), ()> {

20
src/librustc_mir/hair/pattern/_match.rs
View File

@ -237,11 +237,11 @@ use super::{FieldPat, Pat, PatKind, PatRange};
use rustc::hir::def_id::DefId;
use rustc::hir::{HirId, RangeEnd};
use rustc::ty::layout::{Align, Integer, IntegerExt, Size, VariantIdx};
use rustc::ty::layout::{Integer, IntegerExt, Size, VariantIdx};
use rustc::ty::{self, Const, Ty, TyCtxt, TypeFoldable, VariantDef};
use rustc::lint;
use rustc::mir::interpret::{truncate, AllocId, Allocation, ConstValue, Pointer, Scalar};
use rustc::mir::interpret::{truncate, AllocId, ConstValue, Pointer, Scalar};
use rustc::mir::Field;
use rustc::util::captures::Captures;
use rustc::util::common::ErrorReported;
@ -2366,17 +2366,19 @@ fn specialize_one_pattern<'p, 'tcx>(
let (alloc, offset, n, ty) = match value.ty.kind {
ty::Array(t, n) => {
let n = n.eval_usize(cx.tcx, cx.param_env);
// Shortcut for `n == 0` where no matter what `alloc` and `offset` we produce,
// the result would be exactly what we early return here.
if n == 0 {
if ctor_wild_subpatterns.len() as u64 == 0 {
return Some(PatStack::from_slice(&[]));
} else {
return None;
}
}
match value.val {
ty::ConstKind::Value(ConstValue::ByRef { offset, alloc, .. }) => {
(Cow::Borrowed(alloc), offset, n, t)
}
ty::ConstKind::Value(ConstValue::Scalar(Scalar::Raw { data, .. }))
if n == 0 =>
{
let align = Align::from_bytes(data as u64).unwrap();
// empty array
(Cow::Owned(Allocation::zst(align)), Size::ZERO, 0, t)
}
_ => span_bug!(pat.span, "array pattern is {:?}", value,),
}
}