bjoernager/rust
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improve TagEncoding::Niche docs and sanity check

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This commit is contained in:
Ralf Jung 2024-11-30 18:05:48 +01:00
parent 76f3ff6059
commit ce95a44db6
4 changed files with 74 additions and 8 deletions
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16
compiler/rustc_ty_utils/src/layout/invariant.rs
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@ -1,11 +1,11 @@
use std::assert_matches::assert_matches;
use rustc_abi::{BackendRepr, FieldsShape, Scalar, Size, Variants};
use rustc_abi::{BackendRepr, FieldsShape, Scalar, Size, TagEncoding, Variants};
use rustc_middle::bug;
use rustc_middle::ty::layout::{HasTyCtxt, LayoutCx, TyAndLayout};
/// Enforce some basic invariants on layouts.
pub(super) fn partially_check_layout<'tcx>(cx: &LayoutCx<'tcx>, layout: &TyAndLayout<'tcx>) {
pub(super) fn layout_sanity_check<'tcx>(cx: &LayoutCx<'tcx>, layout: &TyAndLayout<'tcx>) {
let tcx = cx.tcx();
// Type-level uninhabitedness should always imply ABI uninhabitedness.
@ -241,7 +241,17 @@ pub(super) fn partially_check_layout<'tcx>(cx: &LayoutCx<'tcx>, layout: &TyAndLa
check_layout_abi(cx, layout);
if let Variants::Multiple { variants, .. } = &layout.variants {
if let Variants::Multiple { variants, tag, tag_encoding, .. } = &layout.variants {
if let TagEncoding::Niche { niche_start, untagged_variant, niche_variants } = tag_encoding {
let niche_size = tag.size(cx);
assert!(*niche_start <= niche_size.unsigned_int_max());
for (idx, variant) in variants.iter_enumerated() {
// Ensure all inhabited variants are accounted for.
if !variant.is_uninhabited() {
assert!(idx == *untagged_variant || niche_variants.contains(&idx));
}
}
}
for variant in variants.iter() {
// No nested "multiple".
assert_matches!(variant.variants, Variants::Single { .. });