diff options
Diffstat (limited to 'compiler/rustc_abi/src/layout.rs')
| -rw-r--r-- | compiler/rustc_abi/src/layout.rs | 25 |
1 files changed, 13 insertions, 12 deletions
diff --git a/compiler/rustc_abi/src/layout.rs b/compiler/rustc_abi/src/layout.rs index a8a1a9057..0706dc18f 100644 --- a/compiler/rustc_abi/src/layout.rs +++ b/compiler/rustc_abi/src/layout.rs @@ -157,8 +157,10 @@ pub trait LayoutCalculator { // for non-ZST uninhabited data (mostly partial initialization). let absent = |fields: &IndexSlice<FieldIdx, Layout<'_>>| { let uninhabited = fields.iter().any(|f| f.abi().is_uninhabited()); - let is_zst = fields.iter().all(|f| f.0.is_zst()); - uninhabited && is_zst + // We cannot ignore alignment; that might lead us to entirely discard a variant and + // produce an enum that is less aligned than it should be! + let is_1zst = fields.iter().all(|f| f.0.is_1zst()); + uninhabited && is_1zst }; let (present_first, present_second) = { let mut present_variants = variants @@ -357,10 +359,8 @@ pub trait LayoutCalculator { // It'll fit, but we need to make some adjustments. match layout.fields { FieldsShape::Arbitrary { ref mut offsets, .. } => { - for (j, offset) in offsets.iter_enumerated_mut() { - if !variants[i][j].0.is_zst() { - *offset += this_offset; - } + for offset in offsets.iter_mut() { + *offset += this_offset; } } _ => { @@ -504,7 +504,7 @@ pub trait LayoutCalculator { // to make room for a larger discriminant. for field_idx in st.fields.index_by_increasing_offset() { let field = &field_layouts[FieldIdx::from_usize(field_idx)]; - if !field.0.is_zst() || field.align().abi.bytes() != 1 { + if !field.0.is_1zst() { start_align = start_align.min(field.align().abi); break; } @@ -603,12 +603,15 @@ pub trait LayoutCalculator { abi = Abi::Scalar(tag); } else { // Try to use a ScalarPair for all tagged enums. + // That's possible only if we can find a common primitive type for all variants. let mut common_prim = None; let mut common_prim_initialized_in_all_variants = true; for (field_layouts, layout_variant) in iter::zip(variants, &layout_variants) { let FieldsShape::Arbitrary { ref offsets, .. } = layout_variant.fields else { panic!(); }; + // We skip *all* ZST here and later check if we are good in terms of alignment. + // This lets us handle some cases involving aligned ZST. let mut fields = iter::zip(field_layouts, offsets).filter(|p| !p.0.0.is_zst()); let (field, offset) = match (fields.next(), fields.next()) { (None, None) => { @@ -954,9 +957,6 @@ fn univariant( }; ( - // Place ZSTs first to avoid "interesting offsets", especially with only one - // or two non-ZST fields. This helps Scalar/ScalarPair layouts. - !f.0.is_zst(), // Then place largest alignments first. cmp::Reverse(alignment_group_key(f)), // Then prioritize niche placement within alignment group according to @@ -1073,9 +1073,10 @@ fn univariant( let size = min_size.align_to(align.abi); let mut layout_of_single_non_zst_field = None; let mut abi = Abi::Aggregate { sized }; - // Unpack newtype ABIs and find scalar pairs. + // Try to make this a Scalar/ScalarPair. if sized && size.bytes() > 0 { - // All other fields must be ZSTs. + // We skip *all* ZST here and later check if we are good in terms of alignment. + // This lets us handle some cases involving aligned ZST. let mut non_zst_fields = fields.iter_enumerated().filter(|&(_, f)| !f.0.is_zst()); match (non_zst_fields.next(), non_zst_fields.next(), non_zst_fields.next()) { |