diff options
Diffstat (limited to 'compiler/rustc_middle/src/ty/layout_sanity_check.rs')
| -rw-r--r-- | compiler/rustc_middle/src/ty/layout_sanity_check.rs | 303 |
1 files changed, 303 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/ty/layout_sanity_check.rs b/compiler/rustc_middle/src/ty/layout_sanity_check.rs new file mode 100644 index 000000000..87c85dcff --- /dev/null +++ b/compiler/rustc_middle/src/ty/layout_sanity_check.rs @@ -0,0 +1,303 @@ +use crate::ty::{ + layout::{LayoutCx, TyAndLayout}, + TyCtxt, +}; +use rustc_target::abi::*; + +use std::cmp; + +/// Enforce some basic invariants on layouts. +pub(super) fn sanity_check_layout<'tcx>( + cx: &LayoutCx<'tcx, TyCtxt<'tcx>>, + layout: &TyAndLayout<'tcx>, +) { + // Type-level uninhabitedness should always imply ABI uninhabitedness. + if cx.tcx.conservative_is_privately_uninhabited(cx.param_env.and(layout.ty)) { + assert!(layout.abi.is_uninhabited()); + } + + if layout.size.bytes() % layout.align.abi.bytes() != 0 { + bug!("size is not a multiple of align, in the following layout:\n{layout:#?}"); + } + + if cfg!(debug_assertions) { + /// Yields non-ZST fields of the type + fn non_zst_fields<'tcx, 'a>( + cx: &'a LayoutCx<'tcx, TyCtxt<'tcx>>, + layout: &'a TyAndLayout<'tcx>, + ) -> impl Iterator<Item = (Size, TyAndLayout<'tcx>)> + 'a { + (0..layout.layout.fields().count()).filter_map(|i| { + let field = layout.field(cx, i); + // Also checking `align == 1` here leads to test failures in + // `layout/zero-sized-array-union.rs`, where a type has a zero-size field with + // alignment 4 that still gets ignored during layout computation (which is okay + // since other fields already force alignment 4). + let zst = field.is_zst(); + (!zst).then(|| (layout.fields.offset(i), field)) + }) + } + + fn skip_newtypes<'tcx>( + cx: &LayoutCx<'tcx, TyCtxt<'tcx>>, + layout: &TyAndLayout<'tcx>, + ) -> TyAndLayout<'tcx> { + if matches!(layout.layout.variants(), Variants::Multiple { .. }) { + // Definitely not a newtype of anything. + return *layout; + } + let mut fields = non_zst_fields(cx, layout); + let Some(first) = fields.next() else { + // No fields here, so this could be a primitive or enum -- either way it's not a newtype around a thing + return *layout + }; + if fields.next().is_none() { + let (offset, first) = first; + if offset == Size::ZERO && first.layout.size() == layout.size { + // This is a newtype, so keep recursing. + // FIXME(RalfJung): I don't think it would be correct to do any checks for + // alignment here, so we don't. Is that correct? + return skip_newtypes(cx, &first); + } + } + // No more newtypes here. + *layout + } + + fn check_layout_abi<'tcx>(cx: &LayoutCx<'tcx, TyCtxt<'tcx>>, layout: &TyAndLayout<'tcx>) { + match layout.layout.abi() { + Abi::Scalar(scalar) => { + // No padding in scalars. + let size = scalar.size(cx); + let align = scalar.align(cx).abi; + assert_eq!( + layout.layout.size(), + size, + "size mismatch between ABI and layout in {layout:#?}" + ); + assert_eq!( + layout.layout.align().abi, + align, + "alignment mismatch between ABI and layout in {layout:#?}" + ); + // Check that this matches the underlying field. + let inner = skip_newtypes(cx, layout); + assert!( + matches!(inner.layout.abi(), Abi::Scalar(_)), + "`Scalar` type {} is newtype around non-`Scalar` type {}", + layout.ty, + inner.ty + ); + match inner.layout.fields() { + FieldsShape::Primitive => { + // Fine. + } + FieldsShape::Union(..) => { + // FIXME: I guess we could also check something here? Like, look at all fields? + return; + } + FieldsShape::Arbitrary { .. } => { + // Should be an enum, the only field is the discriminant. + assert!( + inner.ty.is_enum(), + "`Scalar` layout for non-primitive non-enum type {}", + inner.ty + ); + assert_eq!( + inner.layout.fields().count(), + 1, + "`Scalar` layout for multiple-field type in {inner:#?}", + ); + let offset = inner.layout.fields().offset(0); + let field = inner.field(cx, 0); + // The field should be at the right offset, and match the `scalar` layout. + assert_eq!( + offset, + Size::ZERO, + "`Scalar` field at non-0 offset in {inner:#?}", + ); + assert_eq!( + field.size, size, + "`Scalar` field with bad size in {inner:#?}", + ); + assert_eq!( + field.align.abi, align, + "`Scalar` field with bad align in {inner:#?}", + ); + assert!( + matches!(field.abi, Abi::Scalar(_)), + "`Scalar` field with bad ABI in {inner:#?}", + ); + } + _ => { + panic!("`Scalar` layout for non-primitive non-enum type {}", inner.ty); + } + } + } + Abi::ScalarPair(scalar1, scalar2) => { + // Sanity-check scalar pairs. These are a bit more flexible and support + // padding, but we can at least ensure both fields actually fit into the layout + // and the alignment requirement has not been weakened. + let size1 = scalar1.size(cx); + let align1 = scalar1.align(cx).abi; + let size2 = scalar2.size(cx); + let align2 = scalar2.align(cx).abi; + assert!( + layout.layout.align().abi >= cmp::max(align1, align2), + "alignment mismatch between ABI and layout in {layout:#?}", + ); + let field2_offset = size1.align_to(align2); + assert!( + layout.layout.size() >= field2_offset + size2, + "size mismatch between ABI and layout in {layout:#?}" + ); + // Check that the underlying pair of fields matches. + let inner = skip_newtypes(cx, layout); + assert!( + matches!(inner.layout.abi(), Abi::ScalarPair(..)), + "`ScalarPair` type {} is newtype around non-`ScalarPair` type {}", + layout.ty, + inner.ty + ); + if matches!(inner.layout.variants(), Variants::Multiple { .. }) { + // FIXME: ScalarPair for enums is enormously complicated and it is very hard + // to check anything about them. + return; + } + match inner.layout.fields() { + FieldsShape::Arbitrary { .. } => { + // Checked below. + } + FieldsShape::Union(..) => { + // FIXME: I guess we could also check something here? Like, look at all fields? + return; + } + _ => { + panic!("`ScalarPair` layout with unexpected field shape in {inner:#?}"); + } + } + let mut fields = non_zst_fields(cx, &inner); + let (offset1, field1) = fields.next().unwrap_or_else(|| { + panic!("`ScalarPair` layout for type with not even one non-ZST field: {inner:#?}") + }); + let (offset2, field2) = fields.next().unwrap_or_else(|| { + panic!("`ScalarPair` layout for type with less than two non-ZST fields: {inner:#?}") + }); + assert!( + fields.next().is_none(), + "`ScalarPair` layout for type with at least three non-ZST fields: {inner:#?}" + ); + // The fields might be in opposite order. + let (offset1, field1, offset2, field2) = if offset1 <= offset2 { + (offset1, field1, offset2, field2) + } else { + (offset2, field2, offset1, field1) + }; + // The fields should be at the right offset, and match the `scalar` layout. + assert_eq!( + offset1, + Size::ZERO, + "`ScalarPair` first field at non-0 offset in {inner:#?}", + ); + assert_eq!( + field1.size, size1, + "`ScalarPair` first field with bad size in {inner:#?}", + ); + assert_eq!( + field1.align.abi, align1, + "`ScalarPair` first field with bad align in {inner:#?}", + ); + assert!( + matches!(field1.abi, Abi::Scalar(_)), + "`ScalarPair` first field with bad ABI in {inner:#?}", + ); + assert_eq!( + offset2, field2_offset, + "`ScalarPair` second field at bad offset in {inner:#?}", + ); + assert_eq!( + field2.size, size2, + "`ScalarPair` second field with bad size in {inner:#?}", + ); + assert_eq!( + field2.align.abi, align2, + "`ScalarPair` second field with bad align in {inner:#?}", + ); + assert!( + matches!(field2.abi, Abi::Scalar(_)), + "`ScalarPair` second field with bad ABI in {inner:#?}", + ); + } + Abi::Vector { count, element } => { + // No padding in vectors. Alignment can be strengthened, though. + assert!( + layout.layout.align().abi >= element.align(cx).abi, + "alignment mismatch between ABI and layout in {layout:#?}" + ); + let size = element.size(cx) * count; + assert_eq!( + layout.layout.size(), + size.align_to(cx.data_layout().vector_align(size).abi), + "size mismatch between ABI and layout in {layout:#?}" + ); + } + Abi::Uninhabited | Abi::Aggregate { .. } => {} // Nothing to check. + } + } + + check_layout_abi(cx, layout); + + if let Variants::Multiple { variants, .. } = &layout.variants { + for variant in variants.iter() { + // No nested "multiple". + assert!(matches!(variant.variants(), Variants::Single { .. })); + // Variants should have the same or a smaller size as the full thing, + // and same for alignment. + if variant.size() > layout.size { + bug!( + "Type with size {} bytes has variant with size {} bytes: {layout:#?}", + layout.size.bytes(), + variant.size().bytes(), + ) + } + if variant.align().abi > layout.align.abi { + bug!( + "Type with alignment {} bytes has variant with alignment {} bytes: {layout:#?}", + layout.align.abi.bytes(), + variant.align().abi.bytes(), + ) + } + // Skip empty variants. + if variant.size() == Size::ZERO + || variant.fields().count() == 0 + || variant.abi().is_uninhabited() + { + // These are never actually accessed anyway, so we can skip the coherence check + // for them. They also fail that check, since they have + // `Aggregate`/`Uninhbaited` ABI even when the main type is + // `Scalar`/`ScalarPair`. (Note that sometimes, variants with fields have size + // 0, and sometimes, variants without fields have non-0 size.) + continue; + } + // The top-level ABI and the ABI of the variants should be coherent. + let scalar_coherent = |s1: Scalar, s2: Scalar| { + s1.size(cx) == s2.size(cx) && s1.align(cx) == s2.align(cx) + }; + let abi_coherent = match (layout.abi, variant.abi()) { + (Abi::Scalar(s1), Abi::Scalar(s2)) => scalar_coherent(s1, s2), + (Abi::ScalarPair(a1, b1), Abi::ScalarPair(a2, b2)) => { + scalar_coherent(a1, a2) && scalar_coherent(b1, b2) + } + (Abi::Uninhabited, _) => true, + (Abi::Aggregate { .. }, _) => true, + _ => false, + }; + if !abi_coherent { + bug!( + "Variant ABI is incompatible with top-level ABI:\nvariant={:#?}\nTop-level: {layout:#?}", + variant + ); + } + } + } + } +} |