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use std::assert_matches::assert_matches;
use rustc_middle::bug;
use rustc_middle::ty::layout::{LayoutCx, TyAndLayout};
use rustc_middle::ty::TyCtxt;
use rustc_target::abi::*;
/// 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 layout.ty.is_privately_uninhabited(cx.tcx, cx.param_env) {
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 layout.size.bytes() >= cx.tcx.data_layout.obj_size_bound() {
bug!("size is too large, in the following layout:\n{layout:#?}");
}
if !cfg!(debug_assertions) {
// Stop here, the rest is kind of expensive.
return;
}
/// 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>) {
// Verify the ABI mandated alignment and size.
let align = layout.abi.inherent_align(cx).map(|align| align.abi);
let size = layout.abi.inherent_size(cx);
let Some((align, size)) = align.zip(size) else {
assert_matches!(
layout.layout.abi(),
Abi::Uninhabited | Abi::Aggregate { .. },
"ABI unexpectedly missing alignment and/or size in {layout:#?}"
);
return;
};
assert_eq!(
layout.layout.align().abi,
align,
"alignment mismatch between ABI and layout in {layout:#?}"
);
assert_eq!(
layout.layout.size(),
size,
"size mismatch between ABI and layout in {layout:#?}"
);
// Verify per-ABI invariants
match layout.layout.abi() {
Abi::Scalar(_) => {
// 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) => {
// 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_matches!(
fields.next(),
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.
let size1 = scalar1.size(cx);
let align1 = scalar1.align(cx).abi;
let size2 = scalar2.size(cx);
let align2 = scalar2.align(cx).abi;
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:#?}",
);
let field2_offset = size1.align_to(align2);
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 { element, .. } => {
assert!(align >= element.align(cx).abi); // just sanity-checking `vector_align`.
// FIXME: Do some kind of check of the inner type, like for Scalar and ScalarPair.
}
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`/`Uninhabited` 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
);
}
}
}
}