Track ABI info. in NaiveLayout, and use it for PointerLike checks

THis significantly complicates `NaiveLayout` logic, but is necessary to
ensure that bounds like `NonNull<T>: PointerLike` hold in generic
contexts.

Also implement exact layout computation for structs.
This commit is contained in:
Moulins 2023-06-29 03:55:09 +02:00
parent c30fbb95a6
commit feb20f2fe7
5 changed files with 231 additions and 93 deletions

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@ -15,7 +15,7 @@ use rustc_target::abi::call::FnAbi;
use rustc_target::abi::*;
use rustc_target::spec::{abi::Abi as SpecAbi, HasTargetSpec, PanicStrategy, Target};
use std::cmp::{self, Ordering};
use std::cmp;
use std::fmt;
use std::num::NonZeroUsize;
use std::ops::Bound;
@ -316,8 +316,8 @@ impl<'tcx> SizeSkeleton<'tcx> {
// First, try computing an exact naive layout (this covers simple types with generic
// references, where a full static layout would fail).
if let Ok(layout) = tcx.naive_layout_of(param_env.and(ty)) {
if layout.is_exact {
return Ok(SizeSkeleton::Known(layout.min_size));
if layout.exact {
return Ok(SizeSkeleton::Known(layout.size));
}
}
@ -650,51 +650,146 @@ impl std::ops::DerefMut for TyAndNaiveLayout<'_> {
}
}
/// A naive underestimation of the layout of a type.
/// Extremely simplified representation of a type's layout.
///
///
#[derive(Copy, Clone, Debug, HashStable)]
pub struct NaiveLayout {
pub min_size: Size,
pub min_align: Align,
// If `true`, `min_size` and `min_align` are guaranteed to be exact.
pub is_exact: bool,
pub abi: NaiveAbi,
pub size: Size,
pub align: Align,
/// If `true`, `size` and `align` are exact.
pub exact: bool,
}
#[derive(Copy, Clone, Debug, Eq, PartialEq, HashStable)]
pub enum NaiveAbi {
/// A scalar layout, always implies `exact`.
Scalar(Primitive),
/// An uninhabited layout. (needed to properly track `Scalar`)
Uninhabited,
/// An unsized aggregate. (needed to properly track `Scalar`)
Unsized,
Any,
}
impl NaiveAbi {
#[inline]
pub fn as_aggregate(self) -> Self {
match self {
NaiveAbi::Scalar(_) => NaiveAbi::Any,
_ => self,
}
}
}
impl NaiveLayout {
pub const UNKNOWN: Self = Self { min_size: Size::ZERO, min_align: Align::ONE, is_exact: false };
pub const EMPTY: Self = Self { min_size: Size::ZERO, min_align: Align::ONE, is_exact: true };
pub const EMPTY: Self =
Self { size: Size::ZERO, align: Align::ONE, exact: true, abi: NaiveAbi::Any };
pub fn is_compatible_with(&self, layout: Layout<'_>) -> bool {
let cmp = |cmp: Ordering| match (cmp, self.is_exact) {
(Ordering::Less | Ordering::Equal, false) => true,
(Ordering::Equal, true) => true,
(_, _) => false,
};
pub fn is_refined_by(&self, layout: Layout<'_>) -> bool {
if self.size > layout.size() || self.align > layout.align().abi {
return false;
}
cmp(self.min_size.cmp(&layout.size())) && cmp(self.min_align.cmp(&layout.align().abi))
if let NaiveAbi::Scalar(prim) = self.abi {
assert!(self.exact);
if !matches!(layout.abi(), Abi::Scalar(s) if s.primitive() == prim) {
return false;
}
}
!self.exact || (self.size, self.align) == (layout.size(), layout.align().abi)
}
/// Returns if this layout is known to be pointer-like (`None` if uncertain)
///
/// See the corresponding `Layout::is_pointer_like` method.
pub fn is_pointer_like(&self, dl: &TargetDataLayout) -> Option<bool> {
match self.abi {
NaiveAbi::Scalar(_) => {
assert!(self.exact);
Some(self.size == dl.pointer_size && self.align == dl.pointer_align.abi)
}
NaiveAbi::Uninhabited | NaiveAbi::Unsized => Some(false),
NaiveAbi::Any if self.exact => Some(false),
NaiveAbi::Any => None,
}
}
#[must_use]
pub fn pad_to_align(mut self) -> Self {
self.min_size = self.min_size.align_to(self.min_align);
#[inline]
pub fn packed(mut self, align: Align) -> Self {
if self.align > align {
self.align = align;
self.abi = self.abi.as_aggregate();
}
self
}
#[must_use]
pub fn concat<C: HasDataLayout>(&self, other: &Self, cx: &C) -> Option<Self> {
Some(Self {
min_size: self.min_size.checked_add(other.min_size, cx)?,
min_align: std::cmp::max(self.min_align, other.min_align),
is_exact: self.is_exact && other.is_exact,
})
#[inline]
pub fn align_to(mut self, align: Align) -> Self {
if align > self.align {
self.align = align;
self.abi = self.abi.as_aggregate();
}
self
}
#[must_use]
pub fn union(&self, other: &Self) -> Self {
Self {
min_size: std::cmp::max(self.min_size, other.min_size),
min_align: std::cmp::max(self.min_align, other.min_align),
is_exact: self.is_exact && other.is_exact,
#[inline]
pub fn pad_to_align(mut self, align: Align) -> Self {
let new_size = self.size.align_to(align);
if new_size > self.size {
self.abi = self.abi.as_aggregate();
self.size = new_size;
}
self
}
#[must_use]
#[inline]
pub fn concat(&self, other: &Self, dl: &TargetDataLayout) -> Option<Self> {
use NaiveAbi::*;
let size = self.size.checked_add(other.size, dl)?;
let align = cmp::max(self.align, other.align);
let exact = self.exact && other.exact;
let abi = match (self.abi, other.abi) {
// The uninhabited and unsized ABIs override everything.
(Uninhabited, _) | (_, Uninhabited) => Uninhabited,
(Unsized, _) | (_, Unsized) => Unsized,
// A scalar struct must have a single non ZST-field.
(_, s @ Scalar(_)) if exact && self.size == Size::ZERO => s,
(s @ Scalar(_), _) if exact && other.size == Size::ZERO => s,
// Default case.
(_, _) => Any,
};
Some(Self { abi, size, align, exact })
}
#[must_use]
#[inline]
pub fn union(&self, other: &Self) -> Self {
use NaiveAbi::*;
let size = cmp::max(self.size, other.size);
let align = cmp::max(self.align, other.align);
let exact = self.exact && other.exact;
let abi = match (self.abi, other.abi) {
// The unsized ABI overrides everything.
(Unsized, _) | (_, Unsized) => Unsized,
// A scalar union must have a single non ZST-field.
(_, s @ Scalar(_)) if exact && self.size == Size::ZERO => s,
(s @ Scalar(_), _) if exact && other.size == Size::ZERO => s,
// ...or identical scalar fields.
(Scalar(s1), Scalar(s2)) if s1 == s2 => Scalar(s1),
// Default cases.
(Uninhabited, Uninhabited) => Uninhabited,
(_, _) => Any,
};
Self { abi, size, align, exact }
}
}

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@ -223,9 +223,20 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
return ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS);
}
if let Ok(layout) = tcx.layout_of(key)
&& layout.layout.is_pointer_like(&tcx.data_layout)
{
// First, try computing an exact naive layout in case the type is generic.
let is_pointer_like = if let Ok(layout) = tcx.naive_layout_of(key) {
layout.is_pointer_like(&tcx.data_layout).unwrap_or_else(|| {
// Second, we fall back to full layout computation.
tcx.layout_of(key)
.ok()
.filter(|l| l.layout.is_pointer_like(&tcx.data_layout))
.is_some()
})
} else {
false
};
if is_pointer_like {
// FIXME: We could make this faster by making a no-constraints response
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
} else {

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@ -979,9 +979,20 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
return;
}
if let Ok(layout) = tcx.layout_of(key)
&& layout.layout.is_pointer_like(&tcx.data_layout)
{
// First, try computing an exact naive layout in case the type is generic.
let is_pointer_like = if let Ok(layout) = tcx.naive_layout_of(key) {
layout.is_pointer_like(&tcx.data_layout).unwrap_or_else(|| {
// Second, we fall back to full layout computation.
tcx.layout_of(key)
.ok()
.filter(|l| l.layout.is_pointer_like(&tcx.data_layout))
.is_some()
})
} else {
false
};
if is_pointer_like {
candidates.vec.push(BuiltinCandidate { has_nested: false });
}
}

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@ -5,8 +5,8 @@ use rustc_index::{IndexSlice, IndexVec};
use rustc_middle::mir::{GeneratorLayout, GeneratorSavedLocal};
use rustc_middle::query::{LocalCrate, Providers};
use rustc_middle::ty::layout::{
IntegerExt, LayoutCx, LayoutError, LayoutOf, NaiveLayout, TyAndLayout, TyAndNaiveLayout,
MAX_SIMD_LANES,
IntegerExt, LayoutCx, LayoutError, LayoutOf, NaiveAbi, NaiveLayout, TyAndLayout,
TyAndNaiveLayout, MAX_SIMD_LANES,
};
use rustc_middle::ty::{
self, AdtDef, EarlyBinder, GenericArgsRef, ReprOptions, Ty, TyCtxt, TypeVisitableExt,
@ -90,12 +90,8 @@ fn layout_of<'tcx>(
let cx = LayoutCx { tcx, param_env };
let layout = layout_of_uncached(&cx, ty)?;
if !naive.is_compatible_with(layout) {
bug!(
"the naive layout isn't compatible with the actual layout:\n{:#?}\n{:#?}",
naive,
layout,
);
if !naive.is_refined_by(layout) {
bug!("the naive layout isn't refined by the actual layout:\n{:#?}\n{:#?}", naive, layout,);
}
let layout = TyAndLayout { ty, layout };
@ -120,9 +116,10 @@ fn naive_layout_of_uncached<'tcx>(
let dl = cx.data_layout();
let scalar = |value: Primitive| NaiveLayout {
min_size: value.size(dl),
min_align: value.align(dl).abi,
is_exact: true,
abi: NaiveAbi::Scalar(value),
size: value.size(dl),
align: value.align(dl).abi,
exact: true,
};
let univariant = |fields: &mut dyn Iterator<Item = Ty<'tcx>>,
@ -133,24 +130,29 @@ fn naive_layout_of_uncached<'tcx>(
return Err(error(cx, LayoutError::Unknown(ty)));
}
// For simplicity, ignore inter-field padding; this may underestimate the size.
// FIXME(reference_niches): Be smarter and implement something closer to the real layout logic.
let mut layout = NaiveLayout::UNKNOWN;
let linear = repr.inhibit_struct_field_reordering_opt();
let pack = repr.pack.unwrap_or(Align::MAX);
let mut layout = NaiveLayout::EMPTY;
for field in fields {
let field = cx.naive_layout_of(field)?;
let field = cx.naive_layout_of(field)?.packed(pack);
if linear {
layout = layout.pad_to_align(field.align);
}
layout = layout
.concat(&field, cx)
.concat(&field, dl)
.ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))?;
}
if let Some(align) = repr.align {
layout.min_align = std::cmp::max(layout.min_align, align);
}
if let Some(pack) = repr.pack {
layout.min_align = std::cmp::min(layout.min_align, pack);
layout = layout.align_to(align);
}
Ok(layout.pad_to_align())
if linear {
layout.abi = layout.abi.as_aggregate();
}
Ok(layout.pad_to_align(layout.align))
};
debug_assert!(!ty.has_non_region_infer());
@ -168,17 +170,17 @@ fn naive_layout_of_uncached<'tcx>(
ty::FnPtr(_) => scalar(Pointer(dl.instruction_address_space)),
// The never type.
ty::Never => NaiveLayout::EMPTY,
ty::Never => NaiveLayout { abi: NaiveAbi::Uninhabited, ..NaiveLayout::EMPTY },
// Potentially-wide pointers.
ty::Ref(_, pointee, _) | ty::RawPtr(ty::TypeAndMut { ty: pointee, .. }) => {
let data_ptr = scalar(Pointer(AddressSpace::DATA));
if let Some(metadata) = ptr_metadata_scalar(cx, pointee)? {
// Effectively a (ptr, meta) tuple.
data_ptr
.concat(&scalar(metadata.primitive()), cx)
.ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))?
.pad_to_align()
let l = data_ptr
.concat(&scalar(metadata.primitive()), dl)
.ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))?;
l.pad_to_align(l.align)
} else {
// No metadata, this is a thin pointer.
data_ptr
@ -187,7 +189,7 @@ fn naive_layout_of_uncached<'tcx>(
ty::Dynamic(_, _, ty::DynStar) => {
let ptr = scalar(Pointer(AddressSpace::DATA));
ptr.concat(&ptr, cx).ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))?
ptr.concat(&ptr, dl).ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))?
}
// Arrays and slices.
@ -196,26 +198,29 @@ fn naive_layout_of_uncached<'tcx>(
.ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
let element = cx.naive_layout_of(element)?;
NaiveLayout {
min_size: element
.min_size
abi: element.abi.as_aggregate(),
size: element
.size
.checked_mul(count, cx)
.ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))?,
..*element
}
}
ty::Slice(element) => NaiveLayout {
min_size: Size::ZERO,
// NOTE: this could be unconditionally exact if `NaiveLayout` guaranteed exact align.
..*cx.naive_layout_of(element)?
},
ty::Str => NaiveLayout::EMPTY,
ty::Slice(element) => {
let element = cx.naive_layout_of(element)?;
NaiveLayout { abi: NaiveAbi::Unsized, size: Size::ZERO, ..*element }
}
// Odd unit types.
ty::FnDef(..) | ty::Dynamic(_, _, ty::Dyn) | ty::Foreign(..) => NaiveLayout::EMPTY,
ty::FnDef(..) => NaiveLayout::EMPTY,
// Unsized types.
ty::Str | ty::Dynamic(_, _, ty::Dyn) | ty::Foreign(..) => {
NaiveLayout { abi: NaiveAbi::Unsized, ..NaiveLayout::EMPTY }
}
// FIXME(reference_niches): try to actually compute a reasonable layout estimate,
// without duplicating too much code from `generator_layout`.
ty::Generator(..) => NaiveLayout::UNKNOWN,
ty::Generator(..) => NaiveLayout { exact: false, ..NaiveLayout::EMPTY },
ty::Closure(_, ref substs) => {
univariant(&mut substs.as_closure().upvar_tys(), &ReprOptions::default())?
@ -225,33 +230,50 @@ fn naive_layout_of_uncached<'tcx>(
ty::Adt(def, substs) if def.is_union() => {
let repr = def.repr();
let only_variant = &def.variants()[FIRST_VARIANT];
only_variant.fields.iter().try_fold(NaiveLayout::EMPTY, |layout, f| {
let mut fields = std::iter::once(f.ty(tcx, substs));
univariant(&mut fields, &repr).map(|l| layout.union(&l))
})?
let pack = repr.pack.unwrap_or(Align::MAX);
if repr.pack.is_some() && repr.align.is_some() {
cx.tcx.sess.delay_span_bug(DUMMY_SP, "union cannot be packed and aligned");
return Err(error(cx, LayoutError::Unknown(ty)));
}
let mut layout = NaiveLayout::EMPTY;
for f in &def.variants()[FIRST_VARIANT].fields {
let field = cx.naive_layout_of(f.ty(tcx, substs))?;
layout = layout.union(&field.packed(pack));
}
// Unions are always inhabited, and never scalar if `repr(C)`.
if !matches!(layout.abi, NaiveAbi::Scalar(_)) || repr.inhibit_enum_layout_opt() {
layout.abi = NaiveAbi::Any;
}
if let Some(align) = repr.align {
layout = layout.align_to(align);
}
layout.pad_to_align(layout.align)
}
ty::Adt(def, substs) => {
let repr = def.repr();
let base = if def.is_struct() && !repr.simd() {
// FIXME(reference_niches): compute proper alignment for SIMD types.
NaiveLayout::EMPTY
} else {
// For simplicity, assume that any discriminant field (if it exists)
// gets niched inside one of the variants; this will underestimate the size
// (and sometimes alignment) of enums.
// FIXME(reference_niches): Be smarter and actually take into accoount the discriminant.
let base = NaiveLayout {
// For simplicity, assume that any enum has its discriminant field (if it exists)
// niched inside one of the variants; this will underestimate the size (and sometimes
// alignment) of enums. We also doesn't compute exact alignment for SIMD structs.
// FIXME(reference_niches): Be smarter here.
// Also consider adding a special case for null-optimized enums, so that we can have
// `Option<&T>: PointerLike` in generic contexts.
NaiveLayout::UNKNOWN
exact: !def.is_enum() && !repr.simd(),
// An ADT with no inhabited variants should have an uninhabited ABI.
abi: NaiveAbi::Uninhabited,
..NaiveLayout::EMPTY
};
def.variants().iter().try_fold(base, |layout, v| {
let layout = def.variants().iter().try_fold(base, |layout, v| {
let mut fields = v.fields.iter().map(|f| f.ty(tcx, substs));
let vlayout = univariant(&mut fields, &repr)?;
Ok(layout.union(&vlayout))
})?
})?;
layout.pad_to_align(layout.align)
}
// Types with no meaningful known layout.
@ -354,8 +376,8 @@ fn layout_of_uncached<'tcx>(
};
let (min_addr, max_addr) = dl.address_range_for(
if niches.size { naive.min_size } else { Size::ZERO },
if niches.align { naive.min_align } else { Align::ONE },
if niches.size { naive.size } else { Size::ZERO },
if niches.align { naive.align } else { Align::ONE },
);
*data_ptr.valid_range_mut() =

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@ -9,7 +9,6 @@ note: ...which requires type-checking `make_dyn_star`...
|
LL | fn make_dyn_star<'a, T: PointerLike + Debug + 'a>(t: T) -> impl PointerLike + Debug + 'a {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= note: ...which requires computing layout of `make_dyn_star::{opaque#0}`...
= note: ...which requires computing layout (naive) of `make_dyn_star::{opaque#0}`...
= note: ...which requires normalizing `make_dyn_star::{opaque#0}`...
= note: ...which again requires computing type of `make_dyn_star::{opaque#0}`, completing the cycle