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Remove rustc's notion of "preferred" alignment AKA __alignof #141803

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Remove rustc's notion of "preferred" alignment AKA __alignof #141803

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56c606c
Remove rustc's notion of "preferred" alignment AKA `__alignof`
workingjubilee Feb 12, 2025
f00a7ff
compiler: add Deref to AbiAlign to ease transition
workingjubilee Jun 4, 2025
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20 changes: 7 additions & 13 deletions compiler/rustc_abi/src/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ use rustc_index::bit_set::BitMatrix;
use tracing::debug;

use crate::{
AbiAndPrefAlign, Align, BackendRepr, FieldsShape, HasDataLayout, IndexSlice, IndexVec, Integer,
AbiAlign, Align, BackendRepr, FieldsShape, HasDataLayout, IndexSlice, IndexVec, Integer,
LayoutData, Niche, NonZeroUsize, Primitive, ReprOptions, Scalar, Size, StructKind, TagEncoding,
Variants, WrappingRange,
};
Expand Down Expand Up @@ -173,13 +173,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
// Non-power-of-two vectors have padding up to the next power-of-two.
// If we're a packed repr, remove the padding while keeping the alignment as close
// to a vector as possible.
(
BackendRepr::Memory { sized: true },
AbiAndPrefAlign {
abi: Align::max_aligned_factor(size),
pref: dl.llvmlike_vector_align(size).pref,
},
)
(BackendRepr::Memory { sized: true }, AbiAlign { abi: Align::max_aligned_factor(size) })
} else {
(BackendRepr::SimdVector { element: e_repr, count }, dl.llvmlike_vector_align(size))
};
Expand Down Expand Up @@ -435,13 +429,13 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
}

if let Some(pack) = repr.pack {
align = align.min(AbiAndPrefAlign::new(pack));
align = align.min(AbiAlign::new(pack));
}
// The unadjusted ABI alignment does not include repr(align), but does include repr(pack).
// See documentation on `LayoutS::unadjusted_abi_align`.
let unadjusted_abi_align = align.abi;
if let Some(repr_align) = repr.align {
align = align.max(AbiAndPrefAlign::new(repr_align));
align = align.max(AbiAlign::new(repr_align));
}
// `align` must not be modified after this, or `unadjusted_abi_align` could be inaccurate.
let align = align;
Expand Down Expand Up @@ -1289,7 +1283,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
if let StructKind::Prefixed(prefix_size, prefix_align) = kind {
let prefix_align =
if let Some(pack) = pack { prefix_align.min(pack) } else { prefix_align };
align = align.max(AbiAndPrefAlign::new(prefix_align));
align = align.max(AbiAlign::new(prefix_align));
offset = prefix_size.align_to(prefix_align);
}
for &i in &inverse_memory_index {
Expand All @@ -1308,7 +1302,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {

// Invariant: offset < dl.obj_size_bound() <= 1<<61
let field_align = if let Some(pack) = pack {
field.align.min(AbiAndPrefAlign::new(pack))
field.align.min(AbiAlign::new(pack))
} else {
field.align
};
Expand Down Expand Up @@ -1342,7 +1336,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
// See documentation on `LayoutS::unadjusted_abi_align`.
let unadjusted_abi_align = align.abi;
if let Some(repr_align) = repr.align {
align = align.max(AbiAndPrefAlign::new(repr_align));
align = align.max(AbiAlign::new(repr_align));
}
// `align` must not be modified after this point, or `unadjusted_abi_align` could be inaccurate.
let align = align;
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_abi/src/layout/ty.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ use rustc_data_structures::intern::Interned;
use rustc_macros::HashStable_Generic;

use crate::{
AbiAndPrefAlign, Align, BackendRepr, FieldsShape, Float, HasDataLayout, LayoutData, Niche,
AbiAlign, Align, BackendRepr, FieldsShape, Float, HasDataLayout, LayoutData, Niche,
PointeeInfo, Primitive, Scalar, Size, TargetDataLayout, Variants,
};

Expand Down Expand Up @@ -93,7 +93,7 @@ impl<'a> Layout<'a> {
self.0.0.largest_niche
}

pub fn align(self) -> AbiAndPrefAlign {
pub fn align(self) -> AbiAlign {
self.0.0.align
}

Expand Down
100 changes: 53 additions & 47 deletions compiler/rustc_abi/src/lib.rs
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Expand Up @@ -43,7 +43,7 @@ use std::fmt;
#[cfg(feature = "nightly")]
use std::iter::Step;
use std::num::{NonZeroUsize, ParseIntError};
use std::ops::{Add, AddAssign, Mul, RangeInclusive, Sub};
use std::ops::{Add, AddAssign, Deref, Mul, RangeInclusive, Sub};
use std::str::FromStr;

use bitflags::bitflags;
Expand Down Expand Up @@ -226,22 +226,22 @@ pub const MAX_SIMD_LANES: u64 = 1 << 0xF;
#[derive(Debug, PartialEq, Eq)]
pub struct TargetDataLayout {
pub endian: Endian,
pub i1_align: AbiAndPrefAlign,
pub i8_align: AbiAndPrefAlign,
pub i16_align: AbiAndPrefAlign,
pub i32_align: AbiAndPrefAlign,
pub i64_align: AbiAndPrefAlign,
pub i128_align: AbiAndPrefAlign,
pub f16_align: AbiAndPrefAlign,
pub f32_align: AbiAndPrefAlign,
pub f64_align: AbiAndPrefAlign,
pub f128_align: AbiAndPrefAlign,
pub i1_align: AbiAlign,
pub i8_align: AbiAlign,
pub i16_align: AbiAlign,
pub i32_align: AbiAlign,
pub i64_align: AbiAlign,
pub i128_align: AbiAlign,
pub f16_align: AbiAlign,
pub f32_align: AbiAlign,
pub f64_align: AbiAlign,
pub f128_align: AbiAlign,
pub pointer_size: Size,
pub pointer_align: AbiAndPrefAlign,
pub aggregate_align: AbiAndPrefAlign,
pub pointer_align: AbiAlign,
pub aggregate_align: AbiAlign,

/// Alignments for vector types.
pub vector_align: Vec<(Size, AbiAndPrefAlign)>,
pub vector_align: Vec<(Size, AbiAlign)>,

pub instruction_address_space: AddressSpace,

Expand All @@ -257,22 +257,22 @@ impl Default for TargetDataLayout {
let align = |bits| Align::from_bits(bits).unwrap();
TargetDataLayout {
endian: Endian::Big,
i1_align: AbiAndPrefAlign::new(align(8)),
i8_align: AbiAndPrefAlign::new(align(8)),
i16_align: AbiAndPrefAlign::new(align(16)),
i32_align: AbiAndPrefAlign::new(align(32)),
i64_align: AbiAndPrefAlign { abi: align(32), pref: align(64) },
i128_align: AbiAndPrefAlign { abi: align(32), pref: align(64) },
f16_align: AbiAndPrefAlign::new(align(16)),
f32_align: AbiAndPrefAlign::new(align(32)),
f64_align: AbiAndPrefAlign::new(align(64)),
f128_align: AbiAndPrefAlign::new(align(128)),
i1_align: AbiAlign::new(align(8)),
i8_align: AbiAlign::new(align(8)),
i16_align: AbiAlign::new(align(16)),
i32_align: AbiAlign::new(align(32)),
i64_align: AbiAlign::new(align(32)),
i128_align: AbiAlign::new(align(32)),
f16_align: AbiAlign::new(align(16)),
f32_align: AbiAlign::new(align(32)),
f64_align: AbiAlign::new(align(64)),
f128_align: AbiAlign::new(align(128)),
pointer_size: Size::from_bits(64),
pointer_align: AbiAndPrefAlign::new(align(64)),
aggregate_align: AbiAndPrefAlign { abi: align(0), pref: align(64) },
pointer_align: AbiAlign::new(align(64)),
aggregate_align: AbiAlign { abi: align(8) },
vector_align: vec![
(Size::from_bits(64), AbiAndPrefAlign::new(align(64))),
(Size::from_bits(128), AbiAndPrefAlign::new(align(128))),
(Size::from_bits(64), AbiAlign::new(align(64))),
(Size::from_bits(128), AbiAlign::new(align(128))),
],
instruction_address_space: AddressSpace::DATA,
c_enum_min_size: Integer::I32,
Expand Down Expand Up @@ -330,8 +330,7 @@ impl TargetDataLayout {
.map_err(|err| TargetDataLayoutErrors::InvalidAlignment { cause, err })
};
let abi = parse_bits(s[0], "alignment", cause)?;
let pref = s.get(1).map_or(Ok(abi), |pref| parse_bits(pref, "alignment", cause))?;
Ok(AbiAndPrefAlign { abi: align_from_bits(abi)?, pref: align_from_bits(pref)? })
Ok(AbiAlign::new(align_from_bits(abi)?))
};

let mut dl = TargetDataLayout::default();
Expand Down Expand Up @@ -426,7 +425,7 @@ impl TargetDataLayout {

/// psABI-mandated alignment for a vector type, if any
#[inline]
fn cabi_vector_align(&self, vec_size: Size) -> Option<AbiAndPrefAlign> {
fn cabi_vector_align(&self, vec_size: Size) -> Option<AbiAlign> {
self.vector_align
.iter()
.find(|(size, _align)| *size == vec_size)
Expand All @@ -435,8 +434,8 @@ impl TargetDataLayout {

/// an alignment resembling the one LLVM would pick for a vector
#[inline]
pub fn llvmlike_vector_align(&self, vec_size: Size) -> AbiAndPrefAlign {
self.cabi_vector_align(vec_size).unwrap_or(AbiAndPrefAlign::new(
pub fn llvmlike_vector_align(&self, vec_size: Size) -> AbiAlign {
self.cabi_vector_align(vec_size).unwrap_or(AbiAlign::new(
Align::from_bytes(vec_size.bytes().next_power_of_two()).unwrap(),
))
}
Expand Down Expand Up @@ -864,25 +863,32 @@ impl Align {
/// It is of effectively no consequence for layout in structs and on the stack.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub struct AbiAndPrefAlign {
pub struct AbiAlign {
pub abi: Align,
pub pref: Align,
}

impl AbiAndPrefAlign {
impl AbiAlign {
#[inline]
pub fn new(align: Align) -> AbiAndPrefAlign {
AbiAndPrefAlign { abi: align, pref: align }
pub fn new(align: Align) -> AbiAlign {
AbiAlign { abi: align }
}

#[inline]
pub fn min(self, other: AbiAndPrefAlign) -> AbiAndPrefAlign {
AbiAndPrefAlign { abi: self.abi.min(other.abi), pref: self.pref.min(other.pref) }
pub fn min(self, other: AbiAlign) -> AbiAlign {
AbiAlign { abi: self.abi.min(other.abi) }
}

#[inline]
pub fn max(self, other: AbiAndPrefAlign) -> AbiAndPrefAlign {
AbiAndPrefAlign { abi: self.abi.max(other.abi), pref: self.pref.max(other.pref) }
pub fn max(self, other: AbiAlign) -> AbiAlign {
AbiAlign { abi: self.abi.max(other.abi) }
}
}

impl Deref for AbiAlign {
type Target = Align;

fn deref(&self) -> &Self::Target {
&self.abi
}
}

Expand Down Expand Up @@ -945,7 +951,7 @@ impl Integer {
}
}

pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAlign {
use Integer::*;
let dl = cx.data_layout();

Expand Down Expand Up @@ -1058,7 +1064,7 @@ impl Float {
}
}

pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAlign {
use Float::*;
let dl = cx.data_layout();

Expand Down Expand Up @@ -1102,7 +1108,7 @@ impl Primitive {
}
}

pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAlign {
use Primitive::*;
let dl = cx.data_layout();

Expand Down Expand Up @@ -1225,7 +1231,7 @@ impl Scalar {
}
}

pub fn align(self, cx: &impl HasDataLayout) -> AbiAndPrefAlign {
pub fn align(self, cx: &impl HasDataLayout) -> AbiAlign {
self.primitive().align(cx)
}

Expand Down Expand Up @@ -1731,7 +1737,7 @@ pub struct LayoutData<FieldIdx: Idx, VariantIdx: Idx> {
/// especially in the case of by-pointer struct returns, which allocate stack even when unused.
pub uninhabited: bool,

pub align: AbiAndPrefAlign,
pub align: AbiAlign,
pub size: Size,

/// The largest alignment explicitly requested with `repr(align)` on this type or any field.
Expand Down
6 changes: 1 addition & 5 deletions compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
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Expand Up @@ -812,11 +812,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
dest.write_cvalue(fx, val);
}

sym::pref_align_of
| sym::needs_drop
| sym::type_id
| sym::type_name
| sym::variant_count => {
sym::needs_drop | sym::type_id | sym::type_name | sym::variant_count => {
intrinsic_args!(fx, args => (); intrinsic);

let const_val = fx
Expand Down
6 changes: 1 addition & 5 deletions compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
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Expand Up @@ -151,11 +151,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
}
value
}
sym::pref_align_of
| sym::needs_drop
| sym::type_id
| sym::type_name
| sym::variant_count => {
sym::needs_drop | sym::type_id | sym::type_name | sym::variant_count => {
let value = bx.tcx().const_eval_instance(bx.typing_env(), instance, span).unwrap();
OperandRef::from_const(bx, value, result.layout.ty).immediate_or_packed_pair(bx)
}
Expand Down
15 changes: 2 additions & 13 deletions compiler/rustc_const_eval/src/interpret/intrinsics.rs
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Expand Up @@ -50,13 +50,6 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
ensure_monomorphic_enough(tcx, tp_ty)?;
ConstValue::from_bool(tp_ty.needs_drop(tcx, typing_env))
}
sym::pref_align_of => {
// Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
let layout = tcx
.layout_of(typing_env.as_query_input(tp_ty))
.map_err(|e| err_inval!(Layout(*e)))?;
ConstValue::from_target_usize(layout.align.pref.bytes(), &tcx)
}
sym::type_id => {
ensure_monomorphic_enough(tcx, tp_ty)?;
ConstValue::from_u128(tcx.type_id_hash(tp_ty).as_u128())
Expand Down Expand Up @@ -144,14 +137,10 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
self.write_scalar(Scalar::from_target_usize(result, self), dest)?;
}

sym::pref_align_of
| sym::needs_drop
| sym::type_id
| sym::type_name
| sym::variant_count => {
sym::needs_drop | sym::type_id | sym::type_name | sym::variant_count => {
let gid = GlobalId { instance, promoted: None };
let ty = match intrinsic_name {
sym::pref_align_of | sym::variant_count => self.tcx.types.usize,
sym::variant_count => self.tcx.types.usize,
sym::needs_drop => self.tcx.types.bool,
sym::type_id => self.tcx.types.u128,
sym::type_name => Ty::new_static_str(self.tcx.tcx),
Expand Down
2 changes: 2 additions & 0 deletions compiler/rustc_feature/src/removed.rs
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Expand Up @@ -207,6 +207,8 @@ declare_features! (
/// Allows exhaustive integer pattern matching with `usize::MAX`/`isize::MIN`/`isize::MAX`.
(removed, precise_pointer_size_matching, "1.32.0", Some(56354),
Some("removed in favor of half-open ranges")),
(removed, pref_align_of, "CURRENT_RUSTC_VERSION", Some(91971),
Some("removed due to marginal use and inducing compiler complications")),
(removed, proc_macro_expr, "1.27.0", Some(54727),
Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
(removed, proc_macro_gen, "1.27.0", Some(54727),
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_hir_analysis/src/check/intrinsic.rs
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Expand Up @@ -235,7 +235,7 @@ pub(crate) fn check_intrinsic_type(
sym::abort => (0, 0, vec![], tcx.types.never),
sym::unreachable => (0, 0, vec![], tcx.types.never),
sym::breakpoint => (0, 0, vec![], tcx.types.unit),
sym::size_of | sym::pref_align_of | sym::min_align_of | sym::variant_count => {
sym::size_of | sym::min_align_of | sym::variant_count => {
(1, 0, vec![], tcx.types.usize)
}
sym::size_of_val | sym::min_align_of_val => {
Expand Down
9 changes: 0 additions & 9 deletions library/core/src/intrinsics/mod.rs
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Expand Up @@ -3485,15 +3485,6 @@ pub const fn size_of<T>() -> usize;
#[rustc_intrinsic]
pub const fn min_align_of<T>() -> usize;
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Also in the future, we should then rename this to just align_of.


/// The preferred alignment of a type.
///
/// This intrinsic does not have a stable counterpart.
/// It's "tracking issue" is [#91971](https://github.com/rust-lang/rust/issues/91971).
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
pub const unsafe fn pref_align_of<T>() -> usize;

/// Returns the number of variants of the type `T` cast to a `usize`;
/// if `T` has no variants, returns `0`. Uninhabited variants will be counted.
///
Expand Down
6 changes: 2 additions & 4 deletions tests/ui/abi/c-zst.aarch64-darwin.stderr
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Expand Up @@ -5,9 +5,8 @@ error: fn_abi_of(pass_zst) = FnAbi {
ty: (),
layout: Layout {
size: Size(0 bytes),
align: AbiAndPrefAlign {
align: AbiAlign {
abi: $SOME_ALIGN,
pref: $SOME_ALIGN,
},
backend_repr: Memory {
sized: true,
Expand All @@ -34,9 +33,8 @@ error: fn_abi_of(pass_zst) = FnAbi {
ty: (),
layout: Layout {
size: Size(0 bytes),
align: AbiAndPrefAlign {
align: AbiAlign {
abi: $SOME_ALIGN,
pref: $SOME_ALIGN,
},
backend_repr: Memory {
sized: true,
Expand Down
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