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Merge two different equality specialization traits in core

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This commit is contained in:
Scott McMurray 2023-02-25 22:47:20 -08:00
parent c5c7d2b377
commit 44eec1d9b0
7 changed files with 182 additions and 94 deletions
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73
library/core/src/array/equality.rs
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@ -1,6 +1,5 @@
use crate::cmp::BytewiseEq;
use crate::convert::TryInto;
use crate::num::{NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize};
use crate::num::{NonZeroU128, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize};
#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B, const N: usize> PartialEq<[B; N]> for [A; N]
@ -144,74 +143,14 @@ impl<T: PartialEq<Other>, Other, const N: usize> SpecArrayEq<Other, N> for T {
}
}
impl<T: IsRawEqComparable<U>, U, const N: usize> SpecArrayEq<U, N> for T {
impl<T: BytewiseEq<U>, U, const N: usize> SpecArrayEq<U, N> for T {
fn spec_eq(a: &[T; N], b: &[U; N]) -> bool {
// SAFETY: This is why `IsRawEqComparable` is an `unsafe trait`.
unsafe {
let b = &*b.as_ptr().cast::<[T; N]>();
crate::intrinsics::raw_eq(a, b)
}
// SAFETY: Arrays are compared element-wise, and don't add any padding
// between elements, so when the elements are `BytewiseEq`, we can
// compare the entire array at once.
unsafe { crate::intrinsics::raw_eq(a, crate::mem::transmute(b)) }
}
fn spec_ne(a: &[T; N], b: &[U; N]) -> bool {
!Self::spec_eq(a, b)
}
}
/// `U` exists on here mostly because `min_specialization` didn't let me
/// repeat the `T` type parameter in the above specialization, so instead
/// the `T == U` constraint comes from the impls on this.
/// # Safety
/// - Neither `Self` nor `U` has any padding.
/// - `Self` and `U` have the same layout.
/// - `Self: PartialEq<U>` is byte-wise (this means no floats, among other things)
#[rustc_specialization_trait]
unsafe trait IsRawEqComparable<U>: PartialEq<U> {}
macro_rules! is_raw_eq_comparable {
($($t:ty),+ $(,)?) => {$(
unsafe impl IsRawEqComparable<$t> for $t {}
)+};
}
// SAFETY: All the ordinary integer types have no padding, and are not pointers.
is_raw_eq_comparable!(u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);
// SAFETY: bool and char have *niches*, but no *padding* (and these are not pointer types), so this
// is sound
is_raw_eq_comparable!(bool, char);
// SAFETY: Similarly, the non-zero types have a niche, but no undef and no pointers,
// and they compare like their underlying numeric type.
is_raw_eq_comparable!(
NonZeroU8,
NonZeroU16,
NonZeroU32,
NonZeroU64,
NonZeroU128,
NonZeroUsize,
NonZeroI8,
NonZeroI16,
NonZeroI32,
NonZeroI64,
NonZeroI128,
NonZeroIsize,
);
// SAFETY: The NonZero types have the "null" optimization guaranteed, and thus
// are also safe to equality-compare bitwise inside an `Option`.
// The way `PartialOrd` is defined for `Option` means that this wouldn't work
// for `<` or `>` on the signed types, but since we only do `==` it's fine.
is_raw_eq_comparable!(
Option<NonZeroU8>,
Option<NonZeroU16>,
Option<NonZeroU32>,
Option<NonZeroU64>,
Option<NonZeroU128>,
Option<NonZeroUsize>,
Option<NonZeroI8>,
Option<NonZeroI16>,
Option<NonZeroI32>,
Option<NonZeroI64>,
Option<NonZeroI128>,
Option<NonZeroIsize>,
);

3
library/core/src/cmp.rs
View File

@ -22,6 +22,9 @@
#![stable(feature = "rust1", since = "1.0.0")]
mod bytewise;
pub(crate) use bytewise::BytewiseEq;
use crate::marker::Destruct;
use self::Ordering::*;

83
library/core/src/cmp/bytewise.rs Normal file
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@ -0,0 +1,83 @@
use crate::num::{NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize};
use crate::num::{NonZeroU128, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize};
/// Types where `==` & `!=` are equivalent to comparing their underlying bytes.
///
/// Importantly, this means no floating-point types, as those have different
/// byte representations (like `-0` and `+0`) which compare as the same.
/// Since byte arrays are `Eq`, that implies that these types are probably also
/// `Eq`, but that's not technically required to use this trait.
///
/// `Rhs` is *de facto* always `Self`, but the separate parameter is important
/// to avoid the `specializing impl repeats parameter` error when consuming this.
///
/// # Safety
///
/// - `Self` and `Rhs` have no padding.
/// - `Self` and `Rhs` have the same layout (size and alignment).
/// - Neither `Self` nor `Rhs` have provenance, so integer comparisons are correct.
/// - `<Self as PartialEq<Rhs>>::{eq,ne}` are equivalent to comparing the bytes.
#[rustc_specialization_trait]
pub(crate) unsafe trait BytewiseEq<Rhs = Self>: PartialEq<Rhs> + Sized {}
macro_rules! is_bytewise_comparable {
($($t:ty),+ $(,)?) => {$(
unsafe impl BytewiseEq for $t {}
)+};
}
// SAFETY: All the ordinary integer types have no padding, and are not pointers.
is_bytewise_comparable!(u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);
// SAFETY: These have *niches*, but no *padding* and no *provenance*,
// so we can compare them directly.
is_bytewise_comparable!(bool, char, super::Ordering);
// SAFETY: Similarly, the non-zero types have a niche, but no undef and no pointers,
// and they compare like their underlying numeric type.
is_bytewise_comparable!(
NonZeroU8,
NonZeroU16,
NonZeroU32,
NonZeroU64,
NonZeroU128,
NonZeroUsize,
NonZeroI8,
NonZeroI16,
NonZeroI32,
NonZeroI64,
NonZeroI128,
NonZeroIsize,
);
// SAFETY: The NonZero types have the "null" optimization guaranteed, and thus
// are also safe to equality-compare bitwise inside an `Option`.
// The way `PartialOrd` is defined for `Option` means that this wouldn't work
// for `<` or `>` on the signed types, but since we only do `==` it's fine.
is_bytewise_comparable!(
Option<NonZeroU8>,
Option<NonZeroU16>,
Option<NonZeroU32>,
Option<NonZeroU64>,
Option<NonZeroU128>,
Option<NonZeroUsize>,
Option<NonZeroI8>,
Option<NonZeroI16>,
Option<NonZeroI32>,
Option<NonZeroI64>,
Option<NonZeroI128>,
Option<NonZeroIsize>,
);
macro_rules! is_bytewise_comparable_array_length {
($($n:literal),+ $(,)?) => {$(
// SAFETY: Arrays have no padding between elements, so if the elements are
// `BytewiseEq`, then the whole array can be too.
unsafe impl<T: BytewiseEq<U>, U> BytewiseEq<[U; $n]> for [T; $n] {}
)+};
}
// Frustratingly, this can't be made const-generic as it gets
// error: specializing impl repeats parameter `N`
// so just do it for a couple of plausibly-common ones.
is_bytewise_comparable_array_length!(0, 1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, 64);

4
library/core/src/intrinsics.rs
View File

@ -2093,6 +2093,10 @@ pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
/// Above some backend-decided threshold this will emit calls to `memcmp`,
/// like slice equality does, instead of causing massive code size.
///
/// Since this works by comparing the underlying bytes, the actual `T` is
/// not particularly important. It will be used for its size and alignment,
/// but any validity restrictions will be ignored, not enforced.
///
/// # Safety
///
/// It's UB to call this if any of the *bytes* in `*a` or `*b` are uninitialized or carry a

27
library/core/src/slice/cmp.rs
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@ -1,6 +1,6 @@
//! Comparison traits for `[T]`.
use crate::cmp::{self, Ordering};
use crate::cmp::{self, BytewiseEq, Ordering};
use crate::ffi;
use crate::mem;
@ -77,7 +77,7 @@ impl<A, B> SlicePartialEq<B> for [A]
// Use memcmp for bytewise equality when the types allow
impl<A, B> SlicePartialEq<B> for [A]
where
A: BytewiseEquality<B>,
A: BytewiseEq<B>,
{
fn equal(&self, other: &[B]) -> bool {
if self.len() != other.len() {
@ -203,29 +203,6 @@ fn compare(left: &[Self], right: &[Self]) -> Ordering {
}
}
// Hack to allow specializing on `Eq` even though `Eq` has a method.
#[rustc_unsafe_specialization_marker]
trait MarkerEq<T>: PartialEq<T> {}
impl<T: Eq> MarkerEq<T> for T {}
#[doc(hidden)]
/// Trait implemented for types that can be compared for equality using
/// their bytewise representation
#[rustc_specialization_trait]
trait BytewiseEquality<T>: MarkerEq<T> + Copy {}
macro_rules! impl_marker_for {
($traitname:ident, $($ty:ty)*) => {
$(
impl $traitname<$ty> for $ty { }
)*
}
}
impl_marker_for!(BytewiseEquality,
u8 i8 u16 i16 u32 i32 u64 i64 u128 i128 usize isize char bool);
pub(super) trait SliceContains: Sized {
fn slice_contains(&self, x: &[Self]) -> bool;
}

30
tests/codegen/array-equality.rs
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@ -1,4 +1,4 @@
// compile-flags: -O
// compile-flags: -O -Z merge-functions=disabled
// only-x86_64
#![crate_type = "lib"]
@ -43,6 +43,15 @@
a == b
}
// CHECK-LABEL: @array_char_eq
#[no_mangle]
pub fn array_char_eq(a: [char; 2], b: [char; 2]) -> bool {
// CHECK-NEXT: start:
// CHECK-NEXT: %[[EQ:.+]] = icmp eq i64 %0, %1
// CHECK-NEXT: ret i1 %[[EQ]]
a == b
}
// CHECK-LABEL: @array_eq_zero_short(i48
#[no_mangle]
pub fn array_eq_zero_short(x: [u16; 3]) -> bool {
@ -52,6 +61,25 @@
x == [0; 3]
}
// CHECK-LABEL: @array_eq_none_short(i40
#[no_mangle]
pub fn array_eq_none_short(x: [Option<std::num::NonZeroU8>; 5]) -> bool {
// CHECK-NEXT: start:
// CHECK-NEXT: %[[EQ:.+]] = icmp eq i40 %0, 0
// CHECK-NEXT: ret i1 %[[EQ]]
x == [None; 5]
}
// CHECK-LABEL: @array_eq_zero_nested(
#[no_mangle]
pub fn array_eq_zero_nested(x: [[u8; 3]; 3]) -> bool {
// CHECK: %[[VAL:.+]] = load i72
// CHECK-SAME: align 1
// CHECK: %[[EQ:.+]] = icmp eq i72 %[[VAL]], 0
// CHECK: ret i1 %[[EQ]]
x == [[0; 3]; 3]
}
// CHECK-LABEL: @array_eq_zero_mid(
#[no_mangle]
pub fn array_eq_zero_mid(x: [u16; 8]) -> bool {

56
tests/codegen/slice-ref-equality.rs
View File

@ -1,7 +1,10 @@
// compile-flags: -C opt-level=3 -Zmerge-functions=disabled
// compile-flags: -O -Zmerge-functions=disabled
// ignore-debug (the extra assertions get in the way)
#![crate_type = "lib"]
use std::num::{NonZeroI16, NonZeroU32};
// #71602 reported a simple array comparison just generating a loop.
// This was originally fixed by ensuring it generates a single bcmp,
// but we now generate it as a load+icmp instead. `is_zero_slice` was
@ -36,3 +39,54 @@
// CHECK-NEXT: ret i1 %[[EQ]]
*data == [0; 4]
}
// The following test the extra specializations to make sure that slice
// equality for non-byte types also just emit a `bcmp`, not a loop.
// CHECK-LABEL: @eq_slice_of_nested_u8(
// CHECK-SAME: [[USIZE:i16|i32|i64]] noundef %1
// CHECK-SAME: [[USIZE]] noundef %3
#[no_mangle]
fn eq_slice_of_nested_u8(x: &[[u8; 3]], y: &[[u8; 3]]) -> bool {
// CHECK: icmp eq [[USIZE]] %1, %3
// CHECK: %[[BYTES:.+]] = mul nsw [[USIZE]] %1, 3
// CHECK: tail call{{( noundef)?}} i32 @{{bcmp|memcmp}}({{i8\*|ptr}}
// CHECK-SAME: , [[USIZE]]{{( noundef)?}} %[[BYTES]])
x == y
}
// CHECK-LABEL: @eq_slice_of_i32(
// CHECK-SAME: [[USIZE:i16|i32|i64]] noundef %1
// CHECK-SAME: [[USIZE]] noundef %3
#[no_mangle]
fn eq_slice_of_i32(x: &[i32], y: &[i32]) -> bool {
// CHECK: icmp eq [[USIZE]] %1, %3
// CHECK: %[[BYTES:.+]] = shl nsw [[USIZE]] %1, 2
// CHECK: tail call{{( noundef)?}} i32 @{{bcmp|memcmp}}({{i32\*|ptr}}
// CHECK-SAME: , [[USIZE]]{{( noundef)?}} %[[BYTES]])
x == y
}
// CHECK-LABEL: @eq_slice_of_nonzero(
// CHECK-SAME: [[USIZE:i16|i32|i64]] noundef %1
// CHECK-SAME: [[USIZE]] noundef %3
#[no_mangle]
fn eq_slice_of_nonzero(x: &[NonZeroU32], y: &[NonZeroU32]) -> bool {
// CHECK: icmp eq [[USIZE]] %1, %3
// CHECK: %[[BYTES:.+]] = shl nsw [[USIZE]] %1, 2
// CHECK: tail call{{( noundef)?}} i32 @{{bcmp|memcmp}}({{i32\*|ptr}}
// CHECK-SAME: , [[USIZE]]{{( noundef)?}} %[[BYTES]])
x == y
}
// CHECK-LABEL: @eq_slice_of_option_of_nonzero(
// CHECK-SAME: [[USIZE:i16|i32|i64]] noundef %1
// CHECK-SAME: [[USIZE]] noundef %3
#[no_mangle]
fn eq_slice_of_option_of_nonzero(x: &[Option<NonZeroI16>], y: &[Option<NonZeroI16>]) -> bool {
// CHECK: icmp eq [[USIZE]] %1, %3
// CHECK: %[[BYTES:.+]] = shl nsw [[USIZE]] %1, 1
// CHECK: tail call{{( noundef)?}} i32 @{{bcmp|memcmp}}({{i16\*|ptr}}
// CHECK-SAME: , [[USIZE]]{{( noundef)?}} %[[BYTES]])
x == y
}