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constify TryFrom<Vec> for array #155616

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1 change: 1 addition & 0 deletions library/alloc/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,7 @@
#![feature(const_convert)]
#![feature(const_default)]
#![feature(const_destruct)]
#![feature(const_drop_in_place)]
#![feature(const_eval_select)]
#![feature(const_heap)]
#![feature(const_index)]
Expand Down
6 changes: 5 additions & 1 deletion library/alloc/src/raw_vec/mod.rs
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Expand Up @@ -417,7 +417,8 @@ impl<T, A: Allocator> RawVec<T, A> {
}
}

unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> {
#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
unsafe impl<#[may_dangle] T, A: [const] Allocator> const Drop for RawVec<T, A> {
/// Frees the memory owned by the `RawVec` *without* trying to drop its contents.
fn drop(&mut self) {
// SAFETY: We are in a Drop impl, self.inner will not be used again.
Expand Down Expand Up @@ -861,7 +862,10 @@ impl<A: Allocator> RawVecInner<A> {
}
Ok(())
}
}

#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
const impl<A: [const] Allocator> RawVecInner<A> {
/// # Safety
///
/// This function deallocates the owned allocation, but does not update `ptr` or `cap` to
Expand Down
15 changes: 9 additions & 6 deletions library/alloc/src/vec/mod.rs
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Expand Up @@ -79,9 +79,7 @@ use core::cmp::Ordering;
use core::hash::{Hash, Hasher};
#[cfg(not(no_global_oom_handling))]
use core::iter;
#[cfg(not(no_global_oom_handling))]
use core::marker::Destruct;
use core::marker::{Freeze, PhantomData};
use core::marker::{Destruct, Freeze, PhantomData};
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Lars-Schumann marked this conversation as resolved.
use core::mem::{self, Assume, ManuallyDrop, MaybeUninit, SizedTypeProperties, TransmuteFrom};
use core::ops::{self, Index, IndexMut, Range, RangeBounds};
use core::ptr::{self, NonNull};
Expand Down Expand Up @@ -2184,7 +2182,8 @@ impl<T, A: Allocator> Vec<T, A> {
/// [`spare_capacity_mut()`]: Vec::spare_capacity_mut
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn set_len(&mut self, new_len: usize) {
#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
pub const unsafe fn set_len(&mut self, new_len: usize) {
ub_checks::assert_unsafe_precondition!(
check_library_ub,
"Vec::set_len requires that new_len <= capacity()",
Expand Down Expand Up @@ -4245,7 +4244,8 @@ impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
}

#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
unsafe impl<#[may_dangle] T: [const] Destruct, A: Allocator> const Drop for Vec<T, A> {
fn drop(&mut self) {
unsafe {
// use drop for [T]
Expand Down Expand Up @@ -4464,7 +4464,10 @@ impl From<&str> for Vec<u8> {
}

#[stable(feature = "array_try_from_vec", since = "1.48.0")]
impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T: [const] Destruct, A: [const] Allocator + [const] Destruct, const N: usize> const
TryFrom<Vec<T, A>> for [T; N]
{
type Error = Vec<T, A>;

/// Gets the entire contents of the `Vec<T>` as an array,
Expand Down
36 changes: 19 additions & 17 deletions tests/mir-opt/pre-codegen/slice_iter.enumerated_loop.PreCodegen.after.panic-abort.mir
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Original file line number Diff line number Diff line change
Expand Up @@ -180,23 +180,20 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {

bb4: {
StorageLive(_32);
StorageLive(_29);
StorageLive(_30);
StorageLive(_27);
StorageLive(_13);
StorageLive(_14);
StorageLive(_20);
StorageLive(_24);
StorageLive(_15);
StorageLive(_26);
StorageLive(_16);
StorageLive(_13);
_13 = copy _8;
StorageLive(_14);
_14 = copy _11;
switchInt(const <T as std::mem::SizedTypeProperties>::IS_ZST) -> [0: bb5, otherwise: bb8];
}

bb5: {
StorageLive(_18);
StorageLive(_15);
_15 = copy _14 as std::ptr::NonNull<T> (Transmute);
_16 = copy _13 as *mut T (Transmute);
StorageLive(_17);
Expand All @@ -207,6 +204,7 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
}

bb6: {
StorageDead(_15);
StorageDead(_18);
StorageLive(_19);
_19 = Offset(copy _16, const 1_usize);
Expand All @@ -216,27 +214,27 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
}

bb7: {
StorageDead(_15);
StorageDead(_18);
goto -> bb10;
}

bb8: {
StorageLive(_20);
_20 = copy _14 as usize (Transmute);
switchInt(copy _20) -> [0: bb9, otherwise: bb12];
}

bb9: {
StorageDead(_20);
goto -> bb10;
}

bb10: {
StorageDead(_16);
StorageDead(_26);
StorageDead(_15);
StorageDead(_24);
StorageDead(_20);
StorageDead(_14);
StorageDead(_13);
StorageDead(_16);
StorageDead(_24);
StorageDead(_27);
StorageLive(_21);
StorageLive(_23);
Expand All @@ -246,7 +244,6 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
StorageDead(_23);
StorageDead(_21);
StorageDead(_30);
StorageDead(_29);
StorageDead(_32);
StorageDead(_12);
drop(_2) -> [return: bb11, unwind unreachable];
Expand All @@ -259,24 +256,25 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
bb12: {
_24 = SubUnchecked(copy _20, const 1_usize);
_11 = copy _24 as *const T (Transmute);
StorageDead(_20);
goto -> bb13;
}

bb13: {
StorageLive(_26);
StorageLive(_25);
_25 = copy _13 as *const T (Transmute);
_26 = &(*_25);
StorageDead(_25);
_27 = Option::<&T>::Some(copy _26);
StorageDead(_16);
StorageDead(_26);
StorageDead(_15);
StorageDead(_24);
StorageDead(_20);
StorageDead(_14);
StorageDead(_13);
StorageDead(_16);
StorageDead(_24);
_28 = copy ((_27 as Some).0: &T);
StorageDead(_27);
StorageLive(_29);
_29 = copy _12;
_30 = AddWithOverflow(copy _12, const 1_usize);
assert(!move (_30.1: bool), "attempt to compute `{} + {}`, which would overflow", copy _12, const 1_usize) -> [success: bb14, unwind unreachable];
Expand All @@ -288,9 +286,11 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
_31 = (copy _29, copy _28);
_32 = Option::<(usize, &T)>::Some(move _31);
StorageDead(_31);
StorageDead(_30);
StorageDead(_29);
StorageDead(_30);
StorageLive(_33);
_33 = copy (((_32 as Some).0: (usize, &T)).0: usize);
StorageLive(_34);
_34 = copy (((_32 as Some).0: (usize, &T)).1: &T);
StorageLive(_35);
_35 = &_2;
Expand All @@ -302,6 +302,8 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
bb15: {
StorageDead(_36);
StorageDead(_35);
StorageDead(_34);
StorageDead(_33);
StorageDead(_32);
goto -> bb4;
}
Expand Down
29 changes: 15 additions & 14 deletions tests/mir-opt/pre-codegen/slice_iter.forward_loop.PreCodegen.after.panic-abort.mir
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Original file line number Diff line number Diff line change
Expand Up @@ -142,20 +142,18 @@ fn forward_loop(_1: &[T], _2: impl Fn(&T)) -> () {

bb4: {
StorageLive(_23);
StorageLive(_12);
StorageLive(_13);
StorageLive(_19);
StorageLive(_20);
StorageLive(_14);
StorageLive(_22);
StorageLive(_15);
StorageLive(_12);
_12 = copy _8;
StorageLive(_13);
_13 = copy _11;
switchInt(const <T as std::mem::SizedTypeProperties>::IS_ZST) -> [0: bb5, otherwise: bb8];
}

bb5: {
StorageLive(_17);
StorageLive(_14);
_14 = copy _13 as std::ptr::NonNull<T> (Transmute);
_15 = copy _12 as *mut T (Transmute);
StorageLive(_16);
Expand All @@ -166,6 +164,7 @@ fn forward_loop(_1: &[T], _2: impl Fn(&T)) -> () {
}

bb6: {
StorageDead(_14);
StorageDead(_17);
StorageLive(_18);
_18 = Offset(copy _15, const 1_usize);
Expand All @@ -175,27 +174,27 @@ fn forward_loop(_1: &[T], _2: impl Fn(&T)) -> () {
}

bb7: {
StorageDead(_14);
StorageDead(_17);
goto -> bb10;
}

bb8: {
StorageLive(_19);
_19 = copy _13 as usize (Transmute);
switchInt(copy _19) -> [0: bb9, otherwise: bb12];
}

bb9: {
StorageDead(_19);
goto -> bb10;
}

bb10: {
StorageDead(_15);
StorageDead(_22);
StorageDead(_14);
StorageDead(_20);
StorageDead(_19);
StorageDead(_13);
StorageDead(_12);
StorageDead(_15);
StorageDead(_20);
StorageDead(_23);
drop(_2) -> [return: bb11, unwind unreachable];
}
Expand All @@ -207,22 +206,23 @@ fn forward_loop(_1: &[T], _2: impl Fn(&T)) -> () {
bb12: {
_20 = SubUnchecked(copy _19, const 1_usize);
_11 = copy _20 as *const T (Transmute);
StorageDead(_19);
goto -> bb13;
}

bb13: {
StorageLive(_22);
StorageLive(_21);
_21 = copy _12 as *const T (Transmute);
_22 = &(*_21);
StorageDead(_21);
_23 = Option::<&T>::Some(copy _22);
StorageDead(_15);
StorageDead(_22);
StorageDead(_14);
StorageDead(_20);
StorageDead(_19);
StorageDead(_13);
StorageDead(_12);
StorageDead(_15);
StorageDead(_20);
StorageLive(_24);
_24 = copy ((_23 as Some).0: &T);
StorageLive(_25);
_25 = &_2;
Expand All @@ -234,6 +234,7 @@ fn forward_loop(_1: &[T], _2: impl Fn(&T)) -> () {
bb14: {
StorageDead(_26);
StorageDead(_25);
StorageDead(_24);
StorageDead(_23);
goto -> bb4;
}
Expand Down
6 changes: 6 additions & 0 deletions tests/mir-opt/pre-codegen/slice_iter.range_loop.PreCodegen.after.panic-abort.mir
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Expand Up @@ -72,11 +72,15 @@ fn range_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
}

bb4: {
StorageLive(_7);
_7 = copy _4;
_4 = AddUnchecked(copy _7, const 1_usize);
_8 = Option::<usize>::Some(copy _7);
StorageDead(_7);
Comment on lines +75 to +79
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@oli-obk oli-obk May 7, 2026 •
edited by rustbot
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I mean, this is probably an improvement, but what causes it? Do we have mir-opts that are checking constness of functions out of some reason?

View changes since the review

StorageDead(_6);
StorageLive(_9);
_9 = copy ((_8 as Some).0: usize);
StorageLive(_11);
_10 = Lt(copy _9, copy _3);
assert(move _10, "index out of bounds: the length is {} but the index is {}", copy _3, copy _9) -> [success: bb5, unwind unreachable];
}
Expand All @@ -93,6 +97,8 @@ fn range_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
bb6: {
StorageDead(_13);
StorageDead(_12);
StorageDead(_11);
StorageDead(_9);
StorageDead(_8);
goto -> bb1;
}
Expand Down
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