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Auto merge of #109035 - scottmcm:ptr-read-should-know-undef, r=WaffleLapkin,JakobDegen

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Ensure `ptr::read` gets all the same LLVM `load` metadata that dereferencing does

I was looking into `array::IntoIter` optimization, and noticed that it wasn't annotating the loads with `noundef` for simple things like `array::IntoIter<i32, N>`.  Trying to narrow it down, it seems that was because `MaybeUninit::assume_init_read` isn't marking the load as initialized (<https://rust.godbolt.org/z/Mxd8TPTnv>), which is unfortunate since that's basically its reason to exist.

The root cause is that `ptr::read` is currently implemented via the *untyped* `copy_nonoverlapping`, and thus the `load` doesn't get any type-aware metadata: no `noundef`, no `!range`.  This PR solves that by lowering `ptr::read(p)` to `copy *p` in MIR, for which the backends already do the right thing.

Fortuitiously, this also improves the IR we give to LLVM for things like `mem::replace`, and fixes a couple of long-standing bugs where `ptr::read` on `Copy` types was worse than `*`ing them.

Zulip conversation: <https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Move.20array.3A.3AIntoIter.20to.20ManuallyDrop/near/341189936>

cc `@erikdesjardins` `@JakobDegen` `@workingjubilee` `@the8472`

Fixes #106369
Fixes #73258
This commit is contained in:
bors 2023-03-15 11:44:12 +00:00
commit e4b9f86054
17 changed files with 358 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
compiler/rustc_hir_analysis/src/check/intrinsic.rs
View File

@ -363,6 +363,8 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
sym::likely => (0, vec![tcx.types.bool], tcx.types.bool),
sym::unlikely => (0, vec![tcx.types.bool], tcx.types.bool),
sym::read_via_copy => (1, vec![tcx.mk_imm_ptr(param(0))], param(0)),
sym::discriminant_value => {
let assoc_items = tcx.associated_item_def_ids(
tcx.require_lang_item(hir::LangItem::DiscriminantKind, None),

7
compiler/rustc_lint_defs/src/builtin.rs
View File

@ -1026,12 +1026,13 @@ declare_lint! {
/// ### Example
///
/// ```rust,compile_fail
/// #![feature(const_ptr_read)]
/// #![feature(const_mut_refs)]
/// const FOO: () = unsafe {
/// let x = &[0_u8; 4];
/// let y = x.as_ptr().cast::<u32>();
/// y.read(); // the address of a `u8` array is unknown and thus we don't know if
/// // it is aligned enough for reading a `u32`.
/// let mut z = 123;
/// y.copy_to_nonoverlapping(&mut z, 1); // the address of a `u8` array is unknown
/// // and thus we don't know if it is aligned enough for copying a `u32`.
/// };
/// ```
///

29
compiler/rustc_mir_transform/src/lower_intrinsics.rs
View File

@ -149,6 +149,35 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
terminator.kind = TerminatorKind::Goto { target };
}
}
sym::read_via_copy => {
let [arg] = args.as_slice() else {
span_bug!(terminator.source_info.span, "Wrong number of arguments");
};
let derefed_place =
if let Some(place) = arg.place() && let Some(local) = place.as_local() {
tcx.mk_place_deref(local.into())
} else {
span_bug!(terminator.source_info.span, "Only passing a local is supported");
};
terminator.kind = match *target {
None => {
// No target means this read something uninhabited,
// so it must be unreachable, and we don't need to
// preserve the assignment either.
TerminatorKind::Unreachable
}
Some(target) => {
block.statements.push(Statement {
source_info: terminator.source_info,
kind: StatementKind::Assign(Box::new((
*destination,
Rvalue::Use(Operand::Copy(derefed_place)),
))),
});
TerminatorKind::Goto { target }
}
}
}
sym::discriminant_value => {
if let (Some(target), Some(arg)) = (*target, args[0].place()) {
let arg = tcx.mk_place_deref(arg);

1
compiler/rustc_span/src/symbol.rs
View File

@ -1153,6 +1153,7 @@ symbols! {
read_enum_variant_arg,
read_struct,
read_struct_field,
read_via_copy,
readonly,
realloc,
reason,

10
library/core/src/intrinsics.rs
View File

@ -2020,6 +2020,16 @@ extern "rust-intrinsic" {
#[rustc_safe_intrinsic]
pub fn saturating_sub<T: Copy>(a: T, b: T) -> T;
/// This is an implementation detail of [`crate::ptr::read`] and should
/// not be used anywhere else. See its comments for why this exists.
///
/// This intrinsic can *only* be called where the argument is a local without
/// projections (`read_via_copy(p)`, not `read_via_copy(*p)`) so that it
/// trivially obeys runtime-MIR rules about derefs in operands.
#[cfg(not(bootstrap))]
#[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
pub fn read_via_copy<T>(p: *const T) -> T;
/// Returns the value of the discriminant for the variant in 'v';
/// if `T` has no discriminant, returns `0`.
///

59
library/core/src/ptr/mod.rs
View File

@ -1135,27 +1135,58 @@ pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
#[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn read<T>(src: *const T) -> T {
// We are calling the intrinsics directly to avoid function calls in the generated code
// as `intrinsics::copy_nonoverlapping` is a wrapper function.
extern "rust-intrinsic" {
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
}
// It would be semantically correct to implement this via `copy_nonoverlapping`
// and `MaybeUninit`, as was done before PR #109035. Calling `assume_init`
// provides enough information to know that this is a typed operation.
let mut tmp = MaybeUninit::<T>::uninit();
// SAFETY: the caller must guarantee that `src` is valid for reads.
// `src` cannot overlap `tmp` because `tmp` was just allocated on
// the stack as a separate allocated object.
// However, as of March 2023 the compiler was not capable of taking advantage
// of that information. Thus the implementation here switched to an intrinsic,
// which lowers to `_0 = *src` in MIR, to address a few issues:
//
// Also, since we just wrote a valid value into `tmp`, it is guaranteed
// to be properly initialized.
// - Using `MaybeUninit::assume_init` after a `copy_nonoverlapping` was not
// turning the untyped copy into a typed load. As such, the generated
// `load` in LLVM didn't get various metadata, such as `!range` (#73258),
// `!nonnull`, and `!noundef`, resulting in poorer optimization.
// - Going through the extra local resulted in multiple extra copies, even
// in optimized MIR. (Ignoring StorageLive/Dead, the intrinsic is one
// MIR statement, while the previous implementation was eight.) LLVM
// could sometimes optimize them away, but because `read` is at the core
// of so many things, not having them in the first place improves what we
// hand off to the backend. For example, `mem::replace::<Big>` previously
// emitted 4 `alloca` and 6 `memcpy`s, but is now 1 `alloc` and 3 `memcpy`s.
// - In general, this approach keeps us from getting any more bugs (like
// #106369) that boil down to "`read(p)` is worse than `*p`", as this
// makes them look identical to the backend (or other MIR consumers).
//
// Future enhancements to MIR optimizations might well allow this to return
// to the previous implementation, rather than using an intrinsic.
// SAFETY: the caller must guarantee that `src` is valid for reads.
unsafe {
assert_unsafe_precondition!(
"ptr::read requires that the pointer argument is aligned and non-null",
[T](src: *const T) => is_aligned_and_not_null(src)
);
copy_nonoverlapping(src, tmp.as_mut_ptr(), 1);
tmp.assume_init()
#[cfg(bootstrap)]
{
// We are calling the intrinsics directly to avoid function calls in the
// generated code as `intrinsics::copy_nonoverlapping` is a wrapper function.
extern "rust-intrinsic" {
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
}
// `src` cannot overlap `tmp` because `tmp` was just allocated on
// the stack as a separate allocated object.
let mut tmp = MaybeUninit::<T>::uninit();
copy_nonoverlapping(src, tmp.as_mut_ptr(), 1);
tmp.assume_init()
}
#[cfg(not(bootstrap))]
{
crate::intrinsics::read_via_copy(src)
}
}
}

15
tests/codegen/issues/issue-106369.rs Normal file
View File

@ -0,0 +1,15 @@
// compile-flags: -O
// ignore-debug (the extra assertions get in the way)
#![crate_type = "lib"]
// From <https://github.com/rust-lang/rust/issues/106369#issuecomment-1369095304>
// CHECK-LABEL: @issue_106369(
#[no_mangle]
pub unsafe fn issue_106369(ptr: *const &i32) -> bool {
// CHECK-NOT: icmp
// CHECK: ret i1 true
// CHECK-NOT: icmp
Some(std::ptr::read(ptr)).is_some()
}

38
tests/codegen/issues/issue-73258.rs Normal file
View File

@ -0,0 +1,38 @@
// compile-flags: -O
// ignore-debug (the extra assertions get in the way)
#![crate_type = "lib"]
// Adapted from <https://github.com/rust-lang/rust/issues/73258#issue-637346014>
#[derive(Clone, Copy)]
#[repr(u8)]
pub enum Foo {
A, B, C, D,
}
// CHECK-LABEL: @issue_73258(
#[no_mangle]
pub unsafe fn issue_73258(ptr: *const Foo) -> Foo {
// CHECK-NOT: icmp
// CHECK-NOT: call
// CHECK-NOT: br
// CHECK-NOT: select
// CHECK: %[[R:.+]] = load i8
// CHECK-SAME: !range !
// CHECK-NOT: icmp
// CHECK-NOT: call
// CHECK-NOT: br
// CHECK-NOT: select
// CHECK: ret i8 %[[R]]
// CHECK-NOT: icmp
// CHECK-NOT: call
// CHECK-NOT: br
// CHECK-NOT: select
let k: Option<Foo> = Some(ptr.read());
return k.unwrap();
}

36
tests/codegen/mem-replace-big-type.rs Normal file
View File

@ -0,0 +1,36 @@
// This test ensures that `mem::replace::<T>` only ever calls `@llvm.memcpy`
// with `size_of::<T>()` as the size, and never goes through any wrapper that
// may e.g. multiply `size_of::<T>()` with a variable "count" (which is only
// known to be `1` after inlining).
// compile-flags: -C no-prepopulate-passes -Zinline-mir=no
// ignore-debug: the debug assertions get in the way
#![crate_type = "lib"]
#[repr(C, align(8))]
pub struct Big([u64; 7]);
pub fn replace_big(dst: &mut Big, src: Big) -> Big {
// Before the `read_via_copy` intrinsic, this emitted six `memcpy`s.
std::mem::replace(dst, src)
}
// NOTE(eddyb) the `CHECK-NOT`s ensure that the only calls of `@llvm.memcpy` in
// the entire output, are the direct calls we want, from `ptr::replace`.
// CHECK-NOT: call void @llvm.memcpy
// For a large type, we expect exactly three `memcpy`s
// CHECK-LABEL: define internal void @{{.+}}mem{{.+}}replace{{.+}}sret(%Big)
// CHECK-NOT: alloca
// CHECK: alloca %Big
// CHECK-NOT: alloca
// CHECK-NOT: call void @llvm.memcpy
// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 8 %{{.*}}, {{i8\*|ptr}} align 8 %{{.*}}, i{{.*}} 56, i1 false)
// CHECK-NOT: call void @llvm.memcpy
// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 8 %{{.*}}, {{i8\*|ptr}} align 8 %{{.*}}, i{{.*}} 56, i1 false)
// CHECK-NOT: call void @llvm.memcpy
// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 8 %{{.*}}, {{i8\*|ptr}} align 8 %{{.*}}, i{{.*}} 56, i1 false)
// CHECK-NOT: call void @llvm.memcpy
// CHECK-NOT: call void @llvm.memcpy

21
tests/codegen/mem-replace-direct-memcpy.rs
View File

@ -13,12 +13,21 @@ pub fn replace_byte(dst: &mut u8, src: u8) -> u8 {
}
// NOTE(eddyb) the `CHECK-NOT`s ensure that the only calls of `@llvm.memcpy` in
// the entire output, are the two direct calls we want, from `ptr::replace`.
// the entire output, are the direct calls we want, from `ptr::replace`.
// CHECK-NOT: call void @llvm.memcpy
// CHECK: ; core::mem::replace
// CHECK-NOT: call void @llvm.memcpy
// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 1 %{{.*}}, {{i8\*|ptr}} align 1 %{{.*}}, i{{.*}} 1, i1 false)
// CHECK-NOT: call void @llvm.memcpy
// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 1 %{{.*}}, {{i8\*|ptr}} align 1 %{{.*}}, i{{.*}} 1, i1 false)
// For a small type, we expect one each of `load`/`store`/`memcpy` instead
// CHECK-LABEL: define internal noundef i8 @{{.+}}mem{{.+}}replace
// CHECK-NOT: alloca
// CHECK: alloca i8
// CHECK-NOT: alloca
// CHECK-NOT: call void @llvm.memcpy
// CHECK: load i8
// CHECK-NOT: call void @llvm.memcpy
// CHECK: store i8
// CHECK-NOT: call void @llvm.memcpy
// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 1 %{{.*}}, {{i8\*|ptr}} align 1 %{{.*}}, i{{.*}} 1, i1 false)
// CHECK-NOT: call void @llvm.memcpy
// CHECK-NOT: call void @llvm.memcpy

96
tests/codegen/ptr-read-metadata.rs Normal file
View File

@ -0,0 +1,96 @@
// compile-flags: -O -Z merge-functions=disabled
// no-system-llvm
// ignore-debug (the extra assertions get in the way)
#![crate_type = "lib"]
// Ensure that various forms of reading pointers correctly annotate the `load`s
// with `!noundef` and `!range` metadata to enable extra optimization.
use std::mem::MaybeUninit;
// CHECK-LABEL: define noundef i8 @copy_byte(
#[no_mangle]
pub unsafe fn copy_byte(p: *const u8) -> u8 {
// CHECK-NOT: load
// CHECK: load i8, ptr %p, align 1
// CHECK-SAME: !noundef !
// CHECK-NOT: load
*p
}
// CHECK-LABEL: define noundef i8 @read_byte(
#[no_mangle]
pub unsafe fn read_byte(p: *const u8) -> u8 {
// CHECK-NOT: load
// CHECK: load i8, ptr %p, align 1
// CHECK-SAME: !noundef !
// CHECK-NOT: load
p.read()
}
// CHECK-LABEL: define i8 @read_byte_maybe_uninit(
#[no_mangle]
pub unsafe fn read_byte_maybe_uninit(p: *const MaybeUninit<u8>) -> MaybeUninit<u8> {
// CHECK-NOT: load
// CHECK: load i8, ptr %p, align 1
// CHECK-NOT: noundef
// CHECK-NOT: load
p.read()
}
// CHECK-LABEL: define noundef i8 @read_byte_assume_init(
#[no_mangle]
pub unsafe fn read_byte_assume_init(p: &MaybeUninit<u8>) -> u8 {
// CHECK-NOT: load
// CHECK: load i8, ptr %p, align 1
// CHECK-SAME: !noundef !
// CHECK-NOT: load
p.assume_init_read()
}
// CHECK-LABEL: define noundef i32 @copy_char(
#[no_mangle]
pub unsafe fn copy_char(p: *const char) -> char {
// CHECK-NOT: load
// CHECK: load i32, ptr %p
// CHECK-SAME: !range ![[RANGE:[0-9]+]]
// CHECK-SAME: !noundef !
// CHECK-NOT: load
*p
}
// CHECK-LABEL: define noundef i32 @read_char(
#[no_mangle]
pub unsafe fn read_char(p: *const char) -> char {
// CHECK-NOT: load
// CHECK: load i32, ptr %p
// CHECK-SAME: !range ![[RANGE]]
// CHECK-SAME: !noundef !
// CHECK-NOT: load
p.read()
}
// CHECK-LABEL: define i32 @read_char_maybe_uninit(
#[no_mangle]
pub unsafe fn read_char_maybe_uninit(p: *const MaybeUninit<char>) -> MaybeUninit<char> {
// CHECK-NOT: load
// CHECK: load i32, ptr %p
// CHECK-NOT: range
// CHECK-NOT: noundef
// CHECK-NOT: load
p.read()
}
// CHECK-LABEL: define noundef i32 @read_char_assume_init(
#[no_mangle]
pub unsafe fn read_char_assume_init(p: &MaybeUninit<char>) -> char {
// CHECK-NOT: load
// CHECK: load i32, ptr %p
// CHECK-SAME: !range ![[RANGE]]
// CHECK-SAME: !noundef !
// CHECK-NOT: load
p.assume_init_read()
}
// CHECK: ![[RANGE]] = !{i32 0, i32 1114112}

27
tests/mir-opt/lower_intrinsics.read_via_copy_primitive.LowerIntrinsics.diff Normal file
View File

@ -0,0 +1,27 @@
- // MIR for `read_via_copy_primitive` before LowerIntrinsics
+ // MIR for `read_via_copy_primitive` after LowerIntrinsics
fn read_via_copy_primitive(_1: &i32) -> i32 {
debug r => _1; // in scope 0 at $DIR/lower_intrinsics.rs:+0:32: +0:33
let mut _0: i32; // return place in scope 0 at $DIR/lower_intrinsics.rs:+0:44: +0:47
let mut _2: *const i32; // in scope 0 at $DIR/lower_intrinsics.rs:+1:46: +1:47
scope 1 {
}
bb0: {
StorageLive(_2); // scope 1 at $DIR/lower_intrinsics.rs:+1:46: +1:47
_2 = &raw const (*_1); // scope 1 at $DIR/lower_intrinsics.rs:+1:46: +1:47
- _0 = read_via_copy::<i32>(move _2) -> bb1; // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48
- // mir::Constant
- // + span: $DIR/lower_intrinsics.rs:85:14: 85:45
- // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(*const i32) -> i32 {read_via_copy::<i32>}, val: Value(<ZST>) }
+ _0 = (*_2); // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48
+ goto -> bb1; // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48
}
bb1: {
StorageDead(_2); // scope 1 at $DIR/lower_intrinsics.rs:+1:47: +1:48
return; // scope 0 at $DIR/lower_intrinsics.rs:+2:2: +2:2
}
}

21
tests/mir-opt/lower_intrinsics.read_via_copy_uninhabited.LowerIntrinsics.diff Normal file
View File

@ -0,0 +1,21 @@
- // MIR for `read_via_copy_uninhabited` before LowerIntrinsics
+ // MIR for `read_via_copy_uninhabited` after LowerIntrinsics
fn read_via_copy_uninhabited(_1: &Never) -> Never {
debug r => _1; // in scope 0 at $DIR/lower_intrinsics.rs:+0:34: +0:35
let mut _0: Never; // return place in scope 0 at $DIR/lower_intrinsics.rs:+0:48: +0:53
let mut _2: *const Never; // in scope 0 at $DIR/lower_intrinsics.rs:+1:46: +1:47
scope 1 {
}
bb0: {
StorageLive(_2); // scope 1 at $DIR/lower_intrinsics.rs:+1:46: +1:47
_2 = &raw const (*_1); // scope 1 at $DIR/lower_intrinsics.rs:+1:46: +1:47
- _0 = read_via_copy::<Never>(move _2); // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48
- // mir::Constant
- // + span: $DIR/lower_intrinsics.rs:90:14: 90:45
- // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(*const Never) -> Never {read_via_copy::<Never>}, val: Value(<ZST>) }
+ unreachable; // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48
}
}

12
tests/mir-opt/lower_intrinsics.rs
View File

@ -79,3 +79,15 @@ pub fn with_overflow(a: i32, b: i32) {
let _y = core::intrinsics::sub_with_overflow(a, b);
let _z = core::intrinsics::mul_with_overflow(a, b);
}
// EMIT_MIR lower_intrinsics.read_via_copy_primitive.LowerIntrinsics.diff
pub fn read_via_copy_primitive(r: &i32) -> i32 {
unsafe { core::intrinsics::read_via_copy(r) }
}
// EMIT_MIR lower_intrinsics.read_via_copy_uninhabited.LowerIntrinsics.diff
pub fn read_via_copy_uninhabited(r: &Never) -> Never {
unsafe { core::intrinsics::read_via_copy(r) }
}
pub enum Never {}

6
tests/ui/const-ptr/out_of_bounds_read.stderr
View File

@ -1,7 +1,7 @@
error[E0080]: evaluation of constant value failed
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
|
= note: memory access failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds
= note: dereferencing pointer failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds
|
note: inside `std::ptr::read::<u32>`
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
@ -14,7 +14,7 @@ LL | const _READ: u32 = unsafe { ptr::read(PAST_END_PTR) };
error[E0080]: evaluation of constant value failed
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
|
= note: memory access failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds
= note: dereferencing pointer failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds
|
note: inside `std::ptr::read::<u32>`
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
@ -29,7 +29,7 @@ LL | const _CONST_READ: u32 = unsafe { PAST_END_PTR.read() };
error[E0080]: evaluation of constant value failed
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
|
= note: memory access failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds
= note: dereferencing pointer failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds
|
note: inside `std::ptr::read::<u32>`
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL

24
tests/ui/consts/const-eval/ub-ref-ptr.stderr
View File

@ -148,11 +148,11 @@ LL | const DATA_FN_PTR: fn() = unsafe { mem::transmute(&13) };
HEX_DUMP
}
error: accessing memory with alignment 1, but alignment 4 is required
error[E0080]: evaluation of constant value failed
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
|
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
= note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/104616>
= note: accessing memory with alignment 1, but alignment 4 is required
|
note: inside `std::ptr::read::<u32>`
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
note: inside `ptr::const_ptr::<impl *const u32>::read`
@ -162,25 +162,7 @@ note: inside `UNALIGNED_READ`
|
LL | ptr.read();
| ^^^^^^^^^^
= note: `#[deny(invalid_alignment)]` on by default
error: aborting due to 15 previous errors
For more information about this error, try `rustc --explain E0080`.
Future incompatibility report: Future breakage diagnostic:
error: accessing memory with alignment 1, but alignment 4 is required
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
|
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
= note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/104616>
note: inside `std::ptr::read::<u32>`
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
note: inside `ptr::const_ptr::<impl *const u32>::read`
--> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
note: inside `UNALIGNED_READ`
--> $DIR/ub-ref-ptr.rs:67:5
|
LL | ptr.read();
| ^^^^^^^^^^
= note: `#[deny(invalid_alignment)]` on by default

2
tests/ui/consts/issue-miri-1910.stderr
View File

@ -1,7 +1,7 @@
error[E0080]: evaluation of constant value failed
--> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
|
= note: unable to copy parts of a pointer from memory at ALLOC
= note: unable to turn pointer into raw bytes
|
= help: this code performed an operation that depends on the underlying bytes representing a pointer
= help: the absolute address of a pointer is not known at compile-time, so such operations are not supported