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when an intrinsic has a const-stable fallback body, we can easily expose it on stable

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This commit is contained in:
Ralf Jung 2024-11-02 08:49:49 +01:00
parent 5069434c81
commit a741b33c14
5 changed files with 37 additions and 8 deletions
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16
compiler/rustc_const_eval/src/check_consts/check.rs
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@ -739,6 +739,12 @@ fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location
// We use `intrinsic.const_stable` to determine if this can be safely exposed to
// stable code, rather than `const_stable_indirect`. This is to make
// `#[rustc_const_stable_indirect]` an attribute that is always safe to add.
// We also ask is_safe_to_expose_on_stable_const_fn; this determines whether the intrinsic
// fallback body is safe to expose on stable.
let is_const_stable = intrinsic.const_stable
|| (!intrinsic.must_be_overridden
&& tcx.is_const_fn(callee)
&& is_safe_to_expose_on_stable_const_fn(tcx, callee));
match tcx.lookup_const_stability(callee) {
None => {
// Non-const intrinsic.
@ -748,7 +754,7 @@ fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location
// Intrinsic does not need a separate feature gate (we rely on the
// regular stability checker). However, we have to worry about recursive
// const stability.
if !intrinsic.const_stable && self.enforce_recursive_const_stability() {
if !is_const_stable && self.enforce_recursive_const_stability() {
self.dcx().emit_err(errors::UnmarkedIntrinsicExposed {
span: self.span,
def_path: self.tcx.def_path_str(callee),
@ -763,12 +769,14 @@ fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location
self.check_op(ops::IntrinsicUnstable {
name: intrinsic.name,
feature,
const_stable: intrinsic.const_stable,
const_stable: is_const_stable,
});
}
Some(ConstStability { level: StabilityLevel::Stable { .. }, .. }) => {
// All good. But ensure this is indeed a const-stable intrinsic.
assert!(intrinsic.const_stable);
// All good. Note that a `#[rustc_const_stable]` intrinsic (meaning it
// can be *directly* invoked from stable const code) does not always
// have the `#[rustc_const_stable_intrinsic]` attribute (which controls
// exposing an intrinsic indirectly); we accept this call anyway.
}
}
// This completes the checks for intrinsics.

3
compiler/rustc_middle/src/ty/util.rs
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@ -1789,8 +1789,7 @@ pub fn intrinsic_raw(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ty::Intrinsi
Some(ty::IntrinsicDef {
name: tcx.item_name(def_id.into()),
must_be_overridden: tcx.has_attr(def_id, sym::rustc_intrinsic_must_be_overridden),
const_stable: tcx.has_attr(def_id, sym::rustc_const_stable_intrinsic)
|| tcx.lookup_const_stability(def_id).is_some_and(|s| s.is_const_stable()),
const_stable: tcx.has_attr(def_id, sym::rustc_const_stable_intrinsic),
})
} else {
None

2
tests/ui/consts/auxiliary/unstable_intrinsic.rs
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@ -3,9 +3,11 @@
#[unstable(feature = "unstable", issue = "42")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const unsafe fn size_of_val<T>(x: *const T) -> usize { 42 }
#[unstable(feature = "unstable", issue = "42")]
#[rustc_const_unstable(feature = "unstable", issue = "42")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const unsafe fn min_align_of_val<T>(x: *const T) -> usize { 42 }

12
tests/ui/consts/const-unstable-intrinsic.rs
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@ -30,11 +30,13 @@ const fn const_main() {
#[unstable(feature = "local", issue = "42")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const unsafe fn size_of_val<T>(x: *const T) -> usize { 42 }
#[unstable(feature = "local", issue = "42")]
#[rustc_const_unstable(feature = "local", issue = "42")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const unsafe fn min_align_of_val<T>(x: *const T) -> usize { 42 }
#[stable(feature = "rust1", since = "1.0.0")]
@ -43,6 +45,7 @@ const fn const_main() {
pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
// Const stability attributes are not inherited from parent items.
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
unimplemented!()
}
@ -50,3 +53,12 @@ const fn const_main() {
unsafe { copy(src, dst, count) }
//~^ ERROR cannot be (indirectly) exposed to stable
}
// Ensure that a fallback body is recursively-const-checked.
mod fallback {
#[rustc_intrinsic]
const unsafe fn copy<T>(src: *const T, _dst: *mut T, _count: usize) {
super::size_of_val(src);
//~^ ERROR cannot be (indirectly) exposed to stable
}
}

12
tests/ui/consts/const-unstable-intrinsic.stderr
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@ -60,13 +60,21 @@ LL | const fn const_main() {
|
error: intrinsic `copy::copy` cannot be (indirectly) exposed to stable
--> $DIR/const-unstable-intrinsic.rs:50:14
--> $DIR/const-unstable-intrinsic.rs:53:14
|
LL | unsafe { copy(src, dst, count) }
| ^^^^^^^^^^^^^^^^^^^^^
|
= help: mark the caller as `#[rustc_const_unstable]`, or mark the intrinsic `#[rustc_const_stable_intrinsic]` (but this requires team approval)
error: aborting due to 7 previous errors
error: intrinsic `size_of_val` cannot be (indirectly) exposed to stable
--> $DIR/const-unstable-intrinsic.rs:61:9
|
LL | super::size_of_val(src);
| ^^^^^^^^^^^^^^^^^^^^^^^
|
= help: mark the caller as `#[rustc_const_unstable]`, or mark the intrinsic `#[rustc_const_stable_intrinsic]` (but this requires team approval)
error: aborting due to 8 previous errors
For more information about this error, try `rustc --explain E0658`.