Auto merge of rust-lang#131029 - matthiaskrgr:rollup-rh66wir, r=matthiaskrgr

Rollup of 4 pull requests

Successful merges:

 - rust-lang#123932 (restate GlobalAlloc method safety preconditions in terms of what the caller has to do for greater clarity)
 - rust-lang#129003 (Improve Ord docs)
 - rust-lang#130972 (stabilize const_cell_into_inner)
 - rust-lang#130990 (try to get rid of mir::Const::normalize)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

Diff for: compiler/rustc_codegen_cranelift/patches/0027-stdlib-128bit-atomic-operations.patch

@@ -82,19 +82,6 @@ index d9de37e..8293fce 100644
  #[cfg(target_has_atomic_load_store = "ptr")]
  macro_rules! atomic_int_ptr_sized {
      ( $($target_pointer_width:literal $align:literal)* ) => { $(
-diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs
-index 58b9ba4..91bbd0a 100644
---- a/library/core/src/cell.rs
-+++ b/library/core/src/cell.rs
-@@ -2246,8 +2246,6 @@ unsafe_cell_primitive_into_inner! {
-     u32 "32"
-     i64 "64"
-     u64 "64"
--    i128 "128"
--    u128 "128"
-     isize "ptr"
-     usize "ptr"
- }
 --
 2.26.2.7.g19db9cfb68
 

Diff for: compiler/rustc_middle/src/mir/consts.rs

@@ -221,7 +221,9 @@ pub enum Const<'tcx> {
 }
 
 impl<'tcx> Const<'tcx> {
-    pub fn identity_unevaluated(
+    /// Creates an unevaluated const from a `DefId` for a const item.
+    /// The binders of the const item still need to be instantiated.
+    pub fn from_unevaluated(
         tcx: TyCtxt<'tcx>,
         def_id: DefId,
     ) -> ty::EarlyBinder<'tcx, Const<'tcx>> {
@@ -329,18 +331,6 @@ impl<'tcx> Const<'tcx> {
         }
     }
 
-    /// Normalizes the constant to a value or an error if possible.
-    #[inline]
-    pub fn normalize(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Self {
-        match self.eval(tcx, param_env, DUMMY_SP) {
-            Ok(val) => Self::Val(val, self.ty()),
-            Err(ErrorHandled::Reported(guar, _span)) => {
-                Self::Ty(Ty::new_error(tcx, guar.into()), ty::Const::new_error(tcx, guar.into()))
-            }
-            Err(ErrorHandled::TooGeneric(_span)) => self,
-        }
-    }
-
     #[inline]
     pub fn try_eval_scalar(
         self,

Diff for: compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -699,23 +699,17 @@ impl<'tcx> Cx<'tcx> {
                             }
                         }
                         hir::InlineAsmOperand::Const { ref anon_const } => {
-                            let value = mir::Const::identity_unevaluated(
-                                tcx,
-                                anon_const.def_id.to_def_id(),
-                            )
-                            .instantiate_identity()
-                            .normalize(tcx, self.param_env);
+                            let value =
+                                mir::Const::from_unevaluated(tcx, anon_const.def_id.to_def_id())
+                                    .instantiate_identity();
                             let span = tcx.def_span(anon_const.def_id);
 
                             InlineAsmOperand::Const { value, span }
                         }
                         hir::InlineAsmOperand::SymFn { ref anon_const } => {
-                            let value = mir::Const::identity_unevaluated(
-                                tcx,
-                                anon_const.def_id.to_def_id(),
-                            )
-                            .instantiate_identity()
-                            .normalize(tcx, self.param_env);
+                            let value =
+                                mir::Const::from_unevaluated(tcx, anon_const.def_id.to_def_id())
+                                    .instantiate_identity();
                             let span = tcx.def_span(anon_const.def_id);
 
                             InlineAsmOperand::SymFn { value, span }

Diff for: compiler/rustc_mir_transform/src/jump_threading.rs

@@ -516,9 +516,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
                     // Avoid handling them, though this could be extended in the future.
                     return;
                 }
-                let Some(value) =
-                    value.const_.normalize(self.tcx, self.param_env).try_to_scalar_int()
-                else {
+                let Some(value) = value.const_.try_eval_scalar_int(self.tcx, self.param_env) else {
                     return;
                 };
                 let conds = conditions.map(self.arena, |c| Condition {

Diff for: library/core/src/alloc/global.rs

@@ -124,8 +124,8 @@ pub unsafe trait GlobalAlloc {
     ///
     /// # Safety
     ///
-    /// This function is unsafe because undefined behavior can result
-    /// if the caller does not ensure that `layout` has non-zero size.
+    /// `layout` must have non-zero size. Attempting to allocate for a zero-sized `layout` may
+    /// result in undefined behavior.
     ///
     /// (Extension subtraits might provide more specific bounds on
     /// behavior, e.g., guarantee a sentinel address or a null pointer
@@ -156,14 +156,14 @@ pub unsafe trait GlobalAlloc {
     ///
     /// # Safety
     ///
-    /// This function is unsafe because undefined behavior can result
-    /// if the caller does not ensure all of the following:
+    /// The caller must ensure:
     ///
-    /// * `ptr` must denote a block of memory currently allocated via
-    ///   this allocator,
+    /// * `ptr` is a block of memory currently allocated via this allocator and,
     ///
-    /// * `layout` must be the same layout that was used
-    ///   to allocate that block of memory.
+    /// * `layout` is the same layout that was used to allocate that block of
+    ///   memory.
+    ///
+    /// Otherwise undefined behavior can result.
     #[stable(feature = "global_alloc", since = "1.28.0")]
     unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout);
 
@@ -172,7 +172,8 @@ pub unsafe trait GlobalAlloc {
     ///
     /// # Safety
     ///
-    /// This function is unsafe for the same reasons that `alloc` is.
+    /// The caller has to ensure that `layout` has non-zero size. Like `alloc`
+    /// zero sized `layout` can result in undefined behaviour.
     /// However the allocated block of memory is guaranteed to be initialized.
     ///
     /// # Errors
@@ -220,20 +221,21 @@ pub unsafe trait GlobalAlloc {
     ///
     /// # Safety
     ///
-    /// This function is unsafe because undefined behavior can result
-    /// if the caller does not ensure all of the following:
+    /// The caller must ensure that:
     ///
-    /// * `ptr` must be currently allocated via this allocator,
+    /// * `ptr` is allocated via this allocator,
     ///
-    /// * `layout` must be the same layout that was used
+    /// * `layout` is the same layout that was used
     ///   to allocate that block of memory,
     ///
-    /// * `new_size` must be greater than zero.
+    /// * `new_size` is greater than zero.
     ///
     /// * `new_size`, when rounded up to the nearest multiple of `layout.align()`,
-    ///   must not overflow `isize` (i.e., the rounded value must be less than or
+    ///   does not overflow `isize` (i.e., the rounded value must be less than or
     ///   equal to `isize::MAX`).
     ///
+    /// If these are not followed, undefined behaviour can result.
+    ///
     /// (Extension subtraits might provide more specific bounds on
     /// behavior, e.g., guarantee a sentinel address or a null pointer
     /// in response to a zero-size allocation request.)

Diff for: library/core/src/cell.rs

@@ -514,7 +514,8 @@ impl<T> Cell<T> {
     /// assert_eq!(five, 5);
     /// ```
     #[stable(feature = "move_cell", since = "1.17.0")]
-    #[rustc_const_unstable(feature = "const_cell_into_inner", issue = "78729")]
+    #[rustc_const_stable(feature = "const_cell_into_inner", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
     pub const fn into_inner(self) -> T {
         self.value.into_inner()
     }
@@ -857,7 +858,8 @@ impl<T> RefCell<T> {
     /// let five = c.into_inner();
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_cell_into_inner", issue = "78729")]
+    #[rustc_const_stable(feature = "const_cell_into_inner", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
     #[inline]
     pub const fn into_inner(self) -> T {
         // Since this function takes `self` (the `RefCell`) by value, the
@@ -2100,8 +2102,8 @@ impl<T> UnsafeCell<T> {
     /// ```
     #[inline(always)]
     #[stable(feature = "rust1", since = "1.0.0")]
-    // When this is const stabilized, please remove `primitive_into_inner` below.
-    #[rustc_const_unstable(feature = "const_cell_into_inner", issue = "78729")]
+    #[rustc_const_stable(feature = "const_cell_into_inner", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
     pub const fn into_inner(self) -> T {
         self.value
     }
@@ -2247,47 +2249,6 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<UnsafeCell<U>> for UnsafeCell<T> {}
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
 impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<UnsafeCell<U>> for UnsafeCell<T> {}
 
-// Special cases of UnsafeCell::into_inner where T is a primitive. These are
-// used by Atomic*::into_inner.
-//
-// The real UnsafeCell::into_inner cannot be used yet in a stable const function.
-// That is blocked on a "precise drop analysis" unstable const feature.
-// https://github.com/rust-lang/rust/issues/73255
-macro_rules! unsafe_cell_primitive_into_inner {
-    ($($primitive:ident $atomic:literal)*) => {
-        $(
-            #[cfg(target_has_atomic_load_store = $atomic)]
-            impl UnsafeCell<$primitive> {
-                pub(crate) const fn primitive_into_inner(self) -> $primitive {
-                    self.value
-                }
-            }
-        )*
-    };
-}
-
-unsafe_cell_primitive_into_inner! {
-    i8 "8"
-    u8 "8"
-    i16 "16"
-    u16 "16"
-    i32 "32"
-    u32 "32"
-    i64 "64"
-    u64 "64"
-    i128 "128"
-    u128 "128"
-    isize "ptr"
-    usize "ptr"
-}
-
-#[cfg(target_has_atomic_load_store = "ptr")]
-impl<T> UnsafeCell<*mut T> {
-    pub(crate) const fn primitive_into_inner(self) -> *mut T {
-        self.value
-    }
-}
-
 /// [`UnsafeCell`], but [`Sync`].
 ///
 /// This is just an `UnsafeCell`, except it implements `Sync`

Diff for: library/core/src/cell/once.rs

@@ -309,7 +309,8 @@ impl<T> OnceCell<T> {
     /// ```
     #[inline]
     #[stable(feature = "once_cell", since = "1.70.0")]
-    #[rustc_const_unstable(feature = "const_cell_into_inner", issue = "78729")]
+    #[rustc_const_stable(feature = "const_cell_into_inner", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
     pub const fn into_inner(self) -> Option<T> {
         // Because `into_inner` takes `self` by value, the compiler statically verifies
         // that it is not currently borrowed. So it is safe to move out `Option<T>`.