Rollup merge of #62150 - alex:mem-uninit-refactor, r=RalfJung

Implement mem::{zeroed,uninitialized} in terms of MaybeUninit.

Refs #62061

r? @oli-obk

2 files changed, 9 insertions, 13 deletions

diff --git a/src/libcore/intrinsics.rs b/src/libcore/intrinsics.rs
index 8e53022c287..67430e5bbda 100644
--- a/src/libcore/intrinsics.rs
+++ b/src/libcore/intrinsics.rs
@@ -700,17 +700,15 @@ extern "rust-intrinsic" {
     /// which is unsafe unless `T` is `Copy`. Also, even if T is
     /// `Copy`, an all-zero value may not correspond to any legitimate
     /// state for the type in question.
+    #[unstable(feature = "core_intrinsics",
+               reason = "intrinsics are unlikely to ever be stabilized, instead \
+                         they should be used through stabilized interfaces \
+                         in the rest of the standard library",
+               issue = "0")]
+    #[rustc_deprecated(reason = "no longer used by rustc, will be removed - use MaybeUnint instead",
+                       since = "1.38.0")]
     pub fn init<T>() -> T;
 
-    /// Creates an uninitialized value.
-    ///
-    /// `uninit` is unsafe because there is no guarantee of what its
-    /// contents are. In particular its drop-flag may be set to any
-    /// state, which means it may claim either dropped or
-    /// undropped. In the general case one must use `ptr::write` to
-    /// initialize memory previous set to the result of `uninit`.
-    pub fn uninit<T>() -> T;
-
     /// Moves a value out of scope without running drop glue.
     pub fn forget<T: ?Sized>(_: T);
 
diff --git a/src/libcore/mem/mod.rs b/src/libcore/mem/mod.rs
index b31522db474..b62d81affdd 100644
--- a/src/libcore/mem/mod.rs
+++ b/src/libcore/mem/mod.rs
@@ -450,8 +450,7 @@ pub const fn needs_drop<T>() -> bool {
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn zeroed<T>() -> T {
-    intrinsics::panic_if_uninhabited::<T>();
-    intrinsics::init()
+    MaybeUninit::zeroed().assume_init()
 }
 
 /// Bypasses Rust's normal memory-initialization checks by pretending to
@@ -476,8 +475,7 @@ pub unsafe fn zeroed<T>() -> T {
 #[rustc_deprecated(since = "1.38.0", reason = "use `mem::MaybeUninit` instead")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn uninitialized<T>() -> T {
-    intrinsics::panic_if_uninhabited::<T>();
-    intrinsics::uninit()
+    MaybeUninit::uninit().assume_init()
 }
 
 /// Swaps the values at two mutable locations, without deinitializing either one.