From 78a4d71d0be198b7cdeb6ec4b98ad5c9f9342254 Mon Sep 17 00:00:00 2001
From: Ben Kimock <kimockb@gmail.com>
Date: Sun, 11 Feb 2024 17:18:57 -0500
Subject: [PATCH] Don't use mem::zeroed in vec::IntoIter

---
 library/alloc/src/vec/into_iter.rs | 61 ++++++++++++------------------
 1 file changed, 25 insertions(+), 36 deletions(-)

diff --git a/library/alloc/src/vec/into_iter.rs b/library/alloc/src/vec/into_iter.rs
index 7800560da94f9..52f07ff0450d7 100644
--- a/library/alloc/src/vec/into_iter.rs
+++ b/library/alloc/src/vec/into_iter.rs
@@ -11,7 +11,7 @@ use core::iter::{
     TrustedRandomAccessNoCoerce,
 };
 use core::marker::PhantomData;
-use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
+use core::mem::{ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::num::NonZeroUsize;
 #[cfg(not(no_global_oom_handling))]
 use core::ops::Deref;
@@ -200,27 +200,23 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
     #[inline]
     fn next(&mut self) -> Option<T> {
-        if T::IS_ZST {
-            if self.ptr.as_ptr() == self.end as *mut _ {
-                None
-            } else {
-                // `ptr` has to stay where it is to remain aligned, so we reduce the length by 1 by
-                // reducing the `end`.
-                self.end = self.end.wrapping_byte_sub(1);
-
-                // Make up a value of this ZST.
-                Some(unsafe { mem::zeroed() })
+        let ptr = if T::IS_ZST {
+            if self.ptr.as_ptr() == self.end as *mut T {
+                return None;
             }
+            // `ptr` has to stay where it is to remain aligned, so we reduce the length by 1 by
+            // reducing the `end`.
+            self.end = self.end.wrapping_byte_sub(1);
+            self.ptr
         } else {
-            if self.ptr == non_null!(self.end, T) {
-                None
-            } else {
-                let old = self.ptr;
-                self.ptr = unsafe { old.add(1) };
-
-                Some(unsafe { ptr::read(old.as_ptr()) })
+            if self.ptr == unsafe { NonNull::new_unchecked(self.end as *mut T) } {
+                return None;
             }
-        }
+            let old = self.ptr;
+            self.ptr = unsafe { old.add(1) };
+            old
+        };
+        Some(unsafe { ptr.read() })
     }
 
     #[inline]
@@ -305,7 +301,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         // Also note the implementation of `Self: TrustedRandomAccess` requires
         // that `T: Copy` so reading elements from the buffer doesn't invalidate
         // them for `Drop`.
-        unsafe { if T::IS_ZST { mem::zeroed() } else { self.ptr.add(i).read() } }
+        unsafe { self.ptr.add(i).read() }
     }
 }
 
@@ -313,24 +309,17 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
     #[inline]
     fn next_back(&mut self) -> Option<T> {
+        if self.ptr.as_ptr() == self.end as *mut _ {
+            return None;
+        }
         if T::IS_ZST {
-            if self.end as *mut _ == self.ptr.as_ptr() {
-                None
-            } else {
-                // See above for why 'ptr.offset' isn't used
-                self.end = self.end.wrapping_byte_sub(1);
-
-                // Make up a value of this ZST.
-                Some(unsafe { mem::zeroed() })
-            }
+            // See above for why 'ptr.offset' isn't used
+            self.end = self.end.wrapping_byte_sub(1);
+            Some(unsafe { ptr::read(self.ptr.as_ptr()) })
         } else {
-            if non_null!(self.end, T) == self.ptr {
-                None
-            } else {
-                let new_end = unsafe { non_null!(self.end, T).sub(1) };
-                *non_null!(mut self.end, T) = new_end;
-
-                Some(unsafe { ptr::read(new_end.as_ptr()) })
+            unsafe {
+                self.end = self.end.sub(1);
+                Some(ptr::read(self.end))
             }
         }
     }