Rollup merge of rust-lang#88505 - ibraheemdev:use-unwrap-unchecked, r=kennytm

Use `unwrap_unchecked` where possible

Author: GuillaumeGomez

library/alloc/src/collections/linked_list.rs

@@ -300,7 +300,10 @@ impl<T> LinkedList<T> {
         let tail = self.tail.take();
         let len = mem::replace(&mut self.len, 0);
         if let Some(head) = head {
-            let tail = tail.unwrap_or_else(|| unsafe { core::hint::unreachable_unchecked() });
+            // SAFETY: In a LinkedList, either both the head and tail are None because
+            // the list is empty, or both head and tail are Some because the list is populated.
+            // Since we have verified the head is Some, we are sure the tail is Some too.
+            let tail = unsafe { tail.unwrap_unchecked() };
             Some((head, tail, len))
         } else {
             None

library/core/src/array/mod.rs

@@ -459,11 +459,8 @@ where
     debug_assert!(N <= iter.size_hint().1.unwrap_or(usize::MAX));
     debug_assert!(N <= iter.size_hint().0);
 
-    match collect_into_array(iter) {
-        Some(array) => array,
-        // SAFETY: covered by the function contract.
-        None => unsafe { crate::hint::unreachable_unchecked() },
-    }
+    // SAFETY: covered by the function contract.
+    unsafe { collect_into_array(iter).unwrap_unchecked() }
 }
 
 /// Pulls `N` items from `iter` and returns them as an array. If the iterator

library/core/src/option.rs

@@ -1198,11 +1198,8 @@ impl<T> Option<T> {
     pub fn insert(&mut self, value: T) -> &mut T {
         *self = Some(value);
 
-        match self {
-            Some(v) => v,
-            // SAFETY: the code above just filled the option
-            None => unsafe { hint::unreachable_unchecked() },
-        }
+        // SAFETY: the code above just filled the option
+        unsafe { self.as_mut().unwrap_unchecked() }
     }
 
     /// Inserts `value` into the option if it is [`None`], then