Revert "Make use of NonNull"

This reverts commit 1a8a550.

This didn't actually provide any size optimization benefits, and the
code is slightly simpler without it.

lib.rs

@@ -256,7 +256,7 @@ impl<'a, T: 'a + Array> Drop for Drain<'a, T> {
 #[cfg(feature = "union")]
 union SmallVecData<A: Array> {
     inline: MaybeUninit<A>,
-    heap: (NonNull<A::Item>, usize),
+    heap: (*mut A::Item, usize),
 }
 
 #[cfg(feature = "union")]
@@ -279,24 +279,22 @@ impl<A: Array> SmallVecData<A> {
     }
     #[inline]
     unsafe fn heap(&self) -> (*mut A::Item, usize) {
-        (self.heap.0.as_ptr(), self.heap.1)
+        self.heap
     }
     #[inline]
-    unsafe fn heap_mut(&mut self) -> (*mut A::Item, &mut usize) {
-        (self.heap.0.as_ptr(), &mut self.heap.1)
+    unsafe fn heap_mut(&mut self) -> &mut (*mut A::Item, usize) {
+        &mut self.heap
     }
     #[inline]
     fn from_heap(ptr: *mut A::Item, len: usize) -> SmallVecData<A> {
-        SmallVecData {
-            heap: (NonNull::new(ptr).unwrap(), len),
-        }
+        SmallVecData { heap: (ptr, len) }
     }
 }
 
 #[cfg(not(feature = "union"))]
 enum SmallVecData<A: Array> {
     Inline(MaybeUninit<A>),
-    Heap((NonNull<A::Item>, usize)),
+    Heap((*mut A::Item, usize)),
 }
 
 #[cfg(not(feature = "union"))]
@@ -329,20 +327,20 @@ impl<A: Array> SmallVecData<A> {
     #[inline]
     unsafe fn heap(&self) -> (*mut A::Item, usize) {
         match self {
-            SmallVecData::Heap(data) => (data.0.as_ptr(), data.1),
+            SmallVecData::Heap(data) => *data,
             _ => debug_unreachable!(),
         }
     }
     #[inline]
-    unsafe fn heap_mut(&mut self) -> (*mut A::Item, &mut usize) {
+    unsafe fn heap_mut(&mut self) -> &mut (*mut A::Item, usize) {
         match self {
-            SmallVecData::Heap(data) => (data.0.as_ptr(), &mut data.1),
+            SmallVecData::Heap(data) => data,
             _ => debug_unreachable!(),
         }
     }
     #[inline]
     fn from_heap(ptr: *mut A::Item, len: usize) -> SmallVecData<A> {
-        SmallVecData::Heap((NonNull::new(ptr).unwrap(), len))
+        SmallVecData::Heap((ptr, len))
     }
 }
 
@@ -569,7 +567,7 @@ impl<A: Array> SmallVec<A> {
     fn triple_mut(&mut self) -> (*mut A::Item, &mut usize, usize) {
         unsafe {
             if self.spilled() {
-                let (ptr, len_ptr) = self.data.heap_mut();
+                let &mut (ptr, ref mut len_ptr) = self.data.heap_mut();
                 (ptr, len_ptr, self.capacity)
             } else {
                 (self.data.inline_mut(), &mut self.capacity, A::size())