Make align_of behave like min_align_of.

This removes a footgun, since it is a reasonable assumption to make that
pointers to `T` will be aligned to `align_of::<T>()`. This also matches
the behaviour of C/C++. `min_align_of` is now deprecated.

Closes #21611.

src/liballoc/arc.rs

@@ -77,7 +77,7 @@ use core::atomic;
 use core::atomic::Ordering::{Relaxed, Release, Acquire, SeqCst};
 use core::fmt;
 use core::cmp::Ordering;
-use core::mem::{min_align_of_val, size_of_val};
+use core::mem::{align_of_val, size_of_val};
 use core::intrinsics::drop_in_place;
 use core::mem;
 use core::nonzero::NonZero;
@@ -241,7 +241,7 @@ impl<T: ?Sized> Arc<T> {
 
         if self.inner().weak.fetch_sub(1, Release) == 1 {
             atomic::fence(Acquire);
-            deallocate(ptr as *mut u8, size_of_val(&*ptr), min_align_of_val(&*ptr))
+            deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
         }
     }
 }
@@ -565,7 +565,7 @@ impl<T: ?Sized> Drop for Weak<T> {
             atomic::fence(Acquire);
             unsafe { deallocate(ptr as *mut u8,
                                 size_of_val(&*ptr),
-                                min_align_of_val(&*ptr)) }
+                                align_of_val(&*ptr)) }
         }
     }
 }

src/liballoc/rc.rs

@@ -162,7 +162,7 @@ use core::fmt;
 use core::hash::{Hasher, Hash};
 use core::intrinsics::{assume, drop_in_place};
 use core::marker::{self, Unsize};
-use core::mem::{self, min_align_of, size_of, min_align_of_val, size_of_val, forget};
+use core::mem::{self, align_of, size_of, align_of_val, size_of_val, forget};
 use core::nonzero::NonZero;
 use core::ops::{CoerceUnsized, Deref};
 use core::ptr;
@@ -246,7 +246,7 @@ impl<T> Rc<T> {
                 // destruct the box and skip our Drop
                 // we can ignore the refcounts because we know we're unique
                 deallocate(*rc._ptr as *mut u8, size_of::<RcBox<T>>(),
-                            min_align_of::<RcBox<T>>());
+                            align_of::<RcBox<T>>());
                 forget(rc);
                 Ok(val)
             }
@@ -496,7 +496,7 @@ impl<T: ?Sized> Drop for Rc<T> {
                     if self.weak() == 0 {
                         deallocate(ptr as *mut u8,
                                    size_of_val(&*ptr),
-                                   min_align_of_val(&*ptr))
+                                   align_of_val(&*ptr))
                     }
                 }
             }
@@ -805,7 +805,7 @@ impl<T: ?Sized> Drop for Weak<T> {
                 // the strong pointers have disappeared.
                 if self.weak() == 0 {
                     deallocate(ptr as *mut u8, size_of_val(&*ptr),
-                               min_align_of_val(&*ptr))
+                               align_of_val(&*ptr))
                 }
             }
         }