Stop having two different alignment constants

library/core/src/alloc/global.rs

@@ -284,9 +284,10 @@ pub unsafe trait GlobalAlloc {
     /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
     #[stable(feature = "global_alloc", since = "1.28.0")]
     unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
-        // SAFETY: the caller must ensure that the `new_size` does not overflow.
-        // `layout.align()` comes from a `Layout` and is thus guaranteed to be valid.
-        let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
+        let alignment = layout.alignment();
+        // SAFETY: the caller must ensure that the `new_size` does not overflow
+        // when rounded up to the next multiple of `alignment`.
+        let new_layout = unsafe { Layout::from_size_alignment_unchecked(new_size, alignment) };
         // SAFETY: the caller must ensure that `new_layout` is greater than zero.
         let new_ptr = unsafe { self.alloc(new_layout) };
         if !new_ptr.is_null() {

library/core/src/mem/mod.rs

@@ -1260,7 +1260,10 @@ pub trait SizedTypeProperties: Sized {
 
     #[doc(hidden)]
     #[unstable(feature = "ptr_alignment_type", issue = "102070")]
-    const ALIGNMENT: Alignment = Alignment::of::<Self>();
+    const ALIGNMENT: Alignment = {
+        // This can't panic since type alignment is always a power of two.
+        Alignment::new(Self::ALIGN).unwrap()
+    };
 
     /// `true` if this type requires no storage.
     /// `false` if its [size](size_of) is greater than zero.

library/core/src/ptr/alignment.rs

@@ -52,8 +52,7 @@ impl Alignment {
     #[inline]
     #[must_use]
     pub const fn of<T>() -> Self {
-        // This can't actually panic since type alignment is always a power of two.
-        const { Alignment::new(align_of::<T>()).unwrap() }
+        <T as mem::SizedTypeProperties>::ALIGNMENT
     }
 
     /// Returns the [ABI]-required minimum alignment of the type of the value that `val` points to.

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.GVN.32bit.panic-abort.diff

@@ -44,7 +44,7 @@
           StorageLive(_4);
           StorageLive(_5);
           StorageLive(_6);
--         _6 = const std::ptr::Alignment::of::<[bool; 0]>::{constant#0} as *const [bool; 0] (Transmute);
+-         _6 = const <[bool; 0] as std::mem::SizedTypeProperties>::ALIGNMENT as *const [bool; 0] (Transmute);
 -         _5 = NonNull::<[bool; 0]> { pointer: copy _6 };
 +         _6 = const {0x1 as *const [bool; 0]};
 +         _5 = const NonNull::<[bool; 0]> {{ pointer: {0x1 as *const [bool; 0]} }};

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.GVN.32bit.panic-unwind.diff

@@ -44,7 +44,7 @@
           StorageLive(_4);
           StorageLive(_5);
           StorageLive(_6);
--         _6 = const std::ptr::Alignment::of::<[bool; 0]>::{constant#0} as *const [bool; 0] (Transmute);
+-         _6 = const <[bool; 0] as std::mem::SizedTypeProperties>::ALIGNMENT as *const [bool; 0] (Transmute);
 -         _5 = NonNull::<[bool; 0]> { pointer: copy _6 };
 +         _6 = const {0x1 as *const [bool; 0]};
 +         _5 = const NonNull::<[bool; 0]> {{ pointer: {0x1 as *const [bool; 0]} }};

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.GVN.64bit.panic-abort.diff

@@ -44,7 +44,7 @@
           StorageLive(_4);
           StorageLive(_5);
           StorageLive(_6);
--         _6 = const std::ptr::Alignment::of::<[bool; 0]>::{constant#0} as *const [bool; 0] (Transmute);
+-         _6 = const <[bool; 0] as std::mem::SizedTypeProperties>::ALIGNMENT as *const [bool; 0] (Transmute);
 -         _5 = NonNull::<[bool; 0]> { pointer: copy _6 };
 +         _6 = const {0x1 as *const [bool; 0]};
 +         _5 = const NonNull::<[bool; 0]> {{ pointer: {0x1 as *const [bool; 0]} }};

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.GVN.64bit.panic-unwind.diff

@@ -44,7 +44,7 @@
           StorageLive(_4);
           StorageLive(_5);
           StorageLive(_6);
--         _6 = const std::ptr::Alignment::of::<[bool; 0]>::{constant#0} as *const [bool; 0] (Transmute);
+-         _6 = const <[bool; 0] as std::mem::SizedTypeProperties>::ALIGNMENT as *const [bool; 0] (Transmute);
 -         _5 = NonNull::<[bool; 0]> { pointer: copy _6 };
 +         _6 = const {0x1 as *const [bool; 0]};
 +         _5 = const NonNull::<[bool; 0]> {{ pointer: {0x1 as *const [bool; 0]} }};

tests/mir-opt/gvn_ptr_eq_with_constant.main.GVN.diff

@@ -40,7 +40,7 @@
           StorageLive(_1);
           StorageLive(_2);
           StorageLive(_3);
--         _3 = const std::ptr::Alignment::of::<u8>::{constant#0};
+-         _3 = const <u8 as std::mem::SizedTypeProperties>::ALIGNMENT;
 -         _2 = copy _3 as *mut u8 (Transmute);
 +         _3 = const std::ptr::Alignment {{ _inner_repr_trick: std::ptr::alignment::AlignmentEnum::_Align1Shl0 }};
 +         _2 = const {0x1 as *mut u8};