[stdlib] alignment-checking functions for pointers

Co-authored-by: Karoy Lorentey <[email protected]>

Author: glessard

stdlib/public/core/UnsafeBufferPointer.swift.gyb

@@ -795,6 +795,15 @@ extension Unsafe${Mutable}BufferPointer:
 %  end
 }
 
+extension Unsafe${Mutable}BufferPointer where Element: ~Copyable {
+  @safe
+  @_alwaysEmitIntoClient
+  public func _isWellAligned() -> Bool {
+    guard let p = baseAddress else { return true }
+    return p._isWellAligned()
+  }
+}
+
 extension Unsafe${Mutable}BufferPointer {
 %  if not Mutable:
   /// Creates a buffer over the same memory as the given buffer slice.

stdlib/public/core/UnsafePointer.swift

@@ -469,6 +469,13 @@ extension UnsafePointer where Pointee: ~Copyable {
   }
 }
 
+extension UnsafePointer where Pointee: ~Copyable {
+  @safe
+  @_alwaysEmitIntoClient
+  public func _isWellAligned() -> Bool {
+    (Int(bitPattern: self) & (MemoryLayout<Pointee>.alignment &- 1)) == 0
+  }
+}
 
 /// A pointer for accessing and manipulating data of a
 /// specific type.
@@ -1382,3 +1389,11 @@ extension UnsafeMutablePointer where Pointee: ~Copyable {
     )._unsafelyUnwrappedUnchecked
   }
 }
+
+extension UnsafeMutablePointer where Pointee: ~Copyable {
+  @safe
+  @_alwaysEmitIntoClient
+  public func _isWellAligned() -> Bool {
+    (Int(bitPattern: self) & (MemoryLayout<Pointee>.alignment &- 1)) == 0
+  }
+}