swift-mirror/stdlib/core/Builtin.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

import SwiftShims

// Definitions that make elements of Builtin usable in real code
// without gobs of boilerplate.

/// Returns the contiguous memory footprint of `T`.
///
/// Does not include any dynamically-allocated or "remote" storage.
/// In particular, `sizeof(X.self)`, when `X` is a class type, is the
/// same regardless of how many stored properties `X` has.
@transparent
public func sizeof<T>(_:T.Type) -> Int {
  return Int(Builtin.sizeof(T.self))
}

/// Returns the contiguous memory footprint of  `T`.
///
/// Does not include any dynamically-allocated or "remote" storage.
/// In particular, `sizeof(a)`, when `a` is a class instance, is the
/// same regardless of how many stored properties `a` has.
@transparent
public func sizeofValue<T>(_:T) -> Int {
  return sizeof(T.self)
}

/// Returns the minimum memory alignment of `T`.
@transparent
public func alignof<T>(_:T.Type) -> Int {
  return Int(Builtin.alignof(T.self))
}

/// Returns the minimum memory alignment of `T`.
@transparent
public func alignofValue<T>(_:T) -> Int {
  return alignof(T.self)
}

/// Returns the least possible interval between distinct instances of
/// `T` in memory.  The result is always positive.
@transparent
public func strideof<T>(_:T.Type) -> Int {
  return Int(Builtin.strideof_nonzero(T.self))
}

/// Returns the least possible interval between distinct instances of
/// `T` in memory.  The result is always positive.
@transparent
public func strideofValue<T>(_:T) -> Int {
  return strideof(T.self)
}

func _roundUpToAlignment(offset: Int, alignment: Int) -> Int {
  _sanityCheck(offset >= 0)
  _sanityCheck(alignment > 0)
  _sanityCheck(_isPowerOf2(alignment))
  // Note, given that offset is >= 0, and alignment > 0, we don't
  // need to underflow check the -1, as it can never underflow.
  let x = (offset + alignment &- 1)
  // Note, as alignment is a power of 2, we'll use masking to efficiently
  // get the aligned value
  return x & ~(alignment &- 1)
}

/// Returns a tri-state of 0 = no, 1 = yes, 2 = maybe.
@transparent
func _canBeClass<T>(_: T.Type) -> Int8 {
  return Int8(Builtin.canBeClass(T.self))
}

@availability(*,unavailable,message="it has been renamed 'unsafeBitCast' and has acquired an explicit target type parameter")
@transparent
public func reinterpretCast<T, U>(var x: T) -> U {
  _precondition(sizeof(T.self) == sizeof(U.self),
    "can't reinterpretCast values of different sizes")
  return UnsafeMutablePointer<U>(Builtin.addressof(&x)).memory
}

/// Returns the the bits of `x`, interpreted as having type `U`.
///
/// .. Caution:: Breaks the guarantees of Swift's type system; use
///    with extreme care.  There's almost always a better way to do
///    anything.
///
@transparent
public func unsafeBitCast<T, U>(var x: T, _: U.Type) -> U {
  _precondition(sizeof(T.self) == sizeof(U.self),
    "can't unsafeBitCast between types of different sizes")
  // FIXME: <rdar://problem/18574301> Builtin.reinterpretCast is broken
  // return Builtin.reinterpretCast(x)
  return UnsafeMutablePointer<U>(Builtin.addressof(&x)).memory
}

/// `unsafeBitCast` something to `AnyObject`
@transparent
public func _reinterpretCastToAnyObject<T>(x: T) -> AnyObject {
  return unsafeBitCast(x, AnyObject.self)
}

@transparent
func ==(lhs: Builtin.NativeObject, rhs: Builtin.NativeObject) -> Bool {
  return unsafeBitCast(lhs, Int.self) == unsafeBitCast(rhs, Int.self)
}

@transparent
func !=(lhs: Builtin.NativeObject, rhs: Builtin.NativeObject) -> Bool {
  return !(lhs == rhs)
}

@transparent
func ==(lhs: Builtin.RawPointer, rhs: Builtin.RawPointer) -> Bool {
  return unsafeBitCast(lhs, Int.self) == unsafeBitCast(rhs, Int.self)
}

@transparent
func !=(lhs: Builtin.RawPointer, rhs: Builtin.RawPointer) -> Bool {
  return !(lhs == rhs)
}

/// Tell the optimizer that this code is unreachable if condition is
/// known at compile-time to be true.  If condition is false, or true
/// but not a compile-time constant, this call has no effect.
@transparent
internal func _unreachable(condition: Bool = true) {
  if condition {
    // FIXME: use a parameterized version of Builtin.unreachable when
    // <rdar://problem/16806232> is closed.
    Builtin.unreachable()
  }
}

/// Tell the optimizer that this code is unreachable if this builtin is
/// reachable after constant folding build configuration builtins.
@transparent @noreturn internal
func _conditionallyUnreachable() {
  Builtin.conditionallyUnreachable()
}

@asmname("swift_isClassOrObjCExistential")
func _swift_isClassOrObjCExistential<T>(x: T.Type) -> Bool

/// Returns true iff T is a class type or an @objc existential such as
/// AnyObject
@inline(__always)
internal func _isClassOrObjCExistential<T>(x: T.Type) -> Bool {
  let tmp = _canBeClass(x)

  // Is not a class.
  if tmp == 0 {
    return false
  // Is a class.
  } else if tmp == 1 {
    return true
  }

  // Maybe a class.
  return _swift_isClassOrObjCExistential(x)
}

/// Return an UnsafePointer to the storage used for `object`.  There's
/// not much you can do with this other than use it to identify the
/// object
@transparent
public func unsafeAddressOf(object: AnyObject) -> UnsafePointer<Void> {
  return UnsafePointer(Builtin.bridgeToRawPointer(object))
}

/// Returns: `x as T`
///
/// Requires: `x is T`.  In particular, in -O builds, no test is
/// performed to ensure that `x` actually has dynamic type `T`.
///
/// .. Danger:: trades safety for performance.  Use `unsafeDowncast`
/// only when `x as T` has proven to be a performance problem and you
/// are confident that, always, `x is T`.  It is better than an
/// `unsafeBitCast` because it's more restrictive, and because
/// checking is still performed in debug builds.
@transparent
public func unsafeDowncast<T: AnyObject>(x: AnyObject) -> T {
  _debugPrecondition(x is T, "invalid unsafeDowncast")
  return Builtin.bridgeFromRawPointer(Builtin.bridgeToRawPointer(x))
}

public func _getUnsafePointerToStoredProperties(x: AnyObject)
  -> UnsafeMutablePointer<UInt8> {
  let storedPropertyOffset = _roundUpToAlignment(
    sizeof(_HeapObject.self), alignof(Optional<AnyObject>.self))
  return UnsafeMutablePointer<UInt8>(Builtin.bridgeToRawPointer(x)) +
    storedPropertyOffset
}

//===----------------------------------------------------------------------===//
// Branch hints
//===----------------------------------------------------------------------===//

// Use @semantics to indicate that the optimizer recognizes the
// semantics of these function calls. This won't be necessary with
// mandatory generic inlining.

@transparent @semantics("branchhint") internal
func _branchHint<C: BooleanType>(actual: C, expected: Bool) -> Bool {
  return Bool(Builtin.int_expect_Int1(actual.boolValue.value, expected.value))
}

/// Optimizer hint that `x` is expected to be `true`
@transparent @semantics("fastpath") public
func _fastPath<C: BooleanType>(x: C) -> Bool {
  return _branchHint(x.boolValue, true)
}

/// Optimizer hint that `x` is expected to be `false`
@transparent @semantics("slowpath") public
func _slowPath<C: BooleanType>(x: C) -> Bool {
  return _branchHint(x.boolValue, false)
}

//===--- Runtime shim wrappers --------------------------------------------===//

/// Returns `true` iff the class indicated by `theClass` is non-\ `@objc`.
internal func _usesNativeSwiftReferenceCounting(theClass: AnyClass) -> Bool {
  return _swift_usesNativeSwiftReferenceCounting_class(
    unsafeAddressOf(theClass)
  ) != 0
}

/// Returns: `class_getInstanceSize(theClass)`
internal func _class_getInstanceSize(theClass: AnyClass) -> Int {
  return Int(_swift_class_getInstanceSize_class(
      unsafeAddressOf(theClass)))
}