swift234

stdlib: Add array.props.isNative/needsElementTypeCheck calls

This enables high-level SIL optimizations to speculatively specialize loops into
'fast native swift array' loops vs standard array loops.

This commits adds two semantic calls to Arrays.swift.

   @semantics("array.props.isNative")
   func _getArrayPropertyIsNative() -> Bool

   @semantics("array.props.needsElementTypeCheck")
   func _getArrayPropertyNeedsElementTypeCheck() -> Bool

checkSubscript and getElement get extra arguments to pass in the result of above
function calls. This also allow us to communicate that an array that was made
mutable is always native. The array subscript getter is changed to use the
result of these new calls:

   public subscript(index: Int) -> Element {
     get {
       let isNative = _getArrayPropertyIsNative()
       let needsTypeCheck = _getArrayPropertyNeedsElementTypeCheck()
       _checkSubscript(index, isNative)
       return _getElement(index, isNative, needsTypeCheck)
     }
     mutableAddressWithPinnedNativeOwner {
       _makeMutableAndUniqueOrPinned()
       // When an array was made mutable we know it is a backed by a native
       // array buffer.
       _checkSubscript(index, true)
       return (_getElementAddress(index),
               Builtin.tryPin(Builtin.castToNativeObject(_buffer.owner)))
     }
   }

High-level SIL optimizations will now see a loop like this:

     func f(inout a : A[AClass]) {
         for i in 0..a.count {
           let b = a.props.isNative()
            .. += _getElement(a, i, b)
         }
     }

After proving that ‘a’ does not escape other than to known safe functions, the
optimizer hoists the array property calls out of the loop in a loop versioned
on the array property.

      func f(inout a : A[AClass]) {
        let b2 = a.props.isNative()
        if (!b2) {
          for i in 0..a.count {
             .. += _getElement(a, i, false)
          }
        } else {
          for i in 0..a.count {
            let b = a.props.isNative
            .. += _getElement(a, i, b)
          }
        }
      }

rdar://17955309

Swift SVN r25698