Support for 32-bit platforms (with AnyObject? for now) (swiftlang#15)

* Restore support for 32-bit platforms

On 32-bit platforms, add an extra 32-bit word to both _StringObject and _StringGuts for padding and metadata bit storage.

Padding _StringObject rather than adding two extra words to _StringGuts makes for unattractively discontiguous inline storage. However, _StringObject needs 2 more metadata bits than are available in a 32-bit BridgeObject; shoving an extra word in there was easier than a full code reorganization.

To make use of all this luxurious extra space, on 32-bit platforms, _StringGuts._otherBits always contains the count for contiguous strings, while the new _StringGuts._extraBits stored property contains the start address. This makes extracting an unmanaged view a trivial operation.

* [runtime] SwiftObject, SwiftValue: Simplify -description implementation

Previously, these classes implemented -description and -debugDescription by
1) calling _getSummary in the stdlib to get the Swift String description corresponding to the value, and then
2) calling _convertStringToNSString in the Foundation overlay to convert the resulting String into an NSString.

To hold the Swift String value between the two calls, SwiftObject defined a dummy C++ struct whose layout is supposed match that of Swift Strings.

Instead of updating this struct to the new String representation, this commit collapses the two stages above into a single call into a new generic function, _getDescription (defined in the Foundation overlay), which gets rid of this maintenance chore.

* [runtime] Reflection: Update String representation to follow stdlib changes

* _StringObject: Replace _BridgeObject with AnyObject? on 32-bit platforms

Also, don't store any tagged value in _StringObject on 32-bit -- with AnyObject taking up a full word now, we only have 28 bits available (30 tops), which is not enough to store either a count nor a start address.

* LibcShims: Adjust _swift_stdlib_print_hex for 32-bit platforms.

* [test] Update 32-bit reflection tests

Previous (speculative) update missed a couple of offset/size changes.

* [test] IRGen/lazy_multi_file.swift: Allow for the possibility of an sret param before self.

String is 4 words long on 32 bit platforms, which gets returned via sret on i386.

* [test] DebugInfo/self.swift: Don't expect self to be alloca'd first

On i386, space for a String gets allocated before the self variable.

* _StringGuts: Add _RawBitPattern typealias

* _StringGuts: Fix an overlapping access warning

* _StringVariant: Remove IndexDistance condition

* [runtime] Update mangled symbol

stdlib/public/SDK/Foundation/NSString.swift

@@ -23,8 +23,8 @@ public class NSSimpleCString {}
 public class NSConstantString {}
 
 // Called by the SwiftObject implementation.
-public func _convertStringToNSString(_ string: String) -> NSString {
-  return string._bridgeToObjectiveC()
+public func _getDescription<T>(_ x: T) -> NSString {
+  return String(reflecting: x)._bridgeToObjectiveC()
 }
 
 extension NSString : ExpressibleByStringLiteral {

stdlib/public/core/ReflectionLegacy.swift

@@ -66,16 +66,6 @@ public protocol _Mirror {
   var disposition: _MirrorDisposition { get }
 }
 
-/// An entry point that can be called from C++ code to get the summary string
-/// for an arbitrary object. The memory pointed to by "out" is initialized with
-/// the summary string.
-@_inlineable // FIXME(sil-serialize-all)
-@_silgen_name("swift_getSummary")
-public // COMPILER_INTRINSIC
-func _getSummary<T>(_ out: UnsafeMutablePointer<String>, x: T) {
-  out.initialize(to: String(reflecting: x))
-}
-
 /// Produce a mirror for any value.  The runtime produces a mirror that
 /// structurally reflects values of any type.
 @_inlineable // FIXME(sil-serialize-all)

stdlib/public/core/StringComparable.swift

@@ -80,33 +80,25 @@ extension _StringGuts {
   @effects(readonly)
   public
   static func _compareDeterministicUnicodeCollation(
-    _leftUnsafeStringGutsBitPattern leftBits: (UInt, UInt),
-    _rightUnsafeStringGutsBitPattern rightBits: (UInt, UInt)
+    _leftUnsafeStringGutsBitPattern leftBits: _RawBitPattern,
+    _rightUnsafeStringGutsBitPattern rightBits: _RawBitPattern
   ) -> Int {
-    let left = _StringGuts(
-      object: _StringObject(rawBits: leftBits.0),
-      otherBits: leftBits.1)
-    let right = _StringGuts(
-      object: _StringObject(rawBits: rightBits.0),
-      otherBits: rightBits.1)
+    let left = _StringGuts(rawBits: leftBits)
+    let right = _StringGuts(rawBits: rightBits)
     return _compareDeterministicUnicodeCollation(
       left, 0..<left.count, to: right, 0..<right.count)
   }
   @inline(never)
   @effects(readonly)
   public
   static func _compareDeterministicUnicodeCollation(
-    _leftUnsafeStringGutsBitPattern leftBits: (UInt, UInt),
+    _leftUnsafeStringGutsBitPattern leftBits: _RawBitPattern,
     _ leftRange: Range<Int>,
-    _rightUnsafeStringGutsBitPattern rightBits: (UInt, UInt),
+    _rightUnsafeStringGutsBitPattern rightBits: _RawBitPattern,
     _ rightRange: Range<Int>
   ) -> Int {
-    let left = _StringGuts(
-      object: _StringObject(rawBits: leftBits.0),
-      otherBits: leftBits.1)
-    let right = _StringGuts(
-      object: _StringObject(rawBits: rightBits.0),
-      otherBits: rightBits.1)
+    let left = _StringGuts(rawBits: leftBits)
+    let right = _StringGuts(rawBits: rightBits)
     return _compareDeterministicUnicodeCollation(
       left, leftRange, to: right, rightRange)
   }
@@ -165,8 +157,7 @@ extension _StringGuts {
   @inline(__always)
   @_inlineable
   public func _bitwiseEqualTo(_ other: _StringGuts) -> Bool {
-    return self._object.rawBits == other._object.rawBits
-      && self._otherBits == other._otherBits
+    return self.rawBits == other.rawBits
   }
 
   @_inlineable
@@ -232,11 +223,9 @@ extension _StringGuts {
       return result
     }
 #endif
-    let leftBits = (left._object.rawBits, left._otherBits)
-    let rightBits = (right._object.rawBits, right._otherBits)
     return _compareDeterministicUnicodeCollation(
-      _leftUnsafeStringGutsBitPattern: leftBits, leftRange,
-      _rightUnsafeStringGutsBitPattern: rightBits, rightRange)
+      _leftUnsafeStringGutsBitPattern: left.rawBits, leftRange,
+      _rightUnsafeStringGutsBitPattern: right.rawBits, rightRange)
   }
 
   @_inlineable
@@ -259,11 +248,9 @@ extension _StringGuts {
       return result
     }
 #endif
-    let leftBits = (left._object.rawBits, left._otherBits)
-    let rightBits = (right._object.rawBits, right._otherBits)
     return _compareDeterministicUnicodeCollation(
-      _leftUnsafeStringGutsBitPattern: leftBits,
-      _rightUnsafeStringGutsBitPattern: rightBits)
+      _leftUnsafeStringGutsBitPattern: left.rawBits,
+      _rightUnsafeStringGutsBitPattern: right.rawBits)
   }
 }