Swift SIL: make Function.name and GlobalVariable.name return a StringRef and not a String

and introduce the StringRef struct.
It's more efficient.

Also, rename the `HasName` protocol to `HasShortDescription`, which introduces the new requirement `shortDescription`. This is need because `name` now has `StringRef` type and not `String` anymore

Author: eeckstein

SwiftCompilerSources/Sources/Basic/Utils.swift

@@ -12,6 +12,30 @@
 
 @_exported import BasicBridging
 
+//===----------------------------------------------------------------------===//
+//                              StringRef
+//===----------------------------------------------------------------------===//
+
+public struct StringRef : CustomStringConvertible, CustomReflectable {
+  let _bridged : BridgedStringRef
+
+  public init(bridged: BridgedStringRef) { self._bridged = bridged }
+
+  public var string: String { _bridged.string }
+  public var description: String { string }
+  public var customMirror: Mirror { Mirror(self, children: []) }
+  
+  public static func ==(lhs: StringRef, rhs: StaticString) -> Bool {
+    let lhsBuffer = UnsafeBufferPointer<UInt8>(start: lhs._bridged.data, count: Int(lhs._bridged.length))
+    return rhs.withUTF8Buffer { (rhsBuffer: UnsafeBufferPointer<UInt8>) in
+      if lhsBuffer.count != rhsBuffer.count { return false }
+      return lhsBuffer.elementsEqual(rhsBuffer, by: ==)
+    }
+  }
+  
+  public static func !=(lhs: StringRef, rhs: StaticString) -> Bool { !(lhs == rhs) }
+}
+
 //===----------------------------------------------------------------------===//
 //                            Bridging Utilities
 //===----------------------------------------------------------------------===//

SwiftCompilerSources/Sources/Optimizer/InstructionPasses/SimplifyBeginCOWMutation.swift

@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+import Basic
 import SIL
 
 /// Simplify begin_cow_mutation instructions.

SwiftCompilerSources/Sources/SIL/BasicBlock.swift

@@ -13,7 +13,7 @@
 import Basic
 import SILBridging
 
-final public class BasicBlock : ListNode, CustomStringConvertible, HasName {
+final public class BasicBlock : ListNode, CustomStringConvertible, HasShortDescription {
   public var next: BasicBlock? { SILBasicBlock_next(bridged).block }
   public var previous: BasicBlock? { SILBasicBlock_previous(bridged).block }
 
@@ -28,6 +28,7 @@ final public class BasicBlock : ListNode, CustomStringConvertible, HasName {
     var s = SILBasicBlock_debugDescription(bridged)
     return String(cString: s.c_str())
   }
+  public var shortDescription: String { name }
 
   public var arguments: ArgumentArray { ArgumentArray(block: self) }
 

SwiftCompilerSources/Sources/SIL/Function.swift

@@ -13,18 +13,20 @@
 import Basic
 import SILBridging
 
-final public class Function : CustomStringConvertible, HasName {
+final public class Function : CustomStringConvertible, HasShortDescription {
   public private(set) var effects = FunctionEffects()
 
-  public var name: String {
-    return SILFunction_getName(bridged).string
+  public var name: StringRef {
+    return StringRef(bridged: SILFunction_getName(bridged))
   }
 
   final public var description: String {
     var s = SILFunction_debugDescription(bridged)
     return String(cString: s.c_str())
   }
 
+  public var shortDescription: String { name.string }
+
   public var entryBlock: BasicBlock {
     SILFunction_firstBlock(bridged).block!
   }

SwiftCompilerSources/Sources/SIL/GlobalVariable.swift

@@ -13,16 +13,18 @@
 import Basic
 import SILBridging
 
-final public class GlobalVariable : CustomStringConvertible, HasName {
-  public var name: String {
-    return SILGlobalVariable_getName(bridged).string
+final public class GlobalVariable : CustomStringConvertible, HasShortDescription {
+  public var name: StringRef {
+    return StringRef(bridged: SILGlobalVariable_getName(bridged))
   }
 
   public var description: String {
     var s = SILGlobalVariable_debugDescription(bridged)
     return String(cString: s.c_str())
   }
 
+  public var shortDescription: String { name.string }
+
   // TODO: initializer instructions
 
   var bridged: BridgedGlobalVar { BridgedGlobalVar(obj: SwiftObject(self)) }

SwiftCompilerSources/Sources/SIL/Utils.swift

@@ -85,8 +85,8 @@ public struct ReverseList<NodeType: ListNode> :
 /// full object) in collection descriptions.
 ///
 /// This is useful to make collections, e.g. of BasicBlocks or Functions, readable.
-public protocol HasName {
-  var name: String { get }
+public protocol HasShortDescription {
+  var shortDescription: String { get }
 }
 
 private struct CustomMirrorChild : CustomStringConvertible, CustomReflectable {
@@ -104,8 +104,8 @@ extension FormattedLikeArray {
   /// Display a Sequence in an array like format, e.g. [a, b, c]
   public var description: String {
     "[" + map {
-      if let named = $0 as? HasName {
-        return named.name
+      if let named = $0 as? HasShortDescription {
+        return named.shortDescription
       }
       return String(describing: $0)
     }.joined(separator: ", ") + "]"
@@ -120,8 +120,8 @@ extension FormattedLikeArray {
     }
     let c: [Mirror.Child] = map {
       let val: Any
-      if let named = $0 as? HasName {
-        val = CustomMirrorChild(description: named.name)
+      if let named = $0 as? HasShortDescription {
+        val = CustomMirrorChild(description: named.shortDescription)
       } else {
         val = $0
       }