Merge remote-tracking branch 'origin/master' into master-rebranch

Author: swift-ci

include/swift/Runtime/Concurrent.h

@@ -684,7 +684,7 @@ template <class ElemTy> struct ConcurrentReadableHashMap {
   /// Free all the arrays in the free lists if there are no active readers. If
   /// there are active readers, do nothing.
   void deallocateFreeListIfSafe() {
-    if (ReaderCount.load(std::memory_order_relaxed) == 0)
+    if (ReaderCount.load(std::memory_order_acquire) == 0)
       deallocateFreeList();
   }
 
@@ -857,7 +857,7 @@ template <class ElemTy> struct ConcurrentReadableHashMap {
     ElemTy *elements2;
     do {
       elements = Elements.load(std::memory_order_acquire);
-      indices = Indices.load(SWIFT_MEMORY_ORDER_CONSUME);
+      indices = Indices.load(std::memory_order_acquire);
       elementCount = ElementCount.load(std::memory_order_acquire);
       elements2 = Elements.load(std::memory_order_acquire);
     } while (elements != elements2);

stdlib/public/core/UnicodeHelpers.swift

@@ -397,12 +397,13 @@ extension _StringGuts {
     }
 
     // TODO(String performance): Stack buffer if small enough
-    var cus = Array<UInt16>(repeating: 0, count: count)
-    cus.withUnsafeMutableBufferPointer {
+    let cus = Array<UInt16>(unsafeUninitializedCapacity: count) {
+      buffer, initializedCapacity in
       _cocoaStringCopyCharacters(
         from: self._object.cocoaObject,
         range: start..<end,
-        into: $0.baseAddress._unsafelyUnwrappedUnchecked)
+        into: buffer.baseAddress._unsafelyUnwrappedUnchecked)
+      initializedCapacity = count
     }
     return cus.withUnsafeBufferPointer {
       return Character(String._uncheckedFromUTF16($0))