[SE-0370] pointer family initialization improvements & better buffer slices

stdlib/public/core/ArrayBufferProtocol.swift

@@ -166,7 +166,7 @@ extension _ArrayBufferProtocol {
       // so as not to self-clobber.
       newTailStart.moveInitialize(from: oldTailStart, count: tailCount)
 
-      // Assign over the original subrange
+      // Update the original subrange
       var i = newValues.startIndex
       for j in subrange {
         elements[j] = newValues[i]
@@ -199,17 +199,17 @@ extension _ArrayBufferProtocol {
       let shrinkage = -growth
       if tailCount > shrinkage {   // If the tail length exceeds the shrinkage
 
-        // Assign over the rest of the replaced range with the first
+        // Update the rest of the replaced range with the first
         // part of the tail.
-        newTailStart.moveAssign(from: oldTailStart, count: shrinkage)
+        newTailStart.moveUpdate(from: oldTailStart, count: shrinkage)
 
         // Slide the rest of the tail back
         oldTailStart.moveInitialize(
           from: oldTailStart + shrinkage, count: tailCount - shrinkage)
       }
       else {                      // Tail fits within erased elements
-        // Assign over the start of the replaced range with the tail
-        newTailStart.moveAssign(from: oldTailStart, count: tailCount)
+        // Update the start of the replaced range with the tail
+        newTailStart.moveUpdate(from: oldTailStart, count: tailCount)
 
         // Destroy elements remaining after the tail in subrange
         (newTailStart + tailCount).deinitialize(

stdlib/public/core/Bitset.swift

@@ -118,7 +118,7 @@ extension _UnsafeBitset {
   @inlinable
   @inline(__always)
   internal func clear() {
-    words.assign(repeating: .empty, count: wordCount)
+    words.update(repeating: .empty, count: wordCount)
   }
 }
 

stdlib/public/core/CMakeLists.txt

@@ -227,6 +227,7 @@ set(SWIFTLIB_SOURCES
   CommandLine.swift
   SliceBuffer.swift
   UnfoldSequence.swift
+  UnsafeBufferPointerSlice.swift
   VarArgs.swift
   Zip.swift
   "${SWIFT_SOURCE_DIR}/stdlib/linker-support/magic-symbols-for-install-name.c"

stdlib/public/core/GroupInfo.json

@@ -187,6 +187,7 @@
     "UnsafePointer.swift",
     "UnsafeRawPointer.swift",
     "UnsafeBufferPointer.swift",
+    "UnsafeBufferPointerSlice.swift",
     "UnsafeRawBufferPointer.swift"
   ],
   "Protocols": [

stdlib/public/core/HashTable.swift

@@ -416,7 +416,7 @@ extension _HashTable {
   @_effects(releasenone)
   internal func copyContents(of other: _HashTable) {
     _internalInvariant(bucketCount == other.bucketCount)
-    self.words.assign(from: other.words, count: wordCount)
+    self.words.update(from: other.words, count: wordCount)
   }
 
   /// Insert a new entry with the specified hash value into the table.
@@ -446,7 +446,7 @@ extension _HashTable {
       // without a special case.
       words[0] = Word.allBits.subtracting(elementsBelow: bucketCount)
     } else {
-      words.assign(repeating: .empty, count: wordCount)
+      words.update(repeating: .empty, count: wordCount)
     }
   }
 

stdlib/public/core/StringGuts.swift

@@ -432,7 +432,7 @@ public func _persistCString(_ p: UnsafePointer<CChar>?) -> [CChar]? {
   guard let s = p else { return nil }
   let bytesToCopy = UTF8._nullCodeUnitOffset(in: s) + 1 // +1 for the terminating NUL
   let result = [CChar](unsafeUninitializedCapacity: bytesToCopy) { buf, initedCount in
-    buf.baseAddress!.assign(from: s, count: bytesToCopy)
+    buf.baseAddress!.update(from: s, count: bytesToCopy)
     initedCount = bytesToCopy
   }
   return result