Merge pull request swiftlang#22560 from milseman/name_brand_is_better

[String] Speed up UTF-8 initialization from non-stdlib types

Author: milseman

benchmark/single-source/DataBenchmarks.swift

@@ -164,6 +164,9 @@ public let DataBenchmarks = [
   BenchmarkInfo(name: "DataToStringMedium",
     runFunction: { string($0*200, from: mediumData) }, tags: d,
     legacyFactor: 50),
+  BenchmarkInfo(name: "DataToStringLargeUnicode",
+    runFunction: { string($0*200, from: largeUnicodeData) }, tags: d,
+    legacyFactor: 50),
 
   BenchmarkInfo(name: "StringToDataEmpty",
     runFunction: { data($0*200, from: emptyString) }, tags: d,
@@ -174,6 +177,9 @@ public let DataBenchmarks = [
   BenchmarkInfo(name: "StringToDataMedium",
     runFunction: { data($0*200, from: mediumString) }, tags: d,
     legacyFactor: 50),
+  BenchmarkInfo(name: "StringToDataLargeUnicode",
+    runFunction: { data($0*200, from: largeUnicodeString) }, tags: d,
+    legacyFactor: 50),
 
   BenchmarkInfo(name: "Data.hash.Empty",
     runFunction: { hash($0*10_000, data: Data()) }, tags: d),
@@ -186,9 +192,12 @@ public let DataBenchmarks = [
 let emptyString = ""
 let smallString = "\r\n"
 let mediumString = "\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n"
+let largeUnicodeString = 
+  "Swiftに大幅な改良が施され、𓀀𓀁𓀂𓀃, 🇺🇸🇨🇦🇲🇽" + mediumString
 let emptyData = Data()
 let smallData = Data(smallString.utf8)
 let mediumData = Data(mediumString.utf8)
+let largeUnicodeData = Data(largeUnicodeString.utf8)
 
 let small = sampleData(.small)
 let medium = sampleData(.medium)

stdlib/public/core/String.swift

@@ -401,8 +401,13 @@ extension String {
   public init<C: Collection, Encoding: Unicode.Encoding>(
     decoding codeUnits: C, as sourceEncoding: Encoding.Type
   ) where C.Iterator.Element == Encoding.CodeUnit {
+    guard _fastPath(sourceEncoding == UTF8.self) else {
+      self = String._fromCodeUnits(
+        codeUnits, encoding: sourceEncoding, repair: true)!.0
+      return
+    }
+
     if let contigBytes = codeUnits as? _HasContiguousBytes,
-       sourceEncoding == UTF8.self,
        contigBytes._providesContiguousBytesNoCopy
     {
       self = contigBytes.withUnsafeBytes { rawBufPtr in
@@ -414,8 +419,13 @@ extension String {
       return
     }
 
-    self = String._fromCodeUnits(
-      codeUnits, encoding: sourceEncoding, repair: true)!.0
+    // Just copying to an Array is significantly faster than performing
+    // generic operations
+    self = Array(codeUnits).withUnsafeBufferPointer {
+      let raw = UnsafeRawBufferPointer($0)
+      return String._fromUTF8Repairing(raw.bindMemory(to: UInt8.self)).0
+    }
+    return
   }
 
   /// Calls the given closure with a pointer to the contents of the string,

stdlib/public/core/StringObject.swift

@@ -499,20 +499,20 @@ extension _StringObject {
  ├───┬───┬───┬───┬───┬───┬───┬───┼───┬───┬────┬────┬────┬────┬────┬────────────┤
  │ 0 │ 1 │ 2 │ 3 │ 4 │ 5 │ 6 │ 7 │ 8 │ 9 │ 10 │ 11 │ 12 │ 13 │ 14 │     15     │
  ├───┼───┼───┼───┼───┼───┼───┼───┼───┼───┼────┼────┼────┼────┼────┼────────────┤
- │ a │ b │ c │ d │ e │ f │ g │ h │ i │ j │ k  │ l  │ m  │ n  │ o  │ 1x0x count │
+ │ a │ b │ c │ d │ e │ f │ g │ h │ i │ j │ k  │ l  │ m  │ n  │ o  │ 1x10 count │
  └───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴────┴────┴────┴────┴────┴────────────┘
 
  On 32-bit platforms, we have less space to store code units, and it isn't
  contiguous. However, we still use the above layout for the RawBitPattern
  representation.
 
- ┌───────────────┬───────────────────┬───────┬─────────┐
- │ _count        │_variant .immortal │_discr │ _flags  │
- ├───┬───┬───┬───┼───┬───┬───┬───┬───┼───────┼────┬────┤
- │ 0 │ 1 │ 2 │ 3 │ 4 │ 5 │ 6 │ 7 │ 8 │   9   │ 10 │ 11 │
- ├───┼───┼───┼───┼───┴───┴───┴───┴───┼───────┼────┼────┤
- │ a │ b │ c │ d │   e   f   g   h   │x10 cnt│ i  │ j  │
- └───┴───┴───┴───┴───────────────────┴───────┴────┴────┘
+ ┌───────────────┬───────────────────┬────────┬─────────┐
+ │ _count        │_variant .immortal │ _discr │ _flags  │
+ ├───┬───┬───┬───┼───┬───┬───┬───┬───┼────────┼────┬────┤
+ │ 0 │ 1 │ 2 │ 3 │ 4 │ 5 │ 6 │ 7 │ 8 │   9    │ 10 │ 11 │
+ ├───┼───┼───┼───┼───┴───┴───┴───┴───┼────────┼────┼────┤
+ │ a │ b │ c │ d │   e   f   g   h   │1x10 cnt│ i  │ j  │
+ └───┴───┴───┴───┴───────────────────┴────────┴────┴────┘
 
  */
 extension _StringObject {