[cxx-interop] Add benchmark for conversion between C++ and Swift strings

benchmark/CMakeLists.txt

@@ -202,6 +202,7 @@ set(SWIFT_BENCH_MODULES
     single-source/XorLoop
     cxx-source/CreateObjects
     cxx-source/CxxSetToCollection
+    cxx-source/CxxStringConversion
     cxx-source/CxxVectorSum
     cxx-source/ReadAccessor
 )

benchmark/cxx-source/CxxStringConversion.swift

@@ -0,0 +1,60 @@
+//===--- CxxStringConversion.swift ----------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import TestsUtils
+import CxxStdlibPerformance
+import CxxStdlib
+
+let cxxStringSize = 1_000_000
+let swiftStringSize = 25_000
+
+var cxxString: std.string? = nil
+var swiftString: String? = nil
+
+public let benchmarks = [
+  BenchmarkInfo(
+    name: "CxxStringConversion.swift.to.cxx",
+    runFunction: run_swiftToCxx,
+    tags: [.validation, .bridging, .cxxInterop],
+    setUpFunction: {
+      swiftString = String(repeating: "abc012", count: swiftStringSize / 6)
+    }),
+  BenchmarkInfo(
+    name: "CxxStringConversion.cxx.to.swift",
+    runFunction: run_cxxToSwift,
+    tags: [.validation, .bridging, .cxxInterop],
+    setUpFunction: {
+      cxxString = std.string()
+      for i in 0..<cxxStringSize {
+        let char = std.string.value_type(65 + i % 10) // latin letters A-J
+        cxxString!.push_back(char)
+      }
+    }),
+]
+
+@inline(never)
+public func run_swiftToCxx(_ n: Int) {
+  let str = swiftString!
+  for _ in 0..<n {
+    let x = std.string(str)
+    blackHole(x)
+  }
+}
+
+@inline(never)
+public func run_cxxToSwift(_ n: Int) {
+  let str = cxxString!
+  for _ in 0..<n {
+    let x = String(cxxString: str)
+    blackHole(x)
+  }
+}

benchmark/utils/main.swift

@@ -52,6 +52,7 @@ import CodableTest
 import Combos
 import CreateObjects
 import CxxSetToCollection
+import CxxStringConversion
 import CxxVectorSum
 import DataBenchmarks
 import DeadArray
@@ -239,6 +240,7 @@ register(Combos.benchmarks)
 register(ClassArrayGetter.benchmarks)
 register(CreateObjects.benchmarks)
 register(CxxSetToCollection.benchmarks)
+register(CxxStringConversion.benchmarks)
 register(CxxVectorSum.benchmarks)
 register(DataBenchmarks.benchmarks)
 register(DeadArray.benchmarks)