[benchmark] Add string interpolation benchmarks

Add some benchmarks for when the whole interpolated string is small,
and when it is very large but every segment is pretty small.

Author: milseman

benchmark/single-source/StringInterpolation.swift

@@ -16,6 +16,14 @@ public let StringInterpolation = BenchmarkInfo(
   name: "StringInterpolation",
   runFunction: run_StringInterpolation,
   tags: [.validation, .api, .String])
+public let StringInterpolationSmall = BenchmarkInfo(
+  name: "StringInterpolationSmall",
+  runFunction: run_StringInterpolationSmall,
+  tags: [.validation, .api, .String])
+public let StringInterpolationManySmallSegments = BenchmarkInfo(
+  name: "StringInterpolationManySmallSegments",
+  runFunction: run_StringInterpolationManySmallSegments,
+  tags: [.validation, .api, .String])
 
 class RefTypePrintable : CustomStringConvertible {
   var description: String {
@@ -33,15 +41,66 @@ public func run_StringInterpolation(_ N: Int) {
   for _ in 1...100*N {
     var result = 0
     for _ in 1...reps {
-      let s = "\(anInt) abcdefdhijklmn \(aRefCountedObject) abcdefdhijklmn \u{01}"
+      let s: String = getString(
+        "\(anInt) abcdefdhijklmn \(aRefCountedObject) abcdefdhijklmn \u{01}")
       let utf16 = s.utf16
 
       // FIXME: if String is not stored as UTF-16 on this platform, then the
       // following operation has a non-trivial cost and needs to be replaced
       // with an operation on the native storage type.
-      result = result &+ Int(utf16[utf16.index(before: utf16.endIndex)])
+      result = result &+ Int(utf16.last!)
+      blackHole(s)
+    }
+    CheckResults(result == refResult)
+  }
+}
+
+@inline(never)
+public func run_StringInterpolationSmall(_ N: Int) {
+  let reps = 100
+  let refResult = reps
+  let anInt: Int64 = 0x42
+
+  for _ in 1...100*N {
+    var result = 0
+    for _ in 1...reps {
+      let s: String = getString(
+        "\(getString("int")): \(anInt) \(getString("abc")) \u{01}")
+      result = result &+ Int(s.utf8.last!)
+      blackHole(s)
     }
     CheckResults(result == refResult)
   }
 }
 
+@inline(never)
+public func run_StringInterpolationManySmallSegments(_ N: Int) {
+  let numHex = min(UInt64(N), 0x0FFF_FFFF_FFFF_FFFF)
+  let numOct = min(UInt64(N), 0x0000_03FF_FFFF_FFFF)
+  let numBin = min(UInt64(N), 0x7FFF)
+  let segments = [
+    "abc",
+    String(numHex, radix: 16),
+    "0123456789",
+    String(Double.pi/2),
+    "*barely* small!",
+    String(numOct, radix: 8),
+    "",
+    String(numBin, radix: 2),
+  ]
+  assert(segments.count == 8)
+
+  func getSegment(_ i: Int) -> String {
+    return getString(segments[i])
+  }
+
+  let reps = 100
+  for _ in 1...100*N {
+    for _ in 1...reps {
+      blackHole("""
+        \(getSegment(0)) \(getSegment(1))/\(getSegment(2))_\(getSegment(3))
+        \(getSegment(4)) \(getSegment(5)), \(getSegment(6))~~\(getSegment(7))
+        """)
+    }
+  }
+}

benchmark/utils/main.swift

@@ -276,6 +276,8 @@ registerBenchmark(StringComparison)
 registerBenchmark(StringEdits)
 registerBenchmark(StringEnum)
 registerBenchmark(StringInterpolation)
+registerBenchmark(StringInterpolationSmall)
+registerBenchmark(StringInterpolationManySmallSegments)
 registerBenchmark(StringMatch)
 registerBenchmark(StringRemoveDupes)
 registerBenchmark(StringTests)