benchmarks: Move the setup and teardown functions out of the sample loop.

This is important to minimize the runtime when many samples are taken.

Author: eeckstein

benchmark/utils/DriverUtils.swift

@@ -341,8 +341,9 @@ func runBench(_ test: BenchmarkInfo, _ c: TestConfig) -> BenchResults? {
   }
 
   let sampler = SampleRunner(c)
+  test.setUpFunction?()
+
   for s in 0..<c.numSamples {
-    test.setUpFunction?()
     let nsPerSecond = 1_000_000_000.0 // nanoseconds
     let time_per_sample = UInt64(c.sampleTime * nsPerSecond)
 
@@ -385,8 +386,8 @@ func runBench(_ test: BenchmarkInfo, _ c: TestConfig) -> BenchResults? {
     if c.verbose {
       print("    Sample \(s),\(samples[s])")
     }
-    test.tearDownFunction?()
   }
+  test.tearDownFunction?()
 
   let (mean, sd) = internalMeanSD(samples)
 

benchmark/utils/TestsUtils.swift

@@ -143,8 +143,7 @@ public struct BenchmarkInfo {
   /// Shadow static variable for computed property tearDownFunction.
   private var _tearDownFunction: (() -> ())?
 
-  /// An optional function that if non-null is run immediately after a sample is
-  /// taken.
+  /// An optional function that if non-null is run after samples are taken.
   public var tearDownFunction: (() -> ())? {
     if !shouldRun {
       return nil