benchmarks: add another benchmark for appending multiple array elements.

In contrast to the other similar benchmarks, this benchmark starts with a new array each iteration.

Author: eeckstein

benchmark/single-source/ArrayAppend.swift

@@ -267,6 +267,19 @@ public func run_ArrayPlusEqualFiveElementCollection(_ N: Int) {
   }
 }
 
+@inline(never)
+public func appendThreeElements(_ a: inout [Int]) {
+  a += [1, 2, 3]
+}
+
+@inline(never)
+public func run_ArrayPlusEqualThreeElements(_ N: Int) {
+  for _ in 0..<(10_000 * N) {
+    var a: [Int] = []
+    appendThreeElements(&a)
+  }
+}
+
 // Append the utf8 elements of an ascii string to a [UInt8]
 @inline(never)
 public func run_ArrayAppendAscii(_ N: Int) {

benchmark/utils/main.swift

@@ -167,6 +167,7 @@ addPrecommitTest("ArrayOfRef", run_ArrayOfRef)
 addPrecommitTest("ArrayPlusEqualArrayOfInt", run_ArrayPlusEqualArrayOfInt)
 addPrecommitTest("ArrayPlusEqualFiveElementCollection", run_ArrayPlusEqualFiveElementCollection)
 addPrecommitTest("ArrayPlusEqualSingleElementCollection", run_ArrayPlusEqualSingleElementCollection)
+addPrecommitTest("ArrayPlusEqualThreeElements", run_ArrayPlusEqualThreeElements)
 addPrecommitTest("ArraySubscript", run_ArraySubscript)
 addPrecommitTest("ArrayValueProp", run_ArrayValueProp)
 addPrecommitTest("ArrayValueProp2", run_ArrayValueProp2)