Add a benchmark that explicitly invokes the GC.

test/benchmark/binary_trees_gc.wren

@@ -0,0 +1,60 @@
+// Ported from the Python version.
+
+class Tree {
+  construct new(item, depth) {
+    _item = item
+    if (depth > 0) {
+      var item2 = item + item
+      depth = depth - 1
+      _left = Tree.new(item2 - 1, depth)
+      _right = Tree.new(item2, depth)
+    }
+  }
+
+  check {
+    if (_left == null) {
+      return _item
+    }
+
+    return _item + _left.check - _right.check
+  }
+}
+
+var minDepth = 4
+var maxDepth = 12
+var stretchDepth = maxDepth + 1
+
+var start = System.clock
+
+System.print("stretch tree of depth " + stretchDepth.toString + " check: " +
+    Tree.new(0, stretchDepth).check.toString)
+System.gc()
+
+var longLivedTree = Tree.new(0, maxDepth)
+
+// iterations = 2 ** maxDepth
+var iterations = 1
+for (d in 0...maxDepth) {
+  iterations = iterations * 2
+}
+
+var depth = minDepth
+while (depth < stretchDepth) {
+  var check = 0
+  for (i in 1..iterations) {
+    check = check + Tree.new(i, depth).check + Tree.new(-i, depth).check
+  }
+
+  System.print((iterations * 2).toString + " trees of depth " +
+      depth.toString + " check: " + check.toString)
+  System.gc()
+
+  iterations = iterations / 4
+  depth = depth + 2
+}
+
+System.print("long lived tree of depth " + maxDepth.toString + " check: " +
+    longLivedTree.check.toString)
+System.gc()
+
+System.print("elapsed: " + (System.clock - start).toString)

util/benchmark.py

@@ -59,6 +59,14 @@ BENCHMARK("binary_trees", """stretch tree of depth 13 check: -1
 32 trees of depth 12 check: -32
 long lived tree of depth 12 check: -1""")
 
+BENCHMARK("binary_trees_gc", """stretch tree of depth 13 check: -1
+8192 trees of depth 4 check: -8192
+2048 trees of depth 6 check: -2048
+512 trees of depth 8 check: -512
+128 trees of depth 10 check: -128
+32 trees of depth 12 check: -32
+long lived tree of depth 12 check: -1""")
+
 BENCHMARK("delta_blue", "14065400")
 
 BENCHMARK("fib", r"""317811