Start working on a benchmark for the spread desugaring.

accepted/future-releases/spread-collections/benchmarks/.gitignore

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+/out

accepted/future-releases/spread-collections/benchmarks/Makefile

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+# Runs the benchmarks on a few platforms.
+
+# Note: this assumes:
+#
+# - The language repo's root directory is adjacent to the root directory of the
+#   Dart SDK repo, which is named "dart".
+#
+# - "node" is on your PATH.
+#
+# - You have built the AoT runtime by running this from the SDK root directory:
+#
+#   tools/build.py -m release runtime dart_precompiled_runtime
+
+SDK := "../../../../../dart/sdk"
+
+all: jit dart2js aot
+
+aot:
+	@ echo "AoT"
+	@ mkdir -p out
+	@ $(SDK)/pkg/vm/tool/precompiler2 bin/profile_list_spread.dart out/profile_list_spread.snapshot
+	@ $(SDK)/pkg/vm/tool/dart_precompiled_runtime2 out/profile_list_spread.snapshot
+
+dart2js:
+	@ echo "dart2js"
+	@ mkdir -p out
+	@ $(SDK)/sdk/bin/dart2js bin/profile_list_spread.dart -o out/profile_list_spread.js
+	@ node out/profile_list_spread.js
+
+jit:
+	@ echo "VM JIT"
+	@ $(SDK)/sdk/bin/dart bin/profile_list_spread.dart
+
+.PHONY: all aot dart2js jit

accepted/future-releases/spread-collections/benchmarks/bin/profile_list_spread.dart

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+import 'dart:collection';
+
+const trialMs = 100;
+const lengths = [0, 1, 2, 5, 10, 20, 50, 100, 1000];
+
+var csv = StringBuffer();
+
+class CustomList<T> extends ListBase<T> {
+  final List<T> _inner;
+
+  int get length => _inner.length;
+
+  set length(int value) => _inner.length = value;
+
+  CustomList(this._inner);
+
+  T operator [](int index) => _inner[index];
+
+  void operator []=(int index, T value) => _inner[index] = value;
+}
+
+void main() {
+  for (var length in lengths) {
+    var baseline = runBench("iterate", length, iterate);
+    runBench("List for", length, addList, baseline);
+    runBench("resize and set", length, resizeAndSet, baseline);
+    runBench("addAll()", length, addAll, baseline);
+    runBench("forEach()", length, forEach, baseline);
+    print("");
+  }
+
+//  print("");
+//  print(csv);
+}
+
+double runBench(
+    String name, int length, void Function(List<String>, List<String>) action,
+    [double baseline]) {
+  var from = <String>[];
+  for (var i = 0; i < length; i++) {
+    from.add(String.fromCharCode(i % 26 + 65));
+  }
+
+  var froms = [from, CustomList(from)];
+
+  var rate = benchBest(froms, action);
+
+  if (baseline == null) {
+    print("${length.toString().padLeft(4)} ${name.padRight(15)} "
+        "${rate.toStringAsFixed(2).padLeft(10)} spreads/ms "
+        "                 ${'-' * 20}");
+  } else {
+    var comparison = rate / baseline;
+    var bar = "=" * (comparison * 20).toInt();
+    if (comparison > 4.0) bar = "!!!";
+    print("${length.toString().padLeft(4)} ${name.padRight(15)} "
+        "${rate.toStringAsFixed(2).padLeft(10)} spreads/ms "
+        "${comparison.toStringAsFixed(2).padLeft(6)}x baseline $bar");
+  }
+
+  csv.writeln("$length,$name,$rate");
+  return rate;
+}
+
+/// Runs [bench] a number of times and returns the best (highest) result.
+double benchBest(
+    List<List<String>> froms, void Function(List<String>, List<String>) action) {
+  var best = 0.0;
+  for (var i = 0; i < 4; i++) {
+    var result = bench(froms, action);
+    if (result > best) best = result;
+  }
+
+  return best;
+}
+
+/// Spreads each list in [froms] into the middle of a list using [action].
+///
+/// Returns the number of times it was able to do this per millisecond, on
+/// average. Higher is better.
+double bench(List<List<String>> froms,
+    void Function(List<String>, List<String>) action) {
+  var elapsed = 0;
+  var count = 0;
+  var watch = Stopwatch()..start();
+  do {
+    for (var i = 0; i < froms.length; i++) {
+      var from = froms[i];
+      var to = <String>["a", "b"];
+
+      action(from, to);
+      to.add("b");
+      to.add("c");
+
+      count++;
+    }
+    elapsed = watch.elapsedMilliseconds;
+  } while (elapsed < trialMs);
+
+  return count / elapsed;
+}
+
+void iterate(List<String> from, List<String> to) {
+  for (var e in from) {
+    to.add(e);
+  }
+}
+
+void addList(List<String> from, List<String> to) {
+  var length = from.length;
+  for (var i = 0; i < length; i++) {
+    to.add(from[i]);
+  }
+}
+
+void resizeAndSet(List<String> from, List<String> to) {
+  var length = from.length;
+  var j = to.length;
+  to.length = to.length + length;
+  for (var i = 0; i < length; i++) {
+    to[j] = from[i];
+  }
+}
+
+void addAll(List<String> from, List<String> to) {
+  to.addAll(from);
+}
+
+void forEach(List<String> from, List<String> to) {
+  var temp = to;
+  from.forEach((s) {
+    temp.add(s);
+  });
+  temp = null;
+}

accepted/future-releases/spread-collections/benchmarks/pubspec.yaml

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+name: benchmarks