From 1d05c45765dc939aa7838862746057fb2f82707b Mon Sep 17 00:00:00 2001
From: Anatoli Papirovski <apapirovski@mac.com>
Date: Tue, 1 May 2018 14:22:39 +0200
Subject: [PATCH 1/3] util: improve spliceOne perf

Do less variable allocations and reassignments inside spliceOne
since it's relied on by some performance sensitive code.

                                   confidence improvement
util/splice.js size=10 n=10000000          **      2.95 %
util/splice.js size=100 n=10000000        ***     10.68 %
util/splice.js size=500 n=10000000        ***     11.26 %
---
 benchmark/util/splice-one.js | 22 ++++++++++++++++++++++
 lib/internal/util.js         |  7 ++++---
 2 files changed, 26 insertions(+), 3 deletions(-)
 create mode 100644 benchmark/util/splice-one.js

diff --git a/benchmark/util/splice-one.js b/benchmark/util/splice-one.js
new file mode 100644
index 00000000000000..2c53a812ba6876
--- /dev/null
+++ b/benchmark/util/splice-one.js
@@ -0,0 +1,22 @@
+'use strict';
+
+const common = require('../common');
+
+const bench = common.createBenchmark(main, {
+  n: [1e7],
+  size: [10, 100, 500],
+}, { flags: ['--expose-internals'] });
+
+function main({ n, size, type }) {
+  const { spliceOne } = require('internal/util');
+  const arr = new Array(size);
+  arr.fill('');
+  const pos = Math.floor(size / 2);
+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    spliceOne(arr, pos);
+    arr.push('');
+  }
+  bench.end(n);
+}
diff --git a/lib/internal/util.js b/lib/internal/util.js
index 071563a737815b..7d4f6fa88c3419 100644
--- a/lib/internal/util.js
+++ b/lib/internal/util.js
@@ -322,10 +322,11 @@ function join(output, separator) {
   return str;
 }
 
-// About 1.5x faster than the two-arg version of Array#splice().
+// Depending on the size of the array, this is anywhere between 1.5-10x
+// faster than the two-arg version of Array#splice()
 function spliceOne(list, index) {
-  for (var i = index, k = i + 1, n = list.length; k < n; i += 1, k += 1)
-    list[i] = list[k];
+  for (; index + 1 < list.length; index++)
+    list[index] = list[index + 1];
   list.pop();
 }
 

From d770149272fd34979f5ee08ea34e47214e8e76ff Mon Sep 17 00:00:00 2001
From: Anatoli Papirovski <apapirovski@mac.com>
Date: Tue, 1 May 2018 14:48:50 +0200
Subject: [PATCH 2/3] fixup: address nit

---
 lib/internal/util.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/internal/util.js b/lib/internal/util.js
index 7d4f6fa88c3419..07515e2e090daa 100644
--- a/lib/internal/util.js
+++ b/lib/internal/util.js
@@ -322,8 +322,8 @@ function join(output, separator) {
   return str;
 }
 
-// Depending on the size of the array, this is anywhere between 1.5-10x
-// faster than the two-arg version of Array#splice()
+// As of V8 6.6, depending on the size of the array, this is anywhere
+// between 1.5-10x faster than the two-arg version of Array#splice()
 function spliceOne(list, index) {
   for (; index + 1 < list.length; index++)
     list[index] = list[index + 1];

From 14ed2f2a5eea3320656133c8b162fbe9f86ba0fc Mon Sep 17 00:00:00 2001
From: Anatoli Papirovski <apapirovski@mac.com>
Date: Tue, 1 May 2018 15:09:24 +0200
Subject: [PATCH 3/3] fixup: implement feedback

---
 benchmark/util/splice-one.js         | 17 ++++++++++++++---
 test/parallel/test-benchmark-util.js |  2 ++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/benchmark/util/splice-one.js b/benchmark/util/splice-one.js
index 2c53a812ba6876..5c2a39f6d72a11 100644
--- a/benchmark/util/splice-one.js
+++ b/benchmark/util/splice-one.js
@@ -4,18 +4,29 @@ const common = require('../common');
 
 const bench = common.createBenchmark(main, {
   n: [1e7],
+  pos: ['start', 'middle', 'end'],
   size: [10, 100, 500],
 }, { flags: ['--expose-internals'] });
 
-function main({ n, size, type }) {
+function main({ n, pos, size }) {
   const { spliceOne } = require('internal/util');
   const arr = new Array(size);
   arr.fill('');
-  const pos = Math.floor(size / 2);
+  let index;
+  switch (pos) {
+    case 'end':
+      index = size - 1;
+      break;
+    case 'middle':
+      index = Math.floor(size / 2);
+      break;
+    default: // start
+      index = 0;
+  }
 
   bench.start();
   for (var i = 0; i < n; i++) {
-    spliceOne(arr, pos);
+    spliceOne(arr, index);
     arr.push('');
   }
   bench.end(n);
diff --git a/test/parallel/test-benchmark-util.js b/test/parallel/test-benchmark-util.js
index 9a6ae370b7d312..838e51daac26b4 100644
--- a/test/parallel/test-benchmark-util.js
+++ b/test/parallel/test-benchmark-util.js
@@ -10,6 +10,8 @@ runBenchmark('util',
               'method=Array',
               'n=1',
               'option=none',
+              'pos=start',
+              'size=1',
               'type=',
               'version=native'],
              { NODEJS_BENCHMARK_ZERO_ALLOWED: 1 });