util: improve spliceOne perf

Do less variable allocations and reassignments inside spliceOne
since it's relied on by some performance sensitive code.
PR-URL: #20453
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

Author: apapirovski

benchmark/util/splice-one.js

@@ -0,0 +1,33 @@
+'use strict';
+
+constcommon=require('../common');
+
+constbench=common.createBenchmark(main,{
+n: [1e7],
+pos: ['start','middle','end'],
+size: [10,100,500],
+},{flags: ['--expose-internals']});
+
+functionmain({ n, pos, size }){
+const{ spliceOne }=require('internal/util');
+constarr=newArray(size);
+arr.fill('');
+letindex;
+switch(pos){
+case'end':
+index=size-1;
+break;
+case'middle':
+index=Math.floor(size/2);
+break;
+default: // start
+index=0;
+}
+
+bench.start();
+for(vari=0;i<n;i++){
+spliceOne(arr,index);
+arr.push('');
+}
+bench.end(n);
+}

lib/internal/util.js

@@ -322,10 +322,11 @@ function join(output, separator) {
 returnstr;
 }
 
-// About 1.5x 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()
 functionspliceOne(list,index){
-for(vari=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();
 }
 

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});