fix: avoid re-instantiating SemVer during diff compare

[macno]

Following #539 this small change improves speed by ~10% just calling compare directly on the semver object returned by parse

Performance on branch v7.4.0

╭─macno@cayenne ~/Projects/opensource/node-semver ‹v7.4.0› ╰─➤ node benchmark.js diff(0.0.1, 0.0.1) x 4,290,326 ops/sec ±0.34% (95 runs sampled) diff(0.0.1, 0.0.1-pre) x 2,136,948 ops/sec ±0.06% (94 runs sampled) diff(0.0.1, 0.0.1-pre-2) x 2,123,307 ops/sec ±0.12% (95 runs sampled) diff(1.1.0, 1.1.0-pre) x 2,124,436 ops/sec ±0.12% (102 runs sampled) 

And after the change

╭─macno@cayenne ~/Projects/opensource/node-semver ‹main› ╰─➤ node benchmark.js diff(0.0.1, 0.0.1) x 4,801,698 ops/sec ±0.30% (90 runs sampled) diff(0.0.1, 0.0.1-pre) x 2,323,553 ops/sec ±0.06% (98 runs sampled) diff(0.0.1, 0.0.1-pre-2) x 2,307,169 ops/sec ±0.14% (98 runs sampled) diff(1.1.0, 1.1.0-pre) x 2,319,211 ops/sec ±0.11% (95 runs sampled) 

benchmark.js

const Benchmark = require('benchmark') const diff = require('./functions/diff') const suite = new Benchmark.Suite() const cases = [ ['0.0.1', '0.0.1', null ], ['0.0.1', '0.0.1-pre', 'patch'], ['0.0.1', '0.0.1-pre-2', 'patch'], ['1.1.0', '1.1.0-pre', 'minor'], ] for (const [v1, v2] of cases) { suite.add(`diff(${v1}, ${v2})`, function () { diff(v1, v2) }) } suite .on('cycle', function (event) { console.log(String(event.target)) }) .run({ async: false })