perf: cache this.exclude.shouldInstrument

lib/report.js

@@ -44,6 +44,7 @@ class Report {
       excludeNodeModules: excludeNodeModules
     })
     this.excludeAfterRemap = excludeAfterRemap
+    this.excludeShouldInstrumentCache = new Map()
     this.omitRelative = omitRelative
     this.sourceMapCache = {}
     this.wrapperLength = wrapperLength
@@ -96,7 +97,7 @@ class Report {
         const path = resolve(this.resolve, v8ScriptCov.url)
         const converter = v8toIstanbul(path, this.wrapperLength, sources, (path) => {
           if (this.excludeAfterRemap) {
-            return !this.exclude.shouldInstrument(path)
+            return !this._shouldInstrument(path)
           }
         })
         await converter.load()
@@ -287,7 +288,7 @@ class Report {
         }
       }
       if ((!this.omitRelative || isAbsolute(v8ScriptCov.url))) {
-        if (this.excludeAfterRemap || this.exclude.shouldInstrument(v8ScriptCov.url)) {
+        if (this.excludeAfterRemap || this._shouldInstrument(v8ScriptCov.url)) {
           result.push(v8ScriptCov)
         }
       }
@@ -311,6 +312,23 @@ class Report {
     }
     return cache
   }
+
+  /**
+   * this.exclude.shouldInstrument with cache
+   *
+   * @private
+   * @return {boolean}
+   */
+  _shouldInstrument (filename) {
+    const cacheResult = this.excludeShouldInstrumentCache.get(filename)
+    if (cacheResult !== undefined) {
+      return cacheResult
+    }
+
+    const result = this.exclude.shouldInstrument(filename)
+    this.excludeShouldInstrumentCache.set(filename, result)
+    return result
+  }
 }
 
 module.exports = function (opts) {