perf(fmt): compact cache options in place (#347)

Author: chenjiahan

packages/rstack/src/fmt/cacheStore.ts

@@ -202,33 +202,34 @@ class FmtCacheStoreImpl implements FmtCacheStore {
     return index;
   }
 
+  /** Removes unreferenced option hashes and remaps file entries to the compacted indexes. */
   #compactUnusedOptions(): void {
     if (!this.#optionsUseCounts.includes(0)) {
       return;
     }
 
     const { files, options } = this.#cache;
-    const nextOptions: string[] = [];
-    const nextUseCounts: number[] = [];
-    const remappedIndexes = new Int32Array(options.length).fill(-1);
+    const counts = this.#optionsUseCounts;
+    const remap = new Int32Array(options.length).fill(-1);
+    let nextIndex = 0;
+    this.#optionsIndexes.clear();
     for (let index = 0; index < options.length; index++) {
-      const useCount = this.#optionsUseCounts[index];
-      if (useCount > 0) {
-        remappedIndexes[index] = nextOptions.length;
-        nextOptions.push(options[index]);
-        nextUseCounts.push(useCount);
+      const count = counts[index];
+      if (count > 0) {
+        const option = options[index];
+        remap[index] = nextIndex;
+        options[nextIndex] = option;
+        counts[nextIndex] = count;
+        this.#optionsIndexes.set(option, nextIndex);
+        nextIndex++;
       }
     }
-    for (let offset = 0; offset < files.length; offset += fileEntryWidth) {
-      const currentIndex = files[offset + optionsIndexOffset] as number;
-      files[offset + optionsIndexOffset] = remappedIndexes[currentIndex];
-    }
+    options.length = nextIndex;
+    counts.length = nextIndex;
 
-    options.splice(0, options.length, ...nextOptions);
-    this.#optionsUseCounts.splice(0, this.#optionsUseCounts.length, ...nextUseCounts);
-    this.#optionsIndexes.clear();
-    for (let index = 0; index < options.length; index++) {
-      this.#optionsIndexes.set(options[index], index);
+    for (let offset = 0; offset < files.length; offset += fileEntryWidth) {
+      const index = files[offset + optionsIndexOffset] as number;
+      files[offset + optionsIndexOffset] = remap[index];
     }
   }