Add additional cache for packages' directories

It's important because even if we know the root where
the package is located we need to go through its parts,
and it's not as fast as it could be since implementation
of VirtualFile.findChild() traverse all files in the directory
to find the relevant one

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/index/JvmDependenciesIndexImpl.kt

@@ -21,6 +21,7 @@ import com.intellij.ide.highlighter.JavaFileType
 import com.intellij.openapi.vfs.VfsUtilCore
 import com.intellij.openapi.vfs.VirtualFile
 import com.intellij.util.containers.IntArrayList
+import gnu.trove.THashMap
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
 import java.util.*
@@ -63,6 +64,10 @@ class JvmDependenciesIndexImpl(_roots: List<JavaRoot>): JvmDependenciesIndex {
 
     override val indexedRoots by lazy { roots.asSequence() }
 
+    private val packageCache: Array<out MutableMap<String, VirtualFile?>> by lazy {
+        Array(roots.size) { THashMap<String, VirtualFile?>() }
+    }
+
     // findClassGivenDirectory MUST check whether the class with this classId exists in given package
     override fun <T : Any> findClass(
             classId: ClassId,
@@ -159,7 +164,7 @@ class JvmDependenciesIndexImpl(_roots: List<JavaRoot>): JvmDependenciesIndex {
                 val rootIndex = cacheRootIndices[i]
                 if (rootIndex <= processedRootsUpTo) continue // roots with those indices have been processed by now
 
-                val directoryInRoot = travelPath(rootIndex, packagesPath, reverseCacheIndex, caches) ?: continue
+                val directoryInRoot = travelPath(rootIndex, request.packageFqName, packagesPath, reverseCacheIndex, caches) ?: continue
                 val root = roots[rootIndex]
                 val result = handle(root, directoryInRoot)
                 if (result != null) {
@@ -168,13 +173,19 @@ class JvmDependenciesIndexImpl(_roots: List<JavaRoot>): JvmDependenciesIndex {
             }
             processedRootsUpTo = if (cacheRootIndices.isEmpty) processedRootsUpTo else cacheRootIndices.get(cacheRootIndices.size() - 1)
         }
-        
+
         return notFound()
     }
 
     // try to find a target directory corresponding to package represented by packagesPath in a given root represented by index
     // possibly filling "Cache" objects with new information
-    private fun travelPath(rootIndex: Int, packagesPath: List<String>, fillCachesAfter: Int, cachesPath: List<Cache>): VirtualFile? {
+    private fun travelPath(
+            rootIndex: Int,
+            packageFqName: FqName,
+            packagesPath: List<String>,
+            fillCachesAfter: Int,
+            cachesPath: List<Cache>
+    ): VirtualFile? {
         if (rootIndex >= maxIndex) {
             for (i in (fillCachesAfter + 1)..(cachesPath.size - 1)) {
                 // we all know roots that contain this package by now
@@ -184,6 +195,12 @@ class JvmDependenciesIndexImpl(_roots: List<JavaRoot>): JvmDependenciesIndex {
             return null
         }
 
+        return packageCache[rootIndex].getOrPut(packageFqName.asString()) {
+            doTravelPath(rootIndex, packagesPath, fillCachesAfter, cachesPath)
+        }
+    }
+
+    private fun doTravelPath(rootIndex: Int, packagesPath: List<String>, fillCachesAfter: Int, cachesPath: List<Cache>): VirtualFile? {
         val pathRoot = roots[rootIndex]
         val prefixPathSegments = pathRoot.prefixFqName?.pathSegments()