Added optimization for isReferenceTo. It quickly says false for

references from non-source code to anywhere except same file.

idea/idea-analysis/src/org/jetbrains/kotlin/idea/references/JetSimpleNameReference.kt

@@ -37,6 +37,7 @@ import org.jetbrains.kotlin.idea.caches.resolve.analyze
 import org.jetbrains.kotlin.psi.psiUtil.*
 import com.intellij.psi.impl.light.LightElement
 import com.intellij.openapi.extensions.Extensions
+import org.jetbrains.kotlin.idea.util.ProjectRootsUtil
 import org.jetbrains.kotlin.plugin.references.SimpleNameReferenceExtension
 
 public class JetSimpleNameReference(
@@ -45,6 +46,8 @@ public class JetSimpleNameReference(
 
     override fun isReferenceTo(element: PsiElement?): Boolean {
         if (element != null) {
+            if (!canBeReferenceTo(element)) return false
+
             val extensions = Extensions.getArea(element.getProject()).getExtensionPoint(
                     SimpleNameReferenceExtension.EP_NAME).getExtensions()
             for (extension in extensions) {

idea/idea-analysis/src/org/jetbrains/kotlin/idea/references/referenceUtil.kt

@@ -19,6 +19,7 @@ package org.jetbrains.kotlin.idea.references
 import com.intellij.psi.*
 import org.jetbrains.kotlin.asJava.unwrapped
 import org.jetbrains.kotlin.idea.intentions.OperatorToFunctionIntention
+import org.jetbrains.kotlin.idea.util.ProjectRootsUtil
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.getNonStrictParentOfType
 import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
@@ -43,7 +44,16 @@ public val PsiReference.unwrappedTargets: Set<PsiElement>
         }
     }
 
+//
+public fun PsiReference.canBeReferenceTo(candidateTarget: PsiElement): Boolean {
+    // optimization
+    return getElement().getContainingFile() == candidateTarget.getContainingFile()
+            || ProjectRootsUtil.isInProjectOrLibSource(getElement())
+}
+
 public fun PsiReference.matchesTarget(candidateTarget: PsiElement): Boolean {
+    if (!canBeReferenceTo(candidateTarget)) return false
+
     val unwrappedCandidate = candidateTarget.unwrapped?.getOriginalElement() ?: return false
     val targets = unwrappedTargets
     if (unwrappedCandidate in targets) return true