diff --git a/platform/diff-api/src/com/intellij/diff/util/Side.java b/platform/diff-api/src/com/intellij/diff/util/Side.java
index c783e893bc71..9f05ccca431c 100644
--- a/platform/diff-api/src/com/intellij/diff/util/Side.java
+++ b/platform/diff-api/src/com/intellij/diff/util/Side.java
@@ -129,6 +129,13 @@ public enum Side {
     return isLeft() ? region.first : region.second;
   }
 
+  @Nullable
+  public static <T> Side fromValue(@NotNull List<? extends T> list, @Nullable T value) {
+    assert list.size() == 2;
+    int index = list.indexOf(value);
+    return index != -1 ? fromIndex(index) : null;
+  }
+
   //
   // Fragments
   //
diff --git a/platform/diff-api/src/com/intellij/diff/util/ThreeSide.java b/platform/diff-api/src/com/intellij/diff/util/ThreeSide.java
index 3042b3dc14f7..246a54124075 100644
--- a/platform/diff-api/src/com/intellij/diff/util/ThreeSide.java
+++ b/platform/diff-api/src/com/intellij/diff/util/ThreeSide.java
@@ -92,4 +92,11 @@ public enum ThreeSide {
     assert list.size() == 3;
     return list.get(myIndex);
   }
+
+  @Nullable
+  public static <T> ThreeSide fromValue(@NotNull List<? extends T> list, @Nullable T value) {
+    assert list.size() == 3;
+    int index = list.indexOf(value);
+    return index != -1 ? fromIndex(index) : null;
+  }
 }
diff --git a/platform/diff-impl/src/com/intellij/diff/merge/TextMergeViewer.java b/platform/diff-impl/src/com/intellij/diff/merge/TextMergeViewer.java
index 40c1ac115783..504c0502e012 100644
--- a/platform/diff-impl/src/com/intellij/diff/merge/TextMergeViewer.java
+++ b/platform/diff-impl/src/com/intellij/diff/merge/TextMergeViewer.java
@@ -597,10 +597,8 @@ public class TextMergeViewer implements MergeTool.MergeViewer {
       enterBulkChangeUpdateBlock();
       if (myAllMergeChanges.isEmpty()) return;
 
-      ThreeSide side = null;
-      if (e.getDocument() == getEditor(ThreeSide.LEFT).getDocument()) side = ThreeSide.LEFT;
-      if (e.getDocument() == getEditor(ThreeSide.RIGHT).getDocument()) side = ThreeSide.RIGHT;
-      if (e.getDocument() == getEditor(ThreeSide.BASE).getDocument()) side = ThreeSide.BASE;
+      List<Document> documents = ContainerUtil.map(getEditors(), Editor::getDocument);
+      ThreeSide side = ThreeSide.fromValue(documents, e.getDocument());
       if (side == null) {
         LOG.warn("Unknown document changed");
         return;
diff --git a/platform/diff-impl/src/com/intellij/diff/tools/simple/SimpleDiffViewer.java b/platform/diff-impl/src/com/intellij/diff/tools/simple/SimpleDiffViewer.java
index 5c866d44c81e..850947431cfc 100644
--- a/platform/diff-impl/src/com/intellij/diff/tools/simple/SimpleDiffViewer.java
+++ b/platform/diff-impl/src/com/intellij/diff/tools/simple/SimpleDiffViewer.java
@@ -47,6 +47,7 @@ import com.intellij.openapi.util.Pair;
 import com.intellij.openapi.util.UserDataHolder;
 import com.intellij.openapi.util.text.StringUtil;
 import com.intellij.util.Function;
+import com.intellij.util.containers.ContainerUtil;
 import org.jetbrains.annotations.*;
 
 import javax.swing.*;
@@ -57,6 +58,7 @@ import java.util.Iterator;
 import java.util.List;
 
 import static com.intellij.diff.util.DiffUtil.getLineCount;
+import static com.intellij.util.ObjectUtils.assertNotNull;
 
 public class SimpleDiffViewer extends TwosideTextDiffViewer {
   public static final Logger LOG = Logger.getInstance(SimpleDiffViewer.class);
@@ -309,9 +311,8 @@ public class SimpleDiffViewer extends TwosideTextDiffViewer {
     super.onBeforeDocumentChange(e);
     if (myDiffChanges.isEmpty()) return;
 
-    Side side = null;
-    if (e.getDocument() == getEditor(Side.LEFT).getDocument()) side = Side.LEFT;
-    if (e.getDocument() == getEditor(Side.RIGHT).getDocument()) side = Side.RIGHT;
+    List<Document> documents = ContainerUtil.map(getEditors(), Editor::getDocument);
+    Side side = Side.fromValue(documents, e.getDocument());
     if (side == null) {
       LOG.warn("Unknown document changed");
       return;
@@ -525,13 +526,8 @@ public class SimpleDiffViewer extends TwosideTextDiffViewer {
       }
 
       Editor editor = e.getData(CommonDataKeys.EDITOR);
-      if (editor != getEditor1() && editor != getEditor2()) {
-        e.getPresentation().setEnabledAndVisible(false);
-        return;
-      }
-
-      Side side = Side.fromLeft(editor == getEditor(Side.LEFT));
-      if (!isVisible(side)) {
+      Side side = Side.fromValue(getEditors(), editor);
+      if (side == null || !isVisible(side)) {
         e.getPresentation().setEnabledAndVisible(false);
         return;
       }
@@ -551,9 +547,7 @@ public class SimpleDiffViewer extends TwosideTextDiffViewer {
     @Override
     public void actionPerformed(@NotNull final AnActionEvent e) {
       Editor editor = e.getData(CommonDataKeys.EDITOR);
-      if (editor != getEditor1() && editor != getEditor2()) return;
-
-      final Side side = Side.fromLeft(editor == getEditor(Side.LEFT));
+      final Side side = assertNotNull(Side.fromValue(getEditors(), editor));
       final List<SimpleDiffChange> selectedChanges = getSelectedChanges(side);
       if (selectedChanges.isEmpty()) return;
 
diff --git a/platform/diff-impl/src/com/intellij/diff/tools/simple/SimpleThreesideDiffViewer.java b/platform/diff-impl/src/com/intellij/diff/tools/simple/SimpleThreesideDiffViewer.java
index 433c1a9f692d..02b378e52f2c 100644
--- a/platform/diff-impl/src/com/intellij/diff/tools/simple/SimpleThreesideDiffViewer.java
+++ b/platform/diff-impl/src/com/intellij/diff/tools/simple/SimpleThreesideDiffViewer.java
@@ -41,6 +41,7 @@ import com.intellij.openapi.actionSystem.Separator;
 import com.intellij.openapi.application.ApplicationManager;
 import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.editor.Document;
+import com.intellij.openapi.editor.Editor;
 import com.intellij.openapi.editor.event.DocumentEvent;
 import com.intellij.openapi.progress.ProcessCanceledException;
 import com.intellij.openapi.progress.ProgressIndicator;
@@ -243,10 +244,8 @@ public class SimpleThreesideDiffViewer extends ThreesideTextDiffViewerEx {
     super.onBeforeDocumentChange(e);
     if (myDiffChanges.isEmpty()) return;
 
-    ThreeSide side = null;
-    if (e.getDocument() == getEditor(ThreeSide.LEFT).getDocument()) side = ThreeSide.LEFT;
-    if (e.getDocument() == getEditor(ThreeSide.RIGHT).getDocument()) side = ThreeSide.RIGHT;
-    if (e.getDocument() == getEditor(ThreeSide.BASE).getDocument()) side = ThreeSide.BASE;
+    List<Document> documents = ContainerUtil.map(getEditors(), Editor::getDocument);
+    ThreeSide side = ThreeSide.fromValue(documents, e.getDocument());
     if (side == null) {
       LOG.warn("Unknown document changed");
       return;
diff --git a/platform/diff-impl/src/com/intellij/diff/tools/util/side/TwosideTextDiffViewer.java b/platform/diff-impl/src/com/intellij/diff/tools/util/side/TwosideTextDiffViewer.java
index 636a010fe3de..c5fcd656c6fe 100644
--- a/platform/diff-impl/src/com/intellij/diff/tools/util/side/TwosideTextDiffViewer.java
+++ b/platform/diff-impl/src/com/intellij/diff/tools/util/side/TwosideTextDiffViewer.java
@@ -338,9 +338,7 @@ public abstract class TwosideTextDiffViewer extends TwosideDiffViewer<TextEditor
   private class MyOpenInEditorWithMouseAction extends OpenInEditorWithMouseAction {
     @Override
     protected OpenFileDescriptor getDescriptor(@NotNull Editor editor, int line) {
-      Side side = null;
-      if (editor == getEditor(Side.LEFT)) side = Side.LEFT;
-      if (editor == getEditor(Side.RIGHT)) side = Side.RIGHT;
+      Side side = Side.fromValue(getEditors(), editor);
       if (side == null) return null;
 
       int offset = editor.logicalPositionToOffset(new LogicalPosition(line, 0));