diff --git a/src/main/java/com/android/tools/r8/graph/AppView.java b/src/main/java/com/android/tools/r8/graph/AppView.java
index cc0041b..83ea812 100644
--- a/src/main/java/com/android/tools/r8/graph/AppView.java
+++ b/src/main/java/com/android/tools/r8/graph/AppView.java
@@ -936,7 +936,10 @@
     timing.begin("Rewrite AppView");
 
     boolean changed = appView.setGraphLens(lens);
-    assert changed;
+
+    // Verify that the lens changed, except in the horizontal class merger case, where we install
+    // the lens prior to lens rewriting AppView.
+    assert changed || lens.isHorizontalClassMergerGraphLens();
     assert application.verifyWithLens(appView.appInfo().app().asDirect(), lens);
 
     // The application has already been rewritten with the given applied lens. Therefore, we
@@ -1051,7 +1054,10 @@
   private static void rewriteWithD8Lens(
       NonIdentityGraphLens lens, Timing timing, AppView<AppInfo> appView) {
     boolean changed = appView.setGraphLens(lens);
-    assert changed;
+
+    // Verify that the lens changed, except in the horizontal class merger case, where we install
+    // the lens prior to lens rewriting AppView.
+    assert changed || lens.isHorizontalClassMergerGraphLens();
 
     appView.setArtProfileCollection(
         appView.getArtProfileCollection().rewrittenWithLens(appView, lens, timing));
diff --git a/src/main/java/com/android/tools/r8/horizontalclassmerging/ClassMerger.java b/src/main/java/com/android/tools/r8/horizontalclassmerging/ClassMerger.java
index 459cf9a..efbfad4 100644
--- a/src/main/java/com/android/tools/r8/horizontalclassmerging/ClassMerger.java
+++ b/src/main/java/com/android/tools/r8/horizontalclassmerging/ClassMerger.java
@@ -114,6 +114,10 @@
         profileCollectionAdditions, syntheticArgumentClass, syntheticInitializerConverterBuilder);
     mergeStaticClassInitializers(syntheticInitializerConverterBuilder);
     group.forEach(this::mergeDirectMethods);
+    if (!classInitializerMerger.isEmpty() && classInitializerMerger.isTrivialMerge()) {
+      classInitializerMerger.setObsolete();
+    }
+    instanceInitializerMergers.setObsolete();
   }
 
   void mergeStaticClassInitializers(
@@ -165,7 +169,10 @@
             if (!classMethodsBuilder.isFresh(newMethod)) {
               newMethod = renameDirectMethod(method);
             }
-            classMethodsBuilder.addDirectMethod(definition.toTypeSubstitutedMethod(newMethod));
+            classMethodsBuilder.addDirectMethod(
+                newMethod != method.getReference()
+                    ? definition.toTypeSubstitutedMethod(newMethod)
+                    : method.getDefinition());
             if (definition.getReference() != newMethod) {
               lensBuilder.moveMethod(definition.getReference(), newMethod);
             }
diff --git a/src/main/java/com/android/tools/r8/horizontalclassmerging/HorizontalClassMerger.java b/src/main/java/com/android/tools/r8/horizontalclassmerging/HorizontalClassMerger.java
index 746dbd5..3fa5ee2 100644
--- a/src/main/java/com/android/tools/r8/horizontalclassmerging/HorizontalClassMerger.java
+++ b/src/main/java/com/android/tools/r8/horizontalclassmerging/HorizontalClassMerger.java
@@ -162,6 +162,21 @@
 
     assert verifyNoCyclesInInterfaceHierarchies(appView, groups);
 
+    FieldAccessInfoCollectionModifier fieldAccessInfoCollectionModifier = null;
+    if (mode.isInitial()) {
+      fieldAccessInfoCollectionModifier = createFieldAccessInfoCollectionModifier(groups);
+    } else {
+      assert groups.stream().noneMatch(MergeGroup::hasClassIdField);
+    }
+
+    // Set the new graph lens before finalizing any synthetic code.
+    appView.setGraphLens(horizontalClassMergerGraphLens);
+    codeProvider.setGraphLens(horizontalClassMergerGraphLens);
+
+    // Finalize synthetic code.
+    transformIncompleteCode(groups, horizontalClassMergerGraphLens, executorService);
+    syntheticInitializerConverter.convertInstanceInitializers(executorService);
+
     // Must rewrite AppInfoWithLiveness before pruning the merged classes, to ensure that allocation
     // sites, fields accesses, etc. are correctly transferred to the target classes.
     DexApplication newApplication = getNewApplication(mergedClasses);
@@ -188,7 +203,6 @@
                       .rewrittenWithLens(syntheticItems, horizontalClassMergerGraphLens, timing)));
       appView.rewriteWithD8Lens(horizontalClassMergerGraphLens, timing);
     }
-    codeProvider.setGraphLens(horizontalClassMergerGraphLens);
 
     // Amend art profile collection.
     profileCollectionAdditions
@@ -197,15 +211,10 @@
         .commit(appView);
 
     // Record where the synthesized $r8$classId fields are read and written.
-    if (mode.isInitial()) {
-      createFieldAccessInfoCollectionModifier(groups).modify(appView.withLiveness());
-    } else {
-      assert groups.stream().noneMatch(MergeGroup::hasClassIdField);
+    if (fieldAccessInfoCollectionModifier != null) {
+      fieldAccessInfoCollectionModifier.modify(appView.withLiveness());
     }
 
-    transformIncompleteCode(groups, horizontalClassMergerGraphLens, executorService);
-    syntheticInitializerConverter.convertInstanceInitializers(executorService);
-
     appView.pruneItems(
         prunedItems.toBuilder().setPrunedApp(appView.app()).build(), executorService);
 
diff --git a/src/main/java/com/android/tools/r8/horizontalclassmerging/InstanceInitializerMerger.java b/src/main/java/com/android/tools/r8/horizontalclassmerging/InstanceInitializerMerger.java
index 0cf3a94..62def22 100644
--- a/src/main/java/com/android/tools/r8/horizontalclassmerging/InstanceInitializerMerger.java
+++ b/src/main/java/com/android/tools/r8/horizontalclassmerging/InstanceInitializerMerger.java
@@ -412,6 +412,13 @@
     }
   }
 
+  void setObsolete() {
+    if (hasInstanceInitializerDescription() || !useSyntheticMethod()) {
+      instanceInitializers.forEach(
+          instanceInitializer -> instanceInitializer.getDefinition().setObsolete());
+    }
+  }
+
   private boolean useSyntheticMethod() {
     return !isSingleton() || group.hasClassIdField();
   }
diff --git a/src/main/java/com/android/tools/r8/horizontalclassmerging/InstanceInitializerMergerCollection.java b/src/main/java/com/android/tools/r8/horizontalclassmerging/InstanceInitializerMergerCollection.java
index 952421e..4ce1f2f 100644
--- a/src/main/java/com/android/tools/r8/horizontalclassmerging/InstanceInitializerMergerCollection.java
+++ b/src/main/java/com/android/tools/r8/horizontalclassmerging/InstanceInitializerMergerCollection.java
@@ -141,4 +141,8 @@
     instanceInitializerMergers.forEach(consumer);
     equivalentInstanceInitializerMergers.values().forEach(consumer);
   }
+
+  public void setObsolete() {
+    forEach(InstanceInitializerMerger::setObsolete);
+  }
 }
diff --git a/src/main/java/com/android/tools/r8/horizontalclassmerging/code/ClassInitializerMerger.java b/src/main/java/com/android/tools/r8/horizontalclassmerging/code/ClassInitializerMerger.java
index 6a030d7..09e9911 100644
--- a/src/main/java/com/android/tools/r8/horizontalclassmerging/code/ClassInitializerMerger.java
+++ b/src/main/java/com/android/tools/r8/horizontalclassmerging/code/ClassInitializerMerger.java
@@ -75,9 +75,8 @@
   }
 
   public Code getCode(DexMethod syntheticMethodReference) {
-    assert !classInitializers.isEmpty();
-    ProgramMethod firstClassInitializer = ListUtils.first(classInitializers);
-    if (firstClassInitializer.getDefinition().getCode().isCfCode()) {
+    assert !isEmpty();
+    if (isTrivialMerge()) {
       assert IterableUtils.allIdentical(
           classInitializers,
           classInitializer -> classInitializer.getDefinition().getCode().isCfCode());
@@ -100,6 +99,11 @@
     return null;
   }
 
+  public boolean isTrivialMerge() {
+    ProgramMethod firstClassInitializer = ListUtils.first(classInitializers);
+    return firstClassInitializer.getDefinition().getCode().isCfCode();
+  }
+
   public ComputedApiLevel getApiReferenceLevel(AppView<?> appView) {
     assert !classInitializers.isEmpty();
     return ListUtils.fold(
@@ -108,6 +112,10 @@
         (accApiLevel, method) -> accApiLevel.max(method.getDefinition().getApiLevel()));
   }
 
+  public void setObsolete() {
+    classInitializers.forEach(classInitializer -> classInitializer.getDefinition().setObsolete());
+  }
+
   public static class Builder {
 
     private final ImmutableList.Builder<ProgramMethod> classInitializers = ImmutableList.builder();
@@ -182,7 +190,7 @@
    * Provides a piece of {@link IRCode} that is the concatenation of a collection of class
    * initializers.
    */
-  private static class IRProvider extends Code {
+  static class IRProvider extends Code {
 
     private final ImmutableList<ProgramMethod> classInitializers;
     private final DexMethod syntheticMethodReference;
@@ -261,6 +269,7 @@
                     callerPosition,
                     classInitializer.getOrigin(),
                     RewrittenPrototypeDescription.none());
+        classInitializer.getDefinition().setObsolete();
 
         DexProgramClass downcast = null;
         instructionIterator.previous();
diff --git a/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingTreeFixer.java b/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingTreeFixer.java
index 940b639..eaa1d40 100644
--- a/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingTreeFixer.java
+++ b/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingTreeFixer.java
@@ -583,8 +583,10 @@
         && enumDataMap.representativeType(method.getHolderType()) != method.getHolderType()) {
       assert method.getDefinition().getCode().isEmptyVoidMethod();
       prunedItemsBuilder.addRemovedMethod(method.getReference());
+      method.getDefinition().setObsolete();
     } else if (method.getDefinition().isInstanceInitializer()) {
       prunedItemsBuilder.addRemovedMethod(method.getReference());
+      method.getDefinition().setObsolete();
     } else if (method.getDefinition().isNonPrivateVirtualMethod()) {
       nonPrivateVirtualMethods.add(method.getReference());
     } else {
diff --git a/src/main/java/com/android/tools/r8/optimize/argumentpropagation/ArgumentPropagatorApplicationFixer.java b/src/main/java/com/android/tools/r8/optimize/argumentpropagation/ArgumentPropagatorApplicationFixer.java
index 4ad22f3..4441690 100644
--- a/src/main/java/com/android/tools/r8/optimize/argumentpropagation/ArgumentPropagatorApplicationFixer.java
+++ b/src/main/java/com/android/tools/r8/optimize/argumentpropagation/ArgumentPropagatorApplicationFixer.java
@@ -100,23 +100,26 @@
             return method;
           }
 
-          return method.toTypeSubstitutedMethod(
-              methodReferenceAfterParameterRemoval,
-              builder -> {
-                if (graphLens.hasPrototypeChanges(methodReferenceAfterParameterRemoval)) {
-                  RewrittenPrototypeDescription prototypeChanges =
-                      graphLens.getPrototypeChanges(methodReferenceAfterParameterRemoval);
-                  builder
-                      .apply(prototypeChanges.createParameterAnnotationsRemover(method))
-                      .setGenericSignature(MethodTypeSignature.noSignature());
-                  if (method.isInstance()
-                      && prototypeChanges.getArgumentInfoCollection().isArgumentRemoved(0)) {
-                    builder
-                        .modifyAccessFlags(flags -> flags.demoteFromFinal().promoteToStatic())
-                        .unsetIsLibraryMethodOverride();
-                  }
-                }
-              });
+          DexEncodedMethod replacement =
+              method.toTypeSubstitutedMethod(
+                  methodReferenceAfterParameterRemoval,
+                  builder -> {
+                    if (graphLens.hasPrototypeChanges(methodReferenceAfterParameterRemoval)) {
+                      RewrittenPrototypeDescription prototypeChanges =
+                          graphLens.getPrototypeChanges(methodReferenceAfterParameterRemoval);
+                      builder
+                          .apply(prototypeChanges.createParameterAnnotationsRemover(method))
+                          .setGenericSignature(MethodTypeSignature.noSignature());
+                      if (method.isInstance()
+                          && prototypeChanges.getArgumentInfoCollection().isArgumentRemoved(0)) {
+                        builder
+                            .modifyAccessFlags(flags -> flags.demoteFromFinal().promoteToStatic())
+                            .unsetIsLibraryMethodOverride();
+                      }
+                    }
+                  });
+          method.setObsolete();
+          return replacement;
         });
   }