Eliminate redundant CHECKCAST instructions

CHECKCAST is redundant if the corresponding static type exactly matches the target type.
CHECKCAST instructions to-be-reified should not be eliminated.

KT-14811 Unnecessary checkcast generated in parameterized functions
KT-14963 unnecessary checkcast java/lang/Object

compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/OptimizationMethodVisitor.java

@@ -36,6 +36,7 @@ public class OptimizationMethodVisitor extends TransformationMethodVisitor {
     private static final MethodTransformer[] OPTIMIZATION_TRANSFORMERS = new MethodTransformer[] {
             new CapturedVarsOptimizationMethodTransformer(),
             new RedundantNullCheckV2MethodTransformer(),
+            new RedundantCheckCastEliminationMethodTransformer(),
             new RedundantBoxingMethodTransformer(),
             new RedundantCoercionToUnitTransformer(),
             new DeadCodeEliminationMethodTransformer(),

compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/RedundantCheckCastElimination.kt

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2010-2017 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.codegen.optimization
+
+import org.jetbrains.kotlin.codegen.inline.ReifiedTypeInliner
+import org.jetbrains.kotlin.codegen.optimization.common.OptimizationBasicInterpreter
+import org.jetbrains.kotlin.codegen.optimization.fixStack.top
+import org.jetbrains.kotlin.codegen.optimization.nullCheck.popReferenceValueBefore
+import org.jetbrains.kotlin.codegen.optimization.transformer.MethodTransformer
+import org.jetbrains.kotlin.resolve.jvm.AsmTypes
+import org.jetbrains.kotlin.utils.addToStdlib.cast
+import org.jetbrains.org.objectweb.asm.Opcodes
+import org.jetbrains.org.objectweb.asm.Type
+import org.jetbrains.org.objectweb.asm.tree.*
+
+class RedundantCheckCastEliminationMethodTransformer : MethodTransformer() {
+    override fun transform(internalClassName: String, methodNode: MethodNode) {
+        val insns = methodNode.instructions.toArray()
+        if (!insns.any { it.opcode == Opcodes.CHECKCAST }) return
+
+        val redundantCheckCasts = ArrayList<TypeInsnNode>()
+
+        val frames = analyze(internalClassName, methodNode, OptimizationBasicInterpreter())
+        for (i in insns.indices) {
+            val valueType = frames[i]?.top()?.type ?: continue
+            val insn = insns[i]
+            if (ReifiedTypeInliner.isOperationReifiedMarker(insn.previous)) continue
+
+            if (insn is TypeInsnNode) {
+                val insnType = Type.getObjectType(insn.desc)
+                if (!isTrivialSubtype(insnType, valueType)) continue
+
+                if (insn.opcode == Opcodes.CHECKCAST) {
+                    redundantCheckCasts.add(insn)
+                }
+            }
+        }
+
+        redundantCheckCasts.forEach {
+            methodNode.instructions.remove(it)
+        }
+    }
+
+    private fun isTrivialSubtype(superType: Type, subType: Type) =
+            superType == subType
+}

compiler/testData/codegen/bytecodeText/boxingOptimization/checkcastAndInstanceOf.kt

@@ -20,4 +20,4 @@ fun bar() {
 // 0 valueOf
 // 0 Value\s\(\)
 // 2 INSTANCEOF
-// 2 CHECKCAST
+// 1 CHECKCAST

compiler/testData/codegen/bytecodeText/checkcast/kt14811.kt

@@ -0,0 +1,12 @@
+interface WorldObject {
+    val name: String
+}
+
+fun testB(worldObj: WorldObject) {
+    val y = worldObj.let {
+        println("object name: ${it.name}")
+        it
+    }
+}
+
+// 0 CHECKCAST

compiler/testData/codegen/bytecodeText/checkcast/kt14963.kt

@@ -0,0 +1,3 @@
+fun <T> f(o: Any): T = o as T
+
+// 0 CHECKCAST

compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java

@@ -713,6 +713,18 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/bytecodeText/checkcast"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.ANY, true);
         }
 
+        @TestMetadata("kt14811.kt")
+        public void testKt14811() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/checkcast/kt14811.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("kt14963.kt")
+        public void testKt14963() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/checkcast/kt14963.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("kt15411.kt")
         public void testKt15411() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/checkcast/kt15411.kt");

plugins/android-extensions/android-extensions-compiler/testData/codegen/bytecodeShape/simpleFragmentProperty/simpleFragmentProperty.kt

@@ -17,5 +17,4 @@ public class MyFragment : Fragment() {
 // 1 INVOKEVIRTUAL android/app/Activity\.getFragmentManager
 // 1 INVOKEVIRTUAL android/app/Fragment\.getFragmentManager
 // 2 GETSTATIC test/R\$id\.fragm
-// 2 INVOKEVIRTUAL android/app/FragmentManager\.findFragmentById
-// 2 CHECKCAST android/app/Fragment
+// 2 INVOKEVIRTUAL android/app/FragmentManager\.findFragmentById

plugins/android-extensions/android-extensions-compiler/testData/codegen/bytecodeShape/supportSimpleFragmentProperty/supportSimpleFragmentProperty.kt

@@ -28,5 +28,4 @@ public class MyFragment : Fragment() {
 // 1 INVOKEVIRTUAL android/support/v4/app/FragmentActivity\.getSupportFragmentManager
 // 1 INVOKEVIRTUAL android/support/v4/app/Fragment\.getFragmentManager
 // 2 GETSTATIC test/R\$id\.fragm
-// 2 INVOKEVIRTUAL android/support/v4/app/FragmentManager\.findFragmentById
-// 2 CHECKCAST android/support/v4/app/Fragment
+// 2 INVOKEVIRTUAL android/support/v4/app/FragmentManager\.findFragmentById