KT-16245 Redundant null-check generated for a cast of already non-nul…

…lable value

KT-16194 Code with unnecessary safe call contains redundant boxing/unboxing for primitive values
KT-12839 Two null checks are generated when manually null checking platform type

Recognize some additional cases of trivial null checks and trivial instance-of checks.

A variable is "checked for null", if it is:
- a function parameter checked with 'INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull'
- checked for nullability with 'IFNULL/IFNONNULL'
- checked for nullability with 'INSTANCEOF'
  (if objectref is instance-of T, then objectref is non-null)

Before analyzing nullability, introduce synthetic assumptions for execution branches
where a variable is guaranteed to be null or not null. For example, the following bytecode:

     ALOAD 1 // Ljava/lang/String;
     IFNULL L
     <non-null branch>
  L:
     <null branch>

is transformed to

     ALOAD 1
     IFNULL L1
     NEW java/lang/String
     ASTORE 1            // tells analyzer that variable #1 is non-null
     <non-null branch>
  L:
     <null branch>
  L1:
     ACONST_NULL
     ASTORE 1            // tells analyzer that variable #1 is null
     GOTO L

After the analysis is performed on a preprocessed method,
remember the results for "interesting" instructions
and revert the preprocessing transformations.

After that, perform bytecode transformations as usual.

Do not transform INSTANCEOF to-be-reified, because reification at call site
can introduce null checks. E.g.,

    inline fun <reified T> isNullable() = null is T
    ...
    assert(isNullable<String?>())

compiler/backend/src/org/jetbrains/kotlin/codegen/coroutines/CoroutineTransformationClassBuilder.kt

@@ -421,7 +421,7 @@ private fun InstructionAdapter.generateResumeWithExceptionCheck() {
 
 private fun Type.fieldNameForVar(index: Int) = descriptor.first() + "$" + index
 
-private fun withInstructionAdapter(block: InstructionAdapter.() -> Unit): InsnList {
+inline fun withInstructionAdapter(block: InstructionAdapter.() -> Unit): InsnList {
     val tmpMethodNode = MethodNode()
 
     InstructionAdapter(tmpMethodNode).apply(block)

compiler/backend/src/org/jetbrains/kotlin/codegen/inline/ReifiedTypeInliner.kt

@@ -70,7 +70,7 @@ class ReifiedTypeInliner(private val parametersMapping: TypeParameterMappings?)
         const val REIFIED_OPERATION_MARKER_METHOD_NAME = "reifiedOperationMarker"
         const val NEED_CLASS_REIFICATION_MARKER_METHOD_NAME = "needClassReification"
 
-        private fun isOperationReifiedMarker(insn: AbstractInsnNode) =
+        fun isOperationReifiedMarker(insn: AbstractInsnNode) =
                 isReifiedMarker(insn) { it == REIFIED_OPERATION_MARKER_METHOD_NAME }
 
         private fun isReifiedMarker(insn: AbstractInsnNode, namePredicate: (String) -> Boolean): Boolean {

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

@@ -29,9 +29,13 @@ class DeadCodeEliminationMethodTransformer : MethodTransformer() {
     }
 
     fun transformWithResult(internalClassName: String, methodNode: MethodNode): Result {
+        val frames = analyze(internalClassName, methodNode, OptimizationBasicInterpreter())
+        return removeDeadCodeByFrames(methodNode, frames)
+    }
+
+    fun removeDeadCodeByFrames(methodNode: MethodNode, frames: Array<out Any?>): Result {
         val removedNodes = HashSet<AbstractInsnNode>()
 
-        val frames = analyze(internalClassName, methodNode, OptimizationBasicInterpreter())
         val insnList = methodNode.instructions
         val insnsArray = insnList.toArray()
 
@@ -51,6 +55,7 @@ class DeadCodeEliminationMethodTransformer : MethodTransformer() {
     }
 
     class Result(val removedNodes: Set<AbstractInsnNode>) {
+        fun hasRemovedAnything() = removedNodes.isNotEmpty()
         fun isRemoved(node: AbstractInsnNode) = removedNodes.contains(node)
         fun isAlive(node: AbstractInsnNode) = !isRemoved(node)
     }

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

@@ -24,6 +24,7 @@
 import org.jetbrains.kotlin.codegen.optimization.captured.CapturedVarsOptimizationMethodTransformer;
 import org.jetbrains.kotlin.codegen.optimization.common.UtilKt;
 import org.jetbrains.kotlin.codegen.optimization.nullCheck.RedundantNullCheckMethodTransformer;
+import org.jetbrains.kotlin.codegen.optimization.nullCheck.RedundantNullCheckV2MethodTransformer;
 import org.jetbrains.kotlin.codegen.optimization.transformer.MethodTransformer;
 import org.jetbrains.org.objectweb.asm.MethodVisitor;
 import org.jetbrains.org.objectweb.asm.tree.MethodNode;
@@ -35,7 +36,7 @@ public class OptimizationMethodVisitor extends TransformationMethodVisitor {
 
     private static final MethodTransformer[] OPTIMIZATION_TRANSFORMERS = new MethodTransformer[] {
             new CapturedVarsOptimizationMethodTransformer(),
-            new RedundantNullCheckMethodTransformer(),
+            new RedundantNullCheckV2MethodTransformer(),
             new RedundantBoxingMethodTransformer(),
             new RedundantCoercionToUnitTransformer(),
             new DeadCodeEliminationMethodTransformer(),

compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/StackTransformationUtils.kt

@@ -26,7 +26,7 @@ fun <V : Value> Frame<V>.top(): V? =
         peek(0)
 
 fun <V : Value> Frame<V>.peek(offset: Int): V? =
-        if (stackSize >= offset) getStack(stackSize - offset - 1) else null
+        if (stackSize > offset) getStack(stackSize - offset - 1) else null
 
 class SavedStackDescriptor(
         val savedValues: List<BasicValue>,

compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/nullCheck/NullabilityInterpreter.kt

@@ -25,7 +25,7 @@ import org.jetbrains.org.objectweb.asm.tree.AbstractInsnNode
 import org.jetbrains.org.objectweb.asm.tree.TypeInsnNode
 import org.jetbrains.org.objectweb.asm.tree.analysis.BasicValue
 
-class NullabilityV2Interpreter : OptimizationBasicInterpreter() {
+class NullabilityInterpreter : OptimizationBasicInterpreter() {
     override fun newOperation(insn: AbstractInsnNode): BasicValue? {
         val defaultResult = super.newOperation(insn)
         val resultType = defaultResult?.type

compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/nullCheck/RedundantNullCheckMethodTransformer.kt

@@ -37,18 +37,6 @@ class RedundantNullCheckMethodTransformer : MethodTransformer() {
         }
     }
 
-    private enum class Nullability {
-        NULL, NOT_NULL, NULLABLE
-    }
-
-    private fun BasicValue.getNullability(): Nullability =
-            when (this) {
-                is NullBasicValue -> Nullability.NULL
-                is NotNullBasicValue -> Nullability.NOT_NULL
-                is ProgressionIteratorBasicValue -> Nullability.NOT_NULL
-                else -> Nullability.NULLABLE
-            }
-
     private fun isAlwaysFalse(opcode: Int, nullability: Nullability) =
             (opcode == Opcodes.IFNULL && nullability == Nullability.NOT_NULL) ||
             (opcode == Opcodes.IFNONNULL && nullability == Nullability.NULL)
@@ -70,7 +58,7 @@ class RedundantNullCheckMethodTransformer : MethodTransformer() {
         }
         if (nullCheckIfs.isEmpty()) return false
 
-        val frames = analyze(internalClassName, methodNode, NullabilityV2Interpreter())
+        val frames = analyze(internalClassName, methodNode, NullabilityInterpreter())
 
         val redundantNullCheckIfs = nullCheckIfs.mapNotNull { insn ->
             frames[instructions.indexOf(insn)]?.top()?.let { top ->