org.jetbrains.kotlin.codegen.optimization.RedundantGotoMethodTransformer.kt Maven / Gradle / Ivy
/*
* Copyright 2010-2015 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.optimization.common.isMeaningful
import org.jetbrains.kotlin.codegen.optimization.transformer.MethodTransformer
import org.jetbrains.org.objectweb.asm.Opcodes
import org.jetbrains.org.objectweb.asm.tree.AbstractInsnNode
import org.jetbrains.org.objectweb.asm.tree.JumpInsnNode
import org.jetbrains.org.objectweb.asm.tree.LabelNode
import org.jetbrains.org.objectweb.asm.tree.LineNumberNode
import org.jetbrains.org.objectweb.asm.tree.MethodNode
class RedundantGotoMethodTransformer : MethodTransformer() {
/**
* Removes redundant GOTO's in the following cases:
* (1) subsequent labels
* ...
* goto Label (can be removed)
* Label:
* ...
* (2) indirect goto
* ...
* Label (can be rewrote to Label2)
* ...
* Label:
* goto Label2 (must not be removed due to the previous instruction that can fallthrough on this goto)
* ...
*/
override fun transform(internalClassName: String, methodNode: MethodNode) {
val insns = methodNode.instructions.toArray().apply { reverse() }
val insnsToRemove = arrayListOf()
val currentLabels = hashSetOf()
val labelsToReplace = hashMapOf()
var pendingGoto: JumpInsnNode? = null
for (insn in insns) {
when {
insn is LabelNode -> {
currentLabels.add(insn)
pendingGoto?.let { labelsToReplace[insn] = it }
}
insn.opcode == Opcodes.GOTO -> {
pendingGoto = insn as JumpInsnNode
if (insn.label in currentLabels) {
insnsToRemove.add(insn)
} else {
currentLabels.clear()
}
}
insn is LineNumberNode -> pendingGoto = null
insn.isMeaningful -> {
currentLabels.clear()
pendingGoto = null
}
}
}
// Rewrite branch instructions.
if (!labelsToReplace.isEmpty()) {
insns.filterIsInstance().forEach { rewriteLabelIfNeeded(it, labelsToReplace) }
}
for (insnToRemove in insnsToRemove) {
methodNode.instructions.remove(insnToRemove)
}
}
private fun rewriteLabelIfNeeded(
jumpInsn: JumpInsnNode,
labelsToReplace: Map
) {
val lastJumpInsn = getLastTargetJumpInsn(jumpInsn, labelsToReplace, mutableListOf())
if (lastJumpInsn != null && lastJumpInsn != jumpInsn) {
// Do not remove the old label because it can be used to define a local variable range.
jumpInsn.label = lastJumpInsn.label
}
}
private fun getLastTargetJumpInsn(
jumpInsn: JumpInsnNode,
labelsToReplace: Map,
alreadyVisited: MutableList
): JumpInsnNode? {
labelsToReplace[jumpInsn.label]?.let {
if (alreadyVisited.contains(it)) {
// Cycle detected, do no apply goto optimization
return null
}
alreadyVisited.add(it)
return getLastTargetJumpInsn(it, labelsToReplace, alreadyVisited)
}
return jumpInsn
}
}