org.jetbrains.kotlin.codegen.optimization.DeadCodeEliminationMethodTransformer.kt Maven / Gradle / Ivy

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/*
 * 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.inline.remove
import org.jetbrains.kotlin.codegen.optimization.common.InstructionLivenessAnalyzer
import org.jetbrains.kotlin.codegen.optimization.common.removeEmptyCatchBlocks
import org.jetbrains.kotlin.codegen.optimization.common.removeUnusedLocalVariables
import org.jetbrains.kotlin.codegen.optimization.transformer.MethodTransformer
import org.jetbrains.org.objectweb.asm.tree.AbstractInsnNode
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 DeadCodeEliminationMethodTransformer : MethodTransformer() {
    override fun transform(internalClassName: String, methodNode: MethodNode) {
        val liveness = InstructionLivenessAnalyzer(methodNode).analyze()

        val insnsToRemove = ArrayList()

        val insns = methodNode.instructions.toArray()
        for (i in insns.indices) {
            val insn = insns[i]
            if (shouldRemove(insn, i, liveness)) {
                insnsToRemove.add(insn)
            }
        }

        methodNode.remove(insnsToRemove)

        // Remove empty try-catch blocks to make sure we don't break data flow analysis invariants by dead code elimination.
        methodNode.removeEmptyCatchBlocks()

        methodNode.removeUnusedLocalVariables()
    }

    private fun shouldRemove(insn: AbstractInsnNode, index: Int, liveness: BooleanArray): Boolean {
        if (insn !is LineNumberNode) return !liveness[index]

        // Line number node is "dead" if the corresponding line number interval
        // contains at least one "dead" meaningful instruction and no "live" meaningful instructions.
        var finger: AbstractInsnNode = insn
        var fingerIndex = index
        var hasDeadInsn = false
        while (true) {
            finger = finger.next ?: break
            fingerIndex++
            when (finger) {
                is LabelNode ->
                    continue
                is LineNumberNode ->
                    if (finger.line != insn.line) return hasDeadInsn
                else -> {
                    if (liveness[fingerIndex]) return false
                    hasDeadInsn = true
                }
            }
        }
        return true
    }
}