Add CopyPropagationTransformer

Signed-off-by: Graham <gpe@openrs2.dev>

deob/src/main/java/dev/openrs2/deob/DeobfuscatorModule.kt

@@ -12,6 +12,7 @@ import dev.openrs2.deob.transform.BundlerTransformer
 import dev.openrs2.deob.transform.CanvasTransformer
 import dev.openrs2.deob.transform.ClassLiteralTransformer
 import dev.openrs2.deob.transform.ConstantArgTransformer
+import dev.openrs2.deob.transform.CopyPropagationTransformer
 import dev.openrs2.deob.transform.CounterTransformer
 import dev.openrs2.deob.transform.EmptyClassTransformer
 import dev.openrs2.deob.transform.ExceptionTracingTransformer
@@ -61,6 +62,7 @@ object DeobfuscatorModule : AbstractModule() {
         binder.addBinding().to(FieldOrderTransformer::class.java)
         binder.addBinding().to(BitwiseOpTransformer::class.java)
         binder.addBinding().to(ConstantArgTransformer::class.java)
+        binder.addBinding().to(CopyPropagationTransformer::class.java)
         binder.addBinding().to(UnusedLocalTransformer::class.java)
         binder.addBinding().to(UnusedMethodTransformer::class.java)
         binder.addBinding().to(UnusedArgTransformer::class.java)

deob/src/main/java/dev/openrs2/deob/analysis/CopyAssignment.kt

@@ -0,0 +1,3 @@
+package dev.openrs2.deob.analysis
+
+data class CopyAssignment(val destination: Int, val source: Int)

deob/src/main/java/dev/openrs2/deob/analysis/CopyPropagationAnalyzer.kt

@@ -0,0 +1,79 @@
+package dev.openrs2.deob.analysis
+
+import org.objectweb.asm.Opcodes
+import org.objectweb.asm.tree.AbstractInsnNode
+import org.objectweb.asm.tree.IincInsnNode
+import org.objectweb.asm.tree.MethodNode
+import org.objectweb.asm.tree.VarInsnNode
+import java.util.Collections
+
+class CopyPropagationAnalyzer(owner: String, method: MethodNode) :
+    DataFlowAnalyzer<Set<CopyAssignment>>(owner, method) {
+
+    private val allAssignments = mutableSetOf<CopyAssignment>()
+
+    init {
+        for (insn in method.instructions) {
+            if (insn !is VarInsnNode || !STORE_OPCODES.contains(insn.opcode)) {
+                continue
+            }
+
+            val previous = insn.previous
+            if (previous !is VarInsnNode || !LOAD_OPCODES.contains(previous.opcode)) {
+                continue
+            }
+
+            allAssignments += CopyAssignment(insn.`var`, previous.`var`)
+        }
+    }
+
+    override fun createEntrySet(): Set<CopyAssignment> {
+        return Collections.emptySet()
+    }
+
+    override fun createInitialSet(): Set<CopyAssignment> {
+        return allAssignments
+    }
+
+    override fun join(set1: Set<CopyAssignment>, set2: Set<CopyAssignment>): Set<CopyAssignment> {
+        return set1 intersect set2
+    }
+
+    override fun transfer(set: Set<CopyAssignment>, insn: AbstractInsnNode): Set<CopyAssignment> {
+        return when {
+            insn is VarInsnNode && STORE_OPCODES.contains(insn.opcode) -> {
+                val newSet = set.minusKilledByAssignmentTo(insn.`var`)
+
+                val previous = insn.previous
+                if (previous is VarInsnNode && LOAD_OPCODES.contains(previous.opcode)) {
+                    newSet.plus(CopyAssignment(insn.`var`, previous.`var`))
+                } else {
+                    newSet
+                }
+            }
+            insn is IincInsnNode -> set.minusKilledByAssignmentTo(insn.`var`)
+            else -> set
+        }
+    }
+
+    private fun Set<CopyAssignment>.minusKilledByAssignmentTo(index: Int): Set<CopyAssignment> {
+        return filterTo(mutableSetOf()) { it.source != index && it.destination != index }
+    }
+
+    private companion object {
+        private val LOAD_OPCODES = setOf(
+            Opcodes.ILOAD,
+            Opcodes.LSTORE,
+            Opcodes.FLOAD,
+            Opcodes.DLOAD,
+            Opcodes.ALOAD
+        )
+        private val STORE_OPCODES = setOf(
+            Opcodes.ISTORE,
+            Opcodes.LSTORE,
+            Opcodes.FSTORE,
+            Opcodes.DSTORE,
+            Opcodes.ASTORE
+        )
+    }
+}

deob/src/main/java/dev/openrs2/deob/transform/CopyPropagationTransformer.kt

@@ -0,0 +1,81 @@
+package dev.openrs2.deob.transform
+
+import com.github.michaelbull.logging.InlineLogger
+import dev.openrs2.asm.classpath.ClassPath
+import dev.openrs2.asm.classpath.Library
+import dev.openrs2.asm.transform.Transformer
+import dev.openrs2.deob.analysis.CopyPropagationAnalyzer
+import org.objectweb.asm.Opcodes
+import org.objectweb.asm.tree.ClassNode
+import org.objectweb.asm.tree.MethodNode
+import org.objectweb.asm.tree.VarInsnNode
+import javax.inject.Singleton
+
+/**
+ * A [Transformer] that performs
+ * [copy propagation](https://en.wikipedia.org/wiki/Copy_propagation) of
+ * assignments of one variable to another.
+ *
+ * This is primarily for improving the decompilation of `for` loops. Without
+ * copy propagation, the initializer in many `for` loops declares a different
+ * variable to the one in the increment expression:
+ *
+ * ```
+ * Object[] array = ...
+ * int i = 0;
+ * for (Object[] array2 = array; i < n; i++) {
+ *     // use array2[n]
+ * }
+ * ```
+ *
+ * With copy propagation, the variables match:
+ *
+ * ```
+ * Object[] array = ...
+ * for (int i = 0; i < n; i++) {
+ *     // use array[n]
+ * }
+ * ```
+ */
+@Singleton
+class CopyPropagationTransformer : Transformer() {
+    private var propagatedLocals = 0
+
+    override fun preTransform(classPath: ClassPath) {
+        propagatedLocals = 0
+    }
+
+    override fun transformCode(classPath: ClassPath, library: Library, clazz: ClassNode, method: MethodNode): Boolean {
+        val analyzer = CopyPropagationAnalyzer(clazz.name, method)
+        analyzer.analyze()
+
+        for (insn in method.instructions) {
+            if (insn !is VarInsnNode || !LOAD_OPCODES.contains(insn.opcode)) {
+                continue
+            }
+
+            val set = analyzer.getInSet(insn) ?: continue
+            val assignment = set.singleOrNull { it.destination == insn.`var` } ?: continue
+            insn.`var` = assignment.source
+            propagatedLocals++
+        }
+
+        return false
+    }
+
+    override fun postTransform(classPath: ClassPath) {
+        logger.info { "Propagated $propagatedLocals copies" }
+    }
+
+    private companion object {
+        private val logger = InlineLogger()
+
+        private val LOAD_OPCODES = setOf(
+            Opcodes.ILOAD,
+            Opcodes.LLOAD,
+            Opcodes.FLOAD,
+            Opcodes.DLOAD,
+            Opcodes.ALOAD
+        )
+    }
+}