Fix removal of unused arguments whose local variable slot is re-used

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

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

@@ -15,10 +15,15 @@ class ConstSourceInterpreter : Interpreter<ConstSourceValue>(Opcodes.ASM8) {
         return ConstSourceValue.Unknown(basicValue)
     }
 
+    override fun newParameterValue(isInstanceMethod: Boolean, local: Int, type: Type): ConstSourceValue {
+        val basicValue = basicInterpreter.newParameterValue(isInstanceMethod, local, type)
+        return ConstSourceValue.Arg(basicValue)
+    }
+
     override fun newOperation(insn: AbstractInsnNode): ConstSourceValue {
         val basicValue = basicInterpreter.newOperation(insn)
         return if (insn.intConstant != null) {
-            ConstSourceValue.Single(basicValue, insn)
+            ConstSourceValue.Insn(basicValue, insn)
         } else {
             ConstSourceValue.Unknown(basicValue)
         }
@@ -74,10 +79,10 @@ class ConstSourceInterpreter : Interpreter<ConstSourceValue>(Opcodes.ASM8) {
 
     override fun merge(value1: ConstSourceValue, value2: ConstSourceValue): ConstSourceValue {
         val basicValue = basicInterpreter.merge(value1.basicValue, value2.basicValue)
-        return if (value1 is ConstSourceValue.Single && value1 == value2) {
-            value1
-        } else {
-            ConstSourceValue.Unknown(basicValue)
+        return when {
+            value1 is ConstSourceValue.Arg || value2 is ConstSourceValue.Arg -> ConstSourceValue.Arg(basicValue)
+            value1 == value2 -> value1
+            else -> ConstSourceValue.Unknown(basicValue)
         }
     }
 }

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

@@ -6,7 +6,8 @@ import org.objectweb.asm.tree.analysis.Value
 
 sealed class ConstSourceValue : Value {
     data class Unknown(override val basicValue: BasicValue) : ConstSourceValue()
-    data class Single(override val basicValue: BasicValue, val source: AbstractInsnNode) : ConstSourceValue()
+    data class Insn(override val basicValue: BasicValue, val source: AbstractInsnNode) : ConstSourceValue()
+    data class Arg(override val basicValue: BasicValue) : ConstSourceValue()
 
     abstract val basicValue: BasicValue
 

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

@@ -17,10 +17,12 @@ import org.objectweb.asm.Opcodes
 import org.objectweb.asm.Type
 import org.objectweb.asm.tree.AbstractInsnNode
 import org.objectweb.asm.tree.ClassNode
+import org.objectweb.asm.tree.IincInsnNode
 import org.objectweb.asm.tree.MethodInsnNode
 import org.objectweb.asm.tree.MethodNode
 import org.objectweb.asm.tree.VarInsnNode
 import org.objectweb.asm.tree.analysis.Analyzer
+import org.objectweb.asm.tree.analysis.Frame
 import javax.inject.Inject
 import javax.inject.Singleton
 
@@ -46,6 +48,23 @@ class UnusedArgTransformer @Inject constructor(private val profile: Profile) : T
         }
     }
 
+    private fun retainArg(
+        partition: DisjointSet.Partition<MemberRef>,
+        localToArgMap: Map<Int, Int>,
+        frame: Frame<ConstSourceValue>,
+        local: Int
+    ) {
+        val source = frame.getLocal(local)
+        if (source !is ConstSourceValue.Arg) {
+            return
+        }
+
+        val arg = localToArgMap[local]
+        if (arg != null) {
+            retainedArgs.add(ArgPartition(partition, arg))
+        }
+    }
+
     private fun populateRetainedArgs(classPath: ClassPath, clazz: ClassNode, method: MethodNode) {
         val partition = inheritedMethodSets[MemberRef(clazz, method)]!!
         val localToArgMap = createLocalToArgMap(method)
@@ -62,15 +81,11 @@ class UnusedArgTransformer @Inject constructor(private val profile: Profile) : T
 
             when (val insn = method.instructions[i]) {
                 is VarInsnNode -> {
-                    if (insn.opcode != Opcodes.ILOAD) {
-                        continue@frame
-                    }
-
-                    val arg = localToArgMap[insn.`var`]
-                    if (arg != null) {
-                        retainedArgs.add(ArgPartition(partition, arg))
+                    if (insn.opcode == Opcodes.ILOAD) {
+                        retainArg(partition, localToArgMap, frame, insn.`var`)
                     }
                 }
+                is IincInsnNode -> retainArg(partition, localToArgMap, frame, insn.`var`)
                 is MethodInsnNode -> {
                     val invokePartition = inheritedMethodSets[MemberRef(insn)]
                     if (invokePartition == null) {
@@ -84,7 +99,7 @@ class UnusedArgTransformer @Inject constructor(private val profile: Profile) : T
                     val args = Type.getArgumentTypes(insn.desc).size
                     for (j in 0 until args) {
                         val source = frame.getStack(stackSize - args + j)
-                        if (source !is ConstSourceValue.Single) {
+                        if (source !is ConstSourceValue.Insn) {
                             retainedArgs.add(ArgPartition(invokePartition, j))
                         }
                     }
@@ -133,7 +148,7 @@ class UnusedArgTransformer @Inject constructor(private val profile: Profile) : T
 
             for ((j, argType) in argTypes.withIndex()) {
                 if (argType.sort in INT_SORTS && ArgPartition(partition, j) !in retainedArgs) {
-                    val value = frame.getStack(stackSize - argTypes.size + j) as ConstSourceValue.Single
+                    val value = frame.getStack(stackSize - argTypes.size + j) as ConstSourceValue.Insn
                     deadInsns.add(value.source)
                 } else {
                     newArgTypes.add(argType)