Add support for removing an argument whose local variable slot is used

This obviously doesn't work if the slot is loaded before something is
stored in it, but it does allow us to remove unused arguments whose slot
is re-used for another purpose.

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

asm/src/main/java/dev/openrs2/asm/MethodNodeUtils.kt

@@ -21,16 +21,16 @@ private fun localIndex(access: Int, argTypes: Array<Type>, argIndex: Int): Int {
     return localIndex
 }
 
-private fun remap(i: Int, argType: Type, localIndex: Int): Int {
-    return if (i >= localIndex) {
-        i - argType.size
-    } else {
-        i
+private fun remap(i: Int, argType: Type, localIndex: Int, newLocalIndex: Int): Int {
+    return when {
+        i > localIndex -> i - argType.size
+        i == localIndex -> newLocalIndex
+        else -> i
     }
 }
 
-private fun remapAll(indexes: List<Int>, argType: Type, localIndex: Int): MutableList<Int> {
-    return indexes.mapTo(mutableListOf()) { remap(it, argType, localIndex) }
+private fun remapAll(indexes: List<Int>, argType: Type, localIndex: Int, newLocalIndex: Int): MutableList<Int> {
+    return indexes.mapTo(mutableListOf()) { remap(it, argType, localIndex, newLocalIndex) }
 }
 
 fun MethodNode.removeArgument(argIndex: Int) {
@@ -68,36 +68,65 @@ fun MethodNode.removeArgument(argIndex: Int) {
 
     // remap locals
     val localIndex = localIndex(access, argTypes, argIndex)
-    maxLocals -= argType.size
+    val newLocalIndex = maxLocals - argType.size
 
     if (localVariables != null) {
-        localVariables.removeIf { it.index == localIndex }
         for (v in localVariables) {
-            v.index = remap(v.index, argType, localIndex)
+            v.index = remap(v.index, argType, localIndex, newLocalIndex)
         }
     }
 
     if (visibleLocalVariableAnnotations != null) {
-        visibleLocalVariableAnnotations.removeIf { localIndex in it.index }
         for (annotation in visibleLocalVariableAnnotations) {
-            annotation.index = remapAll(annotation.index, argType, localIndex)
+            annotation.index = remapAll(annotation.index, argType, localIndex, newLocalIndex)
         }
     }
 
     if (invisibleLocalVariableAnnotations != null) {
-        invisibleLocalVariableAnnotations.removeIf { localIndex in it.index }
         for (annotation in invisibleLocalVariableAnnotations) {
-            annotation.index = remapAll(annotation.index, argType, localIndex)
+            annotation.index = remapAll(annotation.index, argType, localIndex, newLocalIndex)
         }
     }
 
+    var newLocalIndexUsed = false
+
     for (insn in instructions) {
         when (insn) {
-            is VarInsnNode -> insn.`var` = remap(insn.`var`, argType, localIndex)
-            is IincInsnNode -> insn.`var` = remap(insn.`var`, argType, localIndex)
+            is VarInsnNode -> {
+                insn.`var` = remap(insn.`var`, argType, localIndex, newLocalIndex)
+
+                if (insn.`var` == newLocalIndex) {
+                    newLocalIndexUsed = true
+                }
+            }
+            is IincInsnNode -> {
+                insn.`var` = remap(insn.`var`, argType, localIndex, newLocalIndex)
+
+                if (insn.`var` == newLocalIndex) {
+                    newLocalIndexUsed = true
+                }
+            }
             is FrameNode -> throw UnsupportedOperationException("SKIP_FRAMES and COMPUTE_FRAMES must be used")
         }
     }
+
+    if (newLocalIndexUsed) {
+        return
+    }
+
+    maxLocals -= argType.size
+
+    if (localVariables != null) {
+        localVariables.removeIf { it.index == newLocalIndex }
+    }
+
+    if (visibleLocalVariableAnnotations != null) {
+        visibleLocalVariableAnnotations.removeIf { newLocalIndex in it.index }
+    }
+
+    if (invisibleLocalVariableAnnotations != null) {
+        invisibleLocalVariableAnnotations.removeIf { newLocalIndex in it.index }
+    }
 }
 
 fun MethodNode.removeDeadCode(owner: String) {