From 7b92ccb24425e9eb26b2ec4ee78e033eb9ca72db Mon Sep 17 00:00:00 2001
From: Major <major@emulate.rs>
Date: Mon, 9 Mar 2020 21:58:21 +0000
Subject: [PATCH] Add RedundantGotoTransformer

Removes GOTO instructions that point to the next instruction, typically
left over from stripping exceptions inserted by the obfuscator.

Although modern decompilers can handle such GOTOs fine, removing them
makes for a nicer IR representation.

Signed-off-by: Major <major@emulate.rs>
---
 .../java/dev/openrs2/deob/Deobfuscator.kt     |  2 +
 .../transform/RedundantGotoTransformer.kt     | 53 +++++++++++++++++++
 2 files changed, 55 insertions(+)
 create mode 100644 deob/src/main/java/dev/openrs2/deob/transform/RedundantGotoTransformer.kt

diff --git a/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt b/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
index b48eb44311..0c9eb0b52b 100644
--- a/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
+++ b/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
@@ -28,6 +28,7 @@ import dev.openrs2.deob.transform.OriginalNameTransformer
 import dev.openrs2.deob.transform.OriginalPcRestoreTransformer
 import dev.openrs2.deob.transform.OriginalPcSaveTransformer
 import dev.openrs2.deob.transform.OverrideTransformer
+import dev.openrs2.deob.transform.RedundantGotoTransformer
 import dev.openrs2.deob.transform.RemapTransformer
 import dev.openrs2.deob.transform.ResetTransformer
 import dev.openrs2.deob.transform.StaticScramblingTransformer
@@ -180,6 +181,7 @@ class Deobfuscator(private val input: Path, private val output: Path) {
             VisibilityTransformer(),
             FinalTransformer(),
             OverrideTransformer(),
+            RedundantGotoTransformer(),
             OriginalPcRestoreTransformer(),
             FernflowerExceptionTransformer()
         )
diff --git a/deob/src/main/java/dev/openrs2/deob/transform/RedundantGotoTransformer.kt b/deob/src/main/java/dev/openrs2/deob/transform/RedundantGotoTransformer.kt
new file mode 100644
index 0000000000..ad104ad7ea
--- /dev/null
+++ b/deob/src/main/java/dev/openrs2/deob/transform/RedundantGotoTransformer.kt
@@ -0,0 +1,53 @@
+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.nextReal
+import dev.openrs2.asm.removeDeadCode
+import dev.openrs2.asm.transform.Transformer
+import org.objectweb.asm.Opcodes
+import org.objectweb.asm.tree.ClassNode
+import org.objectweb.asm.tree.JumpInsnNode
+import org.objectweb.asm.tree.MethodNode
+
+class RedundantGotoTransformer : Transformer() {
+    private var removed = 0
+
+    override fun preTransform(classPath: ClassPath) {
+        removed = 0
+    }
+
+    override fun preTransformMethod(
+        classPath: ClassPath,
+        library: Library,
+        clazz: ClassNode,
+        method: MethodNode
+    ): Boolean {
+        method.removeDeadCode(clazz.name)
+        return false
+    }
+
+    override fun transformCode(classPath: ClassPath, library: Library, clazz: ClassNode, method: MethodNode): Boolean {
+        for (instruction in method.instructions) {
+            if (instruction.opcode == Opcodes.GOTO) {
+                instruction as JumpInsnNode
+
+                if (instruction.nextReal === instruction.label.nextReal) {
+                    method.instructions.remove(instruction)
+                    removed++
+                }
+            }
+        }
+
+        return false
+    }
+
+    override fun postTransform(classPath: ClassPath) {
+        logger.info { "Removed $removed redundant GOTO instructions" }
+    }
+
+    private companion object {
+        private val logger = InlineLogger()
+    }
+}