From 6ffc5197e365cbe4d35d14704edb5f9f2fe4bd30 Mon Sep 17 00:00:00 2001
From: Richard Van Tassel <Ruzihm@users.noreply.github.com>
Date: Thu, 20 Feb 2025 14:16:12 -0500
Subject: [PATCH] Additional label optimization (#2218)

---
 DMCompiler/Optimizer/BytecodeOptimizer.cs | 25 +++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/DMCompiler/Optimizer/BytecodeOptimizer.cs b/DMCompiler/Optimizer/BytecodeOptimizer.cs
index dc1ffb7c7f..cfed5be887 100644
--- a/DMCompiler/Optimizer/BytecodeOptimizer.cs
+++ b/DMCompiler/Optimizer/BytecodeOptimizer.cs
@@ -12,8 +12,17 @@ internal void Optimize(List<IAnnotatedBytecode> input) {
         RemoveUnreferencedLabels(input);
         JoinAndForwardLabels(input);
         RemoveUnreferencedLabels(input);
+        RemoveImmediateJumps(input);
+        RemoveUnreferencedLabels(input);
 
         _peepholeOptimizer.RunPeephole(input);
+
+        // Run label optimizations again due to possibly removed jumps in peephole optimizers
+        RemoveUnreferencedLabels(input);
+        JoinAndForwardLabels(input);
+        RemoveUnreferencedLabels(input);
+        RemoveImmediateJumps(input);
+        RemoveUnreferencedLabels(input);
     }
 
     private void RemoveUnreferencedLabels(List<IAnnotatedBytecode> input) {
@@ -40,6 +49,22 @@ private void RemoveUnreferencedLabels(List<IAnnotatedBytecode> input) {
         }
     }
 
+    /**
+     * <summary>Removes jumps for which the next element is the jump's destination</summary>
+     */
+    private void RemoveImmediateJumps(List<IAnnotatedBytecode> input) {
+        for (int i = input.Count - 2; i >= 0; i--) {
+            if (input[i] is AnnotatedBytecodeInstruction { Opcode: Bytecode.DreamProcOpcode.Jump } instruction) {
+                if (input[i + 1] is AnnotatedBytecodeLabel followingLabel) {
+                    AnnotatedBytecodeLabel jumpLabelName = instruction.GetArg<AnnotatedBytecodeLabel>(0);
+                    if (jumpLabelName.LabelName == followingLabel.LabelName) {
+                        input.RemoveAt(i);
+                    }
+                }
+            }
+        }
+    }
+
     private void JoinAndForwardLabels(List<IAnnotatedBytecode> input) {
         Dictionary<string, string> labelAliases = new();
         for (int i = 0; i < input.Count; i++) {