Add an AppendNoPush optimization

DMCompiler/Bytecode/DreamProcOpcode.cs

@@ -253,7 +253,8 @@ public enum DreamProcOpcode : byte {
     [OpcodeMetadata]
     Abs = 0x83,
     // Peephole optimization opcodes
-    //0x84
+    [OpcodeMetadata(-1, OpcodeArgType.Reference)]
+    AppendNoPush = 0x84,
     [OpcodeMetadata(-1, OpcodeArgType.Reference)]
     AssignNoPush = 0x85,
     [OpcodeMetadata(1, OpcodeArgType.Reference, OpcodeArgType.String)]

DMCompiler/Optimizer/PeepholeOptimizations.cs

@@ -2,6 +2,30 @@
 
 namespace DMCompiler.Optimizer;
 
+// Append [ref]
+// Pop
+// -> AppendNoPush [ref]
+internal sealed class AppendNoPush : IPeepholeOptimization {
+    public ReadOnlySpan<DreamProcOpcode> GetOpcodes() {
+        return [
+            DreamProcOpcode.Append,
+            DreamProcOpcode.Pop
+        ];
+    }
+
+    public void Apply(List<IAnnotatedBytecode> input, int index) {
+        if (index + 1 >= input.Count) {
+            throw new ArgumentOutOfRangeException(nameof(index), "Bytecode index is outside the bounds of the input list.");
+        }
+
+        AnnotatedBytecodeInstruction firstInstruction = (AnnotatedBytecodeInstruction)(input[index]);
+        AnnotatedBytecodeReference assignTarget = firstInstruction.GetArg<AnnotatedBytecodeReference>(0);
+
+        input.RemoveRange(index, 2);
+        input.Insert(index, new AnnotatedBytecodeInstruction(DreamProcOpcode.AppendNoPush, [assignTarget]));
+    }
+}
+
 // Assign [ref]
 // Pop
 // -> AssignNoPush [ref]

OpenDreamRuntime/Procs/DMOpcodeHandlers.cs

@@ -743,6 +743,19 @@ private static void ThrowInvalidAddOperation(DreamValue first, DreamValue second
         }
 
         public static ProcStatus Append(DMProcState state) {
+            state.Push(AppendHelper(state));
+            return ProcStatus.Continue;
+        }
+
+        /// <summary>
+        /// Identical to <see cref="Append"/> except it never pushes the result to the stack
+        /// </summary>
+        public static ProcStatus AppendNoPush(DMProcState state) {
+            AppendHelper(state);
+            return ProcStatus.Continue;
+        }
+
+        private static DreamValue AppendHelper(DMProcState state) {
             DreamReference reference = state.ReadReference();
             DreamValue second = state.Pop();
             DreamValue first = state.GetReferenceValue(reference, peek: true);
@@ -753,12 +766,10 @@ public static ProcStatus Append(DMProcState state) {
             } else if (first.TryGetValueAsDreamObject(out var firstObj)) {
                 if (firstObj != null) {
                     state.PopReference(reference);
-                    state.Push(firstObj.OperatorAppend(second));
-
-                    return ProcStatus.Continue;
-                } else {
-                    result = second;
+                    return firstObj.OperatorAppend(second);
                 }
+
+                result = second;
             } else if (!second.IsNull) {
                 switch (first.Type) {
                     case DreamValue.DreamValueType.Float when second.Type == DreamValue.DreamValueType.Float:
@@ -775,8 +786,7 @@ public static ProcStatus Append(DMProcState state) {
             }
 
             state.AssignReference(reference, result);
-            state.Push(result);
-            return ProcStatus.Continue;
+            return result;
         }
 
         public static ProcStatus Increment(DMProcState state) {

OpenDreamRuntime/Procs/DMProc.cs

@@ -207,6 +207,7 @@ public sealed class DMProcState : ProcState {
             {DreamProcOpcode.Negate, DMOpcodeHandlers.Negate},
             {DreamProcOpcode.Modulus, DMOpcodeHandlers.Modulus},
             {DreamProcOpcode.Append, DMOpcodeHandlers.Append},
+            {DreamProcOpcode.AppendNoPush, DMOpcodeHandlers.AppendNoPush},
             {DreamProcOpcode.CreateRangeEnumerator, DMOpcodeHandlers.CreateRangeEnumerator},
             {DreamProcOpcode.Input, DMOpcodeHandlers.Input},
             {DreamProcOpcode.CompareLessThanOrEqual, DMOpcodeHandlers.CompareLessThanOrEqual},

OpenDreamRuntime/Procs/ProcDecoder.cs

@@ -108,6 +108,7 @@ public ITuple DecodeInstruction() {
             case DreamProcOpcode.OutputReference:
             case DreamProcOpcode.PushReferenceValue:
             case DreamProcOpcode.PopReference:
+            case DreamProcOpcode.AppendNoPush:
             case DreamProcOpcode.AssignNoPush:
             case DreamProcOpcode.ReturnReferenceValue:
                 return (opcode, ReadReference());