Remove unnecessary number index casts

Author: GarboMuffin

src/compiler/iroptimizer.js

@@ -164,6 +164,12 @@ class IROptimizer {
             return InputType.NUMBER;
         }
 
+        case InputOpcode.CAST_NUMBER_INDEX: {
+            const innerType = inputs.target.type;
+            if (innerType & InputType.NUMBER_INDEX) return innerType;
+            return InputType.NUMBER_INDEX;
+        }
+
         case InputOpcode.CAST_NUMBER_OR_NAN: {
             const innerType = inputs.target.type;
             if (innerType & InputType.NUMBER_OR_NAN) return innerType;
@@ -709,6 +715,14 @@ class IROptimizer {
             return input;
         }
 
+        case InputOpcode.CAST_NUMBER_INDEX: {
+            const targetType = input.inputs.target.type;
+            if ((targetType & InputType.NUMBER_INDEX) === targetType) {
+                return input.inputs.target;
+            }
+            return input;
+        }
+
         case InputOpcode.CAST_NUMBER_OR_NAN: {
             const targetType = input.inputs.target.type;
             if ((targetType & InputType.NUMBER_OR_NAN) === targetType) {

test/snapshot/__snapshots__/tw-simple-string-operations.sb3.tw-snapshot

@@ -25,7 +25,7 @@ b0.value = "ababa";
 b1.value = "";
 b2.value = 1;
 for (var a0 = b0.value.length; a0 > 0; a0--) {
-if ((((b0.value)[(b2.value | 0) - 1] || "").toLowerCase() === "a".toLowerCase())) {
+if ((((b0.value)[b2.value - 1] || "").toLowerCase() === "a".toLowerCase())) {
 b1.value = (b1.value + "b");
 } else {
 b1.value = (b1.value + "a");