stop tracking whether ConcatRopes are balanced

Author: Nicolas Laurent

src/main/java/org/truffleruby/core/rope/ConcatRope.java

@@ -16,15 +16,13 @@ public class ConcatRope extends ManagedRope {
 
     private final ManagedRope left;
     private final ManagedRope right;
-    private final boolean balanced;
 
     public ConcatRope(
             ManagedRope left,
             ManagedRope right,
             Encoding encoding,
-            CodeRange codeRange,
-            boolean balanced) {
-        this(left, right, encoding, codeRange, left.characterLength() + right.characterLength(), null, balanced);
+            CodeRange codeRange) {
+        this(left, right, encoding, codeRange, left.characterLength() + right.characterLength(), null);
     }
 
     private ConcatRope(
@@ -33,8 +31,7 @@ private ConcatRope(
             Encoding encoding,
             CodeRange codeRange,
             int characterLength,
-            byte[] bytes,
-            boolean balanced) {
+            byte[] bytes) {
         super(
                 encoding,
                 codeRange,
@@ -43,7 +40,6 @@ private ConcatRope(
                 bytes);
         this.left = left;
         this.right = right;
-        this.balanced = balanced;
     }
 
     @Override
@@ -55,8 +51,7 @@ Rope withEncoding7bit(Encoding newEncoding) {
                 newEncoding,
                 CodeRange.CR_7BIT,
                 characterLength(),
-                getRawBytes(),
-                balanced);
+                getRawBytes());
     }
 
     @Override
@@ -68,8 +63,7 @@ Rope withBinaryEncoding() {
                 ASCIIEncoding.INSTANCE,
                 CodeRange.CR_VALID,
                 byteLength(),
-                getRawBytes(),
-                balanced);
+                getRawBytes());
     }
 
     public ManagedRope getLeft() {
@@ -79,9 +73,4 @@ public ManagedRope getLeft() {
     public ManagedRope getRight() {
         return right;
     }
-
-    public boolean isBalanced() {
-        return balanced;
-    }
-
 }

src/main/java/org/truffleruby/core/rope/RopeNodes.java

@@ -480,32 +480,9 @@ protected Rope concat(ManagedRope left, ManagedRope right, Encoding encoding,
                             left.getCodeRange(),
                             right.getCodeRange(),
                             sameCodeRangeProfile,
-                            brokenCodeRangeProfile),
-                    isBalanced(left, right));
-        }
-
-        private boolean isBalanced(Rope left, Rope right) {
-            // Our definition of balanced is centered around the notion of rebalancing. We could have a simple structure
-            // such as ConcatRope(ConcatRope(LeafRope, LeafRope), LeafRope) that is balanced on its own but may contribute
-            // to an unbalanced rope when combined with another rope of similar structure. To keep things simple, we only
-            // consider ConcatRopes that consist of two non-ConcatRopes balanced as the base case and ConcatRopes that
-            // have balanced ConcatRopes for both children are balanced by induction.
-            if (left instanceof ConcatRope) {
-                if (right instanceof ConcatRope) {
-                    return ((ConcatRope) left).isBalanced() && ((ConcatRope) right).isBalanced();
-                }
-
-                return false;
-            } else {
-                // We treat the concatenation of two non-ConcatRopes as balanced, even if their children not balanced.
-                // E.g., a SubstringRope whose child is an unbalanced ConcatRope arguable isn't balanced. However,
-                // the code is much simpler by handling it this way. Balanced ConcatRopes will never rebalance, but
-                // if they become part of a larger subtree that exceeds the depth threshold, they may be flattened.
-                return !(right instanceof ConcatRope);
-            }
+                            brokenCodeRangeProfile));
         }
 
-
         @SuppressFBWarnings("RV")
         @Specialization(guards = { "!left.isEmpty()", "!right.isEmpty()", "isCodeRangeBroken(left, right)" })
         protected Rope concatCrBroken(ManagedRope left, ManagedRope right, Encoding encoding,