Move the immutability tracking for interned string lookups out of the cache key to save memory.

Author: nirvdrum

src/main/java/org/truffleruby/core/string/TBytesKey.java

@@ -23,35 +23,31 @@ public final class TBytesKey {
     private final byte[] bytes;
     private final int offset;
     private final int length;
-    private final boolean isImmutable;
     private RubyEncoding encoding;
     private final int bytesHashCode;
 
     public TBytesKey(
             byte[] bytes,
             int offset,
             int length,
-            boolean isImmutable,
             int bytesHashCode,
             RubyEncoding encoding) {
         this.bytes = bytes;
         this.offset = offset;
         this.length = length;
-        this.isImmutable = isImmutable;
         this.bytesHashCode = bytesHashCode;
         this.encoding = encoding;
     }
 
     public TBytesKey(byte[] bytes, RubyEncoding encoding) {
-        this(bytes, 0, bytes.length, true, Arrays.hashCode(bytes), encoding);
+        this(bytes, 0, bytes.length, Arrays.hashCode(bytes), encoding);
     }
 
-    public TBytesKey(InternalByteArray byteArray, boolean isImmutable, RubyEncoding encoding) {
+    public TBytesKey(InternalByteArray byteArray, RubyEncoding encoding) {
         this(
                 byteArray.getArray(),
                 byteArray.getOffset(),
                 byteArray.getLength(),
-                isImmutable,
                 hashCode(byteArray),
                 encoding);
     }
@@ -117,7 +113,7 @@ private boolean isPerfectFit() {
         return offset == 0 && length == bytes.length;
     }
 
-    public TBytesKey makeCacheable() {
+    public TBytesKey makeCacheable(boolean isImmutable) {
         if (isImmutable && isPerfectFit()) {
             return new TBytesKey(bytes, encoding);
         }
@@ -127,7 +123,7 @@ public TBytesKey makeCacheable() {
     }
 
     public TBytesKey withNewEncoding(RubyEncoding encoding) {
-        return new TBytesKey(bytes, offset, length, isImmutable, bytesHashCode, encoding);
+        return new TBytesKey(bytes, offset, length, bytesHashCode, encoding);
     }
 
     public TruffleString toTruffleString() {

src/main/java/org/truffleruby/core/string/TStringCache.java

@@ -75,28 +75,27 @@ public TruffleString getTString(TruffleString string, RubyEncoding rubyEncoding)
         assert rubyEncoding != null;
 
         var byteArray = string.getInternalByteArrayUncached(rubyEncoding.tencoding);
-        final TBytesKey key = new TBytesKey(byteArray, TStringUtils.hasImmutableInternalByteArray(string),
-                rubyEncoding);
+        final TBytesKey key = new TBytesKey(byteArray, rubyEncoding);
 
-        return getTString(key);
+        return getTString(key, TStringUtils.hasImmutableInternalByteArray(string));
     }
 
     @TruffleBoundary
     public TruffleString getTString(InternalByteArray byteArray, boolean isImmutable, RubyEncoding rubyEncoding) {
         assert rubyEncoding != null;
 
-        return getTString(new TBytesKey(byteArray, isImmutable, rubyEncoding));
+        return getTString(new TBytesKey(byteArray, rubyEncoding), isImmutable);
     }
 
     @TruffleBoundary
     public TruffleString getTString(byte[] bytes, RubyEncoding rubyEncoding) {
         assert rubyEncoding != null;
 
-        return getTString(new TBytesKey(bytes, rubyEncoding));
+        return getTString(new TBytesKey(bytes, rubyEncoding), true);
     }
 
     @TruffleBoundary
-    private TruffleString getTString(TBytesKey lookupKey) {
+    private TruffleString getTString(TBytesKey lookupKey, boolean isLookupKeyImmutable) {
         final TruffleString tstring = bytesToTString.get(lookupKey);
         var rubyEncoding = lookupKey.getMatchedEncoding();
 
@@ -128,7 +127,7 @@ private TruffleString getTString(TBytesKey lookupKey) {
         }
 
         // Use the new TruffleString bytes in the cache, so we do not keep bytes alive unnecessarily.
-        return bytesToTString.addInCacheIfAbsent(lookupKey.makeCacheable(), newTString);
+        return bytesToTString.addInCacheIfAbsent(lookupKey.makeCacheable(isLookupKeyImmutable), newTString);
     }
 
     public boolean contains(TruffleString string, RubyEncoding encoding) {