cache_fstring_hashcode.diff

diff --git a/core/src/main/java/org/jruby/RubyString.java b/core/src/main/java/org/jruby/RubyString.java
index 2b42e03515..3c2dd7dc11 100644
--- a/core/src/main/java/org/jruby/RubyString.java
+++ b/core/src/main/java/org/jruby/RubyString.java
@@ -1102,12 +1102,16 @@ public class RubyString extends RubyObject implements CharSequence, EncodingCapa
      */
     public static class FString extends RubyString {
         private IRubyObject converted;
+        private final RubyFixnum hash;
+        private final int hashCode;
 
         protected FString(Ruby runtime, RubyClass rubyClass, ByteList value, int cr) {
             super(runtime, rubyClass, value, cr);
 
             // set flag for code that does not use isFrozen
             setFrozen(true);
+
+            hash = RubyFixnum.newFixnum(runtime, hashCode = RubyString.calculateHash(runtime, value, cr));
         }
 
         @Override
@@ -1161,6 +1165,16 @@ public class RubyString extends RubyObject implements CharSequence, EncodingCapa
 
             return super.to_f();
         }
+
+        @Override
+        public RubyFixnum hash() {
+            return hash;
+        }
+
+        @Override
+        public int hashCode() {
+            return hashCode;
+        }
     }
 
     /** rb_str_resize
@@ -1404,12 +1418,16 @@ public class RubyString extends RubyObject implements CharSequence, EncodingCapa
      */
     public int strHashCode(Ruby runtime) {
         final ByteList value = this.value;
+        return calculateHash(runtime, value, scanForCodeRange());
+    }
+
+    private static int calculateHash(Ruby runtime, ByteList value, int cr) {
         final Encoding enc = value.getEncoding();
         long hash = runtime.isSiphashEnabled() ? SipHashInline.hash24(runtime.getHashSeedK0(),
                 runtime.getHashSeedK1(), value.getUnsafeBytes(), value.getBegin(),
                 value.getRealSize()) : PerlHash.hash(runtime.getHashSeedK0(),
                 value.getUnsafeBytes(), value.getBegin(), value.getRealSize());
-        hash ^= (enc.isAsciiCompatible() && scanForCodeRange() == CR_7BIT ? 0 : enc.getIndex());
+        hash ^= (enc.isAsciiCompatible() && cr == CR_7BIT ? 0 : enc.getIndex());
         return (int) hash;
     }