[Truffle] Last of the regexp interpolation specs.

Author: chrisseaton

core/src/main/java/org/jruby/truffle/nodes/core/InteroplatedRegexpNode.java

@@ -42,7 +42,8 @@ public RubyRegexp executeRubyRegexp(VirtualFrame frame) {
             strings[n] = org.jruby.RubyString.newString(getContext().getRuntime(), ((RubyString) toS.call(frame, child, "to_s", null)).getBytes());
         }
 
-        return new RubyRegexp(this, getContext().getCoreLibrary().getRegexpClass(), org.jruby.RubyRegexp.preprocessDRegexp(getContext().getRuntime(), strings, options).getByteList(), options.toOptions());
+        final org.jruby.RubyString preprocessed = org.jruby.RubyRegexp.preprocessDRegexp(getContext().getRuntime(), strings, options);
+        return new RubyRegexp(this, getContext().getCoreLibrary().getRegexpClass(), preprocessed.getByteList(), options.toOptions());
     }
 
     @Override

core/src/main/java/org/jruby/truffle/runtime/core/RubyRegexp.java

@@ -381,7 +381,7 @@ public boolean equals(Object obj) {
 
     public static Regex compile(RubyNode currentNode, RubyContext context, ByteList bytes, int options) {
         RubyNode.notDesignedForCompilation();
-        return compile(currentNode, context, bytes.bytes(), UTF8Encoding.INSTANCE, options);
+        return compile(currentNode, context, bytes.bytes(), bytes.getEncoding(), options);
     }
 
     public static Regex compile(RubyNode currentNode, RubyContext context, byte[] bytes, Encoding encoding, int options) {