Proper instructions for elvis operator

We should not mark elvis operator unused, for the rhs may have desired side-effects

compiler/frontend/src/org/jetbrains/jet/lang/cfg/JetControlFlowBuilder.java

@@ -101,6 +101,7 @@ public interface JetControlFlowBuilder {
     enum PredefinedOperation {
         AND,
         OR,
+        ELVIS,
         NOT_NULL_ASSERTION
     }
     void predefinedOperation(@NotNull JetExpression expression, @Nullable PredefinedOperation operation);

compiler/frontend/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java

@@ -250,7 +250,7 @@ public class JetControlFlowProcessor {
         public void visitBinaryExpression(@NotNull JetBinaryExpression expression) {
             JetSimpleNameExpression operationReference = expression.getOperationReference();
             IElementType operationType = operationReference.getReferencedNameElementType();
-            if (!ImmutableSet.of(ANDAND, OROR, EQ, ELVIS).contains(operationType)) {
+            if (!ImmutableSet.of(ANDAND, OROR, EQ, JetTokens.ELVIS).contains(operationType)) {
                 mark(expression);
             }
             JetExpression right = expression.getRight();
@@ -296,13 +296,14 @@ public class JetControlFlowProcessor {
                     generateBothArguments(expression);
                 }
             }
-            else if (operationType == ELVIS) {
+            else if (operationType == JetTokens.ELVIS) {
                 generateInstructions(expression.getLeft(), false);
                 Label afterElvis = builder.createUnboundLabel();
                 builder.jumpOnTrue(afterElvis);
                 if (right != null) {
                     generateInstructions(right, false);
                 }
+                builder.predefinedOperation(expression, JetControlFlowBuilder.PredefinedOperation.ELVIS);
                 builder.bindLabel(afterElvis);
             }
             else if (operationType == JetTokens.EQEQ || operationType == JetTokens.EXCLEQ) {