cache Expr::getStringValue

javascript/ql/src/semmle/javascript/Expr.qll

@@ -108,7 +108,7 @@ class Expr extends @expr, ExprOrStmt, ExprOrType, AST::ValueNode {
   int getIntValue() { none() }
 
   /** Gets the constant string value this expression evaluates to, if any. */
-  string getStringValue() { none() }
+  cached string getStringValue() { none() }
 
   /** Holds if this expression is impure, that is, its evaluation could have side effects. */
   predicate isImpure() { any() }