C++: Better join-order fix.

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/controlflow/SSAUtils.qll

@@ -153,9 +153,11 @@ library class SSAHelper extends int {
    * Modern Compiler Implementation by Andrew Appel.
    */
   private predicate frontier_phi_node(StackVariable v, BasicBlock b) {
-    exists(BasicBlock x | dominanceFrontier(pragma[only_bind_into](x), b) and ssa_defn_rec(v, x)) and
+    exists(BasicBlock x |
+      dominanceFrontier(x, pragma[only_bind_into](b)) and ssa_defn_rec(pragma[only_bind_into](v), x)
+    ) and
     /* We can also eliminate those nodes where the variable is not live on any incoming edge */
-    live_at_start_of_bb(v, b)
+    live_at_start_of_bb(pragma[only_bind_into](v), b)
   }
 
   private predicate ssa_defn_rec(StackVariable v, BasicBlock b) {