Use shared inDominanceFrontier instead of inDominanceFrontierOf

Note that they are the opposite way round from each other.

Author: owen-mc

go/ql/lib/semmle/go/controlflow/BasicBlocks.qll

@@ -66,14 +66,4 @@ class ReachableBasicBlock extends BasicBlock {
  */
 class ReachableJoinBlock extends ReachableBasicBlock {
   ReachableJoinBlock() { this.getFirstNode().isJoin() }
-
-  /**
-   * Holds if this basic block belongs to the dominance frontier of `b`, that is
-   * `b` dominates a predecessor of this block, but not this block itself.
-   *
-   * Algorithm from Cooper et al., "A Simple, Fast Dominance Algorithm" (Figure 5),
-   * who in turn attribute it to Ferrante et al., "The program dependence graph and
-   * its use in optimization".
-   */
-  predicate inDominanceFrontierOf(ReachableBasicBlock b) { b.inDominanceFrontier(this) }
 }

go/ql/lib/semmle/go/dataflow/SsaImpl.qll

@@ -71,7 +71,7 @@ private module Internal {
   private predicate inDefDominanceFrontier(ReachableJoinBlock bb, SsaSourceVariable v) {
     exists(ReachableBasicBlock defbb, SsaDefinition def |
       def.definesAt(defbb, _, v) and
-      bb.inDominanceFrontierOf(defbb)
+      defbb.inDominanceFrontier(bb)
     )
   }