C++: fix irreducible control flow logic

Author: Robert Marsh

cpp/ql/lib/semmle/code/cpp/rangeanalysis/new/internal/semantic/SemanticSSA.qll

@@ -70,7 +70,7 @@ predicate semBackEdge(SemSsaPhiNode phi, SemSsaVariable inp, SemSsaReadPositionP
   // Conservatively assume that every edge is a back edge if we don't have dominance information.
   (
     phi.getBasicBlock().bbDominates(edge.getOrigBlock()) or
-    irreducibleSccEdge(phi.getBasicBlock(), edge.getOrigBlock()) or
+    irreducibleSccEdge(edge.getOrigBlock(), phi.getBasicBlock()) or
     not edge.getOrigBlock().hasDominanceInformation()
   )
 }

cpp/ql/test/library-tests/ir/range-analysis/test.cpp

@@ -90,7 +90,8 @@ void gotoLoop(bool b1, bool b2)
   {
     for (j = 0; j < 10; ++j)
     {
+      int x;
       main_decode_loop:
     }
   }
-}
+}