C++: Fix internal SCC edges and accept test changes.

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaImpl.qll

@@ -1379,15 +1379,11 @@ class PhiNode extends Definition instanceof SsaImpl::PhiNode {
 
 private PhiNode getAnInput(PhiNode phi) { result = phi.getAnInput() }
 
-private predicate definitionCycle(PhiNode phi) { getAnInput+(phi) = phi }
-
-private predicate hasAnInput(PhiNode phi1, PhiNode phi2) {
-  definitionCycle(phi1) and
-  definitionCycle(phi2) and
-  getAnInput(phi1) = phi2
+private predicate sccEdge(PhiNode phi1, PhiNode phi2) {
+  getAnInput(phi1) = phi2 and getAnInput+(phi2) = phi1
 }
 
-private module PhiCycleEquivalence = QlBuiltins::EquivalenceRelation<PhiNode, hasAnInput/2>;
+private module PhiCycleEquivalence = QlBuiltins::EquivalenceRelation<PhiNode, sccEdge/2>;
 
 private PhiCycle getCycle(PhiNode phi) { result.getAPhiNode() = phi }
 

cpp/ql/test/library-tests/dataflow/certain/test.cpp

@@ -67,11 +67,11 @@ void test(int x, bool b1, bool b2) { // $ certain="SSA def(&x)" certain="SSA def
   int* p = &x; // $ certain="SSA def(&p)" certain="SSA def(p)" certain="SSA def(*p)" 
   int i = 0; // $ certain="SSA def(&i)" certain="SSA def(i)"
   int j = 0; // $ certain="SSA def(&j)" certain="SSA def(j)"
-  while (i < 10) { // $ certain="SSA phi(i)" uncertain="SSA phi(*p)"
+  while (i < 10) { // $ certain="SSA phi(i)" certain="SSA phi(*p)"
   if (b1) {
     *p = 0; // $ certain="SSA def(*p)" 
   }
-  ++i; // $ certain="SSA def(i)" uncertain="SSA phi(*p)"
+  ++i; // $ certain="SSA def(i)" certain="SSA phi(*p)"
   }
   while (j < 10) { // $ uncertain="SSA phi(*p)" certain="SSA phi(j)"
     if (b2) {