Java: Move SSA data flow test and extend it to cover phi-read input edges.

java/ql/test/library-tests/dataflow/ssa/A.java

@@ -0,0 +1,24 @@
+public class A {
+  Object source() { return null; }
+  void sink(Object o) { }
+
+  boolean isSafe(Object o) { return o == null; }
+
+  void foo() {
+    Object x = source();
+    if (!isSafe(x)) {
+      x = null;
+    }
+    sink(x);
+
+    x = source();
+    if (!isSafe(x)) {
+      if (isSafe(x)) {
+        sink(x);
+      } else {
+        throw new RuntimeException();
+      }
+    }
+    sink(x);
+  }
+}

java/ql/test/library-tests/dataflow/ssa/test.ql

@@ -0,0 +1,31 @@
+import java
+import semmle.code.java.controlflow.Guards
+import semmle.code.java.dataflow.DataFlow
+
+private predicate isSafe(Guard g, Expr checked, boolean branch) {
+  exists(MethodCall mc | g = mc |
+    mc.getMethod().hasName("isSafe") and
+    checked = mc.getAnArgument() and
+    branch = true
+  )
+}
+
+module TestConfig implements DataFlow::ConfigSig {
+  predicate isSource(DataFlow::Node source) {
+    source.asExpr().(MethodCall).getMethod().hasName("source")
+  }
+
+  predicate isSink(DataFlow::Node sink) {
+    exists(MethodCall mc | mc.getMethod().hasName("sink") and mc.getAnArgument() = sink.asExpr())
+  }
+
+  predicate isBarrier(DataFlow::Node node) {
+    node = DataFlow::BarrierGuard<isSafe/3>::getABarrierNode()
+  }
+}
+
+module Flow = DataFlow::Global<TestConfig>;
+
+from DataFlow::Node source, DataFlow::Node sink
+where Flow::flow(source, sink)
+select source, sink

java/ql/test/library-tests/pattern-switch/dfg/GuardTest.java

@@ -24,13 +24,6 @@ public class GuardTest {
         break;
 
     }
-
-    String s2 = "string";
-
-    if (!isSafe(s2)) {
-      s2 = null;
-    }
-    sink(s2);
   }
 
 }