Fixes #82

PrunedCFG had been changed to always include an entry and exit node.
The logic for detecting an "empty" ExceptionPrunedCFG inside the PDG
construction code had not been updated appropriately.

.gitignore

@@ -26,6 +26,7 @@ com.ibm.wala.cast.js/lib/
 com.ibm.wala.core.testdata/*.jar
 com.ibm.wala.core.testdata/@dot/
 com.ibm.wala.core.testdata/lib/
+com.ibm.wala.core.testdata/ocaml/
 com.ibm.wala.core.tests/dat/wala.examples.properties
 com.ibm.wala.core.tests/report
 com.ibm.wala.core/@dot

com.ibm.wala.core.testdata/src/slice/JustThrow.java

@@ -0,0 +1,18 @@
+package slice;
+
+import java.io.IOException;
+
+public class JustThrow {
+  
+  private static int throwException() {
+    throw new RuntimeException();
+  }
+    public static void main(String[] argv) throws IOException{
+      doNothing(throwException());
+    }
+    
+    private static void doNothing(int x) {
+
+    }
+
+}

com.ibm.wala.core.tests/src/com/ibm/wala/core/tests/slicer/SlicerTest.java

@@ -692,6 +692,28 @@ public class SlicerTest {
     GraphIntegrity.check(sdg);
   }
 
+  @Test
+  public void testJustThrow() throws ClassHierarchyException, IllegalArgumentException, CancelException, IOException, UnsoundGraphException {
+    AnalysisScope scope = findOrCreateAnalysisScope();
+
+    IClassHierarchy cha = findOrCreateCHA(scope);
+    Iterable<Entrypoint> entrypoints = com.ibm.wala.ipa.callgraph.impl.Util.makeMainEntrypoints(scope, cha,
+        TestConstants.SLICE_JUSTTHROW);
+    AnalysisOptions options = CallGraphTestUtil.makeAnalysisOptions(scope, entrypoints);
+
+    CallGraphBuilder builder = Util.makeZeroOneCFABuilder(options, new AnalysisCache(), cha, scope);
+    CallGraph cg = builder.makeCallGraph(options, null);
+
+    CGNode main = findMainMethod(cg);
+
+    Statement s = findCallToDoNothing(main);
+    System.err.println("Statement: " + s);
+
+    Collection<Statement> slice = Slicer.computeBackwardSlice(s, cg, builder.getPointerAnalysis(), DataDependenceOptions.FULL,
+        ControlDependenceOptions.NO_EXCEPTIONAL_EDGES);
+    dumpSlice(slice);
+  }
+
   public static int countAllocations(Collection<Statement> slice) {
     int count = 0;
     for (Statement s : slice) {

com.ibm.wala.core.tests/src/com/ibm/wala/core/tests/util/TestConstants.java

@@ -139,4 +139,6 @@ public interface TestConstants {
 
   public final static String SLICE_TESTINETADDR = "Lslice/TestInetAddr";
 
+  public final static String SLICE_JUSTTHROW = "Lslice/JustThrow";
+
 }

com.ibm.wala.core/src/com/ibm/wala/ipa/cfg/PrunedCFG.java

@@ -289,10 +289,8 @@ public class PrunedCFG<I, T extends IBasicBlock<I>> extends AbstractNumberedGrap
     Set<T> reachable = DFS.getReachableNodes(temp, Collections.singleton(cfg.entry()));
     Set<T> back = DFS.getReachableNodes(GraphInverter.invert(temp), Collections.singleton(cfg.exit()));
     reachable.retainAll(back);
-/** BEGIN Custom change: entry and exit in every cfg */
     reachable.add(cfg.entry());
     reachable.add(cfg.exit());
-/** END Custom change: entry and exit in every cfg */
         
     this.nodes = new FilteredNodes<T>(cfg, reachable);
     this.edges = new FilteredCFGEdges<I, T>(cfg, nodes, filter);

com.ibm.wala.core/src/com/ibm/wala/ipa/slicer/PDG.java

@@ -28,6 +28,7 @@ import com.ibm.wala.ipa.callgraph.propagation.InstanceKey;
 import com.ibm.wala.ipa.callgraph.propagation.PointerAnalysis;
 import com.ibm.wala.ipa.callgraph.propagation.PointerKey;
 import com.ibm.wala.ipa.cfg.ExceptionPrunedCFG;
+import com.ibm.wala.ipa.cfg.PrunedCFG;
 import com.ibm.wala.ipa.modref.DelegatingExtendedHeapModel;
 import com.ibm.wala.ipa.modref.ExtendedHeapModel;
 import com.ibm.wala.ipa.modref.ModRef;
@@ -62,6 +63,7 @@ import com.ibm.wala.util.collections.MapUtil;
 import com.ibm.wala.util.config.SetOfClasses;
 import com.ibm.wala.util.debug.Assertions;
 import com.ibm.wala.util.debug.UnimplementedError;
+import com.ibm.wala.util.graph.GraphUtil;
 import com.ibm.wala.util.graph.NumberedGraph;
 import com.ibm.wala.util.graph.dominators.Dominators;
 import com.ibm.wala.util.graph.labeled.SlowSparseNumberedLabeledGraph;
@@ -233,14 +235,18 @@ public class PDG implements NumberedGraph<Statement> {
     }
     ControlFlowGraph<SSAInstruction, ISSABasicBlock> controlFlowGraph = ir.getControlFlowGraph();
     if (cOptions.equals(ControlDependenceOptions.NO_EXCEPTIONAL_EDGES)) {
-      controlFlowGraph = ExceptionPrunedCFG.make(controlFlowGraph);
-      // In case the CFG has no nodes left because the only control dependencies
-      // were
-      // exceptional, simply return because at this point there are no nodes.
+      PrunedCFG<SSAInstruction, ISSABasicBlock> prunedCFG = ExceptionPrunedCFG.make(controlFlowGraph);
+      // In case the CFG has only the entry and exit nodes left 
+      // and no edges because the only control dependencies
+      // were exceptional, simply return because at this point there are no nodes.
       // Otherwise, later this may raise an Exception.
-      if (controlFlowGraph.getNumberOfNodes() == 0) {
+      if (prunedCFG.getNumberOfNodes() == 2 
+          && prunedCFG.containsNode(controlFlowGraph.entry()) 
+          && prunedCFG.containsNode(controlFlowGraph.exit())
+          && GraphUtil.countEdges(prunedCFG) == 0) {
         return;
       }
+      controlFlowGraph = prunedCFG;
     } else {
       Assertions.productionAssertion(cOptions.equals(ControlDependenceOptions.FULL));
     }

com.ibm.wala.util/src/com/ibm/wala/util/graph/dominators/DominanceFrontiers.java

@@ -47,7 +47,11 @@ public class DominanceFrontiers<T> {
   }
 
   public Iterator<T> getDominanceFrontier(T n) {
-    return DF.get(n).iterator();
+    Set<T> frontier = DF.get(n);
+    if (frontier == null) {
+      throw new IllegalArgumentException("no dominance frontier for node " + n);
+    }
+    return frontier.iterator();
   }
 
   public boolean isDominatedBy(T node, T master) {