fix issues with the java bytecode frontend

shared-test-resources/miniTestSuite/java6/source/LocalMerging.java

@@ -0,0 +1,33 @@
+public class LocalMerging {
+    public void localMergingWithConstant(int n) {
+        String a = "one";
+        // The branch returns either a local or a constant.
+        // Because of the divergence neither `a` nor `"two"` should be inlined,
+        // but a stack local variable should be created for holding the result of the branch.
+        System.out.println(n == 1 ? a : "two");
+    }
+
+    public void localMergingWithOtherLocal(int n) {
+        String a = "one";
+        String b = "two";
+        // The branch returns either a local or a different local.
+        // Because of the divergence neither `a` nor `b` should be inlined,
+        // but a stack local variable should be created for holding the result of the branch.
+        System.out.println(n == 1 ? a : b);
+    }
+
+    public void localMergingWithDuplicateValue(int n) {
+        String a = "one";
+        // One of the branches for the first argument contains the constant "two"
+        // and the second argument also contains the constant "two".
+        // This test ensures that when the first argument gets replaced by a stack local,
+        // the second argument isn't replaced as well.
+        System.setProperty(n == 1 ? a : "two", "two");
+    }
+
+    public void localMergingWithInlining(int n) {
+        String[] arr = new String[] {"a", "b"};
+        int a = 1;
+        String b = arr[n == 1 ? 0 : a];
+    }
+}

sootup.core/src/main/java/sootup/core/jimple/visitor/ReplaceUseStmtVisitor.java

@@ -71,6 +71,8 @@ public void caseInvokeStmt(@Nonnull JInvokeStmt stmt) {
 
   @Override
   public void caseAssignStmt(@Nonnull JAssignStmt stmt) {
+    // fall back to the original statement when none of the cases set a result
+    setResult(stmt);
 
     // uses on the def side.. e.g. a base in an JArrayRef but NOT with a simple Local!
     final Value leftOp = stmt.getLeftOp();
@@ -106,8 +108,6 @@ public void caseAssignStmt(@Nonnull JAssignStmt stmt) {
       if (exprVisitor.getResult() != rValue) {
         setResult(stmt.withRValue(exprVisitor.getResult()));
       }
-    } else {
-      setResult(stmt);
     }
   }