Fix UnconditionalBranchFolder breaking code

When a goto referenced a goto, which was touched by the condition inversion of
UnconditionalBranchFolder, that goto would not be updated.
Therefore, the other references to the goto point to the wrong effects of the
wrong if branch after the optimization.

src/main/java/soot/jimple/BranchableStmt.java

@@ -0,0 +1,12 @@
+package soot.jimple;
+
+import soot.Unit;
+import soot.UnitBox;
+
+public interface BranchableStmt extends Stmt {
+  public Unit getTarget();
+
+  public void setTarget(Unit target);
+
+  public UnitBox getTargetBox();
+}

src/main/java/soot/jimple/GotoStmt.java

@@ -25,7 +25,7 @@
 import soot.Unit;
 import soot.UnitBox;
 
-public interface GotoStmt extends Stmt {
+public interface GotoStmt extends BranchableStmt {
   public Unit getTarget();
 
   public void setTarget(Unit target);

src/main/java/soot/jimple/internal/JIfStmt.java

@@ -34,6 +34,7 @@
 import soot.baf.Baf;
 import soot.jimple.AbstractJimpleValueSwitch;
 import soot.jimple.BinopExpr;
+import soot.jimple.BranchableStmt;
 import soot.jimple.ConvertToBaf;
 import soot.jimple.EqExpr;
 import soot.jimple.GeExpr;
@@ -50,7 +51,7 @@
 import soot.jimple.StmtSwitch;
 import soot.util.Switch;
 
-public class JIfStmt extends AbstractStmt implements IfStmt {
+public class JIfStmt extends AbstractStmt implements IfStmt, BranchableStmt {
 
   protected final ValueBox conditionBox;
   protected final UnitBox targetBox;

src/main/java/soot/jimple/toolkits/scalar/UnconditionalBranchFolder.java

@@ -39,6 +39,7 @@
 import soot.Unit;
 import soot.UnitBox;
 import soot.Value;
+import soot.jimple.BranchableStmt;
 import soot.jimple.ConditionExpr;
 import soot.jimple.GotoStmt;
 import soot.jimple.IfStmt;
@@ -213,6 +214,37 @@ public Result transform() {
                   succAsGoto.setTarget(ifTarget);
                   stmtAsIfStmt.setTarget(gotoTarget);
                   ifTarget = gotoTarget;
+                  // We need to check whether anyone has a goto to the "goto X", because this no has to also go
+                  // to Y
+
+                  // If we wouldn't do that, we would e.g. go from
+                  // if $i0 == 6 goto label04;
+                  // label03:
+                  // goto label21;
+                  // ...
+                  // goto label3;
+
+                  // to
+                  // if $i0 != 6 goto label21;
+                  // label03:
+                  // goto label04;
+                  // label04:
+                  // ...
+                  // goto label03;
+                  // this would alter the semantics, since the previous go-tos now go to the other branch!
+                  if (!succAsGoto.getBoxesPointingToThis().isEmpty()) {
+                    // we cannot simply use getBoxesPointingToThis, because we do not want to update
+                    // trap references
+                    for (Unit i : units) {
+                      if (i instanceof BranchableStmt) {
+                        BranchableStmt b = (BranchableStmt) i;
+                        if (b.getTarget() == succAsGoto) {
+                          b.setTarget(gotoTarget);
+                        }
+                      }
+                    }
+                  }
+
                   // NOTE: No need to remove the goto [successor] because it
                   // is processed by the next iteration of the main loop.
                   // NOTE: Nothing is removed here, it is a simple refactoring.