[core] Unreachable code due to unnecessary breaks

[nitram84]

Issue details

This sample, compiled with openjdk8, decompiles to unreachable code:

public class UnreachableBreakTest {

    public void unreachableBreak(int i, boolean b1, boolean b2) {
      switch (i) {
        case 0:
          if (b1 && b2) {
            doSomething(1);
            // no break here;
          } else {
            doSomething(2);
            // no break here;
          }
          break;
        default:
          doSomething(0);
          break;
      }
    }

    private void doSomething(int i) {
    }
}

decompiles to:

public class UnreachableBreakTest {
    public void unreachableBreak(int i, boolean b1, boolean b2) {
        switch (i) {
            case 0:
                if (b1 && b2) {
                    doSomething(1);
                    break;
                } else {
                    doSomething(2);
                    break;
                }
                break; // <-- unreachable code
            default:
                doSomething(0);
                break;
        }
    }

    private void doSomething(int i) {
    }
}

Relevant log output or stacktrace

Provide sample and class/method full name

No response

Jadx version

1.5.3, latest git

[skylot]

@nitram84 I commit a fix. I decided to change approach of handling switch break, so this change may be a little unstable, hope you can check it 🙂
Some details: previous approach was to insert break if needed, but it was hard to calculate correct places, mostly because it requires to compare blocks CFG and regions structure. New approach insert break at all places with jump/exit edges early at region maker, and later, in new visitor, apply optimization such as: common code extraction and remove if unreachable. This allows to work only with regions in second visitor and make it easier to understand and maintain.

[nitram84]

Thank you very much. It looks better now. But I think we need more unit tests. I rechecked my samples and found another case:

public class UnreachableBreakTest2 {

  public void doSomething(int i, boolean b1, boolean b2, boolean b3) {
    switch (i) {
      case 0:
        if (b1 == b2) {
          doSomething(1);
          break;
        } else if (b1 == b3) {
          doSomething(2);
          break;
        }
        break;
      default:
        doSomething(3);
        break;
    }
  }

  public void doSomething(int i) {}
}

After your commit jadx generates:

public class UnreachableBreakTest2 {
    public void doSomething(int i, boolean b1, boolean b2, boolean b3) {
        switch (i) {
            case 0:
                if (b1 == b2) {
                    doSomething(1);
                    break;
                } else {
                    if (b1 == b3) {
                        doSomething(2);
                    }
                    break;
                }
                break; // <-- unreachable code here
            default:
                doSomething(3);
                break;
        }
    }

    public void doSomething(int i) {
    }
}

[skylot]

and found another case

@nitram84 fixed, thank you for test case 👍