Bug 190209

Description Olivier Thomann 2007-05-31 09:20:17 EDT

Using v_766, in some cases exception handlers are optimized out, but the corresponding finally or catch blocks are still generated.
This leads to dead bytecodes.

1) The following example leads to unreachable bytecodes from pc 10 to 17.

public class X {
	final int i;
	X() {
	    try {
			return; // intervening finally assigns i
	    } finally {
			i = 1;
	    }
	}
	public static void main(String[] args) { 
		System.out.println("OK"); 
	} 
}

  X();
     0  aload_0 [this]
     1  invokespecial Object() [10]
     4  aload_0 [this]
     5  iconst_1
     6  putfield X.i : int [12]
     9  return
    10  astore_1
    11  aload_0 [this]
    12  iconst_1
    13  putfield X.i : int [12]
    16  aload_1
    17  athrow
      Line numbers:
        [pc: 0, line: 3]
        [pc: 4, line: 7]
        [pc: 9, line: 5]
        [pc: 10, line: 6]
        [pc: 11, line: 7]
        [pc: 16, line: 8]
      Local variable table:
        [pc: 0, pc: 18] local: this index: 0 type: X
      Stack map table: number of frames 1
        [pc: 10, full, stack: {Throwable}, locals: {X}]

The finally block should not be generated or the exception handler should not be optimized out.

2) final public class X
{
    final class MyClass
    {
        void method1(final String s)
        {
        }
    }

    Object method1()
    {
        try
        {
            final MyClass myClass = null;

            try
            {
                return null;
            }
            catch (final Throwable ex)
            {
                myClass.method1(this == null ? "" : "");
            }

            return null;
        }
        finally
        {
            {
            }
        }
    }
    public static void main(String[] args) {
		System.out.print("SUCCESS");
	}
}

In this case the problem comes from the catch block.

  // Method descriptor #15 ()Ljava/lang/Object;
  // Stack: 2, Locals: 3
  Object method1();
     0  aconst_null
     1  astore_1 [myClass]
     2  aconst_null
     3  areturn
     4  pop
     5  aload_1 [myClass]
     6  aload_0 [this]
     7  ifnonnull 15
    10  ldc <String ""> [16]
    12  goto 17
    15  ldc <String ""> [16]
    17  invokevirtual X$MyClass.method1(String) : void [18]
    20  aconst_null
    21  areturn
    22  astore_2
    23  aload_2
    24  athrow
      Exception Table:
        [pc: 0, pc: 2] -> 22 when : any
        [pc: 4, pc: 20] -> 22 when : any
      Line numbers:
        [pc: 0, line: 14]
        [pc: 2, line: 18]
        [pc: 4, line: 20]
        [pc: 5, line: 22]
        [pc: 20, line: 25]
        [pc: 22, line: 28]
        [pc: 23, line: 31]
      Local variable table:
        [pc: 0, pc: 25] local: this index: 0 type: X
        [pc: 2, pc: 22] local: myClass index: 1 type: MyClass
      Stack map table: number of frames 5
        [pc: 4, full, stack: {Throwable}, locals: {X, X$MyClass}]
        [pc: 15, same_locals_1_stack_item, stack: {X$MyClass}]
        [pc: 17, full, stack: {X$MyClass, String}, locals: {X, X$MyClass}]
        [pc: 20, same]
        [pc: 22, full, stack: {Throwable}, locals: {X}]

Bytecodes from 4 to 21 are unreachable because the exception handler for the catch block has been optimized out.