Missing CHECKCAST before unboxing conversion in assignment

ExtendJ 8.1.0-1-g87f5bbc Java SE 8

The following test generates incorrect bytecode:

// Test that Integer unboxing works in runtime.
import java.util.*;

public class Test {
  public static void main(String[] args) {
    Stack<Integer> stack = new Stack<Integer>();
    stack.push(10);
    stack.push(-20);
    stack.push(50);
    stack.pop();
    System.out.println(peek(stack));
  }

  static int peek(Stack<Integer> stack) {
    int res = 0;
    res += stack.peek(); // Conversion: Integer -> int.
    return res;
  }
}

Here is the generated bytecode for the peek method:

  static int peek(java.util.Stack<java.lang.Integer>);
    flags: ACC_STATIC
    Code:
      stack=2, locals=3, args_size=1
         0: iconst_0
         1: istore_2
         2: iload_2
         3: aload_0
         4: invokevirtual #57                 // Method java/util/Stack.peek:()Ljava/lang/Object;
         7: invokevirtual #61                 // Method java/lang/Integer.intValue:()I
        10: iadd
        11: istore_2
        12: iload_2
        13: ireturn

There should be a CHECKCAST before the call to Integer.intValue().

Expected result: the bytecode should be executable.

Actual result: the compiled program fails to run with this error message:

    [junit] [FAIL] runTest[generics/autoboxing_02p](tests.extendj.TestJava7)
    [junit] Error output files differ expected:<[]> but was:<[Error: A JNI error has occurred, please check your installation and try again
    [junit] Exception in thread "main" java.lang.VerifyError: Bad type on operand stack
    [junit] Exception Details:
    [junit]   Location:
    [junit]     Test.peek(Ljava/util/Stack;)I @7: invokevirtual
    [junit]   Reason:
    [junit]     Type 'java/lang/Object' (current frame, stack[1]) is not assignable to 'java/lang/Integer'

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