[Enhanced Switch] Wasteful generation of switch ordinal mapping table for enum switches that are dispatched via enumSwitch indy

[srikanth-sankaran]

Found by code inspection and white box testing:

Consider the following program:

enum E {
	A,
	B,
}

public class X {
	public static void main(String[] args) {
		E e = E.A;
		switch (e) {
			case A :    System.out.println("A"); 
					    break;
			case B:     System.out.println("B");
			            break;
			case null : System.out.println("null");
						break;
		}		
	}
} 

Code produced by ECJ on master/HEAD contains the field $SWITCH_TABLE$E and the method $SWITCH_TABLE$E() which are not needed for an enhanced switch which will use indy enumSwitch bootstrap method to switch.

private static volatile int[] $SWITCH_TABLE$E;
    descriptor: [I
    flags: (0x104a) ACC_PRIVATE, ACC_STATIC, ACC_VOLATILE, ACC_SYNTHETIC

  static int[] $SWITCH_TABLE$E();
    descriptor: ()[I
    flags: (0x1008) ACC_STATIC, ACC_SYNTHETIC
    Code:
      stack=3, locals=1, args_size=0
         0: getstatic     #55                 // Field $SWITCH_TABLE$E:[I
         3: dup
         4: ifnull        8
         7: areturn
         8: pop
         9: invokestatic  #57                 // Method E.values:()[LE;
        12: arraylength
        13: newarray       int
        15: astore_0
        16: aload_0
        17: getstatic     #18                 // Field E.A:LE;
        20: invokevirtual #61                 // Method E.ordinal:()I
        23: iconst_1
        24: iastore
        25: goto          29
        28: pop
        29: aload_0
        30: getstatic     #65                 // Field E.B:LE;
        33: invokevirtual #61                 // Method E.ordinal:()I
        36: iconst_2
        37: iastore
        38: goto          42
        41: pop
        42: aload_0
        43: dup
        44: putstatic     #55                 // Field $SWITCH_TABLE$E:[I
        47: areturn
      Exception table:
         from    to  target type
            16    25    28   Class java/lang/NoSuchFieldError
            29    38    41   Class java/lang/NoSuchFieldError
      LineNumberTable:
        line 6: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
      StackMapTable: number_of_entries = 5
        frame_type = 72 /* same_locals_1_stack_item */
          stack = [ class "[I" ]
        frame_type = 255 /* full_frame */
          offset_delta = 19
          locals = [ class "[I" ]
          stack = [ class java/lang/NoSuchFieldError ]
        frame_type = 0 /* same */
        frame_type = 75 /* same_locals_1_stack_item */
          stack = [ class java/lang/NoSuchFieldError ]
        frame_type = 0 /* same */
}

[srikanth-sankaran]

Javac from JDK23 does better by suppressing its version of the synthetic mapping table Field X$1.$SwitchMap$E