[Enhanced Switch] Bug 575652 - [17][codegen][switch pattern] Unnecessary casts in switch

[srikanth-sankaran]

Carried over from bugzilla.

For this code:

import static java.util.stream.IntStream.rangeClosed;

public interface X {
  static String fizzbuzz(int i) {
    return switch((Integer) i) {
      case Integer v when v % 15 == 0 -> "FizzBuzz";
      case Integer v when v % 5 == 0 -> "Buzz";
      case Integer v when v % 3 == 0 -> "Fizz";
      case Integer v -> "" + v;
    };
  }

  static void main(String[] args) {
    rangeClosed(1, 100).mapToObj(i -> fizzbuzz(i)).forEach(System.out::println);
  }
} 

We generate the following bytecode:

  public static java.lang.String fizzbuzz(int);
    descriptor: (I)Ljava/lang/String;
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=6, args_size=1
         0: iload_0
         1: invokestatic  #8                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
         4: dup
         5: invokestatic  #14                 // Method java/util/Objects.requireNonNull:(Ljava/lang/Object;)Ljava/lang/Object;
         8: pop
         9: astore_1
        10: aload_1
        11: iconst_0
        12: invokedynamic #20,  0             // InvokeDynamic #0:typeSwitch:(Ljava/lang/Object;I)I
        17: tableswitch   { // 0 to 3

                       0: 48

                       1: 76

                       2: 103

                       3: 132
                 default: 132
            }
        48: aload_1
        49: checkcast     #9                  // class java/lang/Integer
        52: astore_2
        53: aload_2
        54: invokevirtual #24                 // Method java/lang/Integer.intValue:()I
        57: bipush        15
        59: irem
        60: ifne          66
        63: goto          71
        66: aload_1
        67: iconst_1
        68: goto          12
        71: ldc           #28                 // String FizzBuzz
        73: goto          145
        76: aload_1
        77: checkcast     #9                  // class java/lang/Integer
        80: astore_3
        81: aload_3
        82: invokevirtual #24                 // Method java/lang/Integer.intValue:()I
        85: iconst_5
        86: irem
        87: ifne          93
        90: goto          98
        93: aload_1
        94: iconst_2
        95: goto          12
        98: ldc           #30                 // String Buzz
       100: goto          145
       103: aload_1
       104: checkcast     #9                  // class java/lang/Integer
       107: astore        4
       109: aload         4
       111: invokevirtual #24                 // Method java/lang/Integer.intValue:()I
       114: iconst_3
       115: irem
       116: ifne          122
       119: goto          127
       122: aload_1
       123: iconst_3
       124: goto          12
       127: ldc           #32                 // String Fizz
       129: goto          145
       132: aload_1
       133: astore        5
       135: aload         5
       137: invokestatic  #34                 // Method java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String;
       140: invokedynamic #39,  0             // InvokeDynamic #1:makeConcatWithConstants:(Ljava/lang/String;)Ljava/lang/String;
       145: areturn

The three instances of checkcast #9 are redundant