RFR: 8314226: Series of colon-style fallthrough switch cases with guards compiled incorrectly

[Aggelos Biboudis]

The `switch` structure is translated in `handleSwitch` where we rewrite pattern matching switches. In some occasions a switch has multiple cases with multiple patterns where the n-th case does not complete normally and falls through to the n+1-st case:


switch (obj) {
   case Integer _ when ((Integer) obj) > 0:
   case String _ when !((String) obj).isEmpty():
      return 1;
   default:
      return -1;
}


This PR addresses that by translating the second case correctly and also replicates the body of the latter to the former (which we can do because no bindings are introduced in either statement blocks by the definition of unnamed variables.).

Previously the code was translated into:


switch (java.lang.runtime.SwitchBootstraps.typeSwitch(selector0$temp, index$1)) {
    case 0:
        Integer _;
        if (!(true && ((Integer)obj) > 0)) {
            index$1 = 1;
            continue;
        }

    case 1 when !((String)obj).isEmpty():
        return 1;

    default:
        return -1;
}


This PR adjusts the translation into:


switch (java.lang.runtime.SwitchBootstraps.typeSwitch(selector0$temp, index$1)) {
case 0:
    Integer _;
    if (!(true && ((Integer)obj) > 0)) {
        index$1 = 1;
        continue;
    }
    return 1;

case 1:
    String _;
    if (!((selector0$temp instanceof String || false) && (true && !((String)obj).isEmpty()))) {
        index$1 = 2;
        continue;
    }
    return 1;
}

-------------

Commit messages:
 - 8314226: Series of colon-style fallthrough switch cases with guards compiled incorrectly

Changes: https://git.openjdk.org/jdk/pull/15532/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15532&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314226
  Stats: 105 lines in 2 files changed: 96 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/15532.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15532/head:pull/15532

PR: https://git.openjdk.org/jdk/pull/15532