Multiple resumption misoptimization

[jiribenes]

The following program discovered by @timsueberkrueb prints something different when ran with optimisations than without:

effect flip(): Bool
effect choice(): Bool

def main() = {
  try {
    val x = do choice()
    val y = do choice()
    println(x.show ++ " " ++ y.show)
  } with choice {
    try {
      resume(do flip())
    } with flip {
      resume(true)
      resume(false)
    }
  }
}

~>

$ effekt --backend=js --no-optimize hello.effekt
true true
true false
false true
false false

$ effekt --backend=js hello.effekt
false false

[timsueberkrueb]

The following program works as expected with and without optimizations:

effect flip(): Bool
effect choice(): Bool

def main() = {
  try {
    try {
      val x = do choice()
      val y = do choice()
      println(x.show ++ " " ++ y.show)
    } with choice {
      resume(do flip())
    }
  } with flip {
    resume(true)
    resume(false)
  }
}

The only difference here is that flip is handled in the outer scope.

[jiribenes]

The optimised IR of the program in the issue description looks like:

def main() = {
  val x: Bool = reset { {p1} => 
    shift(p1) { {k1} => 
      val _1: Unit = resume(k1) { return true };

      resume(k1) {
        return false
      }
    }
  };
  val y: Bool = reset { {p2} => 
    shift(p2) { {k2} => 
      val _2: Unit = resume(k2) { return true };

      resume(k2) {
        return false
      }
    }
  };
  val v_r_left: String = if (x) { return "true" } else { return "false" };
  val v_r_right: String = if (y) { return "true" } else { return "false" };

  let tmp = println(infixConcat(infixConcat(v_r_left, " "), v_r_right))
  return tmp
}