if (!attr) return false;
  return !attr.getValue().empty();
}

// Returns the predecessors of `op` when `op`'s predecessors are wrapped by
// islands.
llvm::SmallVector<Operation*> IslandPredecessors(Operation* op) {
  llvm::SmallVector<Operation*> predecessors;
  for (Value operand : op->getOperands()) {
    if (Operation* pred = operand.getDefiningOp()) {