solidity/test/libyul/yulOptimizerTests/fullSimplify/signextend.yul

{
  let x := 7
  mstore(0, signextend(50, x))
  let y := 255
  mstore(1, signextend(0, y))
}
// ----
// step: fullSimplify
//
// {
//     {
//         mstore(0, 7)
//         mstore(1, 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff)
//     }
// }