// For example:
// b1:
//
//	(some values)
//
// plain -> b2
// b2: <- b1 b2
// Plain -> b2
//
// Algorithm introduction:
//  1. The start memory state of a block is InitMem, a Phi node of type mem or
//     an incoming memory value.
//  2. The start memory state of a block is consistent with the end memory state
//     of its parent nodes. If the start memory state of a block is a Phi value,