type eqclass []*Value

// partitionValues partitions the values into equivalence classes
// based on having all the following features match:
//   - opcode
//   - type
//   - auxint
//   - aux
//   - nargs
//   - block # if a phi op
//   - first two arg's opcodes and auxint
//   - NOT first two arg's aux; that can break CSE.
//
// partitionValues returns a list of equivalence classes, each