//
//	   b        b           b       b
//	\ / \ /    | \  /    \ / |     | |
//	 s0  s1    |  s1      s0 |     | |
//	  \ /      | /         \ |     | |
//	   ss      ss           ss      ss
//
// If all Phi ops in ss have identical variables for slots corresponding to
// s0, s1 and b then the branch can be dropped.
// This optimization often comes up in switch statements with multiple
// expressions in a case clause:
//

// 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