Slicing algo implementation

[XiangyuG]

Implement program slicing algo to speed up synthesis including spec slicing, input packet field slicing and gradual search of grid size.

1. spec slicing: assert (program(x) == pipeline(x)) --> assert(program(x).pkt_1 == pipeline(x).pkt_1 ) + assert(program(x).pkt_2 == pipeline(x).pkt_2 ) + assert(program(x).state_1 == pipeline(x).state_1 )

2. input packet field slicing: specify which packet field have influence the output of our sliced assert

3. gradual search of grid size: search from 1*(min # of alu per stage) to the full grid_size