Optimize is currently missing the elimination of "double not"

[timsherwood]

The pyrtl.optimize code is not eliminating "double not" conditions (reducing them to a single wire). Right now it does some more complex optimizations including CSE but this very simple case gets missed. You can see very clearly from the code below.

import pyrtl

a = pyrtl.Input(1,'a')
q = pyrtl.Output(1,'q')
q <<= ~(~(a))

pyrtl.synthesize()

with open('pre-optimize.svg','w') as f:
    pyrtl.output_to_svg(f)

pyrtl.optimize()

with open('post-optimize.svg','w') as f:
    pyrtl.output_to_svg(f)