synth_ice40: split map_gates off fine

[whitequark]

I am currently looking at some optimizations to be done on iCE40 that would run on the coarse-grain cells. In this case it is very useful to me to be able to stop synthesis before all arch-dependent transformations, but after all arch-independent optimizations have already been done. I.e. see and affect the state just before techmapping, and restart afterwards.

Feel free to close this PR if this is not something desirable, or tell me to also implement this for other synth_* commands.

[cliffordwolf]

Feel free to close this PR if this is not something desirable, or tell me to also implement this for other synth_* commands.

LGTM.

The only thing I'm unsure about is re keeping the name fine for the last pre-map block. For the generic synth command it makes sense to have a corase and fine block. But for the others most of fine has been converted into various map_* blocks and now for them fine is just just the things run between the coarse synthesis stuff an mapping.

Now the name fine is essentially a copy&paste artifact, not a reasonable name for most synth_* commands.

What do you think about renaming fine to something like premap, or maybe simply map as it is the start of the mapping phase?

[whitequark]

What do you think about renaming fine to something like premap, or maybe simply map as it is the start of the mapping phase?

I think map sounds good! I assume you'll make that change?

[cliffordwolf]

Renamed synch_ice40 fine to map in 5fa5dbb.