Hang in nextpnr-ice40 sa placer for SmolDVI design

[MichaelBell]

Building the example design for Icebrekaer from this repo https://github.com/Wren6991/SmolDVI, but using -abc 9 -device u as options to yosys, I see nextpnr hang on maybe 20% of runs.

This is a repro case:
nextpnr-ice40 --placer sa --up5k --package sg48 --pcf smoldvi_icebreaker.pcf --json smoldvi_icebreaker.json --asc smoldvi_icebreaker.asc --pre-pack smoldvi_icebreaker_prepack.py --timing-allow-fail --quiet --log pnr.log --seed 715589835
repro.zip

[gatecat]

I'll look into this, but in a meantime is removing --placer sa and using the default HeAP placer a workaround for now? There should be relatively few cases where SA is actually giving better performance now, and some of those should perhaps really be dealt with by HeAP improvements.

[MichaelBell]

SA does seem to help a little, this is trying to meet timing for HDMI (and failing, but only fractionally with a good seed).