Before

CPU: user 32.61s system 0.28s, MEM: 362.53 MB total, 346.46 MB resident
Yosys 0.8 (git sha1 b003446, clang 7.0.1 -march=x86-64 -mtune=generic -O2 -fno-plt -fPIC -Os)
Time spent: 37% 26x opt_merge (12 sec), 35% 31x opt_expr (11 sec), ...

After placement:
PIOs       13 / 39
PLBs       444 / 660
BRAMs      8 / 30
  place time 17.81s

After

CPU: user 31.40s system 0.28s, MEM: 337.59 MB total, 321.95 MB resident
Yosys 0.8 (git sha1 b003446, clang 7.0.1 -march=x86-64 -mtune=generic -O2 -fno-plt -fPIC -Os)
Time spent: 37% 26x opt_merge (11 sec), 36% 31x opt_expr (11 sec), ...

After placement:
PIOs       13 / 39
PLBs       446 / 660
BRAMs      8 / 30
  place time 18.18s