Benchmark some large program that isn't carefully tuned by using strictness in just the right places (like our core libraries tend to be), to make sure this change doesn't hurt performance there. I nomiate GHC as the candidate program for this test.
Here are the nofib compile times of unmodified GHC vs GHC compiled with -funbox-strict-fields:
-1 s.d. ----- -3.3%
+1 s.d. ----- +2.5%
Average ----- -0.4%
(I compiled GHC by adding the flag to GhcStage2HcOpts and GhcLibHcOpts.)
I can't tell if this is noise or not. At least the compile times seem to have gone down every so slightly.
With these three tests out of the way, are people happy with me turning on the flag by default for the 7.8 release?