Improve consistency checking for family instances
Several compiler-performance tests got worse when I added the new generic default methods (with Pedro):
T3064: peak_megabytes_allocated 24 is more than maximum allowed 16
IndTypesPerf: needs more than the 20M heap it is given
T4801: max_bytes_used 31.4M is more than maximum allowed 30M
For the first two of these we know exactly why: the (necessarily) eager overlap check is reading interface files that are otherwise not read, becuase of the new
Rep type family instances in
Data.Maybe and so on. Both these tests use type families.
For T4801 it's more mysterious. The test does not use type families, and no new interface files are read, but residency increases. So the cause may be different.
I'm pretty sure we can improve matters by propagating a bit more info; specifically, rather than a module simply saying "I have some type familily instances" it can say "I have type family instances for F, G, H".
I have marked the three tests as expect-broken for now, with the ticket to remind me to get back to it.