With CL 190599, along with what we do in greyobject, we ensure
that we only mark allocated heap objects. As a result we can be
more strict in GC:
- Enable "sweep increased allocation count" check, which checks
that the number of mark bits set are no more than the number of
allocation bits.
- Enable invalid pointer check on heap scan. We only trace
allocated heap objects, which should not contain invalid
pointer.
This also makes the libgo runtime more convergent with the gc
runtime.
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/190797
From-SVN: r274678
4f6bdb08ba