When making changes that have a large impact on coverage counter creation, this
makes it easier to see whether the number of physical counters has changed.
(The highest counter ID seen in coverage maps is not necessarily the same as
the number of physical counters actually used by the instrumented code, but
it's the best approximation we can get from looking only at the coverage maps,
and it should be reasonably accurate in most cases.)
The tests in this directory are shared by two different test modes, and can be
run in multiple different ways:
./x.py test coverage-map (compiles to LLVM IR and checks coverage mappings)
./x.py test coverage-run (runs a test binary and checks its coverage report)
./x.py test coverage (runs both coverage-map and coverage-run)
Maintenance note
These tests can be sensitive to small changes in MIR spans or MIR control flow,
especially in HIR-to-MIR lowering or MIR optimizations.
If you haven't touched the coverage code directly, and the tests still pass in
coverage-run mode, then it should usually be OK to just re-bless the mappings
as necessary with ./x.py test coverage-map --bless, without worrying too much
about the exact changes.
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