default instrumentation flag, -Cllvm-args=-sanitizer-coverage-trace-compares, seems to add needless overhead

[0xalpharush]

Is there any value in using trace-cmp without -use_value_profile=1? I ask bc cargo fuzz seems to add this instrumentation by default but libfuzzer's value profile is disabled by default. IIUC but this should be mutually enabled or disabled.

If my understanding is correct, would a PR be accepted to disable this by default?

[nagisa]

There is definitely a lot of improvement that's possible to how fuzz targets are built and run. Most of what we have today is very close to what we figured out on day 1 and the fuzzing ecosystem has had a lot of time to change since.

It would be interesting to see actual examples of how coverage changes without either flag, with just the instrumentation & with both options enabled, though.