Maybe put a tainted flag in it that causes the linker or runtime to fail? Then don't open source or release the modifications to allow the linker/runtime to avoid that failure check and refuse to let anyone check in a "fix" that allows this check to be skipped to an official build...
This surely seems like an incredibly important cost. Surely it's worth doing a bit of ugly magic to be able to keep track of it persistently.
Thanks to both of you for the insightful discussion. A flag would be helpful for testing, but it's true that if it's there, it will be used. Still, this can be tracked as part of a CI system by keeping around a patch for disabling bounds checks and regularly building and benchmarking a patched version. Less nice, but should get the job done.
This surely seems like an incredibly important cost. Surely it's worth doing a bit of ugly magic to be able to keep track of it persistently.