How about the following: 1) Default warnings are cheap, and work fine at -O0.
2) Expensive warnings (-Wall, -Warray-bounds, -Wuninitialized, -Wunused) [not sure about the actual list] that require optimizations, will issue a Warning when they are requested, but the appropriate optimization level has not been asserted, that is required for those warnings to work in their maximal fashion. Or: Specification of the expensive warnings will cause appropriate control flow computations that are required to support those warning levels. (as suggested previously)
