...
Assuming a comforming implementation, eliminating diagnostic messages will eliminate any violation of syntax rules or other constraints.
Exceptions
On many compilers, the highest warning levels produces diagnostic messages for perfectly legitimate, reasonable code, just because that code has a feature that worries the compiler, which isn't smart enough to figure out why the worry is unnecessary. This is permitted by C99 which allows a compiler to produce a diagnostic for any reason it wants.
Priority: P12 Level: L1
Eliminating violations of syntax rules and other constraints can eliminate serious software vulnerabilities that can lead to the execution of arbitrary code with the permissions of the vulnerable process.
...