It should be "C and C++ Implementations" because nothing in the standard requires UB to be exploited for optimization instead of adding run-time checks.
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The standard also doesn't require UB to have run-time checks, which is probably for the goal of performance. There was an implementation in mind when it was designed.
There were C implementations with bounds checking or implementations that trap on use of an invalid pointer or on read of uninitialized variables etc. A large part of UB was introduced for such reasons and not for performance. The standard was (and still is) about allowing a wide range of implementations.