Allegedly the pre and post conditions, in varying degrees of certainty according to the evaluation semantics selected, are propagated to the optimization passes of gcc and llvm. However, I haven’t seen any detailed blog posts or summaries of the effectiveness or reliability of this feature. Sorry it’s not a lot of info, but it was what I knew off hand based on previous reading.

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account42 7 hours ago | parent [-]

But for the most use you'd specifcially want them used for optimizations when they are NOT being evaluated as that's the build where perf matters.

	▲	tsukikage 7 hours ago \| parent [-]
		...yup, looks like there's no way to get the optimisation benefit in "ignore" mode, which is the only mode that doesn't explicitly compile the runtime checks: https://godbolt.org/z/KTx1Pc3aa compare codegen for test3 (the pattern that would be useful) vs test4 (the best we actually have)