I don't think compilers consider undefined behavior a license to kill; I think the problem is genuinely hard. The priciple of explosion[1] tells us that any wro

I don't think compilers consider undefined behavior a license to kill; I think the problem is genuinely hard. The priciple of explosion[1] tells us that any wrong assumption, even the most innocuous looking, can lead to an unboundedly wrong conclusion. The more complex your graph of logical deductions, the worse the problem gets (and good optimizations require a lot of complex logic). It may be possible to limit the bad effects of faulty assumptions by being very careful about how deductions propogate from unreliable assumptions. However it's certainly not easy, especially without throwing out all optimizations that interact with a potentially undefined operation. It is possible to design a languge such that a compiler doesn't need to make assumptions to perform optimizations, if programs are required to give enough information to compilers that they can statically prove properties they need to perform optimizations. But C and C++ are not designed that way, and it can't easily be retrofitted on top of them. [1]: https://en.wikipedia.org/wiki/Principle_of_explosion https://en.wikipedia.org/wiki/Principle_of_explosion