LLVM is a very impressive compiler. I'm really impressed with the warning messages it's able to produce (especially compared with what was available even 2 or

LLVM is a very impressive compiler. I'm really impressed with the warning messages it's able to produce (especially compared with what was available even 2 or 3 years ago). What is more frustrating about modern compilers (and this is not limited to LLVM) is the desire to squeeze out a tiny bit more performance by exploiting undefined behavior. I'm thinking of things like eliminating calls to memset that "don't seem to do anything user-visible," eliminating code based on signed overflow being undefined, and so on. Most of the the undefined behavior that exists in C is there because different machines used to do different things. For example, there used to be non-two's-complement machines. It wasn't put there because C was somehow designed to be hyper-optimized. People who relied on the undefined behavior could legitimately make the same argument that you are now making-- that it worked fine on their machine, which they knew very well. I am curious why nobody has brought up the idea of making memmove as efficiently handled as memset, rather than using undefined behavior here. UB feels like the wrong way to go.