To me the stupid thing is the abuse of undefined behavior for changing the semantic of the code. The fact that a behavior is not defined in the standard doesn't

To me the stupid thing is the abuse of undefined behavior for changing the semantic of the code. The fact that a behavior is not defined in the standard doesn't mean that on a particular hardware platform it doesn't have a particular meaning (and most C programs doesn't need to be portable, since C it's mainly used for embedded these days and thus you are targeting a particular microcontroller/SOC). These optimizations leave for C++ folks. C doesn't need all of that, just leave it as the "high level assembler" that it was in the old days, where if I write an instruction I can picture the assembler output in my mind. Optimizers should not change the code semantics to me. Unfortunately with gcc it's impossible to rely on optimizations, so the only safe option is to turn them off entirely (-O0).