The compiler does not necesarily dictate what is valid c++. If code doesn't work with optimizations enabled, it could either be a bug in the code where its expe

The compiler does not necesarily dictate what is valid c++. If code doesn't work with optimizations enabled, it could either be a bug in the code where its expectations coincided with the compiler's behaviour on something that is undefined in the language when optimizations were turned off or it could be a bug in the compiler where it applied the optimizations incorrectly. There is no "invalid C++, but valid C++-noX-noY-noZ". It's one or the other. The former is a bug in the code; the latter is a bug in the compiler.