Sort of. You're right on what the abstract C++ machine does, but C++ also has the "as if" rule. A compiler can make whatever changes it wants so long as all o

Sort of. You're right on what the abstract C++ machine does, but C++ also has the "as if" rule. A compiler can make whatever changes it wants so long as all observable effects are as if it had generated exactly the program as requested. This is the rule that allows for compiler optimizations to be done. Values stored in memory are not considered to be observable effects, so the compiler is allowed to make whatever changes it wants on that end. However, to the best of my understanding, most types are exposed to other compilation units, so it is hard to establish invariants about how they are used. Unless the compiler can verify that nowhere in the program ever takes the address of a boolean variable in a struct, it isn't allowed to rearrange the struct to avoid having that extra boolean. That might be possible at link-time for statically linked programs, but I'm not sure. Also, my knowledge is mostly from programming in C++ and watching CppCon talks, so I may be out of date from the latest optimization techniques.