In this one section of push_back code, I have now found 4/5 different missed optimizations. For both gcc and llvm. The last one is a saturated add/multiply which is slightly more complex to handle though but should be doable. Basically this code is trying to do a sat_mult(elements, 2*sizeof(element)) with a minimum value of sizeof(element). The sat_mult part i figured out tonight. I wonder how much this could improve the code.