There really ought to be a subset of C that lets you write portable assembly. One where only a defined set of optimisations are allowed and required to be performed, "inline" means always inline, the "register" and "auto" keywords have their original meanings, every stack variable is allocated unless otherwise indicated, every expression has defined evaluation order, every read/write from/to an address is carried out, nothing is ever reordered, and undefined behaviour is switched to machine-specific behaviour. Currently if you need that level of control, your only option is writing it in assembly, which gets painful when you need to support multiple architectures, or want fancy features like autocomplete or structs and functions.