> Major compilers (LLVM, GCC, Intel) are able to vectorize real world code to a useful extent. Try compiling this with recent gcc: uint8_t dumb_checksum(u

> Major compilers (LLVM, GCC, Intel) are able to vectorize real world code to a useful extent. Try compiling this with recent gcc: uint8_t dumb_checksum(uint8_t *ar) { uint8_t ans = 0; for (int i = 0; i < 320; i++) ans += ar[i]; return ans; } You don't get satisfactory results. I, at least, don't have a clear mental model of when gcc will do something reasonable and when it will generate a large amount of bad code.