4 ms·

I've been looking for a DynASM tutorial for ages, and wanted to use it to make a fast BF interpreter-- this is great! I added some optimizations using Flex to

• haberman 13y ago
  Very nice! I wouldn't have thought to use flex to recognize optimizable patterns. :) It crashes for me on OS X but I'll have to try it on Linux. You may have tried this already, but where you have: mov al, byte [PTR] Usually you want to write this instead to avoid a partial register stall (also in case there's junk sitting in the register). movzx eax, byte [PTR]
  • Scaevolus 13y ago
    Hm, the OSX crash is probably because they have a different ABI from Linux -- Google "osx ia32 abi" for details-- I'm probably violating stack alignment. Partial register stalls are where you write part of the register, then read the full register: mov al, byte [PTR] add ebx, eax But I am emitting this: mov al, byte [PTR] add byte [PTR+3], al So there's no stall. I got jit4 about as far as is reasonable for a single-pass compiler, but I intend to implement a proper BF->IR->ASM compiler to implement some more complex multi-pass optimizations I have in mind.
    • haberman 13y ago
      Yes, I have encountered the problem before that OS X crashes on incorrect stack alignment even where other platforms tolerate it. Good point about the stall -- I always thought that partial register stall happened at the point that you do the partial write, since the logical contents of the register now depend on its previous contents. I didn't realize that the dependency logic was sophisticated enough to allow the partial read without depending on the entire register's value.