Some more interesting points:

- Switching to -O3 for gcc (instead of author's default -O2), the C version (exp_volatile_a_b) gets ~30% faster, bringing it down to ~50% of the python-generated llvm - it appears to still be doing the full computation at runtime.

- Switching to -O3 for llc doesn't make any difference for the python-generated llvm version.

- With gcc 4.8 -O2 (instead of 7.3 -O2), I get ~0.06s - it looks like gcc 4.8 decides to inline everything, and gcc 7.3 doesn't.