Debugging Compilers with Optimization Fuel

I didn't really understand what specifically fuel was here - could anyone help me out?

Beyond debugging, it’s a useful idea for tweaking the trade off between compile time and resultant performance. Especially true with JIT or runtime compilation.

LLVM has this as well now, though I believe this blog post predates the LLVM implementation and may have socialized the concept in LLVM circles.

(2011)