JIT

[giann]

LLVM JIT

By function for now. Once it works and proves to be fast enough, see if we can JIT loops and such.

• [x] function based compiling
• [x] "hot" definition and strategy
• [ ] hot spots (loops, something else?)
• [x] build flags, runtime options and API

[giann]

Current state:

• Off by default. Activate by building buzz with -Djit
• Compiles a function when it makes up jit_prof_threshold% of total function calls, or always if buzz is built with -Djit_debug
• Will compile any function called by the function being compiled
• Will ignore functions using fibers or called in a fiber context: we could use LLVM coroutines but that does not solve how this would interact with the VM (for example if a non-compiled function called a compiled function in a fiber)

[giann]

LLVM compilation is really slow:

• ~10ms for ~50 buzz LoC!
• Compiling hot code might be slower than just running it
• We could estimate the trade off and compile only when it seems beneficial, but that would certainly exclude compilation for a lot of smaller use cases where the compiled code would have made a difference

Alternatives:

• DynASM: since it uses the C preprocessor, means we would need to write some C around it
• MIR
• QBE
• Xbyak

[giann]

Done with MIR