With that said, compiling all of Perl 5 with a compiler that knows how to do link time optimization does offer a benefit, even if you can use LTO only on the core itself. This won't be an order of magnitude improvement. If you get 5% performance improvement, be happy.

If all you do is use LLVM's C front-end to compile the complete existing code base to IF, optimise, and then back to C to compile, I think you are probably in the ball park, if a little pessimistic. I'd have said low double digit percentage improvements.

But, if you break out the runtime components from the compile-time components -- ie. everything before the (say*) ${^GLOBALPHASE} = INIT -- and compile the before to C and link it. But then convert the (for want of a better term) "bytecode" to IF and pass it to the LLVM JIT engine, what then?

And what if the IF generated could be saved and the reloaded thus avoiding the perl compilation phase for second and subsequent runs (until edits)?

And how about combining the IF generated from the bytecode with the IF form of the core and linking it to build standalone executables?

Is any of this possible? There is only one way to find out.

(*)I appreciate that you would probably need to intercept, repeatedly, at the ${^GLOBALPHASE} = 'CHECL' or 'UNITCHECK' stages in reality.