Re: JIT compiling with LLVM v9.0

On Thu, Jan 25, 2018 at 11:20:28AM -0800, Andres Freund wrote:
> On 2018-01-25 18:40:53 +0300, Konstantin Knizhnik wrote:
> > Another question is whether it is sensible to redundantly do
> > expensive work (llvm compilation) in all backends.
>
> Right now we kinda have to, but I really want to get rid of that.
> There's some pointers included as constants in the generated code. I
> plan to work on getting rid of that requirement, but after getting
> the basics in (i.e. realistically not this release). Even after
> that I'm personally much more interested in caching the generated
> code inside a backend, rather than across backends. Function
> addresses et al being different between backends would add some
> complications, can be overcome, but I'm doubtful it's immediately
> worth it.

If we go with threading for this part, sharing that state may be
simpler. It seems a lot of work is going into things that threading
does at a much lower developer cost, but that's a different
conversation.

> > So before starting code generation, ExecReadyCompiledExpr can first
> > build signature and check if correspondent library is already present.
> > Also it will be easier to control space used by compiled libraries in
> > this
>
> Right, I definitely think we want to do that at some point not too far
> away in the future. That makes the applicability of JITing much broader.
>
> More advanced forms of this are that you JIT in the background for
> frequently executed code (so not to incur latency the first time
> somebody executes). Aand/or that you emit unoptimized code the first
> time through, which is quite quick, and run the optimizer after the
> query has been executed a number of times.

Both sound pretty neat.

Best,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778

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