Feasibility of cling/llvm interpreter for JIT replacement

Dear Sir/Madam

Our company``, 4Js software, has developed an SQL data base software that runs under different operating systems: Windows, Linux, Mac OS X. This software compiles each SQL statement into a C program that is compiled "on the fly" and executed by our JIT, Just In Time compiler.

We wanted to port it to Apple's iOS, and spent a lot of time retargetting the JIT for supporting the ARM 64 CPU, but to our surprise, when everything was ready, we learned that Apple iOS forbids software to generate dynamically an executable.

After several months of reflections we think we can get around this problem by using a C interpreter. Instead of compiling it to machine code, we would pass the generated C program to a C interpreter that would interpret the C program.

After looking at several interpreters, we think that the llvm based CLING interpreter could do the job. To test these ideas, we have recompiled the llvm/Clang system in a small linux/ARM64 based machine. Our preliminary tests seem to work and cling is able to load the generated program.

There are several possible problems that we see.

The first and most obvious one is the incredible size of the CLING interpreter (200MB stripped). Our whole data base is 80MB stripped. We are targetting an Apple iPad, boosted with 1TO SSD/6GB RAM. What would be the minimum requirements for CLING in terms of RAM size?

The second question is that we have still concerns over the overall approach. Do you see any problems with this architecture? Can it work on principle?

The third question concerns the feasibility of our JIT generating byte codes for the LLVM interpreter, boosting performance and reducing RAM footprint. Would that be a better solution than using the CLING interpreter? Is that possible within Apple's iOS?

And yet another question is the need to modify the CLING interpreter so that it receives its input from a character buffer instead of a file, and other small tweaks. Is that possible?

Are there any copyright issues? Are we allowed to embed the llvm software into our system? Of course we would publish any modifications done to the source code.

We thank you in advance for any answers to the questions above.

Yours sincerely

Jacob Navia

iOS Project Manager

4Js Software.
```28 Quai Gallieni, 92150 Suresnes`


Is there any reason not to use traditional approaches like ChaiScript?


How do you do the strip? I have nightly releases of cling here: the release is around 23MB and unzipped is around 80. I am pretty sure we can strip it further down. That’s a hard question: running ./bin/cling ".q" shows around 23Mb peak rss. ./bin/cling "#include <vector>" ".q" shows 34 Mb and so on. It depends on what sort of things you will be compiling/interpreting. ./bin/cling '#include <iostream>' 'printf("hello world!\n");' works. Did you mean a different use-case?

chaiscript isn't very performant - far away from a real JITer

Yes, that would mean generating chai script and not C, as it is done now. That would mean writing a new back end for a specific port to an specific architecture (iOS) and special casing all the backend of the SQL-->C compiler.

That is (of course) doable, but it is a LOT of work.