LLVMJIT: Support newer LLVM versions

[PhilippvK]

We have a dependency on LLVM 11.0.0 (2020) for the LLVMJIT.

Especially since there are no builds available for LLVM 11 on Ubuntu 22.04+ in the package managers, it would be great to move to a newer LLVM version...

I remember some conversation with Karsten who mentioned that newer LLVM Releases will not work easily with ETISS, but I guess I can just try out and see what needs to be patched.

[JoGei]

LLVM compile times are rather slow, it seems. I don't think upgrading LLVM versions alone will fix this.
I found this work, TPDE, for a fast LLVM-JIT engine from TUM CS colleagues:

• https://github.com/tpde2/tpde
• Pre-print article: https://arxiv.org/abs/2505.22610

Would it make sense to have a look at that, in case we refactor the LLVMJIT in ETISS?

Edit and a little disclaimer:
This would only address the "slow LLVM" backend problem, since we still have to clang the generated C code OR add a M2-ISA-R LLVM-IR backend (would be awesome).

[PhilippvK]

@JoGei my priority would be to drop the need for LLVM 11 which is not available for Ubuntu 24.04+.

Looking into performance improvements has minor relevance, at LLVMJIT is rarely used and TCCJIT outperforms GCCJIT and LLVMJIT for almost any workload < 10M instructions. The main advantage of LLVMJIT vs. GCCJIT is probably that it does not need to spawn shell subprocesses (aka. less overhead)

[PhilippvK]

Adding an LLVM-IR based ETISS JIT would be indeed interesting but I have doubts that it would help a lot. Before anybody invest X months into it, we should first do some minimal experiments to confirm that there is potential.

ASMJIT might be an option to easily get 150MIPS+, even for short programs but might be complicated to implement.

[JoGei]

Dont close.

Full build compatibility llvm-{11--20} is done with PR #224 but ArchImpl requires fix for runtime:

Tested LLVM versions:

llvm	ubuntu-20.04	ubuntu-22.04
11	🟢	🟢
12	🟢	🟢
13	🟢	🟢
14	🟢	🟢
15	🟢	🟢
16	🟡	🟡
17	🟠	🟠
18	🟠	🟠
19	🟠	🟠
20	🟠	🟠

🟡 : requires C++17
🟠 : requires C++17 and requires removal of (no idea why):

etiss/ArchImpl/RV32IMACFD/RV32IMACFD.h

Line 9 in 17e5720

#include <stdio.h>