[LLVMdev] Would DosBox benefit from LLVM JIT?

[Jacek Wielemborek]

Hello,

First of all, I'd like to point out that I am a newbie in this topic
and this is more of a "would it work?" kind of question. I basically
just came up with a difficult problem and decided to research on it.

I recently tried to run Elder Scrolls: Daggerfall on an ARM netbook
Toshiba AC100 and failed even after turning on the latest patches for
"dynamic recompilation". I took a look at the code and here's what I found:

https://github.com/wjp/dosbox/blob/idados/src/cpu/core_dynrec/decoder.h#L34

The relevant macros and functions are defined there:

https://github.com/wjp/dosbox/blob/idados/src/cpu/core_dynrec/risc_armv4le-o3.h

So basically, it looks like there's code that translates instructions
from x86 to a few other platforms in chunks of 32 opcodes. Since this
code was too slow to me, I asked myself the question "how could it speed
up?" and assumed that perhaps LLVM could optimize it on the fly. So,
here's the question - would it be feasible given the assumptions above?
What I am thinking about is a system that would:

1. Generate LLVM IR code instead of native calls and JIT them on the fly,
2. Apply optimizations that I know from Clang.

I saw this example on pastebin [1] and generating functions on the fly
looks rather straightforward, but I am not sure if it would be as easy
if I wanted to translate machine code from one platform to another. Does
LLVM have or integrate with any libraries that would make this
practical? What would be the main challenges? Keep in mind that I would
welcome even a partial answer.

Cheers,
d33tah

[1] http://pastebin.com/f2NSGZGR



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