[LLVMdev] Removing old JIT CodeEmitters for ARM and PPC

[Albert Graef]

On 11/25/2012 11:16 AM, Benjamin Kramer wrote:
> It's possible to coexist, but increases the maintenance burden.

Ok, I understand.

> I can understand your concerns and I wouldn't have proposed this change if the old JIT for ARM and PPC actually worked. When running LLVM's regression tests on a ARM or PPC64 host most of the JIT tests simply fail. That's why the regression tests now run MCJIT by default on those platforms (and tests pass), which won't make the situation any better for the old JIT.

Indeed. Well, I've had reports that people got Pure to run on ARM at
some point, not sure how well it worked, though. ;-) I'm just beginning
to dabble with ARM myself as I'd like to port Pure to Android. Well, I
guess that we'll just continue to use older LLVM versions on ARM for the
time being, if I can get it to work at all with the old JIT. Who knows,
Pure is a rather special language which doesn't utilize all cpu
features, maybe the old JIT supports ARM well enough to run Pure code
even though it fails many of the tests.

> I know that you rely on lazy compilation in your project and the old x86 JIT isn't going away until that is implemented in the MCJIT. However, it requires that someone makes the investment to port it over, not sure what exactly is needed for this.

Is anyone looking into this already? It seems that lazy compilation (or
any kind of incremental compilation; I don't really care as long as I
can swap out the bodies of single functions and the JIT is fast enough)
is the one critical feature that keeps us from using MCJIT for dynamic
language implementations. So it would be nice if someone who knows the
JIT code inside out could have a look at that. I know I'm asking too
much but I'd really like to give MCJIT a try rather sooner than later.
;-) I'm afraid that I don't know enough about the lowlevel parts of the
JIT to have a go at it myself, but I could certainly help testing this
if someone else implements it.

Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr.Graef at t-online.de, ag at muwiinfa.geschichte.uni-mainz.de
WWW:    http://www.musikinformatik.uni-mainz.de/ag