[LLVMdev] MCJIT and Lazy Compilation

[Kaylor, Andrew]

Hi Manny,

What exactly do you need from the JITEventListener API?

The latest MCJIT code has a listener interface that will notify you when an object image is emitted.  I recently committed changes to DebugInfo and the IntelJITEventListener that demonstrate a way to deconstruct the emitted object into function and line number information.  However, there is no clean way to get back to the original llvm::Function that corresponds to any given machine code function.

As for your problem with re-jitting modules, I think it should be possible to use a second instance of MCJIT to emit code for a second module that contains just the function with new parameters and link that against the previously emitted module.  I haven't tried this, so I don't know what pitfalls may be there, but I don't see an obvious reason that it couldn't work.  You would probably need a custom memory manager to handle the function address resolution.  I realize this isn't an ideal solution.  I'm hoping that in the near future a single instance of MCJIT will support multiple modules and be able to do this kind of cross-module linking in a more painless way.

-Andy

From: Manny Ko [mailto:Manny.Ko at imgtec.com]
Sent: Wednesday, February 06, 2013 10:35 AM
To: Kaylor, Andrew; Andrew Sorensen; llvmdev at cs.uiuc.edu
Subject: RE: [LLVMdev] MCJIT and Lazy Compilation


Hi Andy and Andrew,



I am very interested in this discussion as our co. have critical components that are dependent on the old JIT.  We have implemented support for MCJIT mostly to get AVX support.  The difference in module support is forcing us to duplicate a module when we want to JIT the same bitcode with different parameters.  We also have code that depends on the JITEventListener API.



Cheers.

________________________________
From: llvmdev-bounces at cs.uiuc.edu<mailto:llvmdev-bounces at cs.uiuc.edu> [llvmdev-bounces at cs.uiuc.edu] on behalf of Kaylor, Andrew [andrew.kaylor at intel.com]
Sent: Tuesday, February 05, 2013 10:08 AM
To: Andrew Sorensen; llvmdev at cs.uiuc.edu<mailto:llvmdev at cs.uiuc.edu>
Subject: Re: [LLVMdev] MCJIT and Lazy Compilation
Hi Andrew,

I was about to write a belated reply to this message (sorry for the delay), but then I realized that pretty much everything useful that I have to say on the subject is contained in this message (which is in a thread Albert Graef already linked to):

https://groups.google.com/d/msg/llvm-dev/Rk9cWdRX0Wg/Fa1Mn6cyS9UJ

Generally, I do hope that MCJIT will be capable of replacing the old JIT someday soon, though obviously it cannot do so until it provides equivalent functionality.  I doubt it will ever be a "drop-in" replacement, but I hope that minimal rework will be needed.  Most significantly, as can be seen in earlier discussions, things will need to be made Module-centric rather than Function-centric.  It ought to be possible to write a utility class that takes a monolithic Module and breaks it up into sub-Modules for individual functions, but I think that would need to happen outside of the MCJIT engine because not all clients would want that kind of granularity.

There's definitely a lot of work to be done here to get this right, and hopefully we'll get active participation in any design discussions to make sure the solution meets everyone's needs.  I don't have a time table for this right now.  I will file a Bugzilla report as soon as the LLVM server is ready.

-Andy

From: llvmdev-bounces at cs.uiuc.edu<mailto:llvmdev-bounces at cs.uiuc.edu> [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Andrew Sorensen
Sent: Thursday, January 31, 2013 7:56 PM
To: llvmdev at cs.uiuc.edu<mailto:llvmdev at cs.uiuc.edu>
Subject: [LLVMdev] MCJIT and Lazy Compilation

Does anyone have a roadmap for MCJIT with what I think people are
calling lazy compilation.

Is this even on the cards?

I spent the last few hours moving my project (extempore.moso.com.au<http://extempore.moso.com.au>)
over to MCJIT (particularly for ARM), and am a little horrified to discover
no ability to compile, and just as importantly to recompile, at a function level.
This is absolutely mandatory for my project.

I have been looking enviously at MCJIT's ARM+DWARF support for a
couple of years and was under the misapprehension that MCJIT was
attempting to be a *drop-in* replacement for JIT.  So I wasn't overly
concerned about the primary JIT being largely neglected. This is obviously
my fault, I wasn't paying close enough attention.

I am now wondering what the LLVM project, in the large, plans regarding
just-in-time compilation moving forward.  Is MCJIT the future, and
if so what kind of roadmap is there to replicate current JIT functionality.
In my case in relation to function level (re)compilation.

I appreciate everyones efforts, and that we all have our own agendas.
I'm just trying to put my own roadmap in place.

Cheers,
Andrew.
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