[llvm-commits] [RFC] ExecutionEngine API for adding custom passes

[Kaylor, Andrew]

It seems like you should be able to do what you want by creating a custom TargetMachine that implements addPassesToEmitMC but otherwise defers to the a an aggregated TargetMachine instance returned from EngineBuilder::selectTarget().

-Andy

-----Original Message-----
From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-bounces at cs.uiuc.edu] On Behalf Of James Molloy
Sent: Friday, November 02, 2012 1:58 AM
To: Chris Lattner
Cc: llvm-commits at cs.uiuc.edu
Subject: Re: [llvm-commits] [RFC] ExecutionEngine API for adding custom passes

Hi Chris,

The specific use case is that I have a target-independent MachineFunctionPass which records information about the stack frame sizes for each function.

You can generalise this to any client of the MCJIT who wants to control compilation further - for example "lli" with "opt"-like user-defined additional passes. If any of those additional passes are machine function passes, we'd have difficulty with the current interface.

I'm writing this pass outside of LLVM's source tree - I'm a client of LLVM rather than modifying it, so that's why I'm unsure that I'm unable to add the pass to the target.

James


On Fri, 2012-11-02 at 04:47 +0000, Chris Lattner wrote:
> On Oct 31, 2012, at 10:53 AM, James Molloy <James.Molloy at arm.com> wrote:
> 
> > Hi,
> > 
> > I have a use case where I have written a MachineFunctionPass, which 
> > I would like to have run on a Module which I will eventually pass to 
> > the MCJIT.
> > 
> > Currently, the only real way I can do this is by compiling the 
> > module twice, because MachineFunctionPasses need to be added to 
> > PassManagers after ::addPassesToEmit* is called, and the MCJIT 
> > creates its own PassManager and calls that locally itself.
> > 
> > It's really inefficient to have to go through the codegen process 
> > twice just because I can't add a pass to what the MCJIT runs, so 
> > I've attached a proposed addition to the ExecutionEngine interface.
> > 
> > This adds a suite of functions to add "compilation hooks". These 
> > would be unimplemented on the Interpreter and old-style JIT. They 
> > are function pointers that a user would give, that take a 
> > PassManager& argument and allow the user to add passes manually.
> > 
> > Is this something that would be acceptable to have in trunk?
> 
> I don't understand the use case of this.  Is this for a target-independent or target-dependent pass?  If it's target-specific, why not just add it to the target?
> 
> -Chris
> 
> 




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