llvm dev - Mar 2010 - [LLVMdev] Maintaining pass code outside of the LLVM directory

Hi,

I'm developing an LLVM pass and am running into code maintenance  
issues. Specifically, the "Writing an LLVM Pass" document assumes that
the pass directory is placed somewhere in the LLVM source base (e.g.  
lib/Transforms), but this is a problem for me because:

1) Testing the pass against two different LLVM versions is difficult.  
For example, testing with the LLVM 2.6 release and the LLVM 2.7  
prerelease requires either moving the pass directory back and forth or  
maintaining two different copies of the same pass, one in each LLVM  
source base. Neither option is much fun.

2) Mixing custom code with the LLVM source base can lead to dangerous  
mistakes. For example, I had added some extensive debugging code to  
the LLVM source, and I wanted to start over with a clean build, so I  
did "rm -rf" on the LLVM directory. Of course this wiped out my pass  
code as well! (Luckily I had checked in the code to a personal SVN  
repo.)

I really need a way to keep my pass code separate from the LLVM source  
base. I tried to get clever by creating a soft link from my pass  
directory to lib/Transforms, but this doesn't work because the $PWD is  
relative to the link's source directory, even when I cd into the  
link's target directory. This screws up the LEVEL variable in the  
Makefile and causes build errors. I tried to adjust LEVEL to account  
for the new location but that still didn't work.

Any suggestions? Thanks,

Trevor

Dear Trevor,

You can always use the LLVM project infrastructure (documented at 
http://llvm.org/docs/Projects.html).  Numerous projects that use LLVM 
(such as poolalloc and SAFECode) use this infrastructure (or improved 
versions of it; the document may be a little dated).  They have their 
own distinct source trees that can live outside of LLVM's source tree, 
but they reuse LLVM's build system.  Your source code and Makefiles 
should require no modification; you'll simply be rearranging the 
directories and adding a configure script.

If you have any questions or have any problems, please email llvmdev.  
To start your project, I would recommend using either the poolalloc or 
SAFECode projects (see http://safecode.cs.illinois.edu for directions on 
getting SAFECode out of SVN) as a template; the projects/sample project 
in the LLVM source tree may be outdated.

-- John T.

Trevor Harmon wrote:
> Hi,
>
> I'm developing an LLVM pass and am running into code maintenance  
> issues. Specifically, the "Writing an LLVM Pass" document assumes
that
> the pass directory is placed somewhere in the LLVM source base (e.g.  
> lib/Transforms), but this is a problem for me because:
>
> 1) Testing the pass against two different LLVM versions is difficult.  
> For example, testing with the LLVM 2.6 release and the LLVM 2.7  
> prerelease requires either moving the pass directory back and forth or  
> maintaining two different copies of the same pass, one in each LLVM  
> source base. Neither option is much fun.
>
> 2) Mixing custom code with the LLVM source base can lead to dangerous  
> mistakes. For example, I had added some extensive debugging code to  
> the LLVM source, and I wanted to start over with a clean build, so I  
> did "rm -rf" on the LLVM directory. Of course this wiped out my
pass
> code as well! (Luckily I had checked in the code to a personal SVN  
> repo.)
>
> I really need a way to keep my pass code separate from the LLVM source  
> base. I tried to get clever by creating a soft link from my pass  
> directory to lib/Transforms, but this doesn't work because the $PWD is
> relative to the link's source directory, even when I cd into the  
> link's target directory. This screws up the LEVEL variable in the  
> Makefile and causes build errors. I tried to adjust LEVEL to account  
> for the new location but that still didn't work.
>
> Any suggestions? Thanks,
>
> Trevor
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

On Mar 22, 2010, at 9:53 PM, John Criswell wrote:
> You can always use the LLVM project infrastructure (documented at
> http://llvm.org/docs/Projects.html).
Thanks for reminding me of that. I had actually started out with a  
project infrastructure, then switched to a pass implementation alone,  
not realizing I could combine the two. I've now reverted back to my  
old project, integrated the pass code into it, and my problem appears  
to be solved.
> If you have any questions or have any problems, please email llvmdev.
Well, there is one thing... I'm wondering how best to actually run the  
pass after it's been compiled. Currently I'm just invoking
"opt" and
passing it a "-load" parameter with the name of my pass's dynamic
library. I also have to add a couple more "-load" parameters for  
external libraries needed by the pass, followed by the custom  
parameters for the pass itself, and of course the "opt" parameters  
(the name of a bitcode input file, etc.). It gets to be a rather long  
and complex command line, and not a very friendly way of using the pass.

Is there a better way? I suppose I could put the parameters in a shell  
script -- simply a custom wrapper for "opt" -- and put it in the  
project's tools directory. Or maybe I could write some kind of native  
tool that bypasses "opt" altogether and somehow invokes the pass  
through LLVM's API. But that might be overkill. Not sure how others  
typically handle this. Any thoughts? Thanks,

Trevor