llvm dev - Jul 2019 - Looking for an out-of-source "Hello, world" LLVM/Clang pass example

I'm looking for a "Hello, world" pass example that ideally has all
of
the following properties:

  1) Complete.  That is, it should have functional CMakeLists.txt,
     etc. files.

  2) Out-of-source.  That is, it should build against a binary LLVM
     installation.

  3) Modern.  That is, I don't want to use any deprecated APIs or
     CMake macros.

  4) Clang-compatible.  That is, I'd like the pass to be able to run
     directly from Clang instead of having to generate bitcode, run
     opt on it, and then feed it back to Clang for linking.

Does such an example exist and if so, where can I find it?

Here's what I've considered to date:

  * llvm/lib/Transforms/Hello, but this appears to be in-source only.

  * http://llvm.org/docs/WritingAnLLVMPass.html, but this example
    doesn't appear to be runnable directly from Clang.

  * https://llvm.org/docs/CMake.html, but its proposed CMake line of
    "add_llvm_library(LLVMPassname MODULE Pass.cpp)" blows up with

      CMake Error at /usr/local/lib/cmake/llvm/AddLLVM.cmake:659 (install):
        install TARGETS given no LIBRARY DESTINATION for module target
"Hello".
      Call Stack (most recent call first):
        Hello/CMakeLists.txt:3 (add_llvm_library)

    (Perhaps this is fixable with additional CMake macro calls, but
    that's what I list "Complete" as a desideratum.)

  *
https://llvm.org/devmtg/2015-10/slides/GueltonGuinet-BuildingTestingDebuggingASimpleOutOfTreePass.pdf,
    but this uses add_llvm_loadable_module in CMake, which I read in
    some thread is likely to go away, and the legacy pass manager,
    while is also likely to go away, to make the pass usable from
    Clang.

See my predicament?  What's a poor pass-writer to do?

Thanks in advance,
-- Scott

Hi,
> On Jul 10, 2019, at 20:45, Scott Pakin via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> I'm looking for a "Hello, world" pass example that ideally
has all of
> the following properties:
> 
>  1) Complete.  That is, it should have functional CMakeLists.txt,
>     etc. files.
> 
>  2) Out-of-source.  That is, it should build against a binary LLVM
>     installation.
> 
>  3) Modern.  That is, I don't want to use any deprecated APIs or
>     CMake macros.
> 
>  4) Clang-compatible.  That is, I'd like the pass to be able to run
>     directly from Clang instead of having to generate bitcode, run
>     opt on it, and then feed it back to Clang for linking.
> 
> Does such an example exist and if so, where can I find it?
http://www.cs.cornell.edu/~asampson/blog/llvm.html describes how to create an
out-of-source pass (see 'Let’s Write a Pass’). I think it is for LLVM 3.8
though.

Cheers,
Florian

Florian,

On 7/10/19 2:17 PM, Florian Hahn wrote:
> http://www.cs.cornell.edu/~asampson/blog/llvm.html describes how to
> create an out-of-source pass (see 'Let’s Write a Pass’). I think it
> is for LLVM 3.8 though.
Thanks for pointing that out.  I had actually recently stumbled across
that page (and the GitHub repository it references,
https://github.com/sampsyo/llvm-pass-skeleton) while searching for an
answer to my questions but wasn't sure how up-to-date the information
is:

  * Is add_library the currently recommended CMake macro call for
    building an LLVM pass?
    http://llvm.org/docs/WritingAnLLVMPass.html and
    https://llvm.org/docs/CMake.html both point to add_llvm_library,
    which I couldn't get to work.

  * Is the legacy pass manager still the right way to make a pass
    Clang-callable?  There's a currently active thread on this list,
    "Status of the New Pass Manager", that makes me think I have some
    code-rewriting in my future.

-- Scott