[llvm-dev] RFC: PassManager extensions (original) (raw)

David Greene via llvm-dev llvm-dev at lists.llvm.org
Mon Sep 17 10:35:52 PDT 2018

Extension points were a great addition to the PassManager infrastructure. I'm just starting to learn about the new PassManager and am reading Bekket McClane's great series about it.

For a long time I've written passes and then hacked up PassManagerBuilder and friends to add it to the pipeline. Then extensions came along. Now I don't need to hack PassManagerBuilder directly but I do need to hack the thing that sets up extensions. For example, opt.cpp has a call to Coroutines helpers so Coroutines can insert its passes in the pipeline using the extension mechanism. The Coroutines authors had to modify opt.cpp directly to use their in-tree pass.

It strikes me that we are very close to having a mechanism to better encapsulate how a pass gets added to the pipeline. We already have code in each pass' sources that registers the pass with the PassManager. What if, during registration, a callback was made to the pass being registered which would allow the pass to add itself to the pipeline using the extension mechanism? Then all of the code to add a pass to the pipeline would be neatly contained in the pass' own sources, without the need to hack up unrelated code.

I have not begun to implement such a thing, because it may already be in the works and it's mucking around with a critical piece of infrastructure at the same time we're trying to move everyone over to the new version of that infrastructure. Thus, this is just an RFC to see what, if any, interest or plans there are around something like this.

                      -David

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