[llvm] Fix issue with running the same PassManager twice (PR #92823)

[via llvm-commits]

modiking wrote:

> this isn't the right solution. if we're calling `ModuleInlinerWrapperPass::run()` more than once, we're going to keep adding random passes/sub-pass managers to `MPM` and running those.
> 
> we really shouldn't be creating and running pass managers within a `run()`. could you see if we could somehow make it so we do all the pass management once? will probably involve modifying `PassBuilderPipelines.cpp`

Yeah it really is strange that a `pass` contains pass managers. I don't have too much context here but reading through what MIWP does it seems to be a `pass manager` in every aspect expect being a `PassManager`. It looks like a distinction is that MIWP executes a `PassManager` at pass runtime which depending on it's internal state:
```
  if (MaxDevirtIterations == 0)
    MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(std::move(PM)));
  else
    MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(
        createDevirtSCCRepeatedPass(std::move(PM), MaxDevirtIterations)));
```

But given `MaxDevirtIterations` is `const` this isn't really a runtime decision. It seems like MIWP can be replaced with a regular MPM and the decision above be made at pipeline construction. Is that the direction you're suggesting?

https://github.com/llvm/llvm-project/pull/92823