[clang] [llvm] [LLVM] Add IRNormalizer Pass (PR #68176)

[Justin Fargnoli via cfe-commits]

justinfargnoli wrote:

Hi @plotfi, thanks for pinging me on this! Generally speaking, two things deserve additional focus:

- UX testing to find:
  - Improvements to existing features 
  -  New features to add
- Additional testing to ensure that the pass preserves the semantics of the IR. 
  - e.g. I want to add this pass to the `nvcc` optimization pipeline and run it on NVIDIA's internal test suite. 
  - If Meta has similar test suites, it would be great to see if this pass introduces any functional issues on it. 

---

> I cannot reproduce these failures on my x86 machine.

Big thanks to @dtcxzyw for running the test-suite. Since @dtcxzyw did not find any test failures, this MR is ready for another round of review. 

If things look good to @plotfi and @nikic, then we should be good to get this merged!  

https://github.com/llvm/llvm-project/pull/68176