[HashRecognize] Rewrite arePHIsIntertwined (#144878)

The test crc8.le.tc16 is a valid CRC algorithm, but isn't recognized as
such due to a buggy arePHIsIntertwined, which is asymmetric in its
PHINode arguments. There is also a fundamental correctness issue: the
core functionality is to match a XOR that's a recurrence in both PHI
nodes, ignoring casts, but the user of the XOR is never checked. Rewrite
and rename the function.

crc8.le.tc16 is still not recognized as a valid CRC algorithm, due to an
incorrect check for loop iterations exceeding the bitwidth of the
result: in reality, it should not exceed the bitwidth of LHSAux, but we
leave this fix to a follow-up.

Co-authored-by: Piotr Fusik <p.fusik@samsung.com>
3 files changed
tree: 80297e615a033b1c54f9af29756896e023335718
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. flang-rt/
  11. libc/
  12. libclc/
  13. libcxx/
  14. libcxxabi/
  15. libunwind/
  16. lld/
  17. lldb/
  18. llvm/
  19. llvm-libgcc/
  20. mlir/
  21. offload/
  22. openmp/
  23. polly/
  24. runtimes/
  25. third-party/
  26. utils/
  27. .clang-format
  28. .clang-format-ignore
  29. .clang-tidy
  30. .git-blame-ignore-revs
  31. .gitattributes
  32. .gitignore
  33. .mailmap
  34. CODE_OF_CONDUCT.md
  35. CONTRIBUTING.md
  36. LICENSE.TXT
  37. pyproject.toml
  38. README.md
  39. SECURITY.md
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