[mlir][acc] Add utilities for converting acc.loop to scf (#172953)

Add OpenACCUtilsLoop.h/.cpp with utilities for converting acc.loop
operations to SCF dialect operations:

- convertACCLoopToSCFFor: Convert structured acc.loop to scf.for with
loop collapsing support
- convertACCLoopToSCFParallel: Convert acc.loop to scf.parallel
- convertUnstructuredACCLoopToSCFExecuteRegion: Convert unstructured
acc.loop (multi-block) to scf.execute_region

Key features:
- Automatic type conversion between integer types and index
- Inclusive-to-exclusive upper bound conversion
- Trip count calculation with clamping for negative counts
- Constant folding via createOrFold for cleaner IR
- Assertions to prevent misuse (e.g., builder inside loop region)
- Error emission for unsupported cases (loops with results)

Comprehensive unit tests covering these APIs are also added.

---------

Co-authored-by: Scott Manley <rscottmanley@nvidia.com>
5 files changed
tree: 179ff3ce274efc5f25587377bd201381f28222b2
  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. libsycl/
  16. libunwind/
  17. lld/
  18. lldb/
  19. llvm/
  20. llvm-libgcc/
  21. mlir/
  22. offload/
  23. openmp/
  24. orc-rt/
  25. polly/
  26. runtimes/
  27. third-party/
  28. utils/
  29. .clang-format
  30. .clang-format-ignore
  31. .clang-tidy
  32. .git-blame-ignore-revs
  33. .gitattributes
  34. .gitignore
  35. .mailmap
  36. CODE_OF_CONDUCT.md
  37. CONTRIBUTING.md
  38. LICENSE.TXT
  39. pyproject.toml
  40. README.md
  41. SECURITY.md
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