[AArch64][SME] Simplify initialization of the TPIDR2 block (#141049)

This patch updates the definition of `AArch64ISD::INIT_TPIDR2OBJ` to
take the number of save slices (which is currently always all ZA
slices). Using this, we can initialize the TPIDR2 block with a single
STP of the save buffer pointer and the number of save slices. The
reserved bytes (10-15) will be implicitly zeroed as the result of RDSVL
will always be <= 16-bits.

Note: We used to write the number of save slices to the TPIDR2 block
before every call with a lazy save; however, based on 6.6.9 "Changes to
the TPIDR2 block" in the aapcs64 
(https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst#changes-to-the-tpidr2-block), 
it seems we can rely on callers preserving the contents of the TPIDR2 block.
10 files changed
tree: af0507045127db2ca98d01aa991ec9761df3375f
  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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