[AArch64] Optimize memset to use NEON DUP instruction for more sizes (#166030)

This change improves memset code generation for non-zero values on
AArch64 by using NEON's DUP instruction instead of
the less efficient multiplication with 0x01010101 pattern.

For small sizes, the value is extracted from a larger DUP. For
non-power-of-two sizes, overlapping stores are used in some cases.

TargetLowering::findOptimalMemOpLowering is modified to allow explicitly
specifying the size of the constant in cases where the constant is
larger than the store operations.

Fixes #165949
16 files changed
tree: fc9b60bd335c1fcf9544c9a85c01df332cd9ba53
  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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