[AArch64] Correct SCVTF/UCVTF instructions for vector input (#152974)

This pull request improves support for scalar floating-point conversions
from integer vectors on AArch64, specifically for the `scvtf` and
`ucvtf` instructions. It fixes pattern matching so that single-element
conversions from vectors now generate the expected scalar instructions
and adds a new test to verify correct behavior for extracting a lane
from a widened vector.

**Pattern matching and code generation improvements:**
* Added new patterns in `AArch64InstrInfo.td` to correctly match
conversions from `v2i32` to `v1f64` using `scvtf` and `ucvtf`, ensuring
the scalar instructions (`scvtf d0, s0` and `ucvtf d0, s0`) are
generated when extracting a single lane.

**Test updates and additions:**
* Updated `scvtf_f64i32_simple` and `ucvtf_f64i32_simple` tests in
`fprcvt-cvtf.ll` to reflect the correct generation of scalar
instructions, removing previous comments about incorrect codegen and
showing the expected output.
* Added a new test `uitofp_sext_v2i32_extract_lane0` to verify correct
code generation when extracting a lane from a widened vector and
converting to double.
2 files changed
tree: 4e10fbeff6181b587231f7965487e26c07b9d025
  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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