[NFC][TTI] Introduce getInstructionUniformity API for uniformity analysis (#168903)

This patch introduces a new TargetTransformInfo hook
`getInstructionUniformity()`
that provides a unified interface for querying target-specific
uniformity
information about instructions and values.

The new hook returns an `InstructionUniformity` enum with three values:
- Default: Result is uniform if all operands are uniform (standard
propagation)
- AlwaysUniform: Result is always uniform regardless of operands
- NeverUniform: Result can never be assumed uniform

This API wraps the existing `isAlwaysUniform()` and
`isSourceOfDivergence()`
hooks, providing a single entry point for uniformity queries. Both LLVM
IR-level
(via TTI) and MIR-level (via TargetInstrInfo) uniformity analysis have
been
updated to use the new hook.

Target implementations:
- AMDGPU: Wraps existing `isAlwaysUniform()` and
`isSourceOfDivergence()` hooks
- NVPTX: Wraps existing `isSourceOfDivergence()` hook

This is an NFC change - all implementations return conservative defaults
or wrap
existing functionality.

Ref patch:https://github.com/llvm/llvm-project/pull/137639
10 files changed
tree: 7f1daff68342a876063cf709d244a6b1c9de64af
  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
README.md

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