[AMDGPU] Try to reuse register with the constant from compare in v_cndmask (#148740)

For some targets, the optimization X == Const ? X : Y -> X == Const ?
Const : Y can cause extra register usage or redundant immediate encoding
for the constant in cndmask generated from the ternary operation.

This patch detects such cases and reuses the register from the compare
instruction that already holds the constant, instead of materializing it
again for cndmask.

The optimization avoids immediates that can be encoded into cndmask
instruction (including +-0.0), as well as !isNormal() constants.

The change is reworked on the base of #131146

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
3 files changed
tree: 8ece33c94c36a32f13c3933016df624ab9c2e71c
  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. libunwind/
  16. lld/
  17. lldb/
  18. llvm/
  19. llvm-libgcc/
  20. mlir/
  21. offload/
  22. openmp/
  23. polly/
  24. runtimes/
  25. third-party/
  26. utils/
  27. .clang-format
  28. .clang-format-ignore
  29. .clang-tidy
  30. .git-blame-ignore-revs
  31. .gitattributes
  32. .gitignore
  33. .mailmap
  34. CODE_OF_CONDUCT.md
  35. CONTRIBUTING.md
  36. LICENSE.TXT
  37. pyproject.toml
  38. README.md
  39. SECURITY.md
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