DAG: Fold copysign with a known signmask to a disjoint or (#167266)

If the sign bit is a computed sign mask (i.e., we know it's
either +0 or -0), turn this into a disjoint or. This pattern
appears in the pow implementations.

We also need to know the sign bit of the magnitude is 0 for
the or to be disjoint. Unfortunately the DAG's FP tracking is
weak and we did not have a way to check if the sign bit is known
0, so add something for that. Ideally we would get a complete
computeKnownFPClass implementation.

This is intended to help avoid the regression which caused
d3e7c4ce7a3d7 to be reverted.
5 files changed
tree: 4e1e777362d6d8f0b3a3281e3928ec88957e5edc
  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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