[Support] Add KnownBits::isNonPositive() helper and exhaustive test coverage for sign predicates (#175284)

This patch adds:

1. KnownBits::isNonPositive() - Returns true if this value is known to
be non-positive (i.e., the signed maximum value is <= 0). This is
implemented using getSignedMaxValue().isNonPositive().

2. SignPredicatesExhaustive test - An exhaustive test that validates the
correctness of isNegative(), isNonNegative(), isStrictlyPositive(),
isNonPositive(), and isNonZero() by iterating through all possible
KnownBits combinations for 1-bit and 4-bit widths and verifying that the
predicates return true if and only if all possible values represented by
the KnownBits satisfy the predicate.

Fixes #175203
2 files changed
tree: bd73bf4f71a64e151139f6d92009adc0c85c5342
  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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