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llvm / llvm-project / 265b032bdae0550de69ff52b4ef9deaf78bae522
commit265b032bdae0550de69ff52b4ef9deaf78bae522[log] [tgz]
authorkper <kevin.per@protonmail.com>Wed Sep 10 17:54:18 2025 +0200
committerGitHub <noreply@github.com>Wed Sep 10 15:54:18 2025 +0000
tree43b0d0f3ed102a84a84d10b4d33fade5a2007c47
parent61e4d2312d59d059f775734a3a7c96a6914c07b7 [diff]
[InstCombine] Added optimisation for trunc (Pow2 >> x) to i1 (#157030)

Closes #156898

I have added two cases. The first one matches when the constant is
exactly power of 2. The second case was to address the general case
mentioned in the linked issue. I, however, did not really solve the
general case.
We can only emit a `icmp ult` if all the bits are one and that's only
the case when the constant + 1 is a power of 2. Otherwise, we need to
create `icmp eq` for every bit that is one.

Here are a few examples which won't be working with the two cases:
-  constant is `9`: https://alive2.llvm.org/ce/z/S5FLJZ
- subrange in `56`: https://alive2.llvm.org/ce/z/yn_ZNG
- and finally an example as worst case (because it alternates the bits):
https://alive2.llvm.org/ce/z/nDitNA
2 files changed
tree: 43b0d0f3ed102a84a84d10b4d33fade5a2007c47
  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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