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llvm / llvm-project / 56944e606a1ba24e71fc89fad1eabb97e8240d65
commit56944e606a1ba24e71fc89fad1eabb97e8240d65[log] [tgz]
authorThurston Dang <thurston@google.com>Wed Jul 30 08:06:50 2025 -0700
committerGitHub <noreply@github.com>Wed Jul 30 08:06:50 2025 -0700
tree0f7dcf1ac4881165a23474da2962016e2db13d7b
parent254bfe23e3174d5695f4e35212ff352082f05ae4 [diff]
[msan] Approximately handle AVX Galois Field Affine Transformation (#150794)

e.g.,
      <16 x i8> @llvm.x86.vgf2p8affineqb.128(<16 x i8>, <16 x i8>, i8)
      <32 x i8> @llvm.x86.vgf2p8affineqb.256(<32 x i8>, <32 x i8>, i8)
      <64 x i8> @llvm.x86.vgf2p8affineqb.512(<64 x i8>, <64 x i8>, i8)
       Out                                    A          x          b
where A and x are packed matrices, b is a vector, Out = A * x + b in
GF(2)

Multiplication in GF(2) is equivalent to bitwise AND. However, the
matrix computation also includes a parity calculation.

For the bitwise AND of bits V1 and V2, the exact shadow is:
Out_Shadow = (V1_Shadow & V2_Shadow) | (V1 & V2_Shadow) | (V1_Shadow &
V2)

We approximate the shadow of gf2p8affine using:
  Out_Shadow =   _mm512_gf2p8affine_epi64_epi8(x_Shadow, A_shadow, 0)
               | _mm512_gf2p8affine_epi64_epi8(x, A_shadow, 0)
               | _mm512_gf2p8affine_epi64_epi8(x_Shadow, A, 0)
               | _mm512_set1_epi8(b_Shadow)

This approximation has false negatives: if an intermediate dot-product
contains an even number of 1's, the parity is 0.

It has no false positives.

Updates the test from https://github.com/llvm/llvm-project/pull/149258
2 files changed
tree: 0f7dcf1ac4881165a23474da2962016e2db13d7b
  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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