llvm-project

56944e60 - [msan] Approximately handle AVX Galois Field Affine Transformation (#150794)

[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