Query about sandybridge with AES instruction from AVX2

[Jamaika1]

Will adding an AES instruction to get sse4 damage the CPU sandybridge? Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE and PCLMUL instruction set support.

[jan-wassenberg]

Hi @Jamaika1 , Highway's SSE4 target requires AES. This means your CPU can (and will automatically) only use the HWY_SSSE3 target, which is somewhat slower than SSE4.

If you want SSE4 and are sure that the software does not use AES (e.g. the AESRound() intrinsic - JPEG XL currently does not), you could consider changing in targets.cc constexpr uint64_t kGroupSSE4 = Bit(FeatureIndex::kSSE41) | Bit(FeatureIndex::kSSE42) | Bit(FeatureIndex::kCLMUL) | Bit(FeatureIndex::kAES) | kGroupSSSE3; to constexpr uint64_t kGroupSSE4 = Bit(FeatureIndex::kSSE41) | Bit(FeatureIndex::kSSE42) | Bit(FeatureIndex::kCLMUL) | kGroupSSSE3;

The worst that can happen is that software using AES will then crash with SIGILL, but I do not see how that could damage the CPU.

[jan-wassenberg]

Please feel free to reopen if any action is required here :)