https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103774
Bug ID: 103774 Summary: [i386] GCC should swap the arguments to certain functions to generate a single instruction Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: thiago at kde dot org Target Milestone: --- I don't know how widespread this is. Seen in the code generated at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103750. This code: __m256i data1 = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(n)); __m256i data2 = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(n) + 1); __mmask16 mask1 = _mm256_cmpeq_epu16_mask(data1, mch256); __mmask16 mask2 = _mm256_cmpeq_epu16_mask(data2, mch256); Generates: vmovdqu16 (%rdi), %ymm1 vmovdqu16 32(%rdi), %ymm2 vpcmpuw $0, %ymm0, %ymm1, %k0 vpcmpuw $0, %ymm0, %ymm2, %k1 While if you invert the two operands in the cmpeq intrinsics, as in: __m256i data1 = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(n)); __m256i data2 = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(n) + 1); __mmask16 mask1 = _mm256_cmpeq_epu16_mask(mch256, data1); __mmask16 mask2 = _mm256_cmpeq_epu16_mask(mch256, data2); You get: vpcmpuw $0, (%rdi), %ymm0, %k0 vpcmpuw $0, 32(%rdi), %ymm0, %k1 Godbolt link with full copileable source code: https://gcc.godbolt.org/z/rKo666MM7 Clang, ICC (Clang-based) do this. MSVC behaves like GCC.