https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108401
--- Comment #7 from andysem at mail dot ru --- To be clear, I'm not asking the compiler to recognize the particular pattern of alternating 0x00 and 0xFF bytes. Because hardcoding this particular pattern won't improve generated code in other cases. Rather, I'm asking to tune down code transformations for intrinsics. If the developer wrote a sequence of intrinsics to generate a constant then he probably wanted that sequence instead of a simple _mm_set1_epi32 or a load from memory. But, if you're going to improve constant generation, please make it so that it can recognize not only the particular pattern described in this bug. More importantly, it should recognize the all-ones case (as a single pcmpeq) as a starting point. Then it can apply shifts to achieve the final result from the all-ones vector - shifts of any width, length or direction, including psrldq/pslldq. This would improve generated code in a wider range of cases.
