Christophe Lyon <christophe.l...@linaro.org> writes: > This patch adds support for auto-vectorization of average value > computation using vhadd or vrhadd, for both MVE and Neon. > > The patch adds the needed [u]avg<mode>3_[floor|ceil] patterns to > vec-common.md, I'm not sure how to factorize them without introducing > an unspec iterator? > > It also adds tests for 'floor' and for 'ceil', each for MVE and Neon. > > Vectorization works with 8-bit and 16 bit input/output vectors, but > not with 32-bit ones because the vectorizer expects wider types > availability for the intermediate values, but int32_t + int32_t does > not involve wider types in the IR. > > The testcases use a cast to int64_t to workaround this and enable > vectorization with vectors of 32-bit elements.
We're probably in violent agreement here and just phrasing it differently :-), but IMO this isn't a workaround. It would be actively wrong to use V(R)HADD for the (u)int32_t version without the cast: V(R)HADD effectively computes a 33-bit addition result, instead of the 32-bit addition result in the original (cast-free) source code. I guess one could argue that overflow is undefined for int32_t + int32_t and so we could compute the full 33-bit result instead of using modulo arithmetic. That might be too surprising though. It also wouldn't help with uint32_t, since we do need to use modulo arithmetic for uint32_t + uint32_t. So personally I think it would be better to drop the last two paragraphs. The patch LGTM though, thanks. Richard
