https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113134
--- Comment #14 from JuzheZhong <juzhe.zhong at rivai dot ai> --- (In reply to Tamar Christina from comment #13) > (In reply to JuzheZhong from comment #12) > > (In reply to Tamar Christina from comment #11) > > > (In reply to JuzheZhong from comment #10) > > > > (In reply to Tamar Christina from comment #9) > > > > > (In reply to JuzheZhong from comment #8) > > > > > > Suppose the loop mask is generated by whilelo instruction of ARM > > > > > > SVE. > > > > > > > > > > > > Suppose we have 8 elements in a single whole vector. > > > > > > > > > > > > mask = whilo (0, res) if res = 6, then mask = 11111000. > > > > > > data = 12345678 > > > > > > > > > > > > Then if it is early break. You are reversing both data and mask as > > > > > > follows: > > > > > > > > > > > > new_mask = 00011111 > > > > > > new_data = 87654321 > > > > > > > > > > > > Then use the EXTRACT_LAST, we will get value = 1 for early break. > > > > > > > > > > > > Am I right ? > > > > > > > > > > Yeah, the idea being the scalar loop will then run from 1 to 6 to do > > > > > any > > > > > side effects that we couldn't apply. > > > > > > > > > > We went with this approach first because it works for non-masked > > > > > architectures too. In GCC-15 we'll try to implement staying entirely > > > > > inside > > > > > a vector loop by splitting the mask in elements until first active and > > > > > element from first active so we can correctly mask the operations. > > > > > > > > Ok. For the current approach. Isn't it the first element is always > > > > element 0 > > > > ? > > > > > > > > Since for ARM SVE loop mask is generated by whilelo instructions, it > > > > always > > > > set > > > > mask bit from 0 to the last active element - 1. > > > > > > sure, but you can't use BIT_FIELD_REF on VLA vectors. > > > > So, for length partial vector. We can use VEC_EXTRACT with index = 0 since > > VEC_EXTRACT optab allows VLA vectors now for length target. > > Sounds good :) I wonder whether ARM SVE can also use this approach VEC_EXTRACT with index = 0. I guess the only issue is that when mask = all zero. That is, there is no active elements, What behavior should be here for early break ?
