https://gcc.gnu.org/bugzilla/show_bug.cgi?id=73350
--- Comment #6 from Eric Botcazou <ebotcazou at gcc dot gnu.org> --- > The "simplest" way would be to have separate UNSPECs for all ops (but that > explodes the number of unspecs I guess). Currently we get > > (insn 21 20 22 (parallel [ > (set (reg:V16SF 110) > (vec_merge:V16SF (plus:V16SF (reg:V16SF 111) > (reg:V16SF 112)) > (reg:V16SF 113) > (reg:HI 114))) > (unspec [ > (const_int 9 [0x9]) > ] UNSPEC_EMBEDDED_ROUNDING) > ]) > "/home/space/rguenther/install/gcc-7.0/lib64/gcc/x86_64-pc-linux-gnu/7.0.0/ > include/avx512fintrin.h":2113 -1 > (nil)) > > and CSE happily looks into parallels, not interpreting the unspec to affect > the set. Rightfully so, UNSPECs are regular operations and there is no data dependency in the above pattern. So another way would be sth like > > (insn (set (reg:V16SF 110) > (vec_merge:V16SF (plus:V16SF (reg:V16SF 111) > (reg:V16SF 112)) > (reg:V16SF 113) > (reg:HI 114)))) > > (insn (set (reg:V16SF 110) (unspec [ (reg:V16SF 110) (const_int 9) ] > UNSPEC_EMBEDDED_ROUNDING) ]) > > or merging this "rounding operation" into the operation (around the > plus, one of its operands or around the merge). Right, the data dependency needs to be visible somehow or other in the RTL.
