https://gcc.gnu.org/bugzilla/show_bug.cgi?id=73350
--- Comment #7 from Marc Glisse <glisse at gcc dot gnu.org> --- (In reply to Richard Biener from comment #5) > The "simplest" way would be to have separate UNSPECs for all ops (but that > explodes the number of unspecs I guess). Would that be so bad? As far as gcc understands addition, this is not an addition, representing it with 'plus' is a lie. > 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). I guess the unspec alone wouldn't match anything, which prevents constant propagation, but I would still fear combine merging a regular addition with a rounded one (when they simplify), producing a single rounded operation. If you want to wrap plus with unspecs, you may have to put them on both operands and the result to be safe...
