On Sat, Aug 20, 2011 at 2:44 PM, Uros Bizjak <ubiz...@gmail.com> wrote: > On Sat, Aug 20, 2011 at 11:31 PM, H.J. Lu <hjl.to...@gmail.com> wrote: > >> We can also implement MULX with split: >> >> (define_split >> [(parallel [(set (match_operand:<DWI> 0 "register_operand" "") >> (mult:<DWI> >> (zero_extend:<DWI> >> (match_operand:DWIH 1 "nonimmediate_operand" "")) >> (zero_extend:<DWI> >> (match_operand:DWIH 2 "nonimmediate_operand" "")))) >> (clobber (reg:CC FLAGS_REG))])] >> "TARGET_BMI2 >> && ix86_binary_operator_ok (MULT, <MODE>mode, operands)" >> [(set (match_operand:<DWI> 0 "register_operand" "") >> (mult:<DWI> >> (zero_extend:<DWI> >> (match_operand:DWIH 1 "register_operand" "")) >> (zero_extend:<DWI> >> (match_operand:DWIH 2 "nonimmediate_operand" ""))))]) > > Well, this is unconditional splitter, no better than current approach > where the pattern is expanded directly. > > If you want to squeeze out the last 0.005% of performance, you should > add BMI alternative to existing umul pattern, leave the choice of > alternative to RA and split the exact alternative (that is, you need > some true_regnum calls in splitter constraint) after reload to mulx > pattern. Please, see new patterns for how this should be done. > > I'm not against this approach, but after 10 hours of hacking, I just > wanted to leave it to an interested reader ;)
We won't use split then. Thanks. -- H.J.
