On Fri, May 8, 2015 at 3:36 AM, Kenneth Graunke <kenn...@whitecape.org> wrote: > According to Glenn, shifts on R600 have 5x the throughput as multiplies. > > Intel GPUs have strange integer multiplication restrictions - on most > hardware, MUL actually only does a 32-bit x 16-bit multiply. This > means the arguments aren't commutative, which can limit our constant > propagation options. SHL has no such restrictions. > > Shifting is probably reasonable on most people's hardware, so let's just > do that. > > i965 shader-db results (using NIR for VS): > total instructions in shared programs: 7432587 -> 7388982 (-0.59%) > instructions in affected programs: 1360411 -> 1316806 (-3.21%) > helped: 5772 > HURT: 0
Just to close the loop, I ran shader-db with this patch on top of my integer multiplication series, and it doesn't change any instruction counts on i965. (I also tried with all other power-of-two multiplications for shift values < 31.) We may want to do it for other reasons though. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
