On Fri, Mar 20, 2015 at 1:58 PM, Ian Romanick <i...@freedesktop.org> wrote: > From: Ian Romanick <ian.d.roman...@intel.com> > > An expression like -(x * 8) becomes (x * -8). > > Much of the hurt caused by this change appears to be from CSE not being > able to see (x * -8) and (x * 8) as common. Previously -(x * 8) and (x > * 8) would have had a common subexpression. Later patches address this > at the GLSL IR level, but additional work will be needed in NIR and the > i965 backend.
I've got patches that do the opposite of this: pull the negate out of the multiplication. It was a three patch series and one of the patches was never reviewed. I would have just pushed them, but they hurt NIR and I haven't figured out how to fix that yet. The third patch recognizes neg(mul(...)) in the GLSL -> i965 translators and set a source modifier to avoid an additional instruction from the case where we can't eliminate the negates entirely. It's not just recognizing -(x * y) and (x * -y) that's problematic, it's (-x * y) as well. My patches handle that case too. So I'd probably rather not take this patch. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
