On Fri, Mar 20, 2015 at 4:14 PM, Ian Romanick <i...@freedesktop.org> wrote: > On 03/20/2015 02:51 PM, Matt Turner wrote: >> 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. > > Why is pulling the negation off a constant useful?
Right... constants... NIR doesn't know what a negative constant is, at least not at the moment. Sorry for the noise. > This patch only pushes the negation onto a constant, and constant > folding will eliminate that. There's even an assertion in the code to > be sure. :) > > You have links (or a branch) to those patches? I'd like to compare the > results with these patches. > >> 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 irony being that this patch with 19 and 20 are mostly helpful with > NIR. :) > >> 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. > > I think patch 19 & 20 cover all the cases for CSE. > >> 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 _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
