On Thu, Mar 17, 2016 at 10:21 AM, Jason Ekstrand <ja...@jlekstrand.net> wrote:
> This little series prepares the backend compiler for invariant and precise > by removing any potentially unsafe optimizations. The easiest > implementation for invariant and precise seems to be the same: Don't change > the semantics of invariant or precise values. This means that we need to > track what values are invariant or precise and be very careful how we > optimize them. In the backend, it's easier to just not do those > optimizations than to try and plumb that information through accurately. > Fortunately, NIR is doing a good enough job that this can be done with a > minimum of shader-db damage. > There has been some discussion on patches on the ML and in the cube as to how much we want to delete. According to my (admittedly a bit dated) shader-db, we can delete quite a lot without really hurting much. However, not everyone seems comfortable with this. I don't much care about deleting everything I just decided to try it and see what happens. Here are the things I think we do need to do: 1) Get rid of RCP+RSQ 2) Stop constant-folding RCP 3) Make opt_vector_float correct regardless of opt_algebraic handling mov.sat of immediates. I think (1) and (2) are enough for getting "invariant" and "precise" correct. The bugs in opt_vector_float I think are real, but my patches to fix them are equally bogus. The rest of the series is just deleting potentially dead code. I don't care too much either way on that. To summarize, the other potentially deletable things are: 1) the MAD optimization in fs_opt_algebraic 2) the SEL.sat optimization (both fs and vec4) 3) the trivial floating-point algebraic optimizations (most of these are probably precise-safe but they aren't doing anything) 4) MOV.sat on immediates Opinions? --Jason > Jason Ekstrand (9): > i965/fs: Remove the RCP+RSQ peephole > nir/algebraic: Add two more fsat optimizations > i965/fs: Get rid of the sel.sat peephole > i965/fs: Get rid of all remaining algebraic optimizations for floats > i965/fs: Don't constant-fold RCP > i965/vec4: Don't constant propagate saturated values > i965/vec4: Don't allow type conversion in opt_vector_float > i965/vec4: Handle saturated constants in opt_vector_float > i965/vec4: Disable algebraic optimizations on floats > > src/compiler/nir/nir_opt_algebraic.py | 2 + > src/mesa/drivers/dri/i965/brw_fs.cpp | 119 > ++++----------------- > .../drivers/dri/i965/brw_fs_copy_propagation.cpp | 15 --- > src/mesa/drivers/dri/i965/brw_vec4.cpp | 49 ++++----- > .../drivers/dri/i965/brw_vec4_copy_propagation.cpp | 3 + > 5 files changed, 41 insertions(+), 147 deletions(-) > > -- > 2.5.0.400.gff86faf > >
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