[Mesa-dev] [PATCH] nir: add flt comparision simplification

[Timothy Arceri]

On Fri, 2017-01-13 at 08:49 +1100, Timothy Arceri wrote:
> Actually I might just try moving this to the late block as the reason
> for 'is_not_used_by_conditional' is to stop getting in the way of
> ffmas.

Ignore this that just results in the opts doing nothing. The whole
point is to avoid ffmas when they are not making use of the conditional
modifier.

> 
> On Fri, 2017-01-13 at 08:29 +1100, Timothy Arceri wrote:
> > Didn't turn out as useful as I'd hoped, but it will help alot more
> > on
> > i965 by reducing regressions when we drop
> > brw_do_channel_expressions()
> > and brw_do_vector_splitting().
> > 
> > I'm not sure how much sense 'is_not_used_by_conditional' makes on
> > platforms other than i965 but since this is a new opt it at least
> > won't do any harm.
> > 
> > shader-db BDW:
> > 
> > total instructions in shared programs: 13060410 -> 13060242 (-
> > 0.00%)
> > instructions in affected programs: 44880 -> 44712 (-0.37%)
> > helped: 86
> > HURT: 0
> > 
> > total cycles in shared programs: 256585692 -> 256584248 (-0.00%)
> > cycles in affected programs: 8060766 -> 8059322 (-0.02%)
> > helped: 177
> > HURT: 33
> > ---
> >  src/compiler/nir/nir_opt_algebraic.py |  4 ++++
> >  src/compiler/nir/nir_search_helpers.h | 15 +++++++++++++++
> >  2 files changed, 19 insertions(+)
> > 
> > diff --git a/src/compiler/nir/nir_opt_algebraic.py
> > b/src/compiler/nir/nir_opt_algebraic.py
> > index 3c8318c..59f9e43 100644
> > --- a/src/compiler/nir/nir_opt_algebraic.py
> > +++ b/src/compiler/nir/nir_opt_algebraic.py
> > @@ -159,6 +159,10 @@ optimizations = [
> >     # a != 0.0
> >     (('flt', 0.0, ('fabs', a)), ('fne', a, 0.0)),
> >  
> > +   # ignore this opt when the result is used by a bcsel or if so
> > we
> > can make
> > +   # use of conditional modifiers on supported hardware.
> > +   (('flt(is_not_used_by_conditional)', ('fadd(is_used_once)', a,
> > ('fneg', b)), 0.0), ('flt', a, b)),
> > +
> >     (('fge', ('fneg', ('fabs', a)), 0.0), ('feq', a, 0.0)),
> >     (('bcsel', ('flt', b, a), b, a), ('fmin', a, b)),
> >     (('bcsel', ('flt', a, b), b, a), ('fmax', a, b)),
> > diff --git a/src/compiler/nir/nir_search_helpers.h
> > b/src/compiler/nir/nir_search_helpers.h
> > index ddaff52..05bd317 100644
> > --- a/src/compiler/nir/nir_search_helpers.h
> > +++ b/src/compiler/nir/nir_search_helpers.h
> > @@ -158,4 +158,19 @@ is_not_used_by_if(nir_alu_instr *instr)
> >     return list_empty(&instr->dest.dest.ssa.if_uses);
> >  }
> >  
> > +static inline bool
> > +is_not_used_by_conditional(nir_alu_instr *instr)
> > +{
> > +   if (!is_not_used_by_if(instr))
> > +      return false;
> > +
> > +   nir_foreach_use(use, &instr->dest.dest.ssa) {
> > +      if (use->parent_instr->type == nir_instr_type_alu &&
> > +          nir_instr_as_alu(use->parent_instr)->op == nir_op_bcsel)
> > +         return false;
> > +   }
> > +
> > +   return true;
> > +}
> > +
> >  #endif /* _NIR_SEARCH_ */
> 
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