[Mesa-dev] [PATCH 6/8] i965/fs: Handle conditional discards.

[Kenneth Graunke]

On Tuesday, February 24, 2015 01:25:18 PM Connor Abbott wrote:
> On Tue, Feb 24, 2015 at 5:19 AM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> > For conditional discards, we can call emit_bool_to_cond_code to generate
> > the condition in f0.0.  However, we want it in f0.1.  The flag value is
> > always produced by the last instruction emit_bool_to_cond_code
> > generates, so we can simply get the last instruction and patch it up.
> 
> Is this left over from an earlier version? It seems to me like we're
> just doing the dumb thing (rather than emit_bool_to_cond_code()) here
> and letting the i965 optimizer clean it up for both GLSL IR and NIR.

Oops.  Yes :)  I was originally doing:

emit_bool_to_cond_code(new(mem_ctx) ir_expression(ir_unop_logic_not,
                                                  ir->condition))
cmp = (fs_inst *) this->instructions.get_tail();

but that seemed more fragile for no real benefit - it actually emitted
ir->condition as a boolean, then did an AND.z <bool> 1D to produce the
condition code (making cmp an AND!).  Same number of instructions.

I'll fix up the commit message.

> >
> > Nothing generates these today, but that will change shortly.
> >
> > Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> > ---
> >  src/mesa/drivers/dri/i965/brw_fs_nir.cpp     | 22 ++++++++++++++--------
> >  src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 21 ++++++++++++---------
> >  2 files changed, 26 insertions(+), 17 deletions(-)
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > index 90eecae..6354bde 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > @@ -1149,16 +1149,22 @@ fs_visitor::nir_emit_intrinsic(nir_intrinsic_instr *instr)
> >     bool has_indirect = false;
> >
> >     switch (instr->intrinsic) {
> > -   case nir_intrinsic_discard: {
> > +   case nir_intrinsic_discard:
> > +   case nir_intrinsic_discard_if: {
> >        /* We track our discarded pixels in f0.1.  By predicating on it, we can
> > -       * update just the flag bits that aren't yet discarded.  By emitting a
> > -       * CMP of g0 != g0, all our currently executing channels will get turned
> > -       * off.
> > +       * update just the flag bits that aren't yet discarded.  If there's no
> > +       * condition, we emit a CMP of g0 != g0, so all currently executing
> > +       * channels will get turned off.
> >         */
> > -      fs_reg some_reg = fs_reg(retype(brw_vec8_grf(0, 0),
> > -                                    BRW_REGISTER_TYPE_UW));
> > -      fs_inst *cmp = emit(CMP(reg_null_f, some_reg, some_reg,
> > -                              BRW_CONDITIONAL_NZ));
> > +      fs_inst *cmp;
> > +      if (instr->intrinsic == nir_intrinsic_discard_if) {
> > +         cmp = emit(CMP(reg_null_f, get_nir_src(instr->src[0]),
> > +                        fs_reg(0), BRW_CONDITIONAL_Z));
> > +      } else {
> > +         fs_reg some_reg = fs_reg(retype(brw_vec8_grf(0, 0),
> > +                                       BRW_REGISTER_TYPE_UW));
> > +         cmp = emit(CMP(reg_null_f, some_reg, some_reg, BRW_CONDITIONAL_NZ));
> > +      }
> >        cmp->predicate = BRW_PREDICATE_NORMAL;
> >        cmp->flag_subreg = 1;
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> > index b1b75821..75254a1 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> > @@ -2415,17 +2415,20 @@ fs_visitor::visit(ir_swizzle *ir)
> >  void
> >  fs_visitor::visit(ir_discard *ir)
> >  {
> > -   assert(ir->condition == NULL); /* FINISHME */
> > -
> >     /* We track our discarded pixels in f0.1.  By predicating on it, we can
> > -    * update just the flag bits that aren't yet discarded.  By emitting a
> > -    * CMP of g0 != g0, all our currently executing channels will get turned
> > -    * off.
> > +    * update just the flag bits that aren't yet discarded.  If there's no
> > +    * condition, we emit a CMP of g0 != g0, so all currently executing
> > +    * channels will get turned off.
> >      */
> > -   fs_reg some_reg = fs_reg(retype(brw_vec8_grf(0, 0),
> > -                                   BRW_REGISTER_TYPE_UW));
> > -   fs_inst *cmp = emit(CMP(reg_null_f, some_reg, some_reg,
> > -                           BRW_CONDITIONAL_NZ));
> > +   fs_inst *cmp;
> > +   if (ir->condition) {
> > +      ir->condition->accept(this);
> > +      cmp = emit(CMP(reg_null_f, this->result, fs_reg(0), BRW_CONDITIONAL_Z));
> > +   } else {
> > +      fs_reg some_reg = fs_reg(retype(brw_vec8_grf(0, 0),
> > +                                      BRW_REGISTER_TYPE_UW));
> > +      cmp = emit(CMP(reg_null_f, some_reg, some_reg, BRW_CONDITIONAL_NZ));
> > +   }
> >     cmp->predicate = BRW_PREDICATE_NORMAL;
> >     cmp->flag_subreg = 1;
> >
> > --
> > 2.2.2
> >
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/mesa-dev
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