On 06/29/2014 11:18 PM, Matt Turner wrote:
> To implement the unlit_centroid_workaround, previously we emitted
>
> (+f0) pln(8) g20<1>F g16.4<0,1,0>F g4<8,8,1>F { align1 1Q };
> (-f0) pln(8) g20<1>F g16.4<0,1,0>F g2<8,8,1>F { align1 1Q };
>
> where the flag register contains the channel enable bits from g0.
>
> Since the predicates are complementary, the pair of pln instructions
> write to non-overlapping components of the destination, which is the
> case that the dependency control hints are designed for.
>
> Typically setting dependency control hints on predicated instructions
> isn't safe (if an instruction doesn't execute due to the predicate, it
> won't update the scoreboard, leaving it in a bad state) but since we
> must have at least one channel executing (i.e., +f0 is true for some
> channel) by virtue of the fact that the thread is running, we can put
> the +f0 pln instruction last and set the hints:
>
> (-f0) pln(8) g20<1>F g16.4<0,1,0>F g2<8,8,1>F { align1 NoDDClr 1Q };
> (+f0) pln(8) g20<1>F g16.4<0,1,0>F g4<8,8,1>F { align1 NoDDChk 1Q };
And there's no chance of instruction scheduling ever putting something
between? Seems unlikely, but... would be bad.
> ---
> src/mesa/drivers/dri/i965/brw_fs.cpp | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp
> b/src/mesa/drivers/dri/i965/brw_fs.cpp
> index 3b7a170..5a3d1d3 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> @@ -1178,15 +1178,20 @@ fs_visitor::emit_general_interpolation(ir_variable
> *ir)
>
> fs_inst *inst;
> inst = emit_linterp(attr, fs_reg(interp),
> interpolation_mode,
> + false, false);
> + inst->predicate = BRW_PREDICATE_NORMAL;
> + inst->predicate_inverse = true;
> + if (brw->has_pln)
> + inst->no_dd_clear = true;
> +
> + inst = emit_linterp(attr, fs_reg(interp),
> interpolation_mode,
> ir->data.centroid &&
> !key->persample_shading,
> ir->data.sample ||
> key->persample_shading);
> inst->predicate = BRW_PREDICATE_NORMAL;
> inst->predicate_inverse = false;
> + if (brw->has_pln)
> + inst->no_dd_check = true;
>
> - inst = emit_linterp(attr, fs_reg(interp),
> interpolation_mode,
> - false, false);
> - inst->predicate = BRW_PREDICATE_NORMAL;
> - inst->predicate_inverse = true;
> } else {
> emit_linterp(attr, fs_reg(interp), interpolation_mode,
> ir->data.centroid && !key->persample_shading,
>
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