On Tue, Nov 10, 2015 at 1:21 AM, Kenneth Graunke <kenn...@whitecape.org> wrote:
> Normally, we rely on nir_lower_outputs_to_temporaries to create shadow
> variables for outputs, buffering the results and writing them all out
> at the end of the program. However, this is infeasible for tessellation
> control shader outputs.
>
> Tessellation control shaders can generate multiple output vertices, and
> write per-vertex outputs. These are arrays indexed by the vertex
> number; each thread only writes one element, but can read any other
> element - including those being concurrently written by other threads.
> The barrier() intrinsic synchronizes between threads.
>
> Even if we tried to shadow every output element (which is of dubious
> value), we'd have to read updated values in at barrier() time, which
> means we need to allow output reads.
>
> Most stages should continue using nir_lower_outputs_to_temporaries(),
> but in theory drivers could choose not to if they really wanted.
>
> Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
> ---
> src/glsl/nir/nir_intrinsics.h | 2 ++
> src/glsl/nir/nir_lower_io.c | 28 ++++++++++++++++++++--------
> src/glsl/nir/nir_print.c | 2 ++
> src/glsl/nir/nir_validate.c | 1 -
> 4 files changed, 24 insertions(+), 9 deletions(-)
>
> diff --git a/src/glsl/nir/nir_intrinsics.h b/src/glsl/nir/nir_intrinsics.h
> index 26ac7ce..b8d7d6c 100644
> --- a/src/glsl/nir/nir_intrinsics.h
> +++ b/src/glsl/nir/nir_intrinsics.h
> @@ -255,6 +255,8 @@ LOAD(ubo, 1, 1, NIR_INTRINSIC_CAN_ELIMINATE |
> NIR_INTRINSIC_CAN_REORDER)
> LOAD(input, 0, 1, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
> LOAD(per_vertex_input, 1, 1, NIR_INTRINSIC_CAN_ELIMINATE |
> NIR_INTRINSIC_CAN_REORDER)
> LOAD(ssbo, 1, 1, NIR_INTRINSIC_CAN_ELIMINATE)
> +LOAD(output, 0, 1, NIR_INTRINSIC_CAN_ELIMINATE)
> +LOAD(per_vertex_output, 1, 1, NIR_INTRINSIC_CAN_ELIMINATE)
>
> /*
> * Stores work the same way as loads, except now the first register input is
> diff --git a/src/glsl/nir/nir_lower_io.c b/src/glsl/nir/nir_lower_io.c
> index e460160..e81524c 100644
> --- a/src/glsl/nir/nir_lower_io.c
> +++ b/src/glsl/nir/nir_lower_io.c
> @@ -158,6 +158,15 @@ load_op(struct lower_io_state *state,
> nir_intrinsic_load_input;
> }
> break;
> + case nir_var_shader_out:
> + if (per_vertex) {
> + op = has_indirect ? nir_intrinsic_load_per_vertex_output_indirect :
> + nir_intrinsic_load_per_vertex_output;
> + } else {
> + op = has_indirect ? nir_intrinsic_load_output_indirect :
> + nir_intrinsic_load_output;
> + }
> + break;
> case nir_var_uniform:
> op = has_indirect ? nir_intrinsic_load_uniform_indirect :
> nir_intrinsic_load_uniform;
> @@ -188,14 +197,18 @@ nir_lower_io_block(nir_block *block, void *void_state)
> if (state->mode != -1 && state->mode != mode)
> continue;
>
> + if (mode != nir_var_shader_in &&
> + mode != nir_var_shader_out &&
> + mode != nir_var_uniform)
> + continue;
> +
> switch (intrin->intrinsic) {
> case nir_intrinsic_load_var: {
> - if (mode != nir_var_shader_in && mode != nir_var_uniform)
> - continue;
> -
> - bool per_vertex = stage_uses_per_vertex_inputs(state) &&
> - mode == nir_var_shader_in &&
> - !intrin->variables[0]->var->data.patch;
> + bool per_vertex = !intrin->variables[0]->var->data.patch &&
> + ((mode == nir_var_shader_in &&
> + stage_uses_per_vertex_inputs(state)) ||
> + (mode == nir_var_shader_out &&
> + stage_uses_per_vertex_outputs(state)));
With my suggested functions, this would reduce to
is_per_vertex_input() || is_per_vertex_output()
>
> nir_ssa_def *indirect;
> nir_ssa_def *vertex_index;
> @@ -239,8 +252,7 @@ nir_lower_io_block(nir_block *block, void *void_state)
> }
>
> case nir_intrinsic_store_var: {
> - if (intrin->variables[0]->var->data.mode != nir_var_shader_out)
> - continue;
> + assert(mode == nir_var_shader_out);
>
> nir_ssa_def *indirect;
> nir_ssa_def *vertex_index;
> diff --git a/src/glsl/nir/nir_print.c b/src/glsl/nir/nir_print.c
> index 23fcafe..f7f5fdf 100644
> --- a/src/glsl/nir/nir_print.c
> +++ b/src/glsl/nir/nir_print.c
> @@ -448,6 +448,8 @@ print_intrinsic_instr(nir_intrinsic_instr *instr,
> print_state *state)
> case nir_intrinsic_load_per_vertex_input_indirect:
> var_list = &state->shader->inputs;
> break;
> + case nir_intrinsic_load_output:
> + case nir_intrinsic_load_output_indirect:
> case nir_intrinsic_store_output:
> case nir_intrinsic_store_output_indirect:
> case nir_intrinsic_store_per_vertex_output:
> diff --git a/src/glsl/nir/nir_validate.c b/src/glsl/nir/nir_validate.c
> index a42e830..841bace 100644
> --- a/src/glsl/nir/nir_validate.c
> +++ b/src/glsl/nir/nir_validate.c
> @@ -422,7 +422,6 @@ validate_intrinsic_instr(nir_intrinsic_instr *instr,
> validate_state *state)
> assert(instr->variables[0]->var->data.mode != nir_var_shader_in &&
> instr->variables[0]->var->data.mode != nir_var_uniform &&
> instr->variables[0]->var->data.mode != nir_var_shader_storage);
> - assert(instr->variables[1]->var->data.mode != nir_var_shader_out);
> break;
> default:
> break;
> --
> 2.6.2
>
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