[Mesa-dev] [PATCH] nir: Add an IO scalarizing pass using the intrinsic's first_component.

[Timothy Arceri]

On Fri, 2016-08-05 at 16:27 -0700, Eric Anholt wrote:
> vc4 wants to have per-scalar IO load/stores so that dead code
> elimination
> can happen on a more granular basis, which it has been doing in the
> backend using a multiplication by 4 of the intrinsic's
> driver_location.
> We can represent it properly in the NIR using the first_component
> field,
> though.
> ---
> 
> Next part of the vc4 GTN series.  I can't do uniforms because they
> don't have a first-component field.
> 
> NIR developers -- is this the right usage of the first-component
> field?  Also, do I need to be splitting up the variable declarations
> if I do this?  There's a check during shader printing that the
> fractional component of the variable matches the component field of
> the intrinsic, even if the intrinsics's component value would lie
> within the vector variable.

This is just because the field was intended to be used with the
ARB_enhanced_layouts component packing rules, so currently there should
be no way for a component value to lie within the vector variable.

Your use of the component field seems fine to me.

> 
>  src/compiler/Makefile.sources             |   1 +
>  src/compiler/nir/nir.h                    |   1 +
>  src/compiler/nir/nir_lower_io_to_scalar.c | 129
> ++++++++++++++++++++++++++++++
>  3 files changed, 131 insertions(+)
>  create mode 100644 src/compiler/nir/nir_lower_io_to_scalar.c
> 
> diff --git a/src/compiler/Makefile.sources
> b/src/compiler/Makefile.sources
> index 0ff9b23e4c38..04016d32db56 100644
> --- a/src/compiler/Makefile.sources
> +++ b/src/compiler/Makefile.sources
> @@ -201,6 +201,7 @@ NIR_FILES = \
>  	nir/nir_lower_indirect_derefs.c \
>  	nir/nir_lower_io.c \
>  	nir/nir_lower_io_to_temporaries.c \
> +	nir/nir_lower_io_to_scalar.c \
>  	nir/nir_lower_io_types.c \
>  	nir/nir_lower_passthrough_edgeflags.c \
>  	nir/nir_lower_phis_to_scalar.c \
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index 9ce5be2176d9..379a5f8e022e 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2398,6 +2398,7 @@ void nir_lower_alu_to_scalar(nir_shader
> *shader);
>  void nir_lower_load_const_to_scalar(nir_shader *shader);
>  
>  void nir_lower_phis_to_scalar(nir_shader *shader);
> +void nir_lower_io_to_scalar(nir_shader *shader, nir_variable_mode
> mask);
>  
>  void nir_lower_samplers(nir_shader *shader,
>                          const struct gl_shader_program
> *shader_program);
> diff --git a/src/compiler/nir/nir_lower_io_to_scalar.c
> b/src/compiler/nir/nir_lower_io_to_scalar.c
> new file mode 100644
> index 000000000000..f2345d58acfc
> --- /dev/null
> +++ b/src/compiler/nir/nir_lower_io_to_scalar.c
> @@ -0,0 +1,129 @@
> +/*
> + * Copyright © 2016 Broadcom
> + *
> + * Permission is hereby granted, free of charge, to any person
> obtaining a
> + * copy of this software and associated documentation files (the
> "Software"),
> + * to deal in the Software without restriction, including without
> limitation
> + * the rights to use, copy, modify, merge, publish, distribute,
> sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom
> the
> + * Software is furnished to do so, subject to the following
> conditions:
> + *
> + * The above copyright notice and this permission notice (including
> the next
> + * paragraph) shall be included in all copies or substantial
> portions of the
> + * Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
> EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
> MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO
> EVENT SHALL
> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
> OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> OTHER DEALINGS
> + * IN THE SOFTWARE.
> + */
> +
> +#include "nir.h"
> +#include "nir_builder.h"
> +
> +/** @file nir_lower_io_to_scalar.c
> + *
> + * Replaces nir_load_input/nir_store_output operations with
> num_components !=
> + * 1 with individual per-channel operations.
> + */
> +
> +static void
> +lower_load_input_to_scalar(nir_builder *b, nir_intrinsic_instr
> *intr)
> +{
> +   b->cursor = nir_before_instr(&intr->instr);
> +
> +   assert(intr->dest.is_ssa);
> +
> +   nir_ssa_def *loads[4];
> +
> +   for (unsigned i = 0; i < intr->num_components; i++) {
> +      nir_intrinsic_instr *chan_intr =
> +         nir_intrinsic_instr_create(b->shader, intr->intrinsic);
> +      nir_ssa_dest_init(&chan_intr->instr, &chan_intr->dest,
> +                        1, intr->dest.ssa.bit_size, NULL);
> +      chan_intr->num_components = 1;
> +
> +      nir_intrinsic_set_base(chan_intr, nir_intrinsic_base(intr));
> +      nir_intrinsic_set_component(chan_intr,
> nir_intrinsic_component(intr) + i);
> +      /* offset */
> +      chan_intr->src[0] = intr->src[0];
> +
> +      nir_builder_instr_insert(b, &chan_intr->instr);
> +
> +      loads[i] = &chan_intr->dest.ssa;
> +   }
> +
> +   nir_ssa_def_rewrite_uses(&intr->dest.ssa,
> +                            nir_src_for_ssa(nir_vec(b, loads,
> +                                                    intr-
> >num_components)));
> +   nir_instr_remove(&intr->instr);
> +}
> +
> +static void
> +lower_store_output_to_scalar(nir_builder *b, nir_intrinsic_instr
> *intr)
> +{
> +   b->cursor = nir_before_instr(&intr->instr);
> +
> +   nir_ssa_def *value = nir_ssa_for_src(b, intr->src[0], intr-
> >num_components);
> +
> +   for (unsigned i = 0; i < intr->num_components; i++) {
> +      if (!(nir_intrinsic_write_mask(intr) & (1 << i)))
> +         continue;
> +
> +      nir_intrinsic_instr *chan_intr =
> +         nir_intrinsic_instr_create(b->shader, intr->intrinsic);
> +      chan_intr->num_components = 1;
> +
> +      nir_intrinsic_set_base(chan_intr, nir_intrinsic_base(intr));
> +      nir_intrinsic_set_write_mask(chan_intr, 0x1);
> +      nir_intrinsic_set_component(chan_intr,
> nir_intrinsic_component(intr) + i);
> +
> +      /* value */
> +      chan_intr->src[0] = nir_src_for_ssa(nir_channel(b, value, i));
> +      /* offset */
> +      chan_intr->src[1] = intr->src[1];
> +
> +      nir_builder_instr_insert(b, &chan_intr->instr);
> +   }
> +
> +   nir_instr_remove(&intr->instr);
> +}
> +
> +void
> +nir_lower_io_to_scalar(nir_shader *shader, nir_variable_mode mask)
> +{
> +   nir_foreach_function(function, shader) {
> +      if (function->impl) {
> +         nir_builder b;
> +         nir_builder_init(&b, function->impl);
> +
> +         nir_foreach_block(block, function->impl) {
> +            nir_foreach_instr_safe(instr, block) {
> +               if (instr->type != nir_instr_type_intrinsic)
> +                  continue;
> +
> +               nir_intrinsic_instr *intr =
> nir_instr_as_intrinsic(instr);
> +
> +               if (intr->num_components == 1)
> +                  continue;
> +
> +               switch (intr->intrinsic) {
> +               case nir_intrinsic_load_input:
> +                  if (mask & nir_var_shader_in)
> +                     lower_load_input_to_scalar(&b, intr);
> +                  break;
> +               case nir_intrinsic_store_output:
> +                  if (mask & nir_var_shader_out)
> +                     lower_store_output_to_scalar(&b, intr);
> +                  break;
> +               default:
> +                  break;
> +               }
> +            }
> +         }
> +      }
> +   }
> +}