mesa/src/intel/compiler/brw_nir_lower_cs_intrinsics.c

/*
 * Copyright (c) 2016 Intel Corporation
 *
 * 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 "brw_nir.h"
#include "compiler/nir/nir_builder.h"

struct lower_intrinsics_state {
   nir_shader *nir;
   unsigned dispatch_width;
   nir_function_impl *impl;
   bool progress;
   nir_builder builder;
   unsigned local_workgroup_size;
};

static bool
lower_cs_intrinsics_convert_block(struct lower_intrinsics_state *state,
                                  nir_block *block)
{
   bool progress = false;
   nir_builder *b = &state->builder;
   nir_shader *nir = state->nir;

   /* Reuse calculated values inside the block. */
   nir_ssa_def *local_index = NULL;
   nir_ssa_def *local_id = NULL;

   nir_foreach_instr_safe(instr, block) {
      if (instr->type != nir_instr_type_intrinsic)
         continue;

      nir_intrinsic_instr *intrinsic = nir_instr_as_intrinsic(instr);

      b->cursor = nir_after_instr(&intrinsic->instr);

      nir_ssa_def *sysval;
      switch (intrinsic->intrinsic) {
      case nir_intrinsic_load_local_invocation_index:
      case nir_intrinsic_load_local_invocation_id: {
         /* First time we are using those, so let's calculate them. */
         if (!local_index) {
            assert(!local_id);

            nir_ssa_def *subgroup_id;
            if (state->local_workgroup_size <= state->dispatch_width)
               subgroup_id = nir_imm_int(b, 0);
            else
               subgroup_id = nir_load_subgroup_id(b);

            nir_ssa_def *thread_local_id =
               nir_imul_imm(b, subgroup_id, state->dispatch_width);
            nir_ssa_def *channel = nir_load_subgroup_invocation(b);
            nir_ssa_def *linear = nir_iadd(b, channel, thread_local_id);

            nir_ssa_def *size_x;
            nir_ssa_def *size_y;
            if (state->nir->info.cs.local_size_variable) {
               nir_ssa_def *size_xyz = nir_load_local_group_size(b);
               size_x = nir_channel(b, size_xyz, 0);
               size_y = nir_channel(b, size_xyz, 1);
            } else {
               size_x = nir_imm_int(b, nir->info.cs.local_size[0]);
               size_y = nir_imm_int(b, nir->info.cs.local_size[1]);
            }

            /* The local invocation index and ID must respect the following
             *
             *    gl_LocalInvocationID.x =
             *       gl_LocalInvocationIndex % gl_WorkGroupSize.x;
             *    gl_LocalInvocationID.y =
             *       (gl_LocalInvocationIndex / gl_WorkGroupSize.x) %
             *       gl_WorkGroupSize.y;
             *    gl_LocalInvocationID.z =
             *       (gl_LocalInvocationIndex /
             *        (gl_WorkGroupSize.x * gl_WorkGroupSize.y)) %
             *       gl_WorkGroupSize.z;
             *
             * However, the final % gl_WorkGroupSize.z does nothing unless we
             * accidentally end up with a gl_LocalInvocationIndex that is too
             * large so it can safely be omitted.
             */

            if (state->nir->info.cs.derivative_group != DERIVATIVE_GROUP_QUADS) {
               /* If we are not grouping in quads, just set the local invocatio
                * index linearly, and calculate local invocation ID from that.
                */
               local_index = linear;

               nir_ssa_def *id_x, *id_y, *id_z;
               id_x = nir_umod(b, local_index, size_x);
               id_y = nir_umod(b, nir_udiv(b, local_index, size_x), size_y);
               id_z = nir_udiv(b, local_index, nir_imul(b, size_x, size_y));
               local_id = nir_vec3(b, id_x, id_y, id_z);
            } else {
               /* For quads, first we figure out the 2x2 grid the invocation
                * belongs to -- treating extra Z layers as just more rows.
                * Then map that into local invocation ID (trivial) and local
                * invocation index.  Skipping Z simplify index calculation.
                */

               nir_ssa_def *one = nir_imm_int(b, 1);
               nir_ssa_def *double_size_x = nir_ishl(b, size_x, one);

               /* ID within a pair of rows, where each group of 4 is 2x2 quad. */
               nir_ssa_def *row_pair_id = nir_umod(b, linear, double_size_x);
               nir_ssa_def *y_row_pairs = nir_udiv(b, linear, double_size_x);

               nir_ssa_def *x =
                  nir_ior(b,
                          nir_iand(b, row_pair_id, one),
                          nir_iand(b, nir_ishr(b, row_pair_id, one),
                                   nir_imm_int(b, 0xfffffffe)));
               nir_ssa_def *y =
                  nir_ior(b,
                          nir_ishl(b, y_row_pairs, one),
                          nir_iand(b, nir_ishr(b, row_pair_id, one), one));

               local_id = nir_vec3(b, x,
                                   nir_umod(b, y, size_y),
                                   nir_udiv(b, y, size_y));
               local_index = nir_iadd(b, x, nir_imul(b, y, size_x));
            }
         }

         assert(local_id);
         assert(local_index);
         if (intrinsic->intrinsic == nir_intrinsic_load_local_invocation_id)
            sysval = local_id;
         else
            sysval = local_index;
         break;
      }

      case nir_intrinsic_load_subgroup_id:
         if (state->local_workgroup_size > 8)
            continue;

         /* For small workgroup sizes, we know subgroup_id will be zero */
         sysval = nir_imm_int(b, 0);
         break;

      case nir_intrinsic_load_num_subgroups: {
         if (state->nir->info.cs.local_size_variable) {
            nir_ssa_def *size_xyz = nir_load_local_group_size(b);
            nir_ssa_def *size_x = nir_channel(b, size_xyz, 0);
            nir_ssa_def *size_y = nir_channel(b, size_xyz, 1);
            nir_ssa_def *size_z = nir_channel(b, size_xyz, 2);
            nir_ssa_def *size = nir_imul(b, nir_imul(b, size_x, size_y), size_z);

            /* Calculate the equivalent of DIV_ROUND_UP. */
            sysval = nir_idiv(b,
                              nir_iadd_imm(b,
                                 nir_iadd_imm(b, size, state->dispatch_width), -1),
                              nir_imm_int(b, state->dispatch_width));
         } else {
            unsigned local_workgroup_size =
               nir->info.cs.local_size[0] * nir->info.cs.local_size[1] *
               nir->info.cs.local_size[2];
            unsigned num_subgroups =
               DIV_ROUND_UP(local_workgroup_size, state->dispatch_width);
            sysval = nir_imm_int(b, num_subgroups);
         }
         break;
      }

      default:
         continue;
      }

      nir_ssa_def_rewrite_uses(&intrinsic->dest.ssa, nir_src_for_ssa(sysval));
      nir_instr_remove(&intrinsic->instr);

      state->progress = true;
   }

   return progress;
}

static void
lower_cs_intrinsics_convert_impl(struct lower_intrinsics_state *state)
{
   nir_builder_init(&state->builder, state->impl);

   nir_foreach_block(block, state->impl) {
      lower_cs_intrinsics_convert_block(state, block);
   }

   nir_metadata_preserve(state->impl,
                         nir_metadata_block_index | nir_metadata_dominance);
}

bool
brw_nir_lower_cs_intrinsics(nir_shader *nir,
                            unsigned dispatch_width)
{
   assert(nir->info.stage == MESA_SHADER_COMPUTE);

   struct lower_intrinsics_state state = {
      .nir = nir,
      .dispatch_width = dispatch_width,
   };

   if (!nir->info.cs.local_size_variable) {
      state.local_workgroup_size = nir->info.cs.local_size[0] *
                                   nir->info.cs.local_size[1] *
                                   nir->info.cs.local_size[2];
   } else {
      state.local_workgroup_size = nir->info.cs.max_variable_local_size;
   }

   /* Constraints from NV_compute_shader_derivatives. */
   if (nir->info.cs.derivative_group == DERIVATIVE_GROUP_QUADS &&
       !nir->info.cs.local_size_variable) {
      assert(nir->info.cs.local_size[0] % 2 == 0);
      assert(nir->info.cs.local_size[1] % 2 == 0);
   } else if (nir->info.cs.derivative_group == DERIVATIVE_GROUP_LINEAR &&
              !nir->info.cs.local_size_variable) {
      assert(state.local_workgroup_size % 4 == 0);
   }

   nir_foreach_function(function, nir) {
      if (function->impl) {
         state.impl = function->impl;
         lower_cs_intrinsics_convert_impl(&state);
      }
   }

   return state.progress;
}