/*
 * Copyright © 2022 Valve Corporation
 *
 * SPDX-License-Identifier: MIT
 */

#include "ac_gpu_info.h"
#include "ac_nir.h"
#include "nir_builder.h"

/*
 * These NIR passes are used to lower NIR cross-stage I/O intrinsics
 * between task and mesh shader stages into the memory accesses
 * that actually happen on the HW.
 *
 */

typedef struct {
   /* True if the lowering needs to insert shader query. */
   bool has_query;
} lower_tsms_io_state;

static nir_def *
task_num_entries(nir_builder *b,
                 lower_tsms_io_state *s)
{
   nir_def *ring = nir_load_ring_task_draw_amd(b);
   nir_def *bytes = nir_channel(b, ring, 2);
   return nir_udiv_imm(b, bytes, AC_TASK_DRAW_ENTRY_BYTES);
}

static nir_def *
task_payload_entry_bytes(nir_builder *b,
                         lower_tsms_io_state *s)
{
   nir_def *num_entries = task_num_entries(b, s);
   nir_def *ring = nir_load_ring_task_payload_amd(b);
   nir_def *bytes = nir_channel(b, ring, 2);

   /* num_entries must be a power of two,
    * use that to implement a division using a shift.
    */
   nir_def *lsb = nir_find_lsb(b, num_entries);
   return nir_ushr(b, bytes, lsb);
}

static nir_def *
task_workgroup_index(nir_builder *b,
                     lower_tsms_io_state *s)
{
   nir_def *id = nir_load_workgroup_id(b);

   nir_def *x = nir_channel(b, id, 0);
   nir_def *y = nir_channel(b, id, 1);
   nir_def *z = nir_channel(b, id, 2);

   nir_def *grid_size = nir_load_num_workgroups(b);
   nir_def *grid_size_x = nir_channel(b, grid_size, 0);
   nir_def *grid_size_y = nir_channel(b, grid_size, 1);

   return nir_iadd(b, nir_imul(b, nir_imul(b, grid_size_x, grid_size_y), z),
                      nir_iadd(b, nir_imul(b, grid_size_x, y), x));
}

static nir_def *
task_ring_entry_index(nir_builder *b,
                      lower_tsms_io_state *s)
{
   /* Task shader ring_entry shader argument:
    *
    * - It's a copy of write_ptr[31:0] from the task control buffer.
    * - The same value (which is the initial value at dispatch)
    *   seems to be copied to all workgroups in the same dispatch,
    *   therefore a workgroup index needs to be added.
    * - write_ptr must be initialized to num_entries so ring_entry needs
    *   AND with num_entries - 1 to get the correct meaning.
    *   Note that num_entries must be a power of two.
    */
   nir_def *ring_entry = nir_load_task_ring_entry_amd(b);
   nir_def *num_entries = task_num_entries(b, s);
   nir_def *idx = nir_iadd_nuw(b, ring_entry, task_workgroup_index(b, s));
   return nir_iand(b, idx, nir_isub(b, num_entries, nir_imm_int(b, 1)));
}

static nir_def *
task_draw_ready_bit(nir_builder *b,
                    lower_tsms_io_state *s)
{
   /* Value of the ready bit is 1 for odd and 0 for even passes through the draw ring.
    *
    * The ring_entry is a copy of the write_ptr. We use that to determine whether
    * the current pass through the draw ring is odd or even, so we can write the
    * correct value to the draw ready bit.
    *
    * This tells the firmware that it can now start launching mesh shader workgroups.
    * The encoding of the last dword of the draw ring entry is:
    * - bit 0: Draw ready bit.
    *          Its meaning flips on every pass through the entry.
    * - bit 1: Packet end bit.
    *          The firmware uses this to mark the entry after the last one
    *          used by the current task dispatch.
    * - bits [2:31] unused.
    *
    * Task shaders MUST write the draw ready bit to the draw ring
    * before they finish. The firmware waits for the shader to write
    * this bit before it reads the mesh dispatch size to launch the
    * mesh shader workgroups.
    *
    * If the task shader doesn't write this bit, the HW hangs.
    */

   nir_def *ring_entry = nir_load_task_ring_entry_amd(b);
   nir_def *num_entries = task_num_entries(b, s);
   nir_def *workgroup_index = task_workgroup_index(b, s);

   nir_def *idx = nir_iadd_nuw(b, ring_entry, workgroup_index);
   nir_def *one = nir_imm_int(b, 1);
   nir_def *num_entries_minus_1 = nir_isub(b, num_entries, one);
   return nir_u2u8(b, nir_ubfe(b, idx, nir_bit_count(b, num_entries_minus_1), one));
}

static nir_def *
mesh_ring_entry_index(nir_builder *b,
                      lower_tsms_io_state *s)
{
   /* Mesh shader ring_entry shader argument:
    *
    * - It's a copy of the read_ptr[31:0] from the task control buffer.
    * - All workgroups in the same task->mesh dispatch get the same value,
    *   which is fine because they need to read the same entry.
    * - read_ptr must be initialized to num_entries so ring_entry needs
    *   AND with num_entries - 1 to get the correct meaning.
    *   Note that num_entries must be a power of two.
    */
   nir_def *num_entries = task_num_entries(b, s);
   nir_def *num_entries_minus_1 = nir_isub(b, num_entries, nir_imm_int(b, 1));
   return nir_iand(b, nir_load_task_ring_entry_amd(b), num_entries_minus_1);
}

static void
task_write_draw_ring(nir_builder *b,
                     nir_def *store_val,
                     unsigned const_off,
                     lower_tsms_io_state *s)
{
   nir_def *ptr = task_ring_entry_index(b, s);
   nir_def *ring = nir_load_ring_task_draw_amd(b);
   nir_def *scalar_off = nir_imul_imm(b, ptr, AC_TASK_DRAW_ENTRY_BYTES);
   nir_def *vector_off = nir_imm_int(b, 0);
   nir_def *zero = nir_imm_int(b, 0);

   nir_store_buffer_amd(b, store_val, ring, vector_off, scalar_off, zero,
                        .base = const_off, .memory_modes = nir_var_shader_out,
                        .access = ACCESS_COHERENT | ACCESS_CP_GE_COHERENT_AMD);
}

static bool
filter_task_intrinsics(const nir_instr *instr,
                       UNUSED const void *state)
{
   if (instr->type != nir_instr_type_intrinsic)
      return false;

   nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
   return intrin->intrinsic == nir_intrinsic_launch_mesh_workgroups ||
          intrin->intrinsic == nir_intrinsic_store_task_payload ||
          intrin->intrinsic == nir_intrinsic_load_task_payload;
}

static void
task_invocation_query(nir_builder *b, lower_tsms_io_state *s)
{
   if (!s->has_query)
      return;

   const unsigned invocations = b->shader->info.workgroup_size[0] *
                                b->shader->info.workgroup_size[1] *
                                b->shader->info.workgroup_size[2];

   nir_if *if_pipeline_query = nir_push_if(b, nir_load_pipeline_stat_query_enabled_amd(b));
   {
      nir_atomic_add_shader_invocation_count_amd(b, nir_imm_int(b, invocations));
   }
   nir_pop_if(b, if_pipeline_query);
}

static nir_def *
lower_task_launch_mesh_workgroups(nir_builder *b,
                                  nir_intrinsic_instr *intrin,
                                  lower_tsms_io_state *s)
{
   /* This intrinsic must be always in uniform control flow,
    * so we assume that all invocations are active here.
    */

   /* Wait for all necessary stores to finish.
    * Device memory scope is necessary because we need to ensure there is
    * always a waitcnt_vscnt instruction in order to avoid a race condition
    * between payload stores and their loads after mesh shaders launch.
    */
   nir_barrier(b, .execution_scope = SCOPE_WORKGROUP,
                         .memory_scope = SCOPE_DEVICE,
                         .memory_semantics = NIR_MEMORY_ACQ_REL,
                         .memory_modes = nir_var_mem_task_payload | nir_var_shader_out |
                                         nir_var_mem_ssbo | nir_var_mem_global);

   /* On the first invocation, write the full draw ring entry. */
   nir_def *invocation_index = nir_load_local_invocation_index(b);
   nir_if *if_invocation_index_zero = nir_push_if(b, nir_ieq_imm(b, invocation_index, 0));
   {
      nir_def *dimensions = intrin->src[0].ssa;
      nir_def *x = nir_channel(b, dimensions, 0);
      nir_def *y = nir_channel(b, dimensions, 1);
      nir_def *z = nir_channel(b, dimensions, 2);

      /* When either Y or Z are 0, also set X to 0.
       * Not necessary, but speeds up the job of the CP.
       */
      x = nir_bcsel(b, nir_ior(b, nir_ieq_imm(b, y, 0), nir_ieq_imm(b, z, 0)), nir_imm_int(b, 0), x);

      /* Dispatch dimensions of mesh shader workgroups. */
      task_write_draw_ring(b, nir_vec3(b, x, y, z), 0, s);
      /* Prevent the two stores from being reordered. */
      nir_scoped_memory_barrier(b, SCOPE_INVOCATION, NIR_MEMORY_RELEASE, nir_var_shader_out);
      /* Ready bit, only write the low 8 bits. */
      task_write_draw_ring(b, task_draw_ready_bit(b, s), 12, s);

      task_invocation_query(b, s);
   }
   nir_pop_if(b, if_invocation_index_zero);

   return NIR_LOWER_INSTR_PROGRESS_REPLACE;
}

static nir_def *
lower_task_payload_store(nir_builder *b,
                         nir_intrinsic_instr *intrin,
                         lower_tsms_io_state *s)
{
   unsigned write_mask = nir_intrinsic_write_mask(intrin);
   unsigned base = nir_intrinsic_base(intrin);

   nir_def *store_val = intrin->src[0].ssa;
   nir_def *addr = intrin->src[1].ssa;
   nir_def *ring = nir_load_ring_task_payload_amd(b);
   nir_def *ptr = task_ring_entry_index(b, s);
   nir_def *ring_off = nir_imul(b, ptr, task_payload_entry_bytes(b, s));
   nir_def *zero = nir_imm_int(b, 0);

   nir_store_buffer_amd(b, store_val, ring, addr, ring_off, zero, .base = base,
                        .write_mask = write_mask,
                        .memory_modes = nir_var_mem_task_payload,
                        .access = ACCESS_COHERENT);

   return NIR_LOWER_INSTR_PROGRESS_REPLACE;
}

static nir_def *
lower_taskmesh_payload_load(nir_builder *b,
                            nir_intrinsic_instr *intrin,
                            lower_tsms_io_state *s)
{
   unsigned base = nir_intrinsic_base(intrin);
   unsigned num_components = intrin->def.num_components;
   unsigned bit_size = intrin->def.bit_size;

   nir_def *ptr =
      b->shader->info.stage == MESA_SHADER_TASK ?
      task_ring_entry_index(b, s) :
      mesh_ring_entry_index(b, s);

   nir_def *addr = intrin->src[0].ssa;
   nir_def *ring = nir_load_ring_task_payload_amd(b);
   nir_def *ring_off = nir_imul(b, ptr, task_payload_entry_bytes(b, s));
   nir_def *zero = nir_imm_int(b, 0);

   return nir_load_buffer_amd(b, num_components, bit_size, ring, addr, ring_off, zero, .base = base,
                              .memory_modes = nir_var_mem_task_payload,
                              .access = ACCESS_COHERENT);
}

static nir_def *
lower_task_intrinsics(nir_builder *b,
                      nir_instr *instr,
                      void *state)
{
   assert(instr->type == nir_instr_type_intrinsic);
   nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
   lower_tsms_io_state *s = (lower_tsms_io_state *)state;

   switch (intrin->intrinsic) {
      case nir_intrinsic_store_task_payload:
         return lower_task_payload_store(b, intrin, s);
      case nir_intrinsic_load_task_payload:
         return lower_taskmesh_payload_load(b, intrin, s);
      case nir_intrinsic_launch_mesh_workgroups:
         return lower_task_launch_mesh_workgroups(b, intrin, s);
      default:
         UNREACHABLE("unsupported task shader intrinsic");
   }
}

bool
ac_nir_lower_task_outputs_to_mem(nir_shader *shader,
                                 bool has_query)
{
   bool progress = false;

   nir_lower_task_shader_options lower_ts_opt = {
      .payload_to_shared_for_atomics = true,
   };
   progress |= nir_lower_task_shader(shader, lower_ts_opt);

   /* Needed after nir_lower_task_shader */
   progress |= nir_lower_vars_to_ssa(shader);

   lower_tsms_io_state state = {
      .has_query = has_query,
   };

   progress |= nir_shader_lower_instructions(shader,
                                             filter_task_intrinsics,
                                             lower_task_intrinsics,
                                             &state);

   if (progress) {
      /* The nir_shader_lower_instructions pass can't detect the CF changes
       * that are made by lower_task_launch_mesh_workgroups.
       */
      nir_function_impl *impl = nir_shader_get_entrypoint(shader);
      nir_progress(true, impl, nir_metadata_none);
   }

   return progress;
}

static bool
filter_mesh_input_load(const nir_instr *instr,
                       UNUSED const void *state)
{
   if (instr->type != nir_instr_type_intrinsic)
      return false;

   nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
   return intrin->intrinsic == nir_intrinsic_load_task_payload;
}

static nir_def *
lower_mesh_intrinsics(nir_builder *b,
                      nir_instr *instr,
                      void *state)
{
   assert(instr->type == nir_instr_type_intrinsic);
   nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
   lower_tsms_io_state *s = (lower_tsms_io_state *)state;

   if (intrin->intrinsic == nir_intrinsic_load_task_payload)
      return lower_taskmesh_payload_load(b, intrin, s);
   else
      UNREACHABLE("unsupported mesh shader intrinsic");
}

bool
ac_nir_lower_mesh_inputs_to_mem(nir_shader *shader)
{
   lower_tsms_io_state state = {0};

   return nir_shader_lower_instructions(shader,
                                        filter_mesh_input_load,
                                        lower_mesh_intrinsics,
                                        &state);
}
