amd/compiler/aco_scheduler.cpp

/*
 * Copyright © 2018 Valve 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 "aco_builder.h"
#include "aco_ir.h"

#include "common/amdgfxregs.h"

#include <algorithm>
#include <unordered_set>
#include <vector>

#define SMEM_WINDOW_SIZE    (350 - ctx.num_waves * 35)
#define VMEM_WINDOW_SIZE    (1024 - ctx.num_waves * 64)
#define POS_EXP_WINDOW_SIZE 512
#define SMEM_MAX_MOVES      (64 - ctx.num_waves * 4)
#define VMEM_MAX_MOVES      (256 - ctx.num_waves * 16)
/* creating clauses decreases def-use distances, so make it less aggressive the lower num_waves is */
#define VMEM_CLAUSE_MAX_GRAB_DIST (ctx.num_waves * 2)
#define POS_EXP_MAX_MOVES         512

namespace aco {

enum MoveResult {
   move_success,
   move_fail_ssa,
   move_fail_rar,
   move_fail_pressure,
};

/**
 * Cursor for downwards moves, where a single instruction is moved towards
 * or below a group of instruction that hardware can execute as a clause.
 */
struct DownwardsCursor {
   int source_idx; /* Current instruction to consider for moving */

   int insert_idx_clause; /* First clause instruction */
   int insert_idx;        /* First instruction *after* the clause */

   /* Maximum demand of all clause instructions,
    * i.e. from insert_idx_clause (inclusive) to insert_idx (exclusive) */
   RegisterDemand clause_demand;
   /* Maximum demand of instructions from source_idx to insert_idx_clause (both exclusive) */
   RegisterDemand total_demand;

   DownwardsCursor(int current_idx, RegisterDemand initial_clause_demand)
       : source_idx(current_idx - 1), insert_idx_clause(current_idx), insert_idx(current_idx + 1),
         clause_demand(initial_clause_demand)
   {}

   void verify_invariants(const RegisterDemand* register_demand);
};

/**
 * Cursor for upwards moves, where a single instruction is moved below
 * another instruction.
 */
struct UpwardsCursor {
   int source_idx; /* Current instruction to consider for moving */
   int insert_idx; /* Instruction to move in front of */

   /* Maximum demand of instructions from insert_idx (inclusive) to source_idx (exclusive) */
   RegisterDemand total_demand;

   UpwardsCursor(int source_idx_) : source_idx(source_idx_)
   {
      insert_idx = -1; /* to be initialized later */
   }

   bool has_insert_idx() const { return insert_idx != -1; }
   void verify_invariants(const RegisterDemand* register_demand);
};

struct MoveState {
   RegisterDemand max_registers;

   Block* block;
   Instruction* current;
   RegisterDemand* register_demand; /* demand per instruction */
   bool improved_rar;

   std::vector<bool> depends_on;
   /* Two are needed because, for downwards VMEM scheduling, one needs to
    * exclude the instructions in the clause, since new instructions in the
    * clause are not moved past any other instructions in the clause. */
   std::vector<bool> RAR_dependencies;
   std::vector<bool> RAR_dependencies_clause;

   /* for moving instructions before the current instruction to after it */
   DownwardsCursor downwards_init(int current_idx, bool improved_rar, bool may_form_clauses);
   MoveResult downwards_move(DownwardsCursor&, bool clause);
   void downwards_skip(DownwardsCursor&);

   /* for moving instructions after the first use of the current instruction upwards */
   UpwardsCursor upwards_init(int source_idx, bool improved_rar);
   bool upwards_check_deps(UpwardsCursor&);
   void upwards_update_insert_idx(UpwardsCursor&);
   MoveResult upwards_move(UpwardsCursor&);
   void upwards_skip(UpwardsCursor&);
};

struct sched_ctx {
   int16_t num_waves;
   int16_t last_SMEM_stall;
   int last_SMEM_dep_idx;
   MoveState mv;
   bool schedule_pos_exports = true;
   unsigned schedule_pos_export_div = 1;
};

/* This scheduler is a simple bottom-up pass based on ideas from
 * "A Novel Lightweight Instruction Scheduling Algorithm for Just-In-Time Compiler"
 * from Xiaohua Shi and Peng Guo.
 * The basic approach is to iterate over all instructions. When a memory instruction
 * is encountered it tries to move independent instructions from above and below
 * between the memory instruction and it's first user.
 * The novelty is that this scheduler cares for the current register pressure:
 * Instructions will only be moved if the register pressure won't exceed a certain bound.
 */

template <typename T>
void
move_element(T begin_it, size_t idx, size_t before)
{
   if (idx < before) {
      auto begin = std::next(begin_it, idx);
      auto end = std::next(begin_it, before);
      std::rotate(begin, begin + 1, end);
   } else if (idx > before) {
      auto begin = std::next(begin_it, before);
      auto end = std::next(begin_it, idx + 1);
      std::rotate(begin, end - 1, end);
   }
}

void
DownwardsCursor::verify_invariants(const RegisterDemand* register_demand)
{
   assert(source_idx < insert_idx_clause);
   assert(insert_idx_clause < insert_idx);

#ifndef NDEBUG
   RegisterDemand reference_demand;
   for (int i = source_idx + 1; i < insert_idx_clause; ++i) {
      reference_demand.update(register_demand[i]);
   }
   assert(total_demand == reference_demand);

   reference_demand = {};
   for (int i = insert_idx_clause; i < insert_idx; ++i) {
      reference_demand.update(register_demand[i]);
   }
   assert(clause_demand == reference_demand);
#endif
}

DownwardsCursor
MoveState::downwards_init(int current_idx, bool improved_rar_, bool may_form_clauses)
{
   improved_rar = improved_rar_;

   std::fill(depends_on.begin(), depends_on.end(), false);
   if (improved_rar) {
      std::fill(RAR_dependencies.begin(), RAR_dependencies.end(), false);
      if (may_form_clauses)
         std::fill(RAR_dependencies_clause.begin(), RAR_dependencies_clause.end(), false);
   }

   for (const Operand& op : current->operands) {
      if (op.isTemp()) {
         depends_on[op.tempId()] = true;
         if (improved_rar && op.isFirstKill())
            RAR_dependencies[op.tempId()] = true;
      }
   }

   DownwardsCursor cursor(current_idx, register_demand[current_idx]);
   cursor.verify_invariants(register_demand);
   return cursor;
}

/* If add_to_clause is true, the current clause is extended by moving the
 * instruction at source_idx in front of the clause. Otherwise, the instruction
 * is moved past the end of the clause without extending it */
MoveResult
MoveState::downwards_move(DownwardsCursor& cursor, bool add_to_clause)
{
   aco_ptr<Instruction>& instr = block->instructions[cursor.source_idx];

   for (const Definition& def : instr->definitions)
      if (def.isTemp() && depends_on[def.tempId()])
         return move_fail_ssa;

   /* check if one of candidate's operands is killed by depending instruction */
   std::vector<bool>& RAR_deps =
      improved_rar ? (add_to_clause ? RAR_dependencies_clause : RAR_dependencies) : depends_on;
   for (const Operand& op : instr->operands) {
      if (op.isTemp() && RAR_deps[op.tempId()]) {
         // FIXME: account for difference in register pressure
         return move_fail_rar;
      }
   }

   if (add_to_clause) {
      for (const Operand& op : instr->operands) {
         if (op.isTemp()) {
            depends_on[op.tempId()] = true;
            if (op.isFirstKill())
               RAR_dependencies[op.tempId()] = true;
         }
      }
   }

   const int dest_insert_idx = add_to_clause ? cursor.insert_idx_clause : cursor.insert_idx;
   RegisterDemand register_pressure = cursor.total_demand;
   if (!add_to_clause) {
      register_pressure.update(cursor.clause_demand);
   }

   /* Check the new demand of the instructions being moved over */
   const RegisterDemand candidate_diff = get_live_changes(instr);
   if (RegisterDemand(register_pressure - candidate_diff).exceeds(max_registers))
      return move_fail_pressure;

   /* New demand for the moved instruction */
   const RegisterDemand temp = get_temp_registers(instr);
   const RegisterDemand temp2 = get_temp_registers(block->instructions[dest_insert_idx - 1]);
   const RegisterDemand new_demand = register_demand[dest_insert_idx - 1] - temp2 + temp;
   if (new_demand.exceeds(max_registers))
      return move_fail_pressure;

   /* move the candidate below the memory load */
   move_element(block->instructions.begin(), cursor.source_idx, dest_insert_idx);

   /* update register pressure */
   move_element(register_demand, cursor.source_idx, dest_insert_idx);
   for (int i = cursor.source_idx; i < dest_insert_idx - 1; i++)
      register_demand[i] -= candidate_diff;
   register_demand[dest_insert_idx - 1] = new_demand;
   cursor.insert_idx_clause--;
   if (cursor.source_idx != cursor.insert_idx_clause) {
      /* Update demand if we moved over any instructions before the clause */
      cursor.total_demand -= candidate_diff;
   } else {
      assert(cursor.total_demand == RegisterDemand{});
   }
   if (add_to_clause) {
      cursor.clause_demand.update(new_demand);
   } else {
      cursor.clause_demand -= candidate_diff;
      cursor.insert_idx--;
   }

   cursor.source_idx--;
   cursor.verify_invariants(register_demand);
   return move_success;
}

void
MoveState::downwards_skip(DownwardsCursor& cursor)
{
   aco_ptr<Instruction>& instr = block->instructions[cursor.source_idx];

   for (const Operand& op : instr->operands) {
      if (op.isTemp()) {
         depends_on[op.tempId()] = true;
         if (improved_rar && op.isFirstKill()) {
            RAR_dependencies[op.tempId()] = true;
            RAR_dependencies_clause[op.tempId()] = true;
         }
      }
   }
   cursor.total_demand.update(register_demand[cursor.source_idx]);
   cursor.source_idx--;
   cursor.verify_invariants(register_demand);
}

void
UpwardsCursor::verify_invariants(const RegisterDemand* register_demand)
{
#ifndef NDEBUG
   if (!has_insert_idx()) {
      return;
   }

   assert(insert_idx < source_idx);

   RegisterDemand reference_demand;
   for (int i = insert_idx; i < source_idx; ++i) {
      reference_demand.update(register_demand[i]);
   }
   assert(total_demand == reference_demand);
#endif
}

UpwardsCursor
MoveState::upwards_init(int source_idx, bool improved_rar_)
{
   improved_rar = improved_rar_;

   std::fill(depends_on.begin(), depends_on.end(), false);
   std::fill(RAR_dependencies.begin(), RAR_dependencies.end(), false);

   for (const Definition& def : current->definitions) {
      if (def.isTemp())
         depends_on[def.tempId()] = true;
   }

   return UpwardsCursor(source_idx);
}

bool
MoveState::upwards_check_deps(UpwardsCursor& cursor)
{
   aco_ptr<Instruction>& instr = block->instructions[cursor.source_idx];
   for (const Operand& op : instr->operands) {
      if (op.isTemp() && depends_on[op.tempId()])
         return false;
   }
   return true;
}

void
MoveState::upwards_update_insert_idx(UpwardsCursor& cursor)
{
   cursor.insert_idx = cursor.source_idx;
   cursor.total_demand = register_demand[cursor.insert_idx];
}

MoveResult
MoveState::upwards_move(UpwardsCursor& cursor)
{
   assert(cursor.has_insert_idx());

   aco_ptr<Instruction>& instr = block->instructions[cursor.source_idx];
   for (const Operand& op : instr->operands) {
      if (op.isTemp() && depends_on[op.tempId()])
         return move_fail_ssa;
   }

   /* check if candidate uses/kills an operand which is used by a dependency */
   for (const Operand& op : instr->operands) {
      if (op.isTemp() && (!improved_rar || op.isFirstKill()) && RAR_dependencies[op.tempId()])
         return move_fail_rar;
   }

   /* check if register pressure is low enough: the diff is negative if register pressure is
    * decreased */
   const RegisterDemand candidate_diff = get_live_changes(instr);
   const RegisterDemand temp = get_temp_registers(instr);
   if (RegisterDemand(cursor.total_demand + candidate_diff).exceeds(max_registers))
      return move_fail_pressure;
   const RegisterDemand temp2 = get_temp_registers(block->instructions[cursor.insert_idx - 1]);
   const RegisterDemand new_demand =
      register_demand[cursor.insert_idx - 1] - temp2 + candidate_diff + temp;
   if (new_demand.exceeds(max_registers))
      return move_fail_pressure;

   /* move the candidate above the insert_idx */
   move_element(block->instructions.begin(), cursor.source_idx, cursor.insert_idx);

   /* update register pressure */
   move_element(register_demand, cursor.source_idx, cursor.insert_idx);
   register_demand[cursor.insert_idx] = new_demand;
   for (int i = cursor.insert_idx + 1; i <= cursor.source_idx; i++)
      register_demand[i] += candidate_diff;
   cursor.total_demand += candidate_diff;

   cursor.total_demand.update(register_demand[cursor.source_idx]);

   cursor.insert_idx++;
   cursor.source_idx++;

   cursor.verify_invariants(register_demand);

   return move_success;
}

void
MoveState::upwards_skip(UpwardsCursor& cursor)
{
   if (cursor.has_insert_idx()) {
      aco_ptr<Instruction>& instr = block->instructions[cursor.source_idx];
      for (const Definition& def : instr->definitions) {
         if (def.isTemp())
            depends_on[def.tempId()] = true;
      }
      for (const Operand& op : instr->operands) {
         if (op.isTemp())
            RAR_dependencies[op.tempId()] = true;
      }
      cursor.total_demand.update(register_demand[cursor.source_idx]);
   }

   cursor.source_idx++;

   cursor.verify_invariants(register_demand);
}

bool
is_gs_or_done_sendmsg(const Instruction* instr)
{
   if (instr->opcode == aco_opcode::s_sendmsg) {
      uint16_t imm = instr->sopp().imm;
      return (imm & sendmsg_id_mask) == _sendmsg_gs || (imm & sendmsg_id_mask) == _sendmsg_gs_done;
   }
   return false;
}

bool
is_done_sendmsg(const Instruction* instr)
{
   if (instr->opcode == aco_opcode::s_sendmsg)
      return (instr->sopp().imm & sendmsg_id_mask) == _sendmsg_gs_done;
   return false;
}

memory_sync_info
get_sync_info_with_hack(const Instruction* instr)
{
   memory_sync_info sync = get_sync_info(instr);
   if (instr->isSMEM() && !instr->operands.empty() && instr->operands[0].bytes() == 16) {
      // FIXME: currently, it doesn't seem beneficial to omit this due to how our scheduler works
      sync.storage = (storage_class)(sync.storage | storage_buffer);
      sync.semantics =
         (memory_semantics)((sync.semantics | semantic_private) & ~semantic_can_reorder);
   }
   return sync;
}

struct memory_event_set {
   bool has_control_barrier;

   unsigned bar_acquire;
   unsigned bar_release;
   unsigned bar_classes;

   unsigned access_acquire;
   unsigned access_release;
   unsigned access_relaxed;
   unsigned access_atomic;
};

struct hazard_query {
   bool contains_spill;
   bool contains_sendmsg;
   bool uses_exec;
   memory_event_set mem_events;
   unsigned aliasing_storage;      /* storage classes which are accessed (non-SMEM) */
   unsigned aliasing_storage_smem; /* storage classes which are accessed (SMEM) */
};

void
init_hazard_query(hazard_query* query)
{
   query->contains_spill = false;
   query->contains_sendmsg = false;
   query->uses_exec = false;
   memset(&query->mem_events, 0, sizeof(query->mem_events));
   query->aliasing_storage = 0;
   query->aliasing_storage_smem = 0;
}

void
add_memory_event(memory_event_set* set, Instruction* instr, memory_sync_info* sync)
{
   set->has_control_barrier |= is_done_sendmsg(instr);
   if (instr->opcode == aco_opcode::p_barrier) {
      Pseudo_barrier_instruction& bar = instr->barrier();
      if (bar.sync.semantics & semantic_acquire)
         set->bar_acquire |= bar.sync.storage;
      if (bar.sync.semantics & semantic_release)
         set->bar_release |= bar.sync.storage;
      set->bar_classes |= bar.sync.storage;

      set->has_control_barrier |= bar.exec_scope > scope_invocation;
   }

   if (!sync->storage)
      return;

   if (sync->semantics & semantic_acquire)
      set->access_acquire |= sync->storage;
   if (sync->semantics & semantic_release)
      set->access_release |= sync->storage;

   if (!(sync->semantics & semantic_private)) {
      if (sync->semantics & semantic_atomic)
         set->access_atomic |= sync->storage;
      else
         set->access_relaxed |= sync->storage;
   }
}

void
add_to_hazard_query(hazard_query* query, Instruction* instr)
{
   if (instr->opcode == aco_opcode::p_spill || instr->opcode == aco_opcode::p_reload)
      query->contains_spill = true;
   query->contains_sendmsg |= instr->opcode == aco_opcode::s_sendmsg;
   query->uses_exec |= needs_exec_mask(instr);

   memory_sync_info sync = get_sync_info_with_hack(instr);

   add_memory_event(&query->mem_events, instr, &sync);

   if (!(sync.semantics & semantic_can_reorder)) {
      unsigned storage = sync.storage;
      /* images and buffer/global memory can alias */ // TODO: more precisely, buffer images and
                                                      // buffer/global memory can alias
      if (storage & (storage_buffer | storage_image))
         storage |= storage_buffer | storage_image;
      if (instr->isSMEM())
         query->aliasing_storage_smem |= storage;
      else
         query->aliasing_storage |= storage;
   }
}

enum HazardResult {
   hazard_success,
   hazard_fail_reorder_vmem_smem,
   hazard_fail_reorder_ds,
   hazard_fail_reorder_sendmsg,
   hazard_fail_spill,
   hazard_fail_export,
   hazard_fail_barrier,
   /* Must stop at these failures. The hazard query code doesn't consider them
    * when added. */
   hazard_fail_exec,
   hazard_fail_unreorderable,
};

HazardResult
perform_hazard_query(hazard_query* query, Instruction* instr, bool upwards)
{
   /* don't schedule discards downwards */
   if (!upwards && instr->opcode == aco_opcode::p_exit_early_if)
      return hazard_fail_unreorderable;

   if (query->uses_exec) {
      for (const Definition& def : instr->definitions) {
         if (def.isFixed() && def.physReg() == exec)
            return hazard_fail_exec;
      }
   }

   /* don't move exports so that they stay closer together */
   if (instr->isEXP())
      return hazard_fail_export;

   /* don't move non-reorderable instructions */
   if (instr->opcode == aco_opcode::s_memtime || instr->opcode == aco_opcode::s_memrealtime ||
       instr->opcode == aco_opcode::s_setprio || instr->opcode == aco_opcode::s_getreg_b32)
      return hazard_fail_unreorderable;

   memory_event_set instr_set;
   memset(&instr_set, 0, sizeof(instr_set));
   memory_sync_info sync = get_sync_info_with_hack(instr);
   add_memory_event(&instr_set, instr, &sync);

   memory_event_set* first = &instr_set;
   memory_event_set* second = &query->mem_events;
   if (upwards)
      std::swap(first, second);

   /* everything after barrier(acquire) happens after the atomics/control_barriers before
    * everything after load(acquire) happens after the load
    */
   if ((first->has_control_barrier || first->access_atomic) && second->bar_acquire)
      return hazard_fail_barrier;
   if (((first->access_acquire || first->bar_acquire) && second->bar_classes) ||
       ((first->access_acquire | first->bar_acquire) &
        (second->access_relaxed | second->access_atomic)))
      return hazard_fail_barrier;

   /* everything before barrier(release) happens before the atomics/control_barriers after *
    * everything before store(release) happens before the store
    */
   if (first->bar_release && (second->has_control_barrier || second->access_atomic))
      return hazard_fail_barrier;
   if ((first->bar_classes && (second->bar_release || second->access_release)) ||
       ((first->access_relaxed | first->access_atomic) &
        (second->bar_release | second->access_release)))
      return hazard_fail_barrier;

   /* don't move memory barriers around other memory barriers */
   if (first->bar_classes && second->bar_classes)
      return hazard_fail_barrier;

   /* Don't move memory accesses to before control barriers. I don't think
    * this is necessary for the Vulkan memory model, but it might be for GLSL450. */
   unsigned control_classes =
      storage_buffer | storage_atomic_counter | storage_image | storage_shared;
   if (first->has_control_barrier &&
       ((second->access_atomic | second->access_relaxed) & control_classes))
      return hazard_fail_barrier;

   /* don't move memory loads/stores past potentially aliasing loads/stores */
   unsigned aliasing_storage =
      instr->isSMEM() ? query->aliasing_storage_smem : query->aliasing_storage;
   if ((sync.storage & aliasing_storage) && !(sync.semantics & semantic_can_reorder)) {
      unsigned intersect = sync.storage & aliasing_storage;
      if (intersect & storage_shared)
         return hazard_fail_reorder_ds;
      return hazard_fail_reorder_vmem_smem;
   }

   if ((instr->opcode == aco_opcode::p_spill || instr->opcode == aco_opcode::p_reload) &&
       query->contains_spill)
      return hazard_fail_spill;

   if (instr->opcode == aco_opcode::s_sendmsg && query->contains_sendmsg)
      return hazard_fail_reorder_sendmsg;

   return hazard_success;
}

void
schedule_SMEM(sched_ctx& ctx, Block* block, std::vector<RegisterDemand>& register_demand,
              Instruction* current, int idx)
{
   assert(idx != 0);
   int window_size = SMEM_WINDOW_SIZE;
   int max_moves = SMEM_MAX_MOVES;
   int16_t k = 0;

   /* don't move s_memtime/s_memrealtime */
   if (current->opcode == aco_opcode::s_memtime || current->opcode == aco_opcode::s_memrealtime)
      return;

   /* first, check if we have instructions before current to move down */
   hazard_query hq;
   init_hazard_query(&hq);
   add_to_hazard_query(&hq, current);

   DownwardsCursor cursor = ctx.mv.downwards_init(idx, false, false);

   for (int candidate_idx = idx - 1; k < max_moves && candidate_idx > (int)idx - window_size;
        candidate_idx--) {
      assert(candidate_idx >= 0);
      assert(candidate_idx == cursor.source_idx);
      aco_ptr<Instruction>& candidate = block->instructions[candidate_idx];

      /* break if we'd make the previous SMEM instruction stall */
      bool can_stall_prev_smem =
         idx <= ctx.last_SMEM_dep_idx && candidate_idx < ctx.last_SMEM_dep_idx;
      if (can_stall_prev_smem && ctx.last_SMEM_stall >= 0)
         break;

      /* break when encountering another MEM instruction, logical_start or barriers */
      if (candidate->opcode == aco_opcode::p_logical_start)
         break;
      /* only move VMEM instructions below descriptor loads. be more aggressive at higher num_waves
       * to help create more vmem clauses */
      if (candidate->isVMEM() && (cursor.insert_idx - cursor.source_idx > (ctx.num_waves * 4) ||
                                  current->operands[0].size() == 4))
         break;
      /* don't move descriptor loads below buffer loads */
      if (candidate->format == Format::SMEM && current->operands[0].size() == 4 &&
          candidate->operands[0].size() == 2)
         break;

      bool can_move_down = true;

      HazardResult haz = perform_hazard_query(&hq, candidate.get(), false);
      if (haz == hazard_fail_reorder_ds || haz == hazard_fail_spill ||
          haz == hazard_fail_reorder_sendmsg || haz == hazard_fail_barrier ||
          haz == hazard_fail_export)
         can_move_down = false;
      else if (haz != hazard_success)
         break;

      /* don't use LDS/GDS instructions to hide latency since it can
       * significanly worsen LDS scheduling */
      if (candidate->isDS() || !can_move_down) {
         add_to_hazard_query(&hq, candidate.get());
         ctx.mv.downwards_skip(cursor);
         continue;
      }

      MoveResult res = ctx.mv.downwards_move(cursor, false);
      if (res == move_fail_ssa || res == move_fail_rar) {
         add_to_hazard_query(&hq, candidate.get());
         ctx.mv.downwards_skip(cursor);
         continue;
      } else if (res == move_fail_pressure) {
         break;
      }

      if (candidate_idx < ctx.last_SMEM_dep_idx)
         ctx.last_SMEM_stall++;
      k++;
   }

   /* find the first instruction depending on current or find another MEM */
   UpwardsCursor up_cursor = ctx.mv.upwards_init(idx + 1, false);

   bool found_dependency = false;
   /* second, check if we have instructions after current to move up */
   for (int candidate_idx = idx + 1; k < max_moves && candidate_idx < (int)idx + window_size;
        candidate_idx++) {
      assert(candidate_idx == up_cursor.source_idx);
      assert(candidate_idx < (int)block->instructions.size());
      aco_ptr<Instruction>& candidate = block->instructions[candidate_idx];

      if (candidate->opcode == aco_opcode::p_logical_end)
         break;

      /* check if candidate depends on current */
      bool is_dependency = !found_dependency && !ctx.mv.upwards_check_deps(up_cursor);
      /* no need to steal from following VMEM instructions */
      if (is_dependency && candidate->isVMEM())
         break;

      if (found_dependency) {
         HazardResult haz = perform_hazard_query(&hq, candidate.get(), true);
         if (haz == hazard_fail_reorder_ds || haz == hazard_fail_spill ||
             haz == hazard_fail_reorder_sendmsg || haz == hazard_fail_barrier ||
             haz == hazard_fail_export)
            is_dependency = true;
         else if (haz != hazard_success)
            break;
      }

      if (is_dependency) {
         if (!found_dependency) {
            ctx.mv.upwards_update_insert_idx(up_cursor);
            init_hazard_query(&hq);
            found_dependency = true;
         }
      }

      if (is_dependency || !found_dependency) {
         if (found_dependency)
            add_to_hazard_query(&hq, candidate.get());
         else
            k++;
         ctx.mv.upwards_skip(up_cursor);
         continue;
      }

      MoveResult res = ctx.mv.upwards_move(up_cursor);
      if (res == move_fail_ssa || res == move_fail_rar) {
         /* no need to steal from following VMEM instructions */
         if (res == move_fail_ssa && candidate->isVMEM())
            break;
         add_to_hazard_query(&hq, candidate.get());
         ctx.mv.upwards_skip(up_cursor);
         continue;
      } else if (res == move_fail_pressure) {
         break;
      }
      k++;
   }

   ctx.last_SMEM_dep_idx = found_dependency ? up_cursor.insert_idx : 0;
   ctx.last_SMEM_stall = 10 - ctx.num_waves - k;
}

void
schedule_VMEM(sched_ctx& ctx, Block* block, std::vector<RegisterDemand>& register_demand,
              Instruction* current, int idx)
{
   assert(idx != 0);
   int window_size = VMEM_WINDOW_SIZE;
   int max_moves = VMEM_MAX_MOVES;
   int clause_max_grab_dist = VMEM_CLAUSE_MAX_GRAB_DIST;
   bool only_clauses = false;
   int16_t k = 0;

   /* first, check if we have instructions before current to move down */
   hazard_query indep_hq;
   hazard_query clause_hq;
   init_hazard_query(&indep_hq);
   init_hazard_query(&clause_hq);
   add_to_hazard_query(&indep_hq, current);

   DownwardsCursor cursor = ctx.mv.downwards_init(idx, true, true);

   for (int candidate_idx = idx - 1; k < max_moves && candidate_idx > (int)idx - window_size;
        candidate_idx--) {
      assert(candidate_idx == cursor.source_idx);
      assert(candidate_idx >= 0);
      aco_ptr<Instruction>& candidate = block->instructions[candidate_idx];
      bool is_vmem = candidate->isVMEM() || candidate->isFlatLike();

      /* break when encountering another VMEM instruction, logical_start or barriers */
      if (candidate->opcode == aco_opcode::p_logical_start)
         break;

      /* break if we'd make the previous SMEM instruction stall */
      bool can_stall_prev_smem =
         idx <= ctx.last_SMEM_dep_idx && candidate_idx < ctx.last_SMEM_dep_idx;
      if (can_stall_prev_smem && ctx.last_SMEM_stall >= 0)
         break;

      bool part_of_clause = false;
      if (current->isVMEM() == candidate->isVMEM()) {
         int grab_dist = cursor.insert_idx_clause - candidate_idx;
         /* We can't easily tell how much this will decrease the def-to-use
          * distances, so just use how far it will be moved as a heuristic. */
         part_of_clause =
            grab_dist < clause_max_grab_dist + k && should_form_clause(current, candidate.get());
      }

      /* if current depends on candidate, add additional dependencies and continue */
      bool can_move_down = !is_vmem || part_of_clause || candidate->definitions.empty();
      if (only_clauses) {
         /* In case of high register pressure, only try to form clauses,
          * and only if the previous clause is not larger
          * than the current one will be.
          */
         if (part_of_clause) {
            int clause_size = cursor.insert_idx - cursor.insert_idx_clause;
            int prev_clause_size = 1;
            while (should_form_clause(current,
                                      block->instructions[candidate_idx - prev_clause_size].get()))
               prev_clause_size++;
            if (prev_clause_size > clause_size + 1)
               break;
         } else {
            can_move_down = false;
         }
      }
      HazardResult haz =
         perform_hazard_query(part_of_clause ? &clause_hq : &indep_hq, candidate.get(), false);
      if (haz == hazard_fail_reorder_ds || haz == hazard_fail_spill ||
          haz == hazard_fail_reorder_sendmsg || haz == hazard_fail_barrier ||
          haz == hazard_fail_export)
         can_move_down = false;
      else if (haz != hazard_success)
         break;

      if (!can_move_down) {
         if (part_of_clause)
            break;
         add_to_hazard_query(&indep_hq, candidate.get());
         add_to_hazard_query(&clause_hq, candidate.get());
         ctx.mv.downwards_skip(cursor);
         continue;
      }

      Instruction* candidate_ptr = candidate.get();
      MoveResult res = ctx.mv.downwards_move(cursor, part_of_clause);
      if (res == move_fail_ssa || res == move_fail_rar) {
         if (part_of_clause)
            break;
         add_to_hazard_query(&indep_hq, candidate.get());
         add_to_hazard_query(&clause_hq, candidate.get());
         ctx.mv.downwards_skip(cursor);
         continue;
      } else if (res == move_fail_pressure) {
         only_clauses = true;
         if (part_of_clause)
            break;
         add_to_hazard_query(&indep_hq, candidate.get());
         add_to_hazard_query(&clause_hq, candidate.get());
         ctx.mv.downwards_skip(cursor);
         continue;
      }
      if (part_of_clause)
         add_to_hazard_query(&indep_hq, candidate_ptr);
      else
         k++;
      if (candidate_idx < ctx.last_SMEM_dep_idx)
         ctx.last_SMEM_stall++;
   }

   /* find the first instruction depending on current or find another VMEM */
   UpwardsCursor up_cursor = ctx.mv.upwards_init(idx + 1, true);

   bool found_dependency = false;
   /* second, check if we have instructions after current to move up */
   for (int candidate_idx = idx + 1; k < max_moves && candidate_idx < (int)idx + window_size;
        candidate_idx++) {
      assert(candidate_idx == up_cursor.source_idx);
      assert(candidate_idx < (int)block->instructions.size());
      aco_ptr<Instruction>& candidate = block->instructions[candidate_idx];
      bool is_vmem = candidate->isVMEM() || candidate->isFlatLike();

      if (candidate->opcode == aco_opcode::p_logical_end)
         break;

      /* check if candidate depends on current */
      bool is_dependency = false;
      if (found_dependency) {
         HazardResult haz = perform_hazard_query(&indep_hq, candidate.get(), true);
         if (haz == hazard_fail_reorder_ds || haz == hazard_fail_spill ||
             haz == hazard_fail_reorder_vmem_smem || haz == hazard_fail_reorder_sendmsg ||
             haz == hazard_fail_barrier || haz == hazard_fail_export)
            is_dependency = true;
         else if (haz != hazard_success)
            break;
      }

      is_dependency |= !found_dependency && !ctx.mv.upwards_check_deps(up_cursor);
      if (is_dependency) {
         if (!found_dependency) {
            ctx.mv.upwards_update_insert_idx(up_cursor);
            init_hazard_query(&indep_hq);
            found_dependency = true;
         }
      } else if (is_vmem) {
         /* don't move up dependencies of other VMEM instructions */
         for (const Definition& def : candidate->definitions) {
            if (def.isTemp())
               ctx.mv.depends_on[def.tempId()] = true;
         }
      }

      if (is_dependency || !found_dependency) {
         if (found_dependency)
            add_to_hazard_query(&indep_hq, candidate.get());
         else
            k++;
         ctx.mv.upwards_skip(up_cursor);
         continue;
      }

      MoveResult res = ctx.mv.upwards_move(up_cursor);
      if (res == move_fail_ssa || res == move_fail_rar) {
         add_to_hazard_query(&indep_hq, candidate.get());
         ctx.mv.upwards_skip(up_cursor);
         continue;
      } else if (res == move_fail_pressure) {
         break;
      }
      k++;
   }
}

void
schedule_position_export(sched_ctx& ctx, Block* block, std::vector<RegisterDemand>& register_demand,
                         Instruction* current, int idx)
{
   assert(idx != 0);
   int window_size = POS_EXP_WINDOW_SIZE / ctx.schedule_pos_export_div;
   int max_moves = POS_EXP_MAX_MOVES / ctx.schedule_pos_export_div;
   int16_t k = 0;

   DownwardsCursor cursor = ctx.mv.downwards_init(idx, true, false);

   hazard_query hq;
   init_hazard_query(&hq);
   add_to_hazard_query(&hq, current);

   for (int candidate_idx = idx - 1; k < max_moves && candidate_idx > (int)idx - window_size;
        candidate_idx--) {
      assert(candidate_idx >= 0);
      aco_ptr<Instruction>& candidate = block->instructions[candidate_idx];

      if (candidate->opcode == aco_opcode::p_logical_start)
         break;
      if (candidate->isVMEM() || candidate->isSMEM() || candidate->isFlatLike())
         break;

      HazardResult haz = perform_hazard_query(&hq, candidate.get(), false);
      if (haz == hazard_fail_exec || haz == hazard_fail_unreorderable)
         break;

      if (haz != hazard_success) {
         add_to_hazard_query(&hq, candidate.get());
         ctx.mv.downwards_skip(cursor);
         continue;
      }

      MoveResult res = ctx.mv.downwards_move(cursor, false);
      if (res == move_fail_ssa || res == move_fail_rar) {
         add_to_hazard_query(&hq, candidate.get());
         ctx.mv.downwards_skip(cursor);
         continue;
      } else if (res == move_fail_pressure) {
         break;
      }
      k++;
   }
}

void
schedule_block(sched_ctx& ctx, Program* program, Block* block, live& live_vars)
{
   ctx.last_SMEM_dep_idx = 0;
   ctx.last_SMEM_stall = INT16_MIN;
   ctx.mv.block = block;
   ctx.mv.register_demand = live_vars.register_demand[block->index].data();

   /* go through all instructions and find memory loads */
   for (unsigned idx = 0; idx < block->instructions.size(); idx++) {
      Instruction* current = block->instructions[idx].get();

      if (block->kind & block_kind_export_end && current->isEXP() && ctx.schedule_pos_exports) {
         unsigned target = current->exp().dest;
         if (target >= V_008DFC_SQ_EXP_POS && target < V_008DFC_SQ_EXP_PRIM) {
            ctx.mv.current = current;
            schedule_position_export(ctx, block, live_vars.register_demand[block->index], current,
                                     idx);
         }
      }

      if (current->definitions.empty())
         continue;

      if (current->isVMEM() || current->isFlatLike()) {
         ctx.mv.current = current;
         schedule_VMEM(ctx, block, live_vars.register_demand[block->index], current, idx);
      }

      if (current->isSMEM()) {
         ctx.mv.current = current;
         schedule_SMEM(ctx, block, live_vars.register_demand[block->index], current, idx);
      }
   }

   /* resummarize the block's register demand */
   block->register_demand = RegisterDemand();
   for (unsigned idx = 0; idx < block->instructions.size(); idx++) {
      block->register_demand.update(live_vars.register_demand[block->index][idx]);
   }
}

void
schedule_program(Program* program, live& live_vars)
{
   /* don't use program->max_reg_demand because that is affected by max_waves_per_simd */
   RegisterDemand demand;
   for (Block& block : program->blocks)
      demand.update(block.register_demand);
   demand.vgpr += program->config->num_shared_vgprs / 2;

   sched_ctx ctx;
   ctx.mv.depends_on.resize(program->peekAllocationId());
   ctx.mv.RAR_dependencies.resize(program->peekAllocationId());
   ctx.mv.RAR_dependencies_clause.resize(program->peekAllocationId());
   /* Allowing the scheduler to reduce the number of waves to as low as 5
    * improves performance of Thrones of Britannia significantly and doesn't
    * seem to hurt anything else. */
   // TODO: account for possible uneven num_waves on GFX10+
   unsigned wave_fac = program->dev.physical_vgprs / 256;
   if (program->num_waves <= 5 * wave_fac)
      ctx.num_waves = program->num_waves;
   else if (demand.vgpr >= 29)
      ctx.num_waves = 5 * wave_fac;
   else if (demand.vgpr >= 25)
      ctx.num_waves = 6 * wave_fac;
   else
      ctx.num_waves = 7 * wave_fac;
   ctx.num_waves = std::max<uint16_t>(ctx.num_waves, program->min_waves);
   ctx.num_waves = std::min<uint16_t>(ctx.num_waves, program->num_waves);

   /* VMEM_MAX_MOVES and such assume pre-GFX10 wave count */
   ctx.num_waves = std::max<uint16_t>(ctx.num_waves / wave_fac, 1);

   assert(ctx.num_waves > 0);
   ctx.mv.max_registers = {int16_t(get_addr_vgpr_from_waves(program, ctx.num_waves * wave_fac) - 2),
                           int16_t(get_addr_sgpr_from_waves(program, ctx.num_waves * wave_fac))};

   /* NGG culling shaders are very sensitive to position export scheduling.
    * Schedule less aggressively when early primitive export is used, and
    * keep the position export at the very bottom when late primitive export is used.
    */
   if (program->info->has_ngg_culling && program->stage.num_sw_stages() == 1) {
      if (!program->info->has_ngg_early_prim_export)
         ctx.schedule_pos_exports = false;
      else
         ctx.schedule_pos_export_div = 4;
   }

   for (Block& block : program->blocks)
      schedule_block(ctx, program, &block, live_vars);

   /* update max_reg_demand and num_waves */
   RegisterDemand new_demand;
   for (Block& block : program->blocks) {
      new_demand.update(block.register_demand);
   }
   update_vgpr_sgpr_demand(program, new_demand);

/* if enabled, this code asserts that register_demand is updated correctly */
#if 0
   int prev_num_waves = program->num_waves;
   const RegisterDemand prev_max_demand = program->max_reg_demand;

   std::vector<RegisterDemand> demands(program->blocks.size());
   for (unsigned j = 0; j < program->blocks.size(); j++) {
      demands[j] = program->blocks[j].register_demand;
   }

   live live_vars2 = aco::live_var_analysis(program);

   for (unsigned j = 0; j < program->blocks.size(); j++) {
      Block &b = program->blocks[j];
      for (unsigned i = 0; i < b.instructions.size(); i++)
         assert(live_vars.register_demand[b.index][i] == live_vars2.register_demand[b.index][i]);
      assert(b.register_demand == demands[j]);
   }

   assert(program->max_reg_demand == prev_max_demand);
   assert(program->num_waves == prev_num_waves);
#endif
}

} // namespace aco