scheduler.c

/*
 * Copyright (c) 2017 Lima Project
 *
 * 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, sub license,
 * 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 NON-INFRINGEMENT. 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 <limits.h>

#include "ppir.h"


static void ppir_schedule_calc_sched_info(ppir_instr *instr)
{
   int n = 0;
   float extra_reg = 1.0;

   /* update all children's sched info */
   ppir_instr_foreach_pred(instr, dep) {
      ppir_instr *pred = dep->pred;

      if (pred->reg_pressure < 0)
         ppir_schedule_calc_sched_info(pred);

      if (instr->est < pred->est + 1)
         instr->est = pred->est + 1;

      float reg_weight = 1.0 - 1.0 / list_length(&pred->succ_list);
      if (extra_reg > reg_weight)
         extra_reg = reg_weight;

      n++;
   }

   /* leaf instr */
   if (!n) {
      instr->reg_pressure = 0;
      return;
   }

   int i = 0, reg[n];
   ppir_instr_foreach_pred(instr, dep) {
      ppir_instr *pred = dep->pred;
      reg[i++] = pred->reg_pressure;
   }

   /* sort */
   for (i = 0; i < n - 1; i++) {
      for (int j = 0; j < n - i - 1; j++) {
         if (reg[j] > reg[j + 1]) {
            int tmp = reg[j + 1];
            reg[j + 1] = reg[j];
            reg[j] = tmp;
         }
      }
   }

   for (i = 0; i < n; i++) {
      int pressure = reg[i] + n - (i + 1);
      if (pressure > instr->reg_pressure)
         instr->reg_pressure = pressure;
   }

   /* If all children of this instr have multi parents, then this
    * instr need an extra reg to store its result. For example,
    * it's not fair for parent has the same reg pressure as child
    * if n==1 and child's successor>1, because we need 2 reg for
    * this.
    *
    * But we can't add a full reg to the reg_pressure, because the
    * last parent of a multi-successor child doesn't need an extra
    * reg. For example, a single child (with multi successor) instr
    * should has less reg pressure than a two children (with single
    * successor) instr.
    *
    * extra reg = min(all child)(1.0 - 1.0 / num successor)
    */
   instr->reg_pressure += extra_reg;
}

static void ppir_insert_ready_list(struct list_head *ready_list,
                                   ppir_instr *insert_instr)
{
   struct list_head *insert_pos = ready_list;

   list_for_each_entry(ppir_instr, instr, ready_list, list) {
      if (insert_instr->parent_index < instr->parent_index ||
          (insert_instr->parent_index == instr->parent_index &&
           (insert_instr->reg_pressure < instr->reg_pressure ||
            (insert_instr->reg_pressure == instr->reg_pressure &&
             (insert_instr->est >= instr->est))))) {
         insert_pos = &instr->list;
         break;
      }
   }

   list_del(&insert_instr->list);
   list_addtail(&insert_instr->list, insert_pos);
}

static void ppir_schedule_ready_list(ppir_block *block,
                                     struct list_head *ready_list)
{
   if (list_is_empty(ready_list))
      return;

   ppir_instr *instr = list_first_entry(ready_list, ppir_instr, list);
   list_del(&instr->list);

   /* schedule the instr to the block instr list */
   list_add(&instr->list, &block->instr_list);
   instr->scheduled = true;
   block->sched_instr_index--;
   instr->seq = block->sched_instr_base + block->sched_instr_index;

   ppir_instr_foreach_pred(instr, dep) {
      ppir_instr *pred = dep->pred;
      pred->parent_index = block->sched_instr_index;

      bool ready = true;
      ppir_instr_foreach_succ(pred, dep) {
         ppir_instr *succ = dep->succ;
         if (!succ->scheduled) {
            ready = false;
            break;
         }
      }
      /* all successor have been scheduled */
      if (ready)
         ppir_insert_ready_list(ready_list, pred);
   }

   ppir_schedule_ready_list(block, ready_list);
}

/* Register sensitive schedule algorithm from paper:
 * "Register-Sensitive Selection, Duplication, and Sequencing of Instructions"
 * Author: Vivek Sarkar,  Mauricio J. Serrano,  Barbara B. Simons
 */
static void ppir_schedule_block(ppir_block *block)
{
   /* move all instr to instr_list, block->instr_list will
    * contain schedule result */
   struct list_head instr_list;
   list_replace(&block->instr_list, &instr_list);
   list_inithead(&block->instr_list);

   /* step 2 & 3 */
   list_for_each_entry(ppir_instr, instr, &instr_list, list) {
      if (ppir_instr_is_root(instr))
         ppir_schedule_calc_sched_info(instr);
      block->sched_instr_index++;
   }
   block->sched_instr_base = block->comp->sched_instr_base;
   block->comp->sched_instr_base += block->sched_instr_index;

   /* step 4 */
   struct list_head ready_list;
   list_inithead(&ready_list);

   /* step 5 */
   list_for_each_entry_safe(ppir_instr, instr, &instr_list, list) {
      if (ppir_instr_is_root(instr)) {
         instr->parent_index = INT_MAX;
         ppir_insert_ready_list(&ready_list, instr);
      }
   }

   /* step 6 */
   ppir_schedule_ready_list(block, &ready_list);
}

bool ppir_schedule_prog(ppir_compiler *comp)
{
   list_for_each_entry(ppir_block, block, &comp->block_list, list) {
      ppir_schedule_block(block);
   }

   return true;
}