sched.c

gcc库的原代码,对编程有很大帮助.

  if (unit >= 0)
    {
      int instance = unit;
#if MAX_MULTIPLICITY > 1
      /* Find the first free instance of the function unit and use that
	 one.  We assume that one is free.  */
      for (i = function_units[unit].multiplicity - 1; i > 0; i--)
	{
	  if (! actual_hazard_this_instance (unit, instance, insn, clock, 0))
	    break;
	  instance += FUNCTION_UNITS_SIZE;
	}
#endif
      unit_last_insn[instance] = insn;
      unit_tick[instance] = (clock + function_units[unit].max_blockage);
    }
  else
    for (i = 0, unit = ~unit; unit; i++, unit >>= 1)
      if ((unit & 1) != 0)
	schedule_unit (i, insn, clock);
}

/* Return the actual hazard cost of executing INSN on the units encoded by
   UNIT at time CLOCK if the previous actual hazard cost was COST.  */

__inline static int
actual_hazard (unit, insn, clock, cost)
     int unit, clock, cost;
     rtx insn;
{
  int i;

  if (unit >= 0)
    {
      /* Find the instance of the function unit with the minimum hazard.  */
      int instance = unit;
      int best_cost = actual_hazard_this_instance (unit, instance, insn,
						   clock, cost);
      int this_cost;

#if MAX_MULTIPLICITY > 1
      if (best_cost > cost)
	{
	  for (i = function_units[unit].multiplicity - 1; i > 0; i--)
	    {
	      instance += FUNCTION_UNITS_SIZE;
	      this_cost = actual_hazard_this_instance (unit, instance, insn,
						       clock, cost);
	      if (this_cost < best_cost)
		{
		  best_cost = this_cost;
		  if (this_cost <= cost)
		    break;
		}
	    }
	}
#endif
      cost = MAX (cost, best_cost);
    }
  else
    for (i = 0, unit = ~unit; unit; i++, unit >>= 1)
      if ((unit & 1) != 0)
	cost = actual_hazard (i, insn, clock, cost);

  return cost;
}

/* Return the potential hazard cost of executing an instruction on the
   units encoded by UNIT if the previous potential hazard cost was COST.
   An insn with a large blockage time is chosen in preference to one
   with a smaller time; an insn that uses a unit that is more likely
   to be used is chosen in preference to one with a unit that is less
   used.  We are trying to minimize a subsequent actual hazard.  */

__inline static int
potential_hazard (unit, insn, cost)
     int unit, cost;
     rtx insn;
{
  int i, ncost;
  unsigned int minb, maxb;

  if (unit >= 0)
    {
      minb = maxb = function_units[unit].max_blockage;
      if (maxb > 1)
	{
	  if (function_units[unit].blockage_range_function)
	    {
	      maxb = minb = blockage_range (unit, insn);
	      maxb = MAX_BLOCKAGE_COST (maxb);
	      minb = MIN_BLOCKAGE_COST (minb);
	    }

	  if (maxb > 1)
	    {
	      /* Make the number of instructions left dominate.  Make the
		 minimum delay dominate the maximum delay.  If all these
		 are the same, use the unit number to add an arbitrary
		 ordering.  Other terms can be added.  */
	      ncost = minb * 0x40 + maxb;
	      ncost *= (unit_n_insns[unit] - 1) * 0x1000 + unit;
	      if (ncost > cost)
		cost = ncost;
	    }
	}
    }
  else
    for (i = 0, unit = ~unit; unit; i++, unit >>= 1)
      if ((unit & 1) != 0)
	cost = potential_hazard (i, insn, cost);

  return cost;
}

/* Compute cost of executing INSN given the dependence LINK on the insn USED.
   This is the number of virtual cycles taken between instruction issue and
   instruction results.  */

__inline static int
insn_cost (insn, link, used)
     rtx insn, link, used;
{
  register int cost = INSN_COST (insn);

  if (cost == 0)
    {
      recog_memoized (insn);

      /* A USE insn, or something else we don't need to understand.
	 We can't pass these directly to result_ready_cost because it will
	 trigger a fatal error for unrecognizable insns.  */
      if (INSN_CODE (insn) < 0)
	{
	  INSN_COST (insn) = 1;
	  return 1;
	}
      else
	{
	  cost = result_ready_cost (insn);

	  if (cost < 1)
	    cost = 1;

	  INSN_COST (insn) = cost;
	}
    }

  /* A USE insn should never require the value used to be computed.  This
     allows the computation of a function's result and parameter values to
     overlap the return and call.  */
  recog_memoized (used);
  if (INSN_CODE (used) < 0)
    LINK_COST_FREE (link) = 1;

  /* If some dependencies vary the cost, compute the adjustment.  Most
     commonly, the adjustment is complete: either the cost is ignored
     (in the case of an output- or anti-dependence), or the cost is
     unchanged.  These values are cached in the link as LINK_COST_FREE
     and LINK_COST_ZERO.  */

  if (LINK_COST_FREE (link))
    cost = 1;
#ifdef ADJUST_COST
  else if (! LINK_COST_ZERO (link))
    {
      int ncost = cost;

      ADJUST_COST (used, link, insn, ncost);
      if (ncost <= 1)
	LINK_COST_FREE (link) = ncost = 1;
      if (cost == ncost)
	LINK_COST_ZERO (link) = 1;
      cost = ncost;
    }
#endif
  return cost;
}

/* Compute the priority number for INSN.  */

static int
priority (insn)
     rtx insn;
{
  if (insn && GET_RTX_CLASS (GET_CODE (insn)) == 'i')
    {
      int prev_priority;
      int max_priority;
      int this_priority = INSN_PRIORITY (insn);
      rtx prev;

      if (this_priority > 0)
	return this_priority;

      max_priority = 1;

      /* Nonzero if these insns must be scheduled together.  */
      if (SCHED_GROUP_P (insn))
	{
	  prev = insn;
	  while (SCHED_GROUP_P (prev))
	    {
	      prev = PREV_INSN (prev);
	      INSN_REF_COUNT (prev) += 1;
	    }
	}

      for (prev = LOG_LINKS (insn); prev; prev = XEXP (prev, 1))
	{
	  rtx x = XEXP (prev, 0);

	  /* A dependence pointing to a note or deleted insn is always
	     obsolete, because sched_analyze_insn will have created any
	     necessary new dependences which replace it.  Notes and deleted
	     insns can be created when instructions are deleted by insn
	     splitting, or by register allocation.  */
	  if (GET_CODE (x) == NOTE || INSN_DELETED_P (x))
	    {
	      remove_dependence (insn, x);
	      continue;
	    }

	  /* Clear the link cost adjustment bits.  */
	  LINK_COST_FREE (prev) = 0;
#ifdef ADJUST_COST
	  LINK_COST_ZERO (prev) = 0;
#endif

	  /* This priority calculation was chosen because it results in the
	     least instruction movement, and does not hurt the performance
	     of the resulting code compared to the old algorithm.
	     This makes the sched algorithm more stable, which results
	     in better code, because there is less register pressure,
	     cross jumping is more likely to work, and debugging is easier.

	     When all instructions have a latency of 1, there is no need to
	     move any instructions.  Subtracting one here ensures that in such
	     cases all instructions will end up with a priority of one, and
	     hence no scheduling will be done.

	     The original code did not subtract the one, and added the
	     insn_cost of the current instruction to its priority (e.g.
	     move the insn_cost call down to the end).  */

	  prev_priority = priority (x) + insn_cost (x, prev, insn) - 1;

	  if (prev_priority > max_priority)
	    max_priority = prev_priority;
	  INSN_REF_COUNT (x) += 1;
	}

      prepare_unit (insn_unit (insn));
      INSN_PRIORITY (insn) = max_priority;
      return INSN_PRIORITY (insn);
    }
  return 0;
}

/* Remove all INSN_LISTs and EXPR_LISTs from the pending lists and add
   them to the unused_*_list variables, so that they can be reused.  */

static void
free_pending_lists ()
{
  register rtx link, prev_link;

  if (pending_read_insns)
    {
      prev_link = pending_read_insns;
      link = XEXP (prev_link, 1);

      while (link)
	{
	  prev_link = link;
	  link = XEXP (link, 1);
	}

      XEXP (prev_link, 1) = unused_insn_list;
      unused_insn_list = pending_read_insns;
      pending_read_insns = 0;
    }

  if (pending_write_insns)
    {
      prev_link = pending_write_insns;
      link = XEXP (prev_link, 1);

      while (link)
	{
	  prev_link = link;
	  link = XEXP (link, 1);
	}

      XEXP (prev_link, 1) = unused_insn_list;
      unused_insn_list = pending_write_insns;
      pending_write_insns = 0;
    }

  if (pending_read_mems)
    {
      prev_link = pending_read_mems;
      link = XEXP (prev_link, 1);

      while (link)
	{
	  prev_link = link;
	  link = XEXP (link, 1);
	}

      XEXP (prev_link, 1) = unused_expr_list;
      unused_expr_list = pending_read_mems;
      pending_read_mems = 0;
    }

  if (pending_write_mems)
    {
      prev_link = pending_write_mems;
      link = XEXP (prev_link, 1);

      while (link)
	{
	  prev_link = link;
	  link = XEXP (link, 1);
	}

      XEXP (prev_link, 1) = unused_expr_list;
      unused_expr_list = pending_write_mems;
      pending_write_mems = 0;
    }
}

/* Add an INSN and MEM reference pair to a pending INSN_LIST and MEM_LIST.
   The MEM is a memory reference contained within INSN, which we are saving
   so that we can do memory aliasing on it.  */

static void
add_insn_mem_dependence (insn_list, mem_list, insn, mem)
     rtx *insn_list, *mem_list, insn, mem;
{
  register rtx link;

  if (unused_insn_list)
    {
      link = unused_insn_list;
      unused_insn_list = XEXP (link, 1);
    }
  else
    link = rtx_alloc (INSN_LIST);
  XEXP (link, 0) = insn;
  XEXP (link, 1) = *insn_list;
  *insn_list = link;

  if (unused_expr_list)
    {
      link = unused_expr_list;
      unused_expr_list = XEXP (link, 1);
    }
  else
    link = rtx_alloc (EXPR_LIST);
  XEXP (link, 0) = mem;
  XEXP (link, 1) = *mem_list;
  *mem_list = link;

  pending_lists_length++;
}

/* Make a dependency between every memory reference on the pending lists
   and INSN, thus flushing the pending lists.  */

static void
flush_pending_lists (insn)
     rtx insn;
{
  rtx link;

  while (pending_read_insns)
    {
      add_dependence (insn, XEXP (pending_read_insns, 0), REG_DEP_ANTI);

      link = pending_read_insns;
      pending_read_insns = XEXP (pending_read_insns, 1);
      XEXP (link, 1) = unused_insn_list;
      unused_insn_list = link;

      link = pending_read_mems;
      pending_read_mems = XEXP (pending_read_mems, 1);
      XEXP (link, 1) = unused_expr_list;
      unused_expr_list = link;
    }
  while (pending_write_insns)
    {
      add_dependence (insn, XEXP (pending_write_insns, 0), REG_DEP_ANTI);

      link = pending_write_insns;
      pending_write_insns = XEXP (pending_write_insns, 1);
      XEXP (link, 1) = unused_insn_list;
      unused_insn_list = link;

      link = pending_write_mems;
      pending_write_mems = XEXP (pending_write_mems, 1);
      XEXP (link, 1) = unused_expr_list;
      unused_expr_list = link;
    }
  pending_lists_length = 0;

  if (last_pending_memory_flush)
    add_dependence (insn, last_pending_memory_flush, REG_DEP_ANTI);

  last_pending_memory_flush = insn;
}

/* Analyze a single SET or CLOBBER rtx, X, creating all dependencies generated
   by the write to the destination of X, and reads of everything mentioned.  */