tree-ssa-loop.c   [plain text]

/* Loop optimizations over tree-ssa.
   Copyright (C) 2003 Free Software Foundation, Inc.
   
This file is part of GCC.
   
GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version.
   
GCC is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.
   
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING.  If not, write to the Free
Software Foundation, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "rtl.h"
#include "tm_p.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "output.h"
#include "diagnostic.h"
#include "tree-flow.h"
#include "tree-dump.h"
#include "tree-pass.h"
#include "timevar.h"
#include "cfgloop.h"
#include "tree-inline.h"
#include "flags.h"
#include "tree-inline.h"

/* Initializes the loop structures.  DUMP is the file to that the details
   about the analysis should be dumped.  If CANONICALIZE_SSA is true, loop
   closed ssa form is enforced and redundant phi nodes created by creating
   preheaders are cleaned up.  */

struct loops *
tree_loop_optimizer_init (FILE *dump, bool canonicalize_ssa)
{
  struct loops *loops = loop_optimizer_init (dump);

  if (!loops)
    return NULL;

  if (!canonicalize_ssa)
    return loops;

  /* Creation of preheaders may create redundant phi nodes (if the loop is
     entered by more than one edge, but the initial value of the induction
     variable is the same on all of them).  */
  kill_redundant_phi_nodes ();
  rewrite_into_ssa (false);
  bitmap_clear (vars_to_rename);

  rewrite_into_loop_closed_ssa ();

#ifdef ENABLE_CHECKING
  verify_loop_closed_ssa ();
#endif

  return loops;
}

/* The main entry into loop optimization pass.  PHASE indicates which dump file
   from the DUMP_FILES array to use when dumping debugging information.
   FNDECL is the current function decl.  */

static void
tree_ssa_loop_opt (void)
{
  struct loops *loops;

  loops = tree_loop_optimizer_init (dump_file, true);

  if (loops)
    {
#if 0
      /* Test unrolling and peeling.  */
      test_unrolling_and_peeling (loops);
#endif

#if 0
      test_loop_versioning (loops);
#endif

      /* Move the expensive loop invariants.  */
      tree_ssa_lim (loops);

      /* Unswitch the loops.  */
      if (flag_unswitch_loops)
	tree_ssa_unswitch_loops (loops);

      /* Optimize the induction variables.  */
      tree_ssa_iv_optimize (loops);

      loop_optimizer_finalize (loops,
			       (dump_flags & TDF_DETAILS ? dump_file : NULL));

      cleanup_tree_cfg ();
    }
}

static bool
gate_loop (void)
{
  return flag_tree_loop != 0;
}

struct tree_opt_pass pass_loop = 
{
  "loop",				/* name */
  gate_loop,				/* gate */
  tree_ssa_loop_opt,			/* execute */
  NULL,					/* sub */
  NULL,					/* next */
  0,					/* static_pass_number */
  TV_TREE_LOOP,				/* tv_id */
  PROP_cfg,				/* properties_required */
  0,					/* properties_provided */
  0,					/* properties_destroyed */
  TODO_ggc_collect,			/* todo_flags_start */
  TODO_dump_func | TODO_verify_ssa | TODO_ggc_collect	/* todo_flags_finish */
};

/* Check whether we should duplicate HEADER of LOOP.  At most *LIMIT
   instructions should be duplicated, limit is decreased by the actual
   amount.  */

static bool
should_duplicate_loop_header_p (basic_block header, struct loop *loop,
				int *limit)
{
  block_stmt_iterator bsi;
  tree last;

  /* Do not copy one block more than once (we do not really want to do
     loop peeling here).  */
  if (header->aux)
    return false;

  if (!header->succ)
    abort ();
  if (!header->succ->succ_next)
    return false;
  if (header->succ->succ_next->succ_next)
    return false;
  if (flow_bb_inside_loop_p (loop, header->succ->dest)
      && flow_bb_inside_loop_p (loop, header->succ->succ_next->dest))
    return false;

  /* If this is not the original loop header, we want it to have just
     one predecessor in order to match the && pattern.  */
  if (header != loop->header
      && header->pred->pred_next)
    return false;

  last = last_stmt (header);
  if (TREE_CODE (last) != COND_EXPR)
    return false;

  /* Approximately copy the conditions that used to be used in jump.c --
     at most 20 insns and no calls.  */
  for (bsi = bsi_start (header); !bsi_end_p (bsi); bsi_next (&bsi))
    {
      last = bsi_stmt (bsi);

      if (TREE_CODE (last) == LABEL_EXPR)
	continue;

      if (get_call_expr_in (last))
	return false;

      *limit -= estimate_num_insns (last);
      if (*limit < 0)
	return false;
    }

  return true;
}

/* Marks variables defined in basic block BB for rewriting.  */

static void
mark_defs_for_rewrite (basic_block bb)
{
  tree stmt, var;
  block_stmt_iterator bsi;
  stmt_ann_t ann;
  def_optype defs;
  vdef_optype vdefs;
  vuse_optype vuses;
  unsigned i;

  for (stmt = phi_nodes (bb); stmt; stmt = TREE_CHAIN (stmt))
    {
      var = SSA_NAME_VAR (PHI_RESULT (stmt));
      bitmap_set_bit (vars_to_rename, var_ann (var)->uid);

      /* If we have a type_mem_tag, add it as well.  Due to rewriting the
	 variable out of ssa, we lose its name tag, so we use type_mem_tag
	 instead.  */
      var = var_ann (var)->type_mem_tag;
      if (var)
	bitmap_set_bit (vars_to_rename, var_ann (var)->uid);
    }

  for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
    {
      stmt = bsi_stmt (bsi);
      get_stmt_operands (stmt);
      ann = stmt_ann (stmt);

      defs = DEF_OPS (ann);
      for (i = 0; i < NUM_DEFS (defs); i++)
	{
	  var = SSA_NAME_VAR (DEF_OP (defs, i));
	  bitmap_set_bit (vars_to_rename, var_ann (var)->uid);

	  /* If we have a type_mem_tag, add it as well.  Due to rewriting the
	     variable out of ssa, we lose its name tag, so we use type_mem_tag
	     instead.  */
	  var = var_ann (var)->type_mem_tag;
	  if (var)
	    bitmap_set_bit (vars_to_rename, var_ann (var)->uid);
	}

      vdefs = VDEF_OPS (ann);
      for (i = 0; i < NUM_VDEFS (vdefs); i++)
	{
	  var = SSA_NAME_VAR (VDEF_RESULT (vdefs, i));
	  bitmap_set_bit (vars_to_rename, var_ann (var)->uid);
	}

      /* We also need to rewrite vuses, since we will copy the statements
	 and the ssa versions could not be recovered in the copy.  We do
	 not have to do this for operands of VDEFS explicitly, since
	 they have the same underlying variable as the results.  */
      vuses = VUSE_OPS (ann);
      for (i = 0; i < NUM_VUSES (vuses); i++)
	{
	  var = SSA_NAME_VAR (VUSE_OP (vuses, i));
	  bitmap_set_bit (vars_to_rename, var_ann (var)->uid);
	}
    }
}

/* Duplicates destinations of edges in BBS_TO_DUPLICATE.  */

static void
duplicate_blocks (varray_type bbs_to_duplicate)
{
  unsigned i;
  edge preheader_edge, e, e1;
  basic_block header, new_header;
  tree phi;
  size_t old_num_referenced_vars = num_referenced_vars;

  for (i = 0; i < VARRAY_ACTIVE_SIZE (bbs_to_duplicate); i++)
    {
      preheader_edge = VARRAY_GENERIC_PTR_NOGC (bbs_to_duplicate, i);
      header = preheader_edge->dest;

      /* It is sufficient to rewrite the definitions, since the uses of
	 the operands defined outside of the duplicated basic block are
	 still valid (every basic block that dominates the original block
	 also dominates the duplicate).  */
      mark_defs_for_rewrite (header);
    }

  rewrite_vars_out_of_ssa (vars_to_rename);

  for (i = old_num_referenced_vars; i < num_referenced_vars; i++)
    {
      bitmap_set_bit (vars_to_rename, i);
      var_ann (referenced_var (i))->out_of_ssa_tag = 0;
    }

  for (i = 0; i < VARRAY_ACTIVE_SIZE (bbs_to_duplicate); i++)
    {
      preheader_edge = VARRAY_GENERIC_PTR_NOGC (bbs_to_duplicate, i);
      header = preheader_edge->dest;

      /* We might have split the edge into the loop header when we have
	 eliminated the phi nodes, so find the edge to that we want to
	 copy the header.  */
      while (!header->aux)
	{
	  preheader_edge = header->succ;
	  header = preheader_edge->dest;
	}
      header->aux = NULL;

      new_header = duplicate_block (header, preheader_edge);

      /* Add the phi arguments to the outgoing edges.  */
      for (e = header->succ; e; e = e->succ_next)
	{
	  for (e1 = new_header->succ; e1->dest != e->dest; e1 = e1->succ_next)
	    continue;

	  for (phi = phi_nodes (e->dest); phi; phi = TREE_CHAIN (phi))
	    {
	      tree def = phi_element_for_edge (phi, e)->def;
	      add_phi_arg (&phi, def, e1);
	    }
	}
    }
}

/* Checks whether LOOP is a do-while style loop.  */

static bool
do_while_loop_p (struct loop *loop)
{
  tree stmt = last_stmt (loop->latch);

  /* If the latch of the loop is not empty, it is not a do-while loop.  */
  if (stmt
      && TREE_CODE (stmt) != LABEL_EXPR)
    return false;

  /* If the header contains just a condition, it is not a do-while loop.  */
  stmt = last_and_only_stmt (loop->header);
  if (stmt
      && TREE_CODE (stmt) == COND_EXPR)
    return false;

  return true;
}

/* For all loops, copy the condition at the end of the loop body in front
   of the loop.  This is beneficial since it increases effectivity of
   code motion optimizations.  It also saves one jump on entry to the loop.  */

static void
copy_loop_headers (void)
{
  struct loops *loops;
  unsigned i;
  struct loop *loop;
  basic_block header;
  edge preheader_edge;
  varray_type bbs_to_duplicate = NULL;

  loops = tree_loop_optimizer_init (dump_file, false);
  if (!loops)
    return;
  
  /* We are not going to need or update dominators.  */
  free_dominance_info (CDI_DOMINATORS);

  /* We do not try to keep the information about irreductible regions
     up-to-date.  */
  loops->state &= ~LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS;

#ifdef ENABLE_CHECKING
  verify_loop_structure (loops);
#endif

  for (i = 1; i < loops->num; i++)
    {
      /* Copy at most 20 insns.  */
      int limit = 20;

      loop = loops->parray[i];
      preheader_edge = loop_preheader_edge (loop);
      header = preheader_edge->dest;

      /* If the loop is already a do-while style one (either because it was
	 written as such, or because jump threading transformed it into one),
	 we might be in fact peeling the first iteration of the loop.  This
	 in general is not a good idea.  */
      if (do_while_loop_p (loop))
	continue;

      /* Iterate the header copying up to limit; this takes care of the cases
	 like while (a && b) {...}, where we want to have both of the conditions
	 copied.  TODO -- handle while (a || b) - like cases, by not requiring
	 the header to have just a single successor and copying up to
	 postdominator. 
	 
	 We do not really copy the blocks immediately, so that we do not have
	 to worry about updating loop structures, and also so that we do not
	 have to rewrite variables out of and into ssa form for each block.
	 Instead we just record the block into worklist and duplicate all of
	 them at once.  */
      while (should_duplicate_loop_header_p (header, loop, &limit))
	{
	  if (!bbs_to_duplicate)
	    VARRAY_GENERIC_PTR_NOGC_INIT (bbs_to_duplicate, 10,
					  "bbs_to_duplicate");
	  VARRAY_PUSH_GENERIC_PTR_NOGC (bbs_to_duplicate, preheader_edge);
	  header->aux = &header->aux;

	  if (dump_file && (dump_flags & TDF_DETAILS))
	    fprintf (dump_file,
		     "Scheduled basic block %d for duplication.\n",
		     header->index);

	  /* Find a successor of header that is inside a loop; i.e. the new
	     header after the condition is copied.  */
	  if (flow_bb_inside_loop_p (loop, header->succ->dest))
	    preheader_edge = header->succ;
	  else
	    preheader_edge = header->succ->succ_next;
	  header = preheader_edge->dest;
	}
    }

  loop_optimizer_finalize (loops, NULL);

  if (bbs_to_duplicate)
    {
      duplicate_blocks (bbs_to_duplicate);
      VARRAY_FREE (bbs_to_duplicate);
    }

  /* Run cleanup_tree_cfg here regardless of whether we have done anything, so
     that we cleanup the blocks created in order to get the loops into a
     canonical shape.  */
  cleanup_tree_cfg ();
}

static bool
gate_ch (void)
{
  return flag_tree_ch != 0;
}

struct tree_opt_pass pass_ch = 
{
  "ch",					/* name */
  gate_ch,				/* gate */
  copy_loop_headers,			/* execute */
  NULL,					/* sub */
  NULL,					/* next */
  0,					/* static_pass_number */
  TV_TREE_CH,				/* tv_id */
  PROP_cfg | PROP_ssa,			/* properties_required */
  0,					/* properties_provided */
  0,					/* properties_destroyed */
  0,					/* todo_flags_start */
  (TODO_rename_vars
   | TODO_dump_func
   | TODO_verify_ssa)			/* todo_flags_finish */
};