--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/tree-ssa-loop-ivcanon.c	Fri Jul 17 14:47:48 2009 +0900
@@ -0,0 +1,575 @@
+/* Induction variable canonicalization.
+   Copyright (C) 2004, 2005, 2007, 2008 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 3, 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 COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+/* This pass detects the loops that iterate a constant number of times,
+   adds a canonical induction variable (step -1, tested against 0) 
+   and replaces the exit test.  This enables the less powerful rtl
+   level analysis to use this information.
+
+   This might spoil the code in some cases (by increasing register pressure).
+   Note that in the case the new variable is not needed, ivopts will get rid
+   of it, so it might only be a problem when there are no other linear induction
+   variables.  In that case the created optimization possibilities are likely
+   to pay up.
+
+   Additionally in case we detect that it is beneficial to unroll the
+   loop completely, we do it right here to expose the optimization
+   possibilities to the following passes.  */
+
+#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 "cfgloop.h"
+#include "tree-pass.h"
+#include "ggc.h"
+#include "tree-chrec.h"
+#include "tree-scalar-evolution.h"
+#include "params.h"
+#include "flags.h"
+#include "tree-inline.h"
+
+/* Specifies types of loops that may be unrolled.  */
+
+enum unroll_level
+{
+  UL_SINGLE_ITER,	/* Only loops that exit immediately in the first
+			   iteration.  */
+  UL_NO_GROWTH,		/* Only loops whose unrolling will not cause increase
+			   of code size.  */
+  UL_ALL		/* All suitable loops.  */
+};
+
+/* Adds a canonical induction variable to LOOP iterating NITER times.  EXIT
+   is the exit edge whose condition is replaced.  */
+
+static void
+create_canonical_iv (struct loop *loop, edge exit, tree niter)
+{
+  edge in;
+  tree type, var;
+  gimple cond;
+  gimple_stmt_iterator incr_at;
+  enum tree_code cmp;
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "Added canonical iv to loop %d, ", loop->num);
+      print_generic_expr (dump_file, niter, TDF_SLIM);
+      fprintf (dump_file, " iterations.\n");
+    }
+
+  cond = last_stmt (exit->src);
+  in = EDGE_SUCC (exit->src, 0);
+  if (in == exit)
+    in = EDGE_SUCC (exit->src, 1);
+
+  /* Note that we do not need to worry about overflows, since
+     type of niter is always unsigned and all comparisons are
+     just for equality/nonequality -- i.e. everything works
+     with a modulo arithmetics.  */
+
+  type = TREE_TYPE (niter);
+  niter = fold_build2 (PLUS_EXPR, type,
+		       niter,
+		       build_int_cst (type, 1));
+  incr_at = gsi_last_bb (in->src);
+  create_iv (niter,
+	     build_int_cst (type, -1),
+	     NULL_TREE, loop,
+	     &incr_at, false, NULL, &var);
+
+  cmp = (exit->flags & EDGE_TRUE_VALUE) ? EQ_EXPR : NE_EXPR;
+  gimple_cond_set_code (cond, cmp);
+  gimple_cond_set_lhs (cond, var);
+  gimple_cond_set_rhs (cond, build_int_cst (type, 0));
+  update_stmt (cond);
+}
+
+/* Computes an estimated number of insns in LOOP, weighted by WEIGHTS.  */
+
+unsigned
+tree_num_loop_insns (struct loop *loop, eni_weights *weights)
+{
+  basic_block *body = get_loop_body (loop);
+  gimple_stmt_iterator gsi;
+  unsigned size = 1, i;
+
+  for (i = 0; i < loop->num_nodes; i++)
+    for (gsi = gsi_start_bb (body[i]); !gsi_end_p (gsi); gsi_next (&gsi))
+      size += estimate_num_insns (gsi_stmt (gsi), weights);
+  free (body);
+
+  return size;
+}
+
+/* Estimate number of insns of completely unrolled loop.  We assume
+   that the size of the unrolled loop is decreased in the
+   following way (the numbers of insns are based on what
+   estimate_num_insns returns for appropriate statements):
+
+   1) exit condition gets removed (2 insns)
+   2) increment of the control variable gets removed (2 insns)
+   3) All remaining statements are likely to get simplified
+      due to constant propagation.  Hard to estimate; just
+      as a heuristics we decrease the rest by 1/3.
+
+   NINSNS is the number of insns in the loop before unrolling.
+   NUNROLL is the number of times the loop is unrolled.  */
+
+static unsigned HOST_WIDE_INT
+estimated_unrolled_size (unsigned HOST_WIDE_INT ninsns,
+			 unsigned HOST_WIDE_INT nunroll)
+{
+  HOST_WIDE_INT unr_insns = 2 * ((HOST_WIDE_INT) ninsns - 4) / 3;
+  if (unr_insns <= 0)
+    unr_insns = 1;
+  unr_insns *= (nunroll + 1);
+
+  return unr_insns;
+}
+
+/* Tries to unroll LOOP completely, i.e. NITER times.
+   UL determines which loops we are allowed to unroll. 
+   EXIT is the exit of the loop that should be eliminated.  */
+
+static bool
+try_unroll_loop_completely (struct loop *loop,
+			    edge exit, tree niter,
+			    enum unroll_level ul)
+{
+  unsigned HOST_WIDE_INT n_unroll, ninsns, max_unroll, unr_insns;
+  gimple cond;
+
+  if (loop->inner)
+    return false;
+
+  if (!host_integerp (niter, 1))
+    return false;
+  n_unroll = tree_low_cst (niter, 1);
+
+  max_unroll = PARAM_VALUE (PARAM_MAX_COMPLETELY_PEEL_TIMES);
+  if (n_unroll > max_unroll)
+    return false;
+
+  if (n_unroll)
+    {
+      if (ul == UL_SINGLE_ITER)
+	return false;
+
+      ninsns = tree_num_loop_insns (loop, &eni_size_weights);
+
+      unr_insns = estimated_unrolled_size (ninsns, n_unroll);
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "  Loop size: %d\n", (int) ninsns);
+	  fprintf (dump_file, "  Estimated size after unrolling: %d\n",
+		   (int) unr_insns);
+	}
+
+      if (unr_insns > ninsns
+	  && (unr_insns
+	      > (unsigned) PARAM_VALUE (PARAM_MAX_COMPLETELY_PEELED_INSNS)))
+	{
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    fprintf (dump_file, "Not unrolling loop %d "
+		     "(--param max-completely-peeled-insns limit reached).\n",
+		     loop->num);
+	  return false;
+	}
+
+      if (ul == UL_NO_GROWTH
+	  && unr_insns > ninsns)
+	{
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    fprintf (dump_file, "Not unrolling loop %d.\n", loop->num);
+	  return false;
+	}
+    }
+
+  if (n_unroll)
+    {
+      sbitmap wont_exit;
+      edge e;
+      unsigned i;
+      VEC (edge, heap) *to_remove = NULL;
+
+      initialize_original_copy_tables ();
+      wont_exit = sbitmap_alloc (n_unroll + 1);
+      sbitmap_ones (wont_exit);
+      RESET_BIT (wont_exit, 0);
+
+      if (!gimple_duplicate_loop_to_header_edge (loop, loop_preheader_edge (loop),
+						 n_unroll, wont_exit,
+						 exit, &to_remove,
+						 DLTHE_FLAG_UPDATE_FREQ
+						 | DLTHE_FLAG_COMPLETTE_PEEL))
+	{
+          free_original_copy_tables ();
+	  free (wont_exit);
+	  return false;
+	}
+
+      for (i = 0; VEC_iterate (edge, to_remove, i, e); i++)
+	{
+	  bool ok = remove_path (e);
+	  gcc_assert (ok);
+	}
+
+      VEC_free (edge, heap, to_remove);
+      free (wont_exit);
+      free_original_copy_tables ();
+    }
+
+  cond = last_stmt (exit->src);
+  if (exit->flags & EDGE_TRUE_VALUE)
+    gimple_cond_make_true (cond);
+  else
+    gimple_cond_make_false (cond);
+  update_stmt (cond);
+  update_ssa (TODO_update_ssa);
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    fprintf (dump_file, "Unrolled loop %d completely.\n", loop->num);
+
+  return true;
+}
+
+/* Adds a canonical induction variable to LOOP if suitable.
+   CREATE_IV is true if we may create a new iv.  UL determines 
+   which loops we are allowed to completely unroll.  If TRY_EVAL is true, we try
+   to determine the number of iterations of a loop by direct evaluation. 
+   Returns true if cfg is changed.  */
+
+static bool
+canonicalize_loop_induction_variables (struct loop *loop,
+				       bool create_iv, enum unroll_level ul,
+				       bool try_eval)
+{
+  edge exit = NULL;
+  tree niter;
+
+  niter = number_of_latch_executions (loop);
+  if (TREE_CODE (niter) == INTEGER_CST)
+    {
+      exit = single_exit (loop);
+      if (!just_once_each_iteration_p (loop, exit->src))
+	return false;
+    }
+  else
+    {
+      /* If the loop has more than one exit, try checking all of them
+	 for # of iterations determinable through scev.  */
+      if (!single_exit (loop))
+	niter = find_loop_niter (loop, &exit);
+
+      /* Finally if everything else fails, try brute force evaluation.  */
+      if (try_eval
+	  && (chrec_contains_undetermined (niter)
+	      || TREE_CODE (niter) != INTEGER_CST))
+	niter = find_loop_niter_by_eval (loop, &exit);
+
+      if (chrec_contains_undetermined (niter)
+	  || TREE_CODE (niter) != INTEGER_CST)
+	return false;
+    }
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "Loop %d iterates ", loop->num);
+      print_generic_expr (dump_file, niter, TDF_SLIM);
+      fprintf (dump_file, " times.\n");
+    }
+
+  if (try_unroll_loop_completely (loop, exit, niter, ul))
+    return true;
+
+  if (create_iv)
+    create_canonical_iv (loop, exit, niter);
+
+  return false;
+}
+
+/* The main entry point of the pass.  Adds canonical induction variables
+   to the suitable loops.  */
+
+unsigned int
+canonicalize_induction_variables (void)
+{
+  loop_iterator li;
+  struct loop *loop;
+  bool changed = false;
+  
+  FOR_EACH_LOOP (li, loop, 0)
+    {
+      changed |= canonicalize_loop_induction_variables (loop,
+							true, UL_SINGLE_ITER,
+							true);
+    }
+
+  /* Clean up the information about numbers of iterations, since brute force
+     evaluation could reveal new information.  */
+  scev_reset ();
+
+  if (changed)
+    return TODO_cleanup_cfg;
+  return 0;
+}
+
+/* Unroll LOOPS completely if they iterate just few times.  Unless
+   MAY_INCREASE_SIZE is true, perform the unrolling only if the
+   size of the code does not increase.  */
+
+unsigned int
+tree_unroll_loops_completely (bool may_increase_size, bool unroll_outer)
+{
+  loop_iterator li;
+  struct loop *loop;
+  bool changed;
+  enum unroll_level ul;
+
+  do
+    {
+      changed = false;
+
+      FOR_EACH_LOOP (li, loop, LI_ONLY_INNERMOST)
+	{
+	  if (may_increase_size && optimize_loop_for_speed_p (loop)
+	      /* Unroll outermost loops only if asked to do so or they do
+		 not cause code growth.  */
+	      && (unroll_outer
+		  || loop_outer (loop_outer (loop))))
+	    ul = UL_ALL;
+	  else
+	    ul = UL_NO_GROWTH;
+	  changed |= canonicalize_loop_induction_variables
+		       (loop, false, ul, !flag_tree_loop_ivcanon);
+	}
+
+      if (changed)
+	{
+	  /* This will take care of removing completely unrolled loops
+	     from the loop structures so we can continue unrolling now
+	     innermost loops.  */
+	  if (cleanup_tree_cfg ())
+	    update_ssa (TODO_update_ssa_only_virtuals);
+
+	  /* Clean up the information about numbers of iterations, since
+	     complete unrolling might have invalidated it.  */
+	  scev_reset ();
+	}
+    }
+  while (changed);
+
+  return 0;
+}
+
+/* Checks whether LOOP is empty.  */
+
+static bool
+empty_loop_p (struct loop *loop)
+{
+  edge exit;
+  struct tree_niter_desc niter;
+  basic_block *body;
+  gimple_stmt_iterator gsi;
+  unsigned i;
+
+  /* If the loop has multiple exits, it is too hard for us to handle.
+     Similarly, if the exit is not dominating, we cannot determine
+     whether the loop is not infinite.  */
+  exit = single_dom_exit (loop);
+  if (!exit)
+    return false;
+
+  /* The loop must be finite.  */
+  if (!number_of_iterations_exit (loop, exit, &niter, false))
+    return false;
+
+  /* Values of all loop exit phi nodes must be invariants.  */
+  for (gsi = gsi_start(phi_nodes (exit->dest)); !gsi_end_p (gsi); gsi_next (&gsi))
+    {
+      gimple phi = gsi_stmt (gsi);
+      tree def;
+
+      if (!is_gimple_reg (PHI_RESULT (phi)))
+	continue;
+
+      def = PHI_ARG_DEF_FROM_EDGE (phi, exit);
+
+      if (!expr_invariant_in_loop_p (loop, def))
+	return false;
+    }
+
+  /* And there should be no memory modifying or from other reasons
+     unremovable statements.  */
+  body = get_loop_body (loop);
+  for (i = 0; i < loop->num_nodes; i++)
+    {
+      /* Irreducible region might be infinite.  */
+      if (body[i]->flags & BB_IRREDUCIBLE_LOOP)
+	{
+	  free (body);
+	  return false;
+	}
+	
+      for (gsi = gsi_start_bb (body[i]); !gsi_end_p (gsi); gsi_next (&gsi))
+	{
+	  gimple stmt = gsi_stmt (gsi);
+
+	  if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_VIRTUAL_DEFS)
+	      || gimple_has_volatile_ops (stmt))
+	    {
+	      free (body);
+	      return false;
+	    }
+
+	  /* Also, asm statements and calls may have side effects and we
+	     cannot change the number of times they are executed.  */
+	  switch (gimple_code (stmt))
+	    {
+	    case GIMPLE_CALL:
+	      if (gimple_has_side_effects (stmt))
+		{
+		  free (body);
+		  return false;
+		}
+	      break;
+
+	    case GIMPLE_ASM:
+	      /* We cannot remove volatile assembler.  */
+	      if (gimple_asm_volatile_p (stmt))
+		{
+		  free (body);
+		  return false;
+		}
+	      break;
+
+	    default:
+	      break;
+	    }
+	}
+      }
+  free (body);
+
+  return true;
+}
+
+/* Remove LOOP by making it exit in the first iteration.  */
+
+static void
+remove_empty_loop (struct loop *loop)
+{
+  edge exit = single_dom_exit (loop), non_exit;
+  gimple cond_stmt = last_stmt (exit->src);
+  basic_block *body;
+  unsigned n_before, freq_in, freq_h;
+  gcov_type exit_count = exit->count;
+
+  if (dump_file)
+    fprintf (dump_file, "Removing empty loop %d\n", loop->num);
+
+  non_exit = EDGE_SUCC (exit->src, 0);
+  if (non_exit == exit)
+    non_exit = EDGE_SUCC (exit->src, 1);
+
+  if (exit->flags & EDGE_TRUE_VALUE)
+    gimple_cond_make_true (cond_stmt);
+  else
+    gimple_cond_make_false (cond_stmt);
+  update_stmt (cond_stmt);
+
+  /* Let us set the probabilities of the edges coming from the exit block.  */
+  exit->probability = REG_BR_PROB_BASE;
+  non_exit->probability = 0;
+  non_exit->count = 0;
+
+  /* Update frequencies and counts.  Everything before
+     the exit needs to be scaled FREQ_IN/FREQ_H times,
+     where FREQ_IN is the frequency of the entry edge
+     and FREQ_H is the frequency of the loop header.
+     Everything after the exit has zero frequency.  */
+  freq_h = loop->header->frequency;
+  freq_in = EDGE_FREQUENCY (loop_preheader_edge (loop));
+  if (freq_h != 0)
+    {
+      body = get_loop_body_in_dom_order (loop);
+      for (n_before = 1; n_before <= loop->num_nodes; n_before++)
+	if (body[n_before - 1] == exit->src)
+	  break;
+      scale_bbs_frequencies_int (body, n_before, freq_in, freq_h);
+      scale_bbs_frequencies_int (body + n_before, loop->num_nodes - n_before,
+				 0, 1);
+      free (body);
+    }
+
+  /* Number of executions of exit is not changed, thus we need to restore
+     the original value.  */
+  exit->count = exit_count;
+}
+
+/* Removes LOOP if it is empty.  Returns true if LOOP is removed.  CHANGED
+   is set to true if LOOP or any of its subloops is removed.  */
+
+static bool
+try_remove_empty_loop (struct loop *loop, bool *changed)
+{
+  bool nonempty_subloop = false;
+  struct loop *sub;
+
+  /* First, all subloops must be removed.  */
+  for (sub = loop->inner; sub; sub = sub->next)
+    nonempty_subloop |= !try_remove_empty_loop (sub, changed);
+
+  if (nonempty_subloop || !empty_loop_p (loop))
+    return false;
+
+  remove_empty_loop (loop);
+  *changed = true;
+  return true;
+}
+
+/* Remove the empty loops.  */
+
+unsigned int
+remove_empty_loops (void)
+{
+  bool changed = false;
+  struct loop *loop;
+
+  for (loop = current_loops->tree_root->inner; loop; loop = loop->next)
+    try_remove_empty_loop (loop, &changed);
+
+  if (changed)
+    {
+      scev_reset ();
+      return TODO_cleanup_cfg;
+    }
+  return 0;
+}
+