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[/] [openrisc/] [trunk/] [gnu-src/] [gcc-4.2.2/] [gcc/] [tree-ssa-loop-unswitch.c] - Blame information for rev 304

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1 38 julius
/* Loop unswitching.
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   Copyright (C) 2004, 2005, 2007 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 3, or (at your option) any
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later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3.  If not see
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<http://www.gnu.org/licenses/>.  */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "tm.h"
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#include "tree.h"
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#include "rtl.h"
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#include "tm_p.h"
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#include "hard-reg-set.h"
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#include "basic-block.h"
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#include "output.h"
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#include "diagnostic.h"
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#include "tree-flow.h"
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#include "tree-dump.h"
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#include "timevar.h"
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#include "cfgloop.h"
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#include "domwalk.h"
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#include "params.h"
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#include "tree-pass.h"
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/* This file implements the loop unswitching, i.e. transformation of loops like
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   while (A)
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     {
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       if (inv)
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         B;
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       X;
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       if (!inv)
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         C;
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     }
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   where inv is the loop invariant, into
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   if (inv)
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     {
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       while (A)
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         {
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           B;
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           X;
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         }
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     }
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   else
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     {
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       while (A)
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         {
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           X;
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           C;
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         }
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     }
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   Inv is considered invariant iff the values it compares are both invariant;
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   tree-ssa-loop-im.c ensures that all the suitable conditions are in this
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   shape.  */
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static struct loop *tree_unswitch_loop (struct loops *, struct loop *, basic_block,
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                                   tree);
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static bool tree_unswitch_single_loop (struct loops *, struct loop *, int);
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static tree tree_may_unswitch_on (basic_block, struct loop *);
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/* Main entry point.  Perform loop unswitching on all suitable LOOPS.  */
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unsigned int
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tree_ssa_unswitch_loops (struct loops *loops)
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{
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  int i, num;
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  struct loop *loop;
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  bool changed = false;
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  /* Go through inner loops (only original ones).  */
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  num = loops->num;
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  for (i = 1; i < num; i++)
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    {
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      /* Removed loop?  */
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      loop = loops->parray[i];
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      if (!loop)
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        continue;
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      if (loop->inner)
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        continue;
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      changed |= tree_unswitch_single_loop (loops, loop, 0);
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    }
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  if (changed)
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    return TODO_cleanup_cfg;
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  return 0;
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}
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/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its
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   basic blocks (for what it means see comments below).  */
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static tree
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tree_may_unswitch_on (basic_block bb, struct loop *loop)
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{
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  tree stmt, def, cond, use;
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  basic_block def_bb;
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  ssa_op_iter iter;
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  /* BB must end in a simple conditional jump.  */
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  stmt = last_stmt (bb);
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  if (!stmt || TREE_CODE (stmt) != COND_EXPR)
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    return NULL_TREE;
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  /* Condition must be invariant.  */
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  FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
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    {
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      def = SSA_NAME_DEF_STMT (use);
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      def_bb = bb_for_stmt (def);
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      if (def_bb
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          && flow_bb_inside_loop_p (loop, def_bb))
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        return NULL_TREE;
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    }
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  cond = COND_EXPR_COND (stmt);
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  /* To keep the things simple, we do not directly remove the conditions,
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     but just replace tests with 0/1.  Prevent the infinite loop where we
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     would unswitch again on such a condition.  */
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  if (integer_zerop (cond) || integer_nonzerop (cond))
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    return NULL_TREE;
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  return cond;
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}
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/* Simplifies COND using checks in front of the entry of the LOOP.  Just very
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   simplish (sufficient to prevent us from duplicating loop in unswitching
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   unnecessarily).  */
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static tree
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simplify_using_entry_checks (struct loop *loop, tree cond)
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{
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  edge e = loop_preheader_edge (loop);
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  tree stmt;
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  while (1)
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    {
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      stmt = last_stmt (e->src);
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      if (stmt
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          && TREE_CODE (stmt) == COND_EXPR
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          && operand_equal_p (COND_EXPR_COND (stmt), cond, 0))
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        return (e->flags & EDGE_TRUE_VALUE
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                ? boolean_true_node
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                : boolean_false_node);
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      if (!single_pred_p (e->src))
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        return cond;
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      e = single_pred_edge (e->src);
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      if (e->src == ENTRY_BLOCK_PTR)
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        return cond;
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    }
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}
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/* Unswitch single LOOP.  NUM is number of unswitchings done; we do not allow
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   it to grow too much, it is too easy to create example on that the code would
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   grow exponentially.  */
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static bool
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tree_unswitch_single_loop (struct loops *loops, struct loop *loop, int num)
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{
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  basic_block *bbs;
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  struct loop *nloop;
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  unsigned i;
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  tree cond = NULL_TREE, stmt;
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  bool changed = false;
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  /* Do not unswitch too much.  */
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  if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL))
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    {
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      if (dump_file && (dump_flags & TDF_DETAILS))
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        fprintf (dump_file, ";; Not unswitching anymore, hit max level\n");
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      return false;
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    }
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  /* Only unswitch innermost loops.  */
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  if (loop->inner)
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    {
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      if (dump_file && (dump_flags & TDF_DETAILS))
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        fprintf (dump_file, ";; Not unswitching, not innermost loop\n");
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      return false;
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    }
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  /* The loop should not be too large, to limit code growth.  */
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  if (tree_num_loop_insns (loop)
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      > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS))
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    {
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      if (dump_file && (dump_flags & TDF_DETAILS))
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        fprintf (dump_file, ";; Not unswitching, loop too big\n");
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      return false;
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    }
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  i = 0;
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  bbs = get_loop_body (loop);
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  while (1)
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    {
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      /* Find a bb to unswitch on.  */
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      for (; i < loop->num_nodes; i++)
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        if ((cond = tree_may_unswitch_on (bbs[i], loop)))
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          break;
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      if (i == loop->num_nodes)
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        {
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          free (bbs);
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          return changed;
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        }
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      cond = simplify_using_entry_checks (loop, cond);
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      stmt = last_stmt (bbs[i]);
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      if (integer_nonzerop (cond))
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        {
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          /* Remove false path.  */
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          COND_EXPR_COND (stmt) = boolean_true_node;
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          changed = true;
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        }
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      else if (integer_zerop (cond))
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        {
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          /* Remove true path.  */
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          COND_EXPR_COND (stmt) = boolean_false_node;
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          changed = true;
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        }
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      else
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        break;
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      update_stmt (stmt);
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      i++;
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    }
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  if (dump_file && (dump_flags & TDF_DETAILS))
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    fprintf (dump_file, ";; Unswitching loop\n");
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  initialize_original_copy_tables ();
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  /* Unswitch the loop on this condition.  */
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  nloop = tree_unswitch_loop (loops, loop, bbs[i], cond);
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  if (!nloop)
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    {
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      free_original_copy_tables ();
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      free (bbs);
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      return changed;
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    }
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  /* Update the SSA form after unswitching.  */
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  update_ssa (TODO_update_ssa);
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  free_original_copy_tables ();
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  /* Invoke itself on modified loops.  */
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  tree_unswitch_single_loop (loops, nloop, num + 1);
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  tree_unswitch_single_loop (loops, loop, num + 1);
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  free (bbs);
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  return true;
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}
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/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON.  We only support
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   unswitching of innermost loops.  COND is the condition determining which
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   loop is entered -- the new loop is entered if COND is true.  Returns NULL
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   if impossible, new loop otherwise.  */
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278
static struct loop *
279
tree_unswitch_loop (struct loops *loops, struct loop *loop,
280
                    basic_block unswitch_on, tree cond)
281
{
282
  basic_block condition_bb;
283
 
284
  /* Some sanity checking.  */
285
  gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on));
286
  gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2);
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  gcc_assert (loop->inner == NULL);
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  return loop_version (loops, loop, unshare_expr (cond),
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                       &condition_bb, false);
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}

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