[thirdparty/gcc.git] / gcc / tree-ssa-loop-unswitch.c

/* Loop unswitching.
   Copyright (C) 2004, 2005 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 "timevar.h"
#include "cfgloop.h"
#include "domwalk.h"
#include "params.h"
#include "tree-pass.h"

/* This file implements the loop unswitching, i.e. transformation of loops like

   while (A)
     {
       if (inv)
         B;

       X;

       if (!inv)
	 C;
     }

   where inv is the loop invariant, into

   if (inv)
     {
       while (A)
	 {
           B;
	   X;
	 }
     }
   else
     {
       while (A)
	 {
	   X;
	   C;
	 }
     }

   Inv is considered invariant iff the values it compares are both invariant;
   tree-ssa-loop-im.c ensures that all the suitable conditions are in this
   shape.  */

static struct loop *tree_unswitch_loop (struct loops *, struct loop *, basic_block,
				   tree);
static bool tree_unswitch_single_loop (struct loops *, struct loop *, int);
static tree tree_may_unswitch_on (basic_block, struct loop *);

/* Main entry point.  Perform loop unswitching on all suitable LOOPS.  */

void
tree_ssa_unswitch_loops (struct loops *loops)
{
  int i, num;
  struct loop *loop;
  bool changed = false;

  /* Go through inner loops (only original ones).  */
  num = loops->num;

  for (i = 1; i < num; i++)
    {
      /* Removed loop?  */
      loop = loops->parray[i];
      if (!loop)
	continue;

      if (loop->inner)
	continue;

      changed |= tree_unswitch_single_loop (loops, loop, 0);
    }

  if (changed)
    cleanup_tree_cfg_loop ();
}

/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its
   basic blocks (for what it means see comments below).  */

static tree
tree_may_unswitch_on (basic_block bb, struct loop *loop)
{
  tree stmt, def, cond, use;
  basic_block def_bb;
  ssa_op_iter iter;

  /* BB must end in a simple conditional jump.  */
  stmt = last_stmt (bb);
  if (!stmt || TREE_CODE (stmt) != COND_EXPR)
    return NULL_TREE;

  /* Condition must be invariant.  */
  FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
    {
      def = SSA_NAME_DEF_STMT (use);
      def_bb = bb_for_stmt (def);
      if (def_bb
	  && flow_bb_inside_loop_p (loop, def_bb))
	return NULL_TREE;
    }

  cond = COND_EXPR_COND (stmt);
  /* To keep the things simple, we do not directly remove the conditions,
     but just replace tests with 0/1.  Prevent the infinite loop where we
     would unswitch again on such a condition.  */
  if (integer_zerop (cond) || integer_nonzerop (cond))
    return NULL_TREE;

  return cond;
}

/* Simplifies COND using checks in front of the entry of the LOOP.  Just very
   simplish (sufficient to prevent us from duplicating loop in unswitching
   unnecessarily).  */

static tree
simplify_using_entry_checks (struct loop *loop, tree cond)
{
  edge e = loop_preheader_edge (loop);
  tree stmt;

  while (1)
    {
      stmt = last_stmt (e->src);
      if (stmt
	  && TREE_CODE (stmt) == COND_EXPR
	  && operand_equal_p (COND_EXPR_COND (stmt), cond, 0))
	return (e->flags & EDGE_TRUE_VALUE
		? boolean_true_node
		: boolean_false_node);

      if (!single_pred_p (e->src))
	return cond;

      e = single_pred_edge (e->src);
      if (e->src == ENTRY_BLOCK_PTR)
	return cond;
    }
}

/* Unswitch single LOOP.  NUM is number of unswitchings done; we do not allow
   it to grow too much, it is too easy to create example on that the code would
   grow exponentially.  */

static bool
tree_unswitch_single_loop (struct loops *loops, struct loop *loop, int num)
{
  basic_block *bbs;
  struct loop *nloop;
  unsigned i;
  tree cond = NULL_TREE, stmt;
  bool changed = false;

  /* Do not unswitch too much.  */
  if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
	fprintf (dump_file, ";; Not unswitching anymore, hit max level\n");
      return false;
    }

  /* Only unswitch innermost loops.  */
  if (loop->inner)
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
	fprintf (dump_file, ";; Not unswitching, not innermost loop\n");
      return false;
    }

  /* The loop should not be too large, to limit code growth.  */
  if (tree_num_loop_insns (loop)
      > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
	fprintf (dump_file, ";; Not unswitching, loop too big\n");
      return false;
    }

  i = 0;
  bbs = get_loop_body (loop);
  
  while (1)
    {
      /* Find a bb to unswitch on.  */
      for (; i < loop->num_nodes; i++)
	if ((cond = tree_may_unswitch_on (bbs[i], loop)))
	  break;

      if (i == loop->num_nodes)
	{
	  free (bbs);
	  return changed;
	}

      cond = simplify_using_entry_checks (loop, cond);
      stmt = last_stmt (bbs[i]);
      if (integer_nonzerop (cond))
	{
	  /* Remove false path.  */
	  COND_EXPR_COND (stmt) = boolean_true_node;
	  changed = true;
	}
      else if (integer_zerop (cond))
	{
	  /* Remove true path.  */
	  COND_EXPR_COND (stmt) = boolean_false_node;
	  changed = true;
	}
      else
	break;

      update_stmt (stmt);
      i++;
    }

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, ";; Unswitching loop\n");

  /* Unswitch the loop on this condition.  */
  nloop = tree_unswitch_loop (loops, loop, bbs[i], cond);
  if (!nloop)
    return changed;

  /* Update the SSA form after unswitching.  */
  update_ssa (TODO_update_ssa);

  /* Invoke itself on modified loops.  */
  tree_unswitch_single_loop (loops, nloop, num + 1);
  tree_unswitch_single_loop (loops, loop, num + 1);
  return true;
}

/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON.  We only support
   unswitching of innermost loops.  COND is the condition determining which
   loop is entered -- the new loop is entered if COND is true.  Returns NULL
   if impossible, new loop otherwise.  */

static struct loop *
tree_unswitch_loop (struct loops *loops, struct loop *loop,
		    basic_block unswitch_on, tree cond)
{
  basic_block condition_bb;

  /* Some sanity checking.  */
  gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on));
  gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2);
  gcc_assert (loop->inner == NULL);

  return loop_version (loops, loop, unshare_expr (cond), 
		       &condition_bb);
}
Commit	Line	Data
92fc4a2f	1	/* Loop unswitching.
c6c81aa6	2	Copyright (C) 2004, 2005 Free Software Foundation, Inc.
92fc4a2f ZD	3
	4	This file is part of GCC.
	5
	6	GCC is free software; you can redistribute it and/or modify it
	7	under the terms of the GNU General Public License as published by the
	8	Free Software Foundation; either version 2, or (at your option) any
	9	later version.
	10
	11	GCC is distributed in the hope that it will be useful, but WITHOUT
	12	ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	13	FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	14	for more details.
	15
	16	You should have received a copy of the GNU General Public License
	17	along with GCC; see the file COPYING. If not, write to the Free
	18	Software Foundation, 59 Temple Place - Suite 330, Boston, MA
	19	02111-1307, USA. */
	20
	21	#include "config.h"
	22	#include "system.h"
	23	#include "coretypes.h"
	24	#include "tm.h"
	25	#include "tree.h"
	26	#include "rtl.h"
	27	#include "tm_p.h"
	28	#include "hard-reg-set.h"
	29	#include "basic-block.h"
	30	#include "output.h"
	31	#include "diagnostic.h"
	32	#include "tree-flow.h"
	33	#include "tree-dump.h"
	34	#include "timevar.h"
	35	#include "cfgloop.h"
	36	#include "domwalk.h"
	37	#include "params.h"
	38	#include "tree-pass.h"
	39
	40	/* This file implements the loop unswitching, i.e. transformation of loops like
	41
	42	while (A)
	43	{
	44	if (inv)
	45	B;
	46
	47	X;
	48
	49	if (!inv)
	50	C;
	51	}
	52
	53	where inv is the loop invariant, into
	54
	55	if (inv)
	56	{
	57	while (A)
	58	{
	59	B;
	60	X;
	61	}
	62	}
	63	else
	64	{
	65	while (A)
	66	{
67	X;
68	C;
69	}
70	}
71
72	Inv is considered invariant iff the values it compares are both invariant;
73	tree-ssa-loop-im.c ensures that all the suitable conditions are in this
74	shape. */
75
76	static struct loop tree_unswitch_loop (struct loops , struct loop *, basic_block,
77	tree);
78	static bool tree_unswitch_single_loop (struct loops , struct loop , int);
79	static tree tree_may_unswitch_on (basic_block, struct loop *);
80
81	/* Main entry point. Perform loop unswitching on all suitable LOOPS. */
82
83	void
84	tree_ssa_unswitch_loops (struct loops *loops)
85	{
86	int i, num;
87	struct loop *loop;
88	bool changed = false;
89
90	/* Go through inner loops (only original ones). */
91	num = loops->num;
92
93	for (i = 1; i < num; i++)
94	{
95	/* Removed loop? */
96	loop = loops->parray[i];
97	if (!loop)
98	continue;
99
100	if (loop->inner)
101	continue;
102
103	changed \|= tree_unswitch_single_loop (loops, loop, 0);
92fc4a2f ZD	104	}
92fc4a2f ZD	105
92fc4a2f ZD	106	if (changed)
92fc4a2f ZD	107	cleanup_tree_cfg_loop ();
92fc4a2f ZD	108	}
	109
	110	/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its
	111	basic blocks (for what it means see comments below). */
	112
	113	static tree
	114	tree_may_unswitch_on (basic_block bb, struct loop *loop)
	115	{
f47c96aa	116	tree stmt, def, cond, use;
92fc4a2f	117	basic_block def_bb;
f47c96aa	118	ssa_op_iter iter;
92fc4a2f ZD	119
	120	/* BB must end in a simple conditional jump. */
	121	stmt = last_stmt (bb);
	122	if (!stmt \|\| TREE_CODE (stmt) != COND_EXPR)
	123	return NULL_TREE;
	124
	125	/* Condition must be invariant. */
f47c96aa	126	FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
92fc4a2f	127	{
f47c96aa	128	def = SSA_NAME_DEF_STMT (use);
92fc4a2f ZD	129	def_bb = bb_for_stmt (def);
	130	if (def_bb
	131	&& flow_bb_inside_loop_p (loop, def_bb))
	132	return NULL_TREE;
	133	}
	134
	135	cond = COND_EXPR_COND (stmt);
	136	/* To keep the things simple, we do not directly remove the conditions,
	137	but just replace tests with 0/1. Prevent the infinite loop where we
	138	would unswitch again on such a condition. */
	139	if (integer_zerop (cond) \|\| integer_nonzerop (cond))
	140	return NULL_TREE;
	141
	142	return cond;
	143	}
	144
	145	/* Simplifies COND using checks in front of the entry of the LOOP. Just very
	146	simplish (sufficient to prevent us from duplicating loop in unswitching
e75220c8	147	unnecessarily). */
92fc4a2f ZD	148
	149	static tree
	150	simplify_using_entry_checks (struct loop *loop, tree cond)
	151	{
	152	edge e = loop_preheader_edge (loop);
	153	tree stmt;
	154
	155	while (1)
	156	{
	157	stmt = last_stmt (e->src);
	158	if (stmt
	159	&& TREE_CODE (stmt) == COND_EXPR
	160	&& operand_equal_p (COND_EXPR_COND (stmt), cond, 0))
	161	return (e->flags & EDGE_TRUE_VALUE
	162	? boolean_true_node
	163	: boolean_false_node);
	164
c5cbcccf	165	if (!single_pred_p (e->src))
92fc4a2f ZD	166	return cond;
92fc4a2f ZD	167
c5cbcccf	168	e = single_pred_edge (e->src);
92fc4a2f ZD	169	if (e->src == ENTRY_BLOCK_PTR)
	170	return cond;
	171	}
	172	}
	173
	174	/* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow
	175	it to grow too much, it is too easy to create example on that the code would
	176	grow exponentially. */
	177
	178	static bool
	179	tree_unswitch_single_loop (struct loops loops, struct loop loop, int num)
	180	{
	181	basic_block *bbs;
	182	struct loop *nloop;
	183	unsigned i;
	184	tree cond = NULL_TREE, stmt;
	185	bool changed = false;
	186
	187	/* Do not unswitch too much. */
	188	if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL))
	189	{
	190	if (dump_file && (dump_flags & TDF_DETAILS))
	191	fprintf (dump_file, ";; Not unswitching anymore, hit max level\n");
	192	return false;
	193	}
	194
	195	/* Only unswitch innermost loops. */
	196	if (loop->inner)
	197	{
	198	if (dump_file && (dump_flags & TDF_DETAILS))
	199	fprintf (dump_file, ";; Not unswitching, not innermost loop\n");
	200	return false;
	201	}
	202
	203	/* The loop should not be too large, to limit code growth. */
	204	if (tree_num_loop_insns (loop)
	205	> (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS))
	206	{
	207	if (dump_file && (dump_flags & TDF_DETAILS))
	208	fprintf (dump_file, ";; Not unswitching, loop too big\n");
	209	return false;
	210	}
	211
	212	i = 0;
	213	bbs = get_loop_body (loop);
	214
	215	while (1)
	216	{
	217	/* Find a bb to unswitch on. */
	218	for (; i < loop->num_nodes; i++)
	219	if ((cond = tree_may_unswitch_on (bbs[i], loop)))
	220	break;
	221
	222	if (i == loop->num_nodes)
	223	{
	224	free (bbs);
	225	return changed;
	226	}
	227
	228	cond = simplify_using_entry_checks (loop, cond);
	229	stmt = last_stmt (bbs[i]);
	230	if (integer_nonzerop (cond))
	231	{
	232	/* Remove false path. */
233	COND_EXPR_COND (stmt) = boolean_true_node;
234	changed = true;
235	}
236	else if (integer_zerop (cond))
237	{
238	/* Remove true path. */
239	COND_EXPR_COND (stmt) = boolean_false_node;
240	changed = true;
241	}
242	else
243	break;
244
f430bae8	245	update_stmt (stmt);
92fc4a2f ZD	246	i++;
	247	}
	248
	249	if (dump_file && (dump_flags & TDF_DETAILS))
	250	fprintf (dump_file, ";; Unswitching loop\n");
	251
	252	/* Unswitch the loop on this condition. */
	253	nloop = tree_unswitch_loop (loops, loop, bbs[i], cond);
	254	if (!nloop)
	255	return changed;
	256
84d65814 DN	257	/* Update the SSA form after unswitching. */
	258	update_ssa (TODO_update_ssa);
	259
92fc4a2f ZD	260	/* Invoke itself on modified loops. */
	261	tree_unswitch_single_loop (loops, nloop, num + 1);
	262	tree_unswitch_single_loop (loops, loop, num + 1);
	263	return true;
	264	}
	265
	266	/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support
	267	unswitching of innermost loops. COND is the condition determining which
	268	loop is entered -- the new loop is entered if COND is true. Returns NULL
	269	if impossible, new loop otherwise. */
	270
	271	static struct loop *
	272	tree_unswitch_loop (struct loops loops, struct loop loop,
	273	basic_block unswitch_on, tree cond)
	274	{
	275	basic_block condition_bb;
	276
	277	/* Some sanity checking. */
	278	gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on));
628f6a4e	279	gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2);
92fc4a2f ZD	280	gcc_assert (loop->inner == NULL);
92fc4a2f ZD	281
1cb7dfc3 MH	282	return loop_version (loops, loop, unshare_expr (cond),
1cb7dfc3 MH	283	&condition_bb);
92fc4a2f	284	}