2 Copyright (C) 2004, 2005, 2007, 2008, 2010 Free Software Foundation, Inc.
4 This file is part of GCC.
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 3, or (at your option) any
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
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
22 #include "coretypes.h"
26 #include "basic-block.h"
27 #include "tree-flow.h"
30 #include "tree-pass.h"
31 #include "tree-inline.h"
33 /* This file implements the loop unswitching, i.e. transformation of loops like
46 where inv is the loop invariant, into
65 Inv is considered invariant iff the values it compares are both invariant;
66 tree-ssa-loop-im.c ensures that all the suitable conditions are in this
69 static struct loop
*tree_unswitch_loop (struct loop
*, basic_block
, tree
);
70 static bool tree_unswitch_single_loop (struct loop
*, int);
71 static tree
tree_may_unswitch_on (basic_block
, struct loop
*);
73 /* Main entry point. Perform loop unswitching on all suitable loops. */
76 tree_ssa_unswitch_loops (void)
82 /* Go through inner loops (only original ones). */
83 FOR_EACH_LOOP (li
, loop
, LI_ONLY_INNERMOST
)
85 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
86 fprintf (dump_file
, ";; Considering loop %d\n", loop
->num
);
88 /* Do not unswitch in cold regions. */
89 if (optimize_loop_for_size_p (loop
))
91 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
92 fprintf (dump_file
, ";; Not unswitching cold loops\n");
96 /* The loop should not be too large, to limit code growth. */
97 if (tree_num_loop_insns (loop
, &eni_size_weights
)
98 > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS
))
100 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
101 fprintf (dump_file
, ";; Not unswitching, loop too big\n");
105 changed
|= tree_unswitch_single_loop (loop
, 0);
109 return TODO_cleanup_cfg
;
113 /* Checks whether we can unswitch LOOP on condition at end of BB -- one of its
114 basic blocks (for what it means see comments below). */
117 tree_may_unswitch_on (basic_block bb
, struct loop
*loop
)
124 /* BB must end in a simple conditional jump. */
125 stmt
= last_stmt (bb
);
126 if (!stmt
|| gimple_code (stmt
) != GIMPLE_COND
)
129 /* To keep the things simple, we do not directly remove the conditions,
130 but just replace tests with 0 != 0 resp. 1 != 0. Prevent the infinite
131 loop where we would unswitch again on such a condition. */
132 if (gimple_cond_true_p (stmt
) || gimple_cond_false_p (stmt
))
135 /* Condition must be invariant. */
136 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
138 def
= SSA_NAME_DEF_STMT (use
);
139 def_bb
= gimple_bb (def
);
141 && flow_bb_inside_loop_p (loop
, def_bb
))
145 cond
= build2 (gimple_cond_code (stmt
), boolean_type_node
,
146 gimple_cond_lhs (stmt
), gimple_cond_rhs (stmt
));
151 /* Simplifies COND using checks in front of the entry of the LOOP. Just very
152 simplish (sufficient to prevent us from duplicating loop in unswitching
156 simplify_using_entry_checks (struct loop
*loop
, tree cond
)
158 edge e
= loop_preheader_edge (loop
);
163 stmt
= last_stmt (e
->src
);
165 && gimple_code (stmt
) == GIMPLE_COND
166 && gimple_cond_code (stmt
) == TREE_CODE (cond
)
167 && operand_equal_p (gimple_cond_lhs (stmt
),
168 TREE_OPERAND (cond
, 0), 0)
169 && operand_equal_p (gimple_cond_rhs (stmt
),
170 TREE_OPERAND (cond
, 1), 0))
171 return (e
->flags
& EDGE_TRUE_VALUE
173 : boolean_false_node
);
175 if (!single_pred_p (e
->src
))
178 e
= single_pred_edge (e
->src
);
179 if (e
->src
== ENTRY_BLOCK_PTR
)
184 /* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow
185 it to grow too much, it is too easy to create example on that the code would
186 grow exponentially. */
189 tree_unswitch_single_loop (struct loop
*loop
, int num
)
194 tree cond
= NULL_TREE
;
196 bool changed
= false;
199 bbs
= get_loop_body (loop
);
200 found
= loop
->num_nodes
;
204 /* Find a bb to unswitch on. */
205 for (; i
< loop
->num_nodes
; i
++)
206 if ((cond
= tree_may_unswitch_on (bbs
[i
], loop
)))
209 if (i
== loop
->num_nodes
)
212 && num
> PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL
)
213 && (dump_flags
& TDF_DETAILS
))
214 fprintf (dump_file
, ";; Not unswitching anymore, hit max level\n");
216 if (found
== loop
->num_nodes
)
224 cond
= simplify_using_entry_checks (loop
, cond
);
225 stmt
= last_stmt (bbs
[i
]);
226 if (integer_nonzerop (cond
))
228 /* Remove false path. */
229 gimple_cond_set_condition_from_tree (stmt
, boolean_true_node
);
232 else if (integer_zerop (cond
))
234 /* Remove true path. */
235 gimple_cond_set_condition_from_tree (stmt
, boolean_false_node
);
238 /* Do not unswitch too much. */
239 else if (num
> PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL
))
244 /* In nested tree_unswitch_single_loop first optimize all conditions
245 using entry checks, then discover still reachable blocks in the
246 loop and find the condition only among those still reachable bbs. */
249 if (found
== loop
->num_nodes
)
266 basic_block
*tos
, *worklist
;
268 /* When called recursively, first do a quick discovery
269 of reachable bbs after the above changes and only
270 consider conditions in still reachable bbs. */
271 tos
= worklist
= XNEWVEC (basic_block
, loop
->num_nodes
);
273 for (i
= 0; i
< loop
->num_nodes
; i
++)
274 bbs
[i
]->flags
&= ~BB_REACHABLE
;
276 /* Start with marking header. */
278 bbs
[0]->flags
|= BB_REACHABLE
;
280 /* Iterate: find everything reachable from what we've already seen
281 within the same innermost loop. Don't look through false edges
282 if condition is always true or true edges if condition is
284 while (tos
!= worklist
)
286 basic_block b
= *--tos
;
291 if (EDGE_COUNT (b
->succs
) == 2)
293 gimple stmt
= last_stmt (b
);
295 && gimple_code (stmt
) == GIMPLE_COND
)
297 if (gimple_cond_true_p (stmt
))
298 flags
= EDGE_FALSE_VALUE
;
299 else if (gimple_cond_false_p (stmt
))
300 flags
= EDGE_TRUE_VALUE
;
304 FOR_EACH_EDGE (e
, ei
, b
->succs
)
306 basic_block dest
= e
->dest
;
308 if (dest
->loop_father
== loop
309 && !(dest
->flags
& BB_REACHABLE
)
310 && !(e
->flags
& flags
))
313 dest
->flags
|= BB_REACHABLE
;
320 /* Find a bb to unswitch on. */
321 for (; found
< loop
->num_nodes
; found
++)
322 if ((bbs
[found
]->flags
& BB_REACHABLE
)
323 && (cond
= tree_may_unswitch_on (bbs
[found
], loop
)))
326 if (found
== loop
->num_nodes
)
333 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
334 fprintf (dump_file
, ";; Unswitching loop\n");
336 initialize_original_copy_tables ();
337 /* Unswitch the loop on this condition. */
338 nloop
= tree_unswitch_loop (loop
, bbs
[found
], cond
);
341 free_original_copy_tables ();
346 /* Update the SSA form after unswitching. */
347 update_ssa (TODO_update_ssa
);
348 free_original_copy_tables ();
350 /* Invoke itself on modified loops. */
351 tree_unswitch_single_loop (nloop
, num
+ 1);
352 tree_unswitch_single_loop (loop
, num
+ 1);
357 /* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support
358 unswitching of innermost loops. COND is the condition determining which
359 loop is entered -- the new loop is entered if COND is true. Returns NULL
360 if impossible, new loop otherwise. */
363 tree_unswitch_loop (struct loop
*loop
,
364 basic_block unswitch_on
, tree cond
)
367 edge edge_true
, edge_false
;
369 /* Some sanity checking. */
370 gcc_assert (flow_bb_inside_loop_p (loop
, unswitch_on
));
371 gcc_assert (EDGE_COUNT (unswitch_on
->succs
) == 2);
372 gcc_assert (loop
->inner
== NULL
);
374 extract_true_false_edges_from_block (unswitch_on
, &edge_true
, &edge_false
);
375 prob_true
= edge_true
->probability
;
376 return loop_version (loop
, unshare_expr (cond
),
377 NULL
, prob_true
, prob_true
,
378 REG_BR_PROB_BASE
- prob_true
, false);