1 /* Induction variable canonicalization.
2 Copyright (C) 2004, 2005 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 2, 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 COPYING. If not, write to the Free
18 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
21 /* This pass detects the loops that iterate a constant number of times,
22 adds a canonical induction variable (step -1, tested against 0)
23 and replaces the exit test. This enables the less powerful rtl
24 level analysis to use this information.
26 This might spoil the code in some cases (by increasing register pressure).
27 Note that in the case the new variable is not needed, ivopts will get rid
28 of it, so it might only be a problem when there are no other linear induction
29 variables. In that case the created optimization possibilities are likely
32 Additionally in case we detect that it is beneficial to unroll the
33 loop completely, we do it right here to expose the optimization
34 possibilities to the following passes. */
38 #include "coretypes.h"
43 #include "hard-reg-set.h"
44 #include "basic-block.h"
46 #include "diagnostic.h"
47 #include "tree-flow.h"
48 #include "tree-dump.h"
50 #include "tree-pass.h"
52 #include "tree-chrec.h"
53 #include "tree-scalar-evolution.h"
56 #include "tree-inline.h"
58 /* Specifies types of loops that may be unrolled. */
62 UL_SINGLE_ITER
, /* Only loops that exit immediately in the first
64 UL_NO_GROWTH
, /* Only loops whose unrolling will not cause increase
66 UL_ALL
/* All suitable loops. */
69 /* Adds a canonical induction variable to LOOP iterating NITER times. EXIT
70 is the exit edge whose condition is replaced. */
73 create_canonical_iv (struct loop
*loop
, edge exit
, tree niter
)
77 block_stmt_iterator incr_at
;
80 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
82 fprintf (dump_file
, "Added canonical iv to loop %d, ", loop
->num
);
83 print_generic_expr (dump_file
, niter
, TDF_SLIM
);
84 fprintf (dump_file
, " iterations.\n");
87 cond
= last_stmt (exit
->src
);
88 in
= EDGE_SUCC (exit
->src
, 0);
90 in
= EDGE_SUCC (exit
->src
, 1);
92 /* Note that we do not need to worry about overflows, since
93 type of niter is always unsigned and all comparisons are
94 just for equality/nonequality -- i.e. everything works
95 with a modulo arithmetics. */
97 type
= TREE_TYPE (niter
);
98 niter
= fold_build2 (PLUS_EXPR
, type
,
100 build_int_cst (type
, 1));
101 incr_at
= bsi_last (in
->src
);
103 build_int_cst (type
, -1),
105 &incr_at
, false, NULL
, &var
);
107 cmp
= (exit
->flags
& EDGE_TRUE_VALUE
) ? EQ_EXPR
: NE_EXPR
;
108 COND_EXPR_COND (cond
) = build2 (cmp
, boolean_type_node
,
110 build_int_cst (type
, 0));
114 /* Computes an estimated number of insns in LOOP. */
117 tree_num_loop_insns (struct loop
*loop
)
119 basic_block
*body
= get_loop_body (loop
);
120 block_stmt_iterator bsi
;
121 unsigned size
= 1, i
;
123 for (i
= 0; i
< loop
->num_nodes
; i
++)
124 for (bsi
= bsi_start (body
[i
]); !bsi_end_p (bsi
); bsi_next (&bsi
))
125 size
+= estimate_num_insns (bsi_stmt (bsi
));
131 /* Estimate number of insns of completely unrolled loop. We assume
132 that the size of the unrolled loop is decreased in the
133 following way (the numbers of insns are based on what
134 estimate_num_insns returns for appropriate statements):
136 1) exit condition gets removed (2 insns)
137 2) increment of the control variable gets removed (2 insns)
138 3) All remaining statements are likely to get simplified
139 due to constant propagation. Hard to estimate; just
140 as a heuristics we decrease the rest by 1/3.
142 NINSNS is the number of insns in the loop before unrolling.
143 NUNROLL is the number of times the loop is unrolled. */
145 static unsigned HOST_WIDE_INT
146 estimated_unrolled_size (unsigned HOST_WIDE_INT ninsns
,
147 unsigned HOST_WIDE_INT nunroll
)
149 HOST_WIDE_INT unr_insns
= 2 * ((HOST_WIDE_INT
) ninsns
- 4) / 3;
152 unr_insns
*= (nunroll
+ 1);
157 /* Tries to unroll LOOP completely, i.e. NITER times. LOOPS is the
158 loop tree. UL determines which loops we are allowed to unroll.
159 EXIT is the exit of the loop that should be eliminated. */
162 try_unroll_loop_completely (struct loops
*loops ATTRIBUTE_UNUSED
,
164 edge exit
, tree niter
,
165 enum unroll_level ul
)
167 unsigned HOST_WIDE_INT n_unroll
, ninsns
, max_unroll
, unr_insns
;
168 tree old_cond
, cond
, dont_exit
, do_exit
;
173 if (!host_integerp (niter
, 1))
175 n_unroll
= tree_low_cst (niter
, 1);
177 max_unroll
= PARAM_VALUE (PARAM_MAX_COMPLETELY_PEEL_TIMES
);
178 if (n_unroll
> max_unroll
)
183 if (ul
== UL_SINGLE_ITER
)
186 ninsns
= tree_num_loop_insns (loop
);
188 if (n_unroll
* ninsns
189 > (unsigned) PARAM_VALUE (PARAM_MAX_COMPLETELY_PEELED_INSNS
))
192 if (ul
== UL_NO_GROWTH
)
194 unr_insns
= estimated_unrolled_size (ninsns
, n_unroll
);
196 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
198 fprintf (dump_file
, " Loop size: %d\n", (int) ninsns
);
199 fprintf (dump_file
, " Estimated size after unrolling: %d\n",
203 if (unr_insns
> ninsns
)
205 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
206 fprintf (dump_file
, "Not unrolling loop %d:\n", loop
->num
);
212 if (exit
->flags
& EDGE_TRUE_VALUE
)
214 dont_exit
= boolean_false_node
;
215 do_exit
= boolean_true_node
;
219 dont_exit
= boolean_true_node
;
220 do_exit
= boolean_false_node
;
222 cond
= last_stmt (exit
->src
);
227 edge
*edges_to_remove
= XNEWVEC (edge
, n_unroll
);
228 unsigned int n_to_remove
= 0;
230 old_cond
= COND_EXPR_COND (cond
);
231 COND_EXPR_COND (cond
) = dont_exit
;
233 initialize_original_copy_tables ();
235 wont_exit
= sbitmap_alloc (n_unroll
+ 1);
236 sbitmap_ones (wont_exit
);
237 RESET_BIT (wont_exit
, 0);
239 if (!tree_duplicate_loop_to_header_edge (loop
, loop_preheader_edge (loop
),
240 loops
, n_unroll
, wont_exit
,
241 exit
, edges_to_remove
,
243 DLTHE_FLAG_UPDATE_FREQ
244 | DLTHE_FLAG_COMPLETTE_PEEL
))
246 COND_EXPR_COND (cond
) = old_cond
;
248 free_original_copy_tables ();
250 free (edges_to_remove
);
254 free (edges_to_remove
);
255 free_original_copy_tables ();
258 COND_EXPR_COND (cond
) = do_exit
;
261 update_ssa (TODO_update_ssa
);
263 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
264 fprintf (dump_file
, "Unrolled loop %d completely.\n", loop
->num
);
269 /* Adds a canonical induction variable to LOOP if suitable. LOOPS is the loops
270 tree. CREATE_IV is true if we may create a new iv. UL determines
271 which loops we are allowed to completely unroll. If TRY_EVAL is true, we try
272 to determine the number of iterations of a loop by direct evaluation.
273 Returns true if cfg is changed. */
276 canonicalize_loop_induction_variables (struct loops
*loops
, struct loop
*loop
,
277 bool create_iv
, enum unroll_level ul
,
283 niter
= number_of_iterations_in_loop (loop
);
284 if (TREE_CODE (niter
) == INTEGER_CST
)
286 exit
= loop
->single_exit
;
287 if (!just_once_each_iteration_p (loop
, exit
->src
))
290 /* The result of number_of_iterations_in_loop is by one higher than
291 we expect (i.e. it returns number of executions of the exit
292 condition, not of the loop latch edge). */
293 niter
= fold_build2 (MINUS_EXPR
, TREE_TYPE (niter
), niter
,
294 build_int_cst (TREE_TYPE (niter
), 1));
298 /* If the loop has more than one exit, try checking all of them
299 for # of iterations determinable through scev. */
300 if (!loop
->single_exit
)
301 niter
= find_loop_niter (loop
, &exit
);
303 /* Finally if everything else fails, try brute force evaluation. */
305 && (chrec_contains_undetermined (niter
)
306 || TREE_CODE (niter
) != INTEGER_CST
))
307 niter
= find_loop_niter_by_eval (loop
, &exit
);
309 if (chrec_contains_undetermined (niter
)
310 || TREE_CODE (niter
) != INTEGER_CST
)
314 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
316 fprintf (dump_file
, "Loop %d iterates ", loop
->num
);
317 print_generic_expr (dump_file
, niter
, TDF_SLIM
);
318 fprintf (dump_file
, " times.\n");
321 if (try_unroll_loop_completely (loops
, loop
, exit
, niter
, ul
))
325 create_canonical_iv (loop
, exit
, niter
);
330 /* The main entry point of the pass. Adds canonical induction variables
331 to the suitable LOOPS. */
334 canonicalize_induction_variables (struct loops
*loops
)
338 bool changed
= false;
340 for (i
= 1; i
< loops
->num
; i
++)
342 loop
= loops
->parray
[i
];
345 changed
|= canonicalize_loop_induction_variables (loops
, loop
,
346 true, UL_SINGLE_ITER
,
350 /* Clean up the information about numbers of iterations, since brute force
351 evaluation could reveal new information. */
355 return TODO_cleanup_cfg
;
359 /* Unroll LOOPS completely if they iterate just few times. Unless
360 MAY_INCREASE_SIZE is true, perform the unrolling only if the
361 size of the code does not increase. */
364 tree_unroll_loops_completely (struct loops
*loops
, bool may_increase_size
)
368 bool changed
= false;
369 enum unroll_level ul
;
371 for (i
= 1; i
< loops
->num
; i
++)
373 loop
= loops
->parray
[i
];
378 if (may_increase_size
&& maybe_hot_bb_p (loop
->header
))
382 changed
|= canonicalize_loop_induction_variables (loops
, loop
,
384 !flag_tree_loop_ivcanon
);
387 /* Clean up the information about numbers of iterations, since complete
388 unrolling might have invalidated it. */
392 return TODO_cleanup_cfg
;
396 /* Checks whether LOOP is empty. */
399 empty_loop_p (struct loop
*loop
)
402 struct tree_niter_desc niter
;
405 block_stmt_iterator bsi
;
409 /* If the loop has multiple exits, it is too hard for us to handle.
410 Similarly, if the exit is not dominating, we cannot determine
411 whether the loop is not infinite. */
412 exit
= single_dom_exit (loop
);
416 /* The loop must be finite. */
417 if (!number_of_iterations_exit (loop
, exit
, &niter
, false))
420 /* Values of all loop exit phi nodes must be invariants. */
421 for (phi
= phi_nodes (exit
->dest
); phi
; phi
= PHI_CHAIN (phi
))
423 if (!is_gimple_reg (PHI_RESULT (phi
)))
426 def
= PHI_ARG_DEF_FROM_EDGE (phi
, exit
);
428 if (!expr_invariant_in_loop_p (loop
, def
))
432 /* And there should be no memory modifying or from other reasons
433 unremovable statements. */
434 body
= get_loop_body (loop
);
435 for (i
= 0; i
< loop
->num_nodes
; i
++)
437 /* Irreducible region might be infinite. */
438 if (body
[i
]->flags
& BB_IRREDUCIBLE_LOOP
)
444 for (bsi
= bsi_start (body
[i
]); !bsi_end_p (bsi
); bsi_next (&bsi
))
446 stmt
= bsi_stmt (bsi
);
447 if (!ZERO_SSA_OPERANDS (stmt
, SSA_OP_VIRTUAL_DEFS
)
448 || stmt_ann (stmt
)->has_volatile_ops
)
454 /* Also, asm statements and calls may have side effects and we
455 cannot change the number of times they are executed. */
456 switch (TREE_CODE (stmt
))
460 stmt
= get_call_expr_in (stmt
);
465 if (TREE_SIDE_EFFECTS (stmt
))
473 /* We cannot remove volatile assembler. */
474 if (ASM_VOLATILE_P (stmt
))
491 /* Remove LOOP by making it exit in the first iteration. */
494 remove_empty_loop (struct loop
*loop
)
496 edge exit
= single_dom_exit (loop
), non_exit
;
497 tree cond_stmt
= last_stmt (exit
->src
);
500 unsigned n_before
, freq_in
, freq_h
;
501 gcov_type exit_count
= exit
->count
;
503 non_exit
= EDGE_SUCC (exit
->src
, 0);
504 if (non_exit
== exit
)
505 non_exit
= EDGE_SUCC (exit
->src
, 1);
507 if (exit
->flags
& EDGE_TRUE_VALUE
)
508 do_exit
= boolean_true_node
;
510 do_exit
= boolean_false_node
;
512 COND_EXPR_COND (cond_stmt
) = do_exit
;
513 update_stmt (cond_stmt
);
515 /* Let us set the probabilities of the edges coming from the exit block. */
516 exit
->probability
= REG_BR_PROB_BASE
;
517 non_exit
->probability
= 0;
520 /* Update frequencies and counts. Everything before
521 the exit needs to be scaled FREQ_IN/FREQ_H times,
522 where FREQ_IN is the frequency of the entry edge
523 and FREQ_H is the frequency of the loop header.
524 Everything after the exit has zero frequency. */
525 freq_h
= loop
->header
->frequency
;
526 freq_in
= EDGE_FREQUENCY (loop_preheader_edge (loop
));
529 body
= get_loop_body_in_dom_order (loop
);
530 for (n_before
= 1; n_before
<= loop
->num_nodes
; n_before
++)
531 if (body
[n_before
- 1] == exit
->src
)
533 scale_bbs_frequencies_int (body
, n_before
, freq_in
, freq_h
);
534 scale_bbs_frequencies_int (body
+ n_before
, loop
->num_nodes
- n_before
,
539 /* Number of executions of exit is not changed, thus we need to restore
540 the original value. */
541 exit
->count
= exit_count
;
544 /* Removes LOOP if it is empty. Returns true if LOOP is removed. CHANGED
545 is set to true if LOOP or any of its subloops is removed. */
548 try_remove_empty_loop (struct loop
*loop
, bool *changed
)
550 bool nonempty_subloop
= false;
553 /* First, all subloops must be removed. */
554 for (sub
= loop
->inner
; sub
; sub
= sub
->next
)
555 nonempty_subloop
|= !try_remove_empty_loop (sub
, changed
);
557 if (nonempty_subloop
|| !empty_loop_p (loop
))
560 remove_empty_loop (loop
);
565 /* Remove the empty LOOPS. */
568 remove_empty_loops (struct loops
*loops
)
570 bool changed
= false;
573 for (loop
= loops
->tree_root
->inner
; loop
; loop
= loop
->next
)
574 try_remove_empty_loop (loop
, &changed
);
579 return TODO_cleanup_cfg
;