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5f240ec4 | 1 | /* Loop header copying on trees. |
66647d44 | 2 | Copyright (C) 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc. |
b8698a0f | 3 | |
5f240ec4 | 4 | This file is part of GCC. |
b8698a0f | 5 | |
5f240ec4 ZD |
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 | |
9dcd6f09 | 8 | Free Software Foundation; either version 3, or (at your option) any |
5f240ec4 | 9 | later version. |
b8698a0f | 10 | |
5f240ec4 ZD |
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. | |
b8698a0f | 15 | |
5f240ec4 | 16 | You should have received a copy of the GNU General Public License |
9dcd6f09 NC |
17 | along with GCC; see the file COPYING3. If not see |
18 | <http://www.gnu.org/licenses/>. */ | |
5f240ec4 ZD |
19 | |
20 | #include "config.h" | |
21 | #include "system.h" | |
22 | #include "coretypes.h" | |
23 | #include "tm.h" | |
24 | #include "tree.h" | |
25 | #include "rtl.h" | |
26 | #include "tm_p.h" | |
27 | #include "hard-reg-set.h" | |
28 | #include "basic-block.h" | |
29 | #include "output.h" | |
30 | #include "diagnostic.h" | |
31 | #include "tree-flow.h" | |
32 | #include "tree-dump.h" | |
33 | #include "tree-pass.h" | |
34 | #include "timevar.h" | |
35 | #include "cfgloop.h" | |
36 | #include "tree-inline.h" | |
37 | #include "flags.h" | |
38 | #include "tree-inline.h" | |
39 | ||
40 | /* Duplicates headers of loops if they are small enough, so that the statements | |
41 | in the loop body are always executed when the loop is entered. This | |
b01d837f | 42 | increases effectiveness of code motion optimizations, and reduces the need |
5f240ec4 ZD |
43 | for loop preconditioning. */ |
44 | ||
45 | /* Check whether we should duplicate HEADER of LOOP. At most *LIMIT | |
46 | instructions should be duplicated, limit is decreased by the actual | |
47 | amount. */ | |
48 | ||
49 | static bool | |
50 | should_duplicate_loop_header_p (basic_block header, struct loop *loop, | |
51 | int *limit) | |
52 | { | |
726a989a RB |
53 | gimple_stmt_iterator bsi; |
54 | gimple last; | |
5f240ec4 ZD |
55 | |
56 | /* Do not copy one block more than once (we do not really want to do | |
57 | loop peeling here). */ | |
58 | if (header->aux) | |
59 | return false; | |
60 | ||
cc870036 JH |
61 | /* Loop header copying usually increases size of the code. This used not to |
62 | be true, since quite often it is possible to verify that the condition is | |
63 | satisfied in the first iteration and therefore to eliminate it. Jump | |
64 | threading handles these cases now. */ | |
65 | if (optimize_loop_for_size_p (loop)) | |
66 | return false; | |
67 | ||
628f6a4e | 68 | gcc_assert (EDGE_COUNT (header->succs) > 0); |
c5cbcccf | 69 | if (single_succ_p (header)) |
5f240ec4 | 70 | return false; |
628f6a4e BE |
71 | if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest) |
72 | && flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 1)->dest)) | |
5f240ec4 ZD |
73 | return false; |
74 | ||
75 | /* If this is not the original loop header, we want it to have just | |
76 | one predecessor in order to match the && pattern. */ | |
c5cbcccf | 77 | if (header != loop->header && !single_pred_p (header)) |
5f240ec4 ZD |
78 | return false; |
79 | ||
80 | last = last_stmt (header); | |
726a989a | 81 | if (gimple_code (last) != GIMPLE_COND) |
5f240ec4 ZD |
82 | return false; |
83 | ||
84 | /* Approximately copy the conditions that used to be used in jump.c -- | |
85 | at most 20 insns and no calls. */ | |
726a989a | 86 | for (bsi = gsi_start_bb (header); !gsi_end_p (bsi); gsi_next (&bsi)) |
5f240ec4 | 87 | { |
726a989a | 88 | last = gsi_stmt (bsi); |
5f240ec4 | 89 | |
726a989a | 90 | if (gimple_code (last) == GIMPLE_LABEL) |
5f240ec4 ZD |
91 | continue; |
92 | ||
b5b8b0ac AO |
93 | if (is_gimple_debug (last)) |
94 | continue; | |
95 | ||
726a989a | 96 | if (is_gimple_call (last)) |
5f240ec4 ZD |
97 | return false; |
98 | ||
7f9bc51b | 99 | *limit -= estimate_num_insns (last, &eni_size_weights); |
5f240ec4 ZD |
100 | if (*limit < 0) |
101 | return false; | |
102 | } | |
103 | ||
104 | return true; | |
105 | } | |
106 | ||
5f240ec4 ZD |
107 | /* Checks whether LOOP is a do-while style loop. */ |
108 | ||
109 | static bool | |
110 | do_while_loop_p (struct loop *loop) | |
111 | { | |
726a989a | 112 | gimple stmt = last_stmt (loop->latch); |
5f240ec4 ZD |
113 | |
114 | /* If the latch of the loop is not empty, it is not a do-while loop. */ | |
115 | if (stmt | |
726a989a | 116 | && gimple_code (stmt) != GIMPLE_LABEL) |
5f240ec4 ZD |
117 | return false; |
118 | ||
119 | /* If the header contains just a condition, it is not a do-while loop. */ | |
120 | stmt = last_and_only_stmt (loop->header); | |
121 | if (stmt | |
726a989a | 122 | && gimple_code (stmt) == GIMPLE_COND) |
5f240ec4 ZD |
123 | return false; |
124 | ||
125 | return true; | |
126 | } | |
127 | ||
128 | /* For all loops, copy the condition at the end of the loop body in front | |
129 | of the loop. This is beneficial since it increases efficiency of | |
130 | code motion optimizations. It also saves one jump on entry to the loop. */ | |
131 | ||
c2924966 | 132 | static unsigned int |
5f240ec4 ZD |
133 | copy_loop_headers (void) |
134 | { | |
42fd6772 | 135 | loop_iterator li; |
5f240ec4 ZD |
136 | struct loop *loop; |
137 | basic_block header; | |
33156717 JH |
138 | edge exit, entry; |
139 | basic_block *bbs, *copied_bbs; | |
42759f1e | 140 | unsigned n_bbs; |
33156717 | 141 | unsigned bbs_size; |
5f240ec4 | 142 | |
598ec7bd ZD |
143 | loop_optimizer_init (LOOPS_HAVE_PREHEADERS |
144 | | LOOPS_HAVE_SIMPLE_LATCHES); | |
d51157de ZD |
145 | if (number_of_loops () <= 1) |
146 | { | |
147 | loop_optimizer_finalize (); | |
148 | return 0; | |
149 | } | |
5f240ec4 ZD |
150 | |
151 | #ifdef ENABLE_CHECKING | |
d73be268 | 152 | verify_loop_structure (); |
5f240ec4 ZD |
153 | #endif |
154 | ||
5ed6ace5 MD |
155 | bbs = XNEWVEC (basic_block, n_basic_blocks); |
156 | copied_bbs = XNEWVEC (basic_block, n_basic_blocks); | |
33156717 | 157 | bbs_size = n_basic_blocks; |
42759f1e | 158 | |
42fd6772 | 159 | FOR_EACH_LOOP (li, loop, 0) |
5f240ec4 ZD |
160 | { |
161 | /* Copy at most 20 insns. */ | |
162 | int limit = 20; | |
163 | ||
42759f1e | 164 | header = loop->header; |
5f240ec4 ZD |
165 | |
166 | /* If the loop is already a do-while style one (either because it was | |
167 | written as such, or because jump threading transformed it into one), | |
168 | we might be in fact peeling the first iteration of the loop. This | |
169 | in general is not a good idea. */ | |
170 | if (do_while_loop_p (loop)) | |
171 | continue; | |
172 | ||
173 | /* Iterate the header copying up to limit; this takes care of the cases | |
174 | like while (a && b) {...}, where we want to have both of the conditions | |
175 | copied. TODO -- handle while (a || b) - like cases, by not requiring | |
176 | the header to have just a single successor and copying up to | |
42759f1e ZD |
177 | postdominator. */ |
178 | ||
179 | exit = NULL; | |
180 | n_bbs = 0; | |
5f240ec4 ZD |
181 | while (should_duplicate_loop_header_p (header, loop, &limit)) |
182 | { | |
5f240ec4 ZD |
183 | /* Find a successor of header that is inside a loop; i.e. the new |
184 | header after the condition is copied. */ | |
628f6a4e BE |
185 | if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest)) |
186 | exit = EDGE_SUCC (header, 0); | |
5f240ec4 | 187 | else |
628f6a4e | 188 | exit = EDGE_SUCC (header, 1); |
42759f1e | 189 | bbs[n_bbs++] = header; |
33156717 | 190 | gcc_assert (bbs_size > n_bbs); |
42759f1e | 191 | header = exit->dest; |
5f240ec4 | 192 | } |
5f240ec4 | 193 | |
42759f1e ZD |
194 | if (!exit) |
195 | continue; | |
5f240ec4 | 196 | |
42759f1e ZD |
197 | if (dump_file && (dump_flags & TDF_DETAILS)) |
198 | fprintf (dump_file, | |
199 | "Duplicating header of the loop %d up to edge %d->%d.\n", | |
200 | loop->num, exit->src->index, exit->dest->index); | |
201 | ||
202 | /* Ensure that the header will have just the latch as a predecessor | |
203 | inside the loop. */ | |
c5cbcccf | 204 | if (!single_pred_p (exit->dest)) |
598ec7bd | 205 | exit = single_pred_edge (split_edge (exit)); |
42759f1e | 206 | |
33156717 | 207 | entry = loop_preheader_edge (loop); |
33156717 | 208 | |
726a989a | 209 | if (!gimple_duplicate_sese_region (entry, exit, bbs, n_bbs, copied_bbs)) |
42759f1e ZD |
210 | { |
211 | fprintf (dump_file, "Duplication failed.\n"); | |
212 | continue; | |
213 | } | |
214 | ||
4df28528 ILT |
215 | /* If the loop has the form "for (i = j; i < j + 10; i++)" then |
216 | this copying can introduce a case where we rely on undefined | |
217 | signed overflow to eliminate the preheader condition, because | |
218 | we assume that "j < j + 10" is true. We don't want to warn | |
219 | about that case for -Wstrict-overflow, because in general we | |
220 | don't warn about overflow involving loops. Prevent the | |
726a989a | 221 | warning by setting the no_warning flag in the condition. */ |
4df28528 ILT |
222 | if (warn_strict_overflow > 0) |
223 | { | |
224 | unsigned int i; | |
225 | ||
226 | for (i = 0; i < n_bbs; ++i) | |
227 | { | |
726a989a | 228 | gimple_stmt_iterator bsi; |
e233ac97 | 229 | |
726a989a RB |
230 | for (bsi = gsi_start_bb (copied_bbs[i]); |
231 | !gsi_end_p (bsi); | |
232 | gsi_next (&bsi)) | |
e233ac97 | 233 | { |
726a989a RB |
234 | gimple stmt = gsi_stmt (bsi); |
235 | if (gimple_code (stmt) == GIMPLE_COND) | |
236 | gimple_set_no_warning (stmt, true); | |
237 | else if (is_gimple_assign (stmt)) | |
e233ac97 | 238 | { |
726a989a RB |
239 | enum tree_code rhs_code = gimple_assign_rhs_code (stmt); |
240 | if (TREE_CODE_CLASS (rhs_code) == tcc_comparison) | |
241 | gimple_set_no_warning (stmt, true); | |
e233ac97 ILT |
242 | } |
243 | } | |
4df28528 ILT |
244 | } |
245 | } | |
246 | ||
42759f1e ZD |
247 | /* Ensure that the latch and the preheader is simple (we know that they |
248 | are not now, since there was the loop exit condition. */ | |
598ec7bd ZD |
249 | split_edge (loop_preheader_edge (loop)); |
250 | split_edge (loop_latch_edge (loop)); | |
5f240ec4 ZD |
251 | } |
252 | ||
42759f1e | 253 | free (bbs); |
33156717 | 254 | free (copied_bbs); |
42759f1e | 255 | |
598ec7bd | 256 | loop_optimizer_finalize (); |
c2924966 | 257 | return 0; |
5f240ec4 ZD |
258 | } |
259 | ||
260 | static bool | |
261 | gate_ch (void) | |
262 | { | |
263 | return flag_tree_ch != 0; | |
264 | } | |
265 | ||
b8698a0f | 266 | struct gimple_opt_pass pass_ch = |
5f240ec4 | 267 | { |
8ddbbcae JH |
268 | { |
269 | GIMPLE_PASS, | |
5f240ec4 ZD |
270 | "ch", /* name */ |
271 | gate_ch, /* gate */ | |
272 | copy_loop_headers, /* execute */ | |
273 | NULL, /* sub */ | |
274 | NULL, /* next */ | |
275 | 0, /* static_pass_number */ | |
276 | TV_TREE_CH, /* tv_id */ | |
42759f1e | 277 | PROP_cfg | PROP_ssa, /* properties_required */ |
5f240ec4 ZD |
278 | 0, /* properties_provided */ |
279 | 0, /* properties_destroyed */ | |
280 | 0, /* todo_flags_start */ | |
b8698a0f | 281 | TODO_cleanup_cfg | TODO_dump_func |
8ddbbcae JH |
282 | | TODO_verify_ssa /* todo_flags_finish */ |
283 | } | |
5f240ec4 | 284 | }; |