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5f240ec4 | 1 | /* Loop header copying on trees. |
23a5b65a | 2 | Copyright (C) 2004-2014 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" | |
5f240ec4 | 25 | #include "tm_p.h" |
5f240ec4 | 26 | #include "basic-block.h" |
2fb9a547 AM |
27 | #include "tree-ssa-alias.h" |
28 | #include "internal-fn.h" | |
29 | #include "gimple-expr.h" | |
30 | #include "is-a.h" | |
442b4905 | 31 | #include "gimple.h" |
5be5c238 | 32 | #include "gimple-iterator.h" |
442b4905 AM |
33 | #include "gimple-ssa.h" |
34 | #include "tree-cfg.h" | |
35 | #include "tree-into-ssa.h" | |
5f240ec4 | 36 | #include "tree-pass.h" |
5f240ec4 ZD |
37 | #include "cfgloop.h" |
38 | #include "tree-inline.h" | |
39 | #include "flags.h" | |
4484a35a | 40 | #include "tree-ssa-threadedge.h" |
5f240ec4 ZD |
41 | |
42 | /* Duplicates headers of loops if they are small enough, so that the statements | |
43 | in the loop body are always executed when the loop is entered. This | |
b01d837f | 44 | increases effectiveness of code motion optimizations, and reduces the need |
5f240ec4 ZD |
45 | for loop preconditioning. */ |
46 | ||
47 | /* Check whether we should duplicate HEADER of LOOP. At most *LIMIT | |
48 | instructions should be duplicated, limit is decreased by the actual | |
49 | amount. */ | |
50 | ||
51 | static bool | |
52 | should_duplicate_loop_header_p (basic_block header, struct loop *loop, | |
53 | int *limit) | |
54 | { | |
726a989a RB |
55 | gimple_stmt_iterator bsi; |
56 | gimple last; | |
5f240ec4 ZD |
57 | |
58 | /* Do not copy one block more than once (we do not really want to do | |
59 | loop peeling here). */ | |
60 | if (header->aux) | |
61 | return false; | |
62 | ||
cc870036 JH |
63 | /* Loop header copying usually increases size of the code. This used not to |
64 | be true, since quite often it is possible to verify that the condition is | |
65 | satisfied in the first iteration and therefore to eliminate it. Jump | |
66 | threading handles these cases now. */ | |
67 | if (optimize_loop_for_size_p (loop)) | |
68 | return false; | |
69 | ||
628f6a4e | 70 | gcc_assert (EDGE_COUNT (header->succs) > 0); |
c5cbcccf | 71 | if (single_succ_p (header)) |
5f240ec4 | 72 | return false; |
628f6a4e BE |
73 | if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest) |
74 | && flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 1)->dest)) | |
5f240ec4 ZD |
75 | return false; |
76 | ||
77 | /* If this is not the original loop header, we want it to have just | |
78 | one predecessor in order to match the && pattern. */ | |
c5cbcccf | 79 | if (header != loop->header && !single_pred_p (header)) |
5f240ec4 ZD |
80 | return false; |
81 | ||
82 | last = last_stmt (header); | |
726a989a | 83 | if (gimple_code (last) != GIMPLE_COND) |
5f240ec4 ZD |
84 | return false; |
85 | ||
86 | /* Approximately copy the conditions that used to be used in jump.c -- | |
87 | at most 20 insns and no calls. */ | |
726a989a | 88 | for (bsi = gsi_start_bb (header); !gsi_end_p (bsi); gsi_next (&bsi)) |
5f240ec4 | 89 | { |
726a989a | 90 | last = gsi_stmt (bsi); |
5f240ec4 | 91 | |
726a989a | 92 | if (gimple_code (last) == GIMPLE_LABEL) |
5f240ec4 ZD |
93 | continue; |
94 | ||
b5b8b0ac AO |
95 | if (is_gimple_debug (last)) |
96 | continue; | |
97 | ||
726a989a | 98 | if (is_gimple_call (last)) |
5f240ec4 ZD |
99 | return false; |
100 | ||
7f9bc51b | 101 | *limit -= estimate_num_insns (last, &eni_size_weights); |
5f240ec4 ZD |
102 | if (*limit < 0) |
103 | return false; | |
104 | } | |
105 | ||
106 | return true; | |
107 | } | |
108 | ||
5f240ec4 ZD |
109 | /* Checks whether LOOP is a do-while style loop. */ |
110 | ||
71343877 | 111 | static bool |
5f240ec4 ZD |
112 | do_while_loop_p (struct loop *loop) |
113 | { | |
726a989a | 114 | gimple stmt = last_stmt (loop->latch); |
5f240ec4 ZD |
115 | |
116 | /* If the latch of the loop is not empty, it is not a do-while loop. */ | |
117 | if (stmt | |
726a989a | 118 | && gimple_code (stmt) != GIMPLE_LABEL) |
5f240ec4 ZD |
119 | return false; |
120 | ||
121 | /* If the header contains just a condition, it is not a do-while loop. */ | |
122 | stmt = last_and_only_stmt (loop->header); | |
123 | if (stmt | |
726a989a | 124 | && gimple_code (stmt) == GIMPLE_COND) |
5f240ec4 ZD |
125 | return false; |
126 | ||
127 | return true; | |
128 | } | |
129 | ||
130 | /* For all loops, copy the condition at the end of the loop body in front | |
131 | of the loop. This is beneficial since it increases efficiency of | |
132 | code motion optimizations. It also saves one jump on entry to the loop. */ | |
133 | ||
be55bfe6 TS |
134 | namespace { |
135 | ||
136 | const pass_data pass_data_ch = | |
137 | { | |
138 | GIMPLE_PASS, /* type */ | |
139 | "ch", /* name */ | |
140 | OPTGROUP_LOOP, /* optinfo_flags */ | |
be55bfe6 TS |
141 | TV_TREE_CH, /* tv_id */ |
142 | ( PROP_cfg | PROP_ssa ), /* properties_required */ | |
143 | 0, /* properties_provided */ | |
144 | 0, /* properties_destroyed */ | |
145 | 0, /* todo_flags_start */ | |
3bea341f | 146 | TODO_cleanup_cfg, /* todo_flags_finish */ |
be55bfe6 TS |
147 | }; |
148 | ||
149 | class pass_ch : public gimple_opt_pass | |
150 | { | |
151 | public: | |
152 | pass_ch (gcc::context *ctxt) | |
153 | : gimple_opt_pass (pass_data_ch, ctxt) | |
154 | {} | |
155 | ||
156 | /* opt_pass methods: */ | |
157 | virtual bool gate (function *) { return flag_tree_ch != 0; } | |
158 | virtual unsigned int execute (function *); | |
159 | ||
160 | }; // class pass_ch | |
161 | ||
162 | unsigned int | |
163 | pass_ch::execute (function *fun) | |
5f240ec4 | 164 | { |
5f240ec4 ZD |
165 | struct loop *loop; |
166 | basic_block header; | |
33156717 JH |
167 | edge exit, entry; |
168 | basic_block *bbs, *copied_bbs; | |
42759f1e | 169 | unsigned n_bbs; |
33156717 | 170 | unsigned bbs_size; |
5f240ec4 | 171 | |
598ec7bd ZD |
172 | loop_optimizer_init (LOOPS_HAVE_PREHEADERS |
173 | | LOOPS_HAVE_SIMPLE_LATCHES); | |
be55bfe6 | 174 | if (number_of_loops (fun) <= 1) |
d51157de ZD |
175 | { |
176 | loop_optimizer_finalize (); | |
177 | return 0; | |
178 | } | |
5f240ec4 | 179 | |
be55bfe6 TS |
180 | bbs = XNEWVEC (basic_block, n_basic_blocks_for_fn (fun)); |
181 | copied_bbs = XNEWVEC (basic_block, n_basic_blocks_for_fn (fun)); | |
182 | bbs_size = n_basic_blocks_for_fn (fun); | |
42759f1e | 183 | |
f0bd40b1 | 184 | FOR_EACH_LOOP (loop, 0) |
5f240ec4 ZD |
185 | { |
186 | /* Copy at most 20 insns. */ | |
187 | int limit = 20; | |
188 | ||
42759f1e | 189 | header = loop->header; |
5f240ec4 ZD |
190 | |
191 | /* If the loop is already a do-while style one (either because it was | |
192 | written as such, or because jump threading transformed it into one), | |
193 | we might be in fact peeling the first iteration of the loop. This | |
194 | in general is not a good idea. */ | |
195 | if (do_while_loop_p (loop)) | |
196 | continue; | |
197 | ||
198 | /* Iterate the header copying up to limit; this takes care of the cases | |
199 | like while (a && b) {...}, where we want to have both of the conditions | |
200 | copied. TODO -- handle while (a || b) - like cases, by not requiring | |
201 | the header to have just a single successor and copying up to | |
42759f1e ZD |
202 | postdominator. */ |
203 | ||
204 | exit = NULL; | |
205 | n_bbs = 0; | |
5f240ec4 ZD |
206 | while (should_duplicate_loop_header_p (header, loop, &limit)) |
207 | { | |
5f240ec4 ZD |
208 | /* Find a successor of header that is inside a loop; i.e. the new |
209 | header after the condition is copied. */ | |
628f6a4e BE |
210 | if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest)) |
211 | exit = EDGE_SUCC (header, 0); | |
5f240ec4 | 212 | else |
628f6a4e | 213 | exit = EDGE_SUCC (header, 1); |
42759f1e | 214 | bbs[n_bbs++] = header; |
33156717 | 215 | gcc_assert (bbs_size > n_bbs); |
42759f1e | 216 | header = exit->dest; |
5f240ec4 | 217 | } |
5f240ec4 | 218 | |
42759f1e ZD |
219 | if (!exit) |
220 | continue; | |
5f240ec4 | 221 | |
42759f1e ZD |
222 | if (dump_file && (dump_flags & TDF_DETAILS)) |
223 | fprintf (dump_file, | |
224 | "Duplicating header of the loop %d up to edge %d->%d.\n", | |
225 | loop->num, exit->src->index, exit->dest->index); | |
226 | ||
227 | /* Ensure that the header will have just the latch as a predecessor | |
228 | inside the loop. */ | |
c5cbcccf | 229 | if (!single_pred_p (exit->dest)) |
598ec7bd | 230 | exit = single_pred_edge (split_edge (exit)); |
42759f1e | 231 | |
33156717 | 232 | entry = loop_preheader_edge (loop); |
33156717 | 233 | |
6e02b5f5 | 234 | propagate_threaded_block_debug_into (exit->dest, entry->dest); |
f14540b6 SE |
235 | if (!gimple_duplicate_sese_region (entry, exit, bbs, n_bbs, copied_bbs, |
236 | true)) | |
42759f1e ZD |
237 | { |
238 | fprintf (dump_file, "Duplication failed.\n"); | |
239 | continue; | |
240 | } | |
241 | ||
4df28528 ILT |
242 | /* If the loop has the form "for (i = j; i < j + 10; i++)" then |
243 | this copying can introduce a case where we rely on undefined | |
244 | signed overflow to eliminate the preheader condition, because | |
245 | we assume that "j < j + 10" is true. We don't want to warn | |
246 | about that case for -Wstrict-overflow, because in general we | |
247 | don't warn about overflow involving loops. Prevent the | |
726a989a | 248 | warning by setting the no_warning flag in the condition. */ |
4df28528 ILT |
249 | if (warn_strict_overflow > 0) |
250 | { | |
251 | unsigned int i; | |
252 | ||
253 | for (i = 0; i < n_bbs; ++i) | |
254 | { | |
726a989a | 255 | gimple_stmt_iterator bsi; |
e233ac97 | 256 | |
726a989a RB |
257 | for (bsi = gsi_start_bb (copied_bbs[i]); |
258 | !gsi_end_p (bsi); | |
259 | gsi_next (&bsi)) | |
e233ac97 | 260 | { |
726a989a RB |
261 | gimple stmt = gsi_stmt (bsi); |
262 | if (gimple_code (stmt) == GIMPLE_COND) | |
263 | gimple_set_no_warning (stmt, true); | |
264 | else if (is_gimple_assign (stmt)) | |
e233ac97 | 265 | { |
726a989a RB |
266 | enum tree_code rhs_code = gimple_assign_rhs_code (stmt); |
267 | if (TREE_CODE_CLASS (rhs_code) == tcc_comparison) | |
268 | gimple_set_no_warning (stmt, true); | |
e233ac97 ILT |
269 | } |
270 | } | |
4df28528 ILT |
271 | } |
272 | } | |
273 | ||
42759f1e ZD |
274 | /* Ensure that the latch and the preheader is simple (we know that they |
275 | are not now, since there was the loop exit condition. */ | |
598ec7bd ZD |
276 | split_edge (loop_preheader_edge (loop)); |
277 | split_edge (loop_latch_edge (loop)); | |
5f240ec4 ZD |
278 | } |
279 | ||
197ce793 | 280 | update_ssa (TODO_update_ssa); |
42759f1e | 281 | free (bbs); |
33156717 | 282 | free (copied_bbs); |
42759f1e | 283 | |
598ec7bd | 284 | loop_optimizer_finalize (); |
c2924966 | 285 | return 0; |
5f240ec4 ZD |
286 | } |
287 | ||
27a4cd48 DM |
288 | } // anon namespace |
289 | ||
290 | gimple_opt_pass * | |
291 | make_pass_ch (gcc::context *ctxt) | |
292 | { | |
293 | return new pass_ch (ctxt); | |
294 | } |