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67514449 RG |
1 | /* Backward propagation of indirect loads through PHIs. |
2 | Copyright (C) 2007, 2008 Free Software Foundation, Inc. | |
3 | Contributed by Richard Guenther <rguenther@suse.de> | |
4 | ||
5 | This file is part of GCC. | |
6 | ||
7 | GCC is free software; you can redistribute it and/or modify | |
8 | it under the terms of the GNU General Public License as published by | |
9 | the Free Software Foundation; either version 3, or (at your option) | |
10 | any later version. | |
11 | ||
12 | GCC is distributed in the hope that it will be useful, | |
13 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
15 | GNU General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU General Public License | |
18 | along with GCC; see the file COPYING3. If not see | |
19 | <http://www.gnu.org/licenses/>. */ | |
20 | ||
21 | #include "config.h" | |
22 | #include "system.h" | |
23 | #include "coretypes.h" | |
24 | #include "tm.h" | |
25 | #include "ggc.h" | |
26 | #include "tree.h" | |
27 | #include "rtl.h" | |
28 | #include "tm_p.h" | |
29 | #include "basic-block.h" | |
30 | #include "timevar.h" | |
31 | #include "diagnostic.h" | |
32 | #include "tree-flow.h" | |
33 | #include "tree-pass.h" | |
34 | #include "tree-dump.h" | |
35 | #include "langhooks.h" | |
36 | #include "flags.h" | |
37 | ||
38 | /* This pass propagates indirect loads through the PHI node for its | |
39 | address to make the load source possiby non-addressable and to | |
40 | allow for PHI optimization to trigger. | |
41 | ||
42 | For example the pass changes | |
43 | ||
44 | # addr_1 = PHI <&a, &b> | |
45 | tmp_1 = *addr_1; | |
46 | ||
47 | to | |
48 | ||
49 | # tmp_1 = PHI <a, b> | |
50 | ||
51 | but also handles more complex cenarios like | |
52 | ||
53 | D.2077_2 = &this_1(D)->a1; | |
54 | ... | |
55 | ||
56 | # b_12 = PHI <&c(2), D.2077_2(3)> | |
57 | D.2114_13 = *b_12; | |
58 | ... | |
59 | ||
60 | # b_15 = PHI <b_12(4), &b(5)> | |
61 | D.2080_5 = &this_1(D)->a0; | |
62 | ... | |
63 | ||
64 | # b_18 = PHI <D.2080_5(6), &c(7)> | |
65 | ... | |
66 | ||
67 | # b_21 = PHI <b_15(8), b_18(9)> | |
68 | D.2076_8 = *b_21; | |
69 | ||
70 | where the addresses loaded are defined by PHIs itself. | |
71 | The above happens for | |
72 | ||
73 | std::max(std::min(a0, c), std::min(std::max(a1, c), b)) | |
74 | ||
75 | where this pass transforms it to a form later PHI optimization | |
76 | recognizes and transforms it to the simple | |
77 | ||
78 | D.2109_10 = this_1(D)->a1; | |
79 | D.2110_11 = c; | |
80 | D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>; | |
81 | D.2115_14 = b; | |
82 | D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>; | |
83 | D.2119_16 = this_1(D)->a0; | |
84 | D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>; | |
85 | D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>; | |
86 | ||
87 | The pass does a dominator walk processing loads using a basic-block | |
88 | local analysis and stores the result for use by transformations on | |
89 | dominated basic-blocks. */ | |
90 | ||
91 | ||
92 | /* Structure to keep track of the value of a dereferenced PHI result | |
93 | and the set of virtual operands used for that dereference. */ | |
94 | ||
95 | struct phiprop_d | |
96 | { | |
97 | tree value; | |
98 | tree vop_stmt; | |
99 | }; | |
100 | ||
101 | /* Verify if the value recorded for NAME in PHIVN is still valid at | |
102 | the start of basic block BB. */ | |
103 | ||
104 | static bool | |
105 | phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb) | |
106 | { | |
107 | tree vop_stmt = phivn[SSA_NAME_VERSION (name)].vop_stmt; | |
108 | ssa_op_iter ui; | |
109 | tree vuse; | |
110 | ||
111 | /* The def stmts of all virtual uses need to be post-dominated | |
112 | by bb. */ | |
113 | FOR_EACH_SSA_TREE_OPERAND (vuse, vop_stmt, ui, SSA_OP_VUSE) | |
114 | { | |
115 | tree use_stmt; | |
116 | imm_use_iterator ui2; | |
117 | bool ok = true; | |
118 | ||
119 | FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse) | |
120 | { | |
121 | /* If BB does not dominate a VDEF, the value is invalid. */ | |
122 | if (((TREE_CODE (use_stmt) == GIMPLE_MODIFY_STMT | |
123 | && !ZERO_SSA_OPERANDS (use_stmt, SSA_OP_VDEF)) | |
124 | || TREE_CODE (use_stmt) == PHI_NODE) | |
125 | && !dominated_by_p (CDI_DOMINATORS, bb_for_stmt (use_stmt), bb)) | |
126 | { | |
127 | ok = false; | |
128 | BREAK_FROM_IMM_USE_STMT (ui2); | |
129 | } | |
130 | } | |
131 | if (!ok) | |
132 | return false; | |
133 | } | |
134 | ||
135 | return true; | |
136 | } | |
137 | ||
138 | /* Insert a new phi node for the dereference of PHI at basic_block | |
139 | BB with the virtual operands from USE_STMT. */ | |
140 | ||
141 | static tree | |
142 | phiprop_insert_phi (basic_block bb, tree phi, tree use_stmt, | |
143 | struct phiprop_d *phivn, size_t n) | |
144 | { | |
145 | tree res, new_phi; | |
146 | edge_iterator ei; | |
147 | edge e; | |
148 | ||
149 | /* Build a new PHI node to replace the definition of | |
150 | the indirect reference lhs. */ | |
151 | res = GIMPLE_STMT_OPERAND (use_stmt, 0); | |
152 | SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb); | |
153 | ||
154 | /* Add PHI arguments for each edge inserting loads of the | |
155 | addressable operands. */ | |
156 | FOR_EACH_EDGE (e, ei, bb->preds) | |
157 | { | |
158 | tree old_arg, new_var, tmp; | |
159 | ||
160 | old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); | |
161 | while (TREE_CODE (old_arg) == SSA_NAME | |
162 | && (SSA_NAME_VERSION (old_arg) >= n | |
163 | || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE)) | |
164 | { | |
165 | tree def_stmt = SSA_NAME_DEF_STMT (old_arg); | |
166 | old_arg = GIMPLE_STMT_OPERAND (def_stmt, 1); | |
167 | } | |
168 | ||
169 | if (TREE_CODE (old_arg) == SSA_NAME) | |
170 | /* Reuse a formerly created dereference. */ | |
171 | new_var = phivn[SSA_NAME_VERSION (old_arg)].value; | |
172 | else | |
173 | { | |
174 | old_arg = TREE_OPERAND (old_arg, 0); | |
175 | new_var = create_tmp_var (TREE_TYPE (old_arg), NULL); | |
176 | tmp = build2 (GIMPLE_MODIFY_STMT, void_type_node, | |
177 | NULL_TREE, unshare_expr (old_arg)); | |
178 | if (TREE_CODE (TREE_TYPE (old_arg)) == COMPLEX_TYPE | |
179 | || TREE_CODE (TREE_TYPE (old_arg)) == VECTOR_TYPE) | |
180 | DECL_GIMPLE_REG_P (new_var) = 1; | |
181 | add_referenced_var (new_var); | |
182 | new_var = make_ssa_name (new_var, tmp); | |
183 | GIMPLE_STMT_OPERAND (tmp, 0) = new_var; | |
184 | ||
185 | bsi_insert_on_edge (e, tmp); | |
186 | ||
187 | update_stmt (tmp); | |
188 | mark_symbols_for_renaming (tmp); | |
189 | } | |
190 | ||
191 | add_phi_arg (new_phi, new_var, e); | |
192 | } | |
193 | ||
194 | update_stmt (new_phi); | |
195 | ||
196 | return res; | |
197 | } | |
198 | ||
199 | /* Propagate between the phi node arguments of PHI in BB and phi result | |
200 | users. For now this matches | |
201 | # p_2 = PHI <&x, &y> | |
202 | <Lx>:; | |
203 | p_3 = p_2; | |
204 | z_2 = *p_3; | |
205 | and converts it to | |
206 | # z_2 = PHI <x, y> | |
207 | <Lx>:; | |
208 | Returns true if a transformation was done and edge insertions | |
209 | need to be committed. Global data PHIVN and N is used to track | |
210 | past transformation results. We need to be especially careful here | |
211 | with aliasing issues as we are moving memory reads. */ | |
212 | ||
213 | static bool | |
214 | propagate_with_phi (basic_block bb, tree phi, struct phiprop_d *phivn, size_t n) | |
215 | { | |
216 | tree ptr = PHI_RESULT (phi); | |
217 | tree use_stmt, res = NULL_TREE; | |
218 | block_stmt_iterator bsi; | |
219 | imm_use_iterator ui; | |
220 | use_operand_p arg_p, use; | |
221 | ssa_op_iter i; | |
222 | bool phi_inserted; | |
223 | ||
224 | if (MTAG_P (SSA_NAME_VAR (ptr)) | |
225 | || !POINTER_TYPE_P (TREE_TYPE (ptr)) | |
226 | || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr)))) | |
227 | return false; | |
228 | ||
229 | /* Check if we can "cheaply" dereference all phi arguments. */ | |
230 | FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE) | |
231 | { | |
232 | tree arg = USE_FROM_PTR (arg_p); | |
233 | /* Walk the ssa chain until we reach a ssa name we already | |
234 | created a value for or we reach a definition of the form | |
235 | ssa_name_n = &var; */ | |
236 | while (TREE_CODE (arg) == SSA_NAME | |
237 | && !SSA_NAME_IS_DEFAULT_DEF (arg) | |
238 | && (SSA_NAME_VERSION (arg) >= n | |
239 | || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE)) | |
240 | { | |
241 | tree def_stmt = SSA_NAME_DEF_STMT (arg); | |
242 | if (TREE_CODE (def_stmt) != GIMPLE_MODIFY_STMT) | |
243 | return false; | |
244 | arg = GIMPLE_STMT_OPERAND (def_stmt, 1); | |
245 | } | |
246 | if ((TREE_CODE (arg) != ADDR_EXPR | |
247 | /* Avoid to have to decay *&a to a[0] later. */ | |
248 | || !is_gimple_reg_type (TREE_TYPE (TREE_OPERAND (arg, 0)))) | |
249 | && !(TREE_CODE (arg) == SSA_NAME | |
250 | && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE | |
251 | && phivn_valid_p (phivn, arg, bb))) | |
252 | return false; | |
253 | } | |
254 | ||
255 | /* Find a dereferencing use. First follow (single use) ssa | |
256 | copy chains for ptr. */ | |
257 | while (single_imm_use (ptr, &use, &use_stmt) | |
258 | && TREE_CODE (use_stmt) == GIMPLE_MODIFY_STMT | |
259 | && GIMPLE_STMT_OPERAND (use_stmt, 1) == ptr | |
260 | && TREE_CODE (GIMPLE_STMT_OPERAND (use_stmt, 0)) == SSA_NAME) | |
261 | ptr = GIMPLE_STMT_OPERAND (use_stmt, 0); | |
262 | ||
263 | /* Replace the first dereference of *ptr if there is one and if we | |
264 | can move the loads to the place of the ptr phi node. */ | |
265 | phi_inserted = false; | |
266 | FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr) | |
267 | { | |
268 | ssa_op_iter ui2; | |
269 | tree vuse; | |
270 | ||
271 | /* Check whether this is a load of *ptr. */ | |
272 | if (!(TREE_CODE (use_stmt) == GIMPLE_MODIFY_STMT | |
273 | && TREE_CODE (GIMPLE_STMT_OPERAND (use_stmt, 0)) == SSA_NAME | |
274 | && TREE_CODE (GIMPLE_STMT_OPERAND (use_stmt, 1)) == INDIRECT_REF | |
275 | && TREE_OPERAND (GIMPLE_STMT_OPERAND (use_stmt, 1), 0) == ptr | |
276 | /* We cannot replace a load that may throw or is volatile. */ | |
277 | && !tree_can_throw_internal (use_stmt))) | |
278 | continue; | |
279 | ||
280 | /* Check if we can move the loads. The def stmts of all virtual uses | |
281 | need to be post-dominated by bb. */ | |
282 | FOR_EACH_SSA_TREE_OPERAND (vuse, use_stmt, ui2, SSA_OP_VUSE) | |
283 | { | |
284 | tree def_stmt = SSA_NAME_DEF_STMT (vuse); | |
285 | if (!SSA_NAME_IS_DEFAULT_DEF (vuse) | |
286 | && (bb_for_stmt (def_stmt) == bb | |
287 | || !dominated_by_p (CDI_DOMINATORS, | |
288 | bb, bb_for_stmt (def_stmt)))) | |
289 | goto next; | |
290 | } | |
291 | ||
292 | /* Found a proper dereference. Insert a phi node if this | |
293 | is the first load transformation. */ | |
294 | if (!phi_inserted) | |
295 | { | |
296 | res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n); | |
297 | ||
298 | /* Remember the value we created for *ptr. */ | |
299 | phivn[SSA_NAME_VERSION (ptr)].value = res; | |
300 | phivn[SSA_NAME_VERSION (ptr)].vop_stmt = use_stmt; | |
301 | ||
302 | /* Remove old stmt. The phi is taken care of by DCE, if we | |
303 | want to delete it here we also have to delete all intermediate | |
304 | copies. */ | |
305 | bsi = bsi_for_stmt (use_stmt); | |
306 | bsi_remove (&bsi, 0); | |
307 | ||
308 | phi_inserted = true; | |
309 | } | |
310 | else | |
311 | { | |
312 | /* Further replacements are easy, just make a copy out of the | |
313 | load. */ | |
314 | GIMPLE_STMT_OPERAND (use_stmt, 1) = res; | |
315 | update_stmt (use_stmt); | |
316 | } | |
317 | ||
318 | next:; | |
319 | /* Continue searching for a proper dereference. */ | |
320 | } | |
321 | ||
322 | return phi_inserted; | |
323 | } | |
324 | ||
325 | /* Helper walking the dominator tree starting from BB and processing | |
326 | phi nodes with global data PHIVN and N. */ | |
327 | ||
328 | static bool | |
329 | tree_ssa_phiprop_1 (basic_block bb, struct phiprop_d *phivn, size_t n) | |
330 | { | |
331 | bool did_something = false; | |
332 | basic_block son; | |
333 | tree phi; | |
334 | ||
335 | for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) | |
336 | did_something |= propagate_with_phi (bb, phi, phivn, n); | |
337 | ||
338 | for (son = first_dom_son (CDI_DOMINATORS, bb); | |
339 | son; | |
340 | son = next_dom_son (CDI_DOMINATORS, son)) | |
341 | did_something |= tree_ssa_phiprop_1 (son, phivn, n); | |
342 | ||
343 | return did_something; | |
344 | } | |
345 | ||
346 | /* Main entry for phiprop pass. */ | |
347 | ||
348 | static unsigned int | |
349 | tree_ssa_phiprop (void) | |
350 | { | |
351 | struct phiprop_d *phivn; | |
352 | ||
353 | calculate_dominance_info (CDI_DOMINATORS); | |
354 | ||
355 | phivn = XCNEWVEC (struct phiprop_d, num_ssa_names); | |
356 | ||
357 | if (tree_ssa_phiprop_1 (ENTRY_BLOCK_PTR, phivn, num_ssa_names)) | |
358 | bsi_commit_edge_inserts (); | |
359 | ||
360 | free (phivn); | |
361 | ||
362 | return 0; | |
363 | } | |
364 | ||
365 | static bool | |
366 | gate_phiprop (void) | |
367 | { | |
368 | return 1; | |
369 | } | |
370 | ||
8ddbbcae JH |
371 | struct gimple_opt_pass pass_phiprop = |
372 | { | |
373 | { | |
374 | GIMPLE_PASS, | |
67514449 RG |
375 | "phiprop", /* name */ |
376 | gate_phiprop, /* gate */ | |
377 | tree_ssa_phiprop, /* execute */ | |
378 | NULL, /* sub */ | |
379 | NULL, /* next */ | |
380 | 0, /* static_pass_number */ | |
381 | TV_TREE_PHIPROP, /* tv_id */ | |
382 | PROP_cfg | PROP_ssa, /* properties_required */ | |
383 | 0, /* properties_provided */ | |
384 | 0, /* properties_destroyed */ | |
385 | 0, /* todo_flags_start */ | |
386 | TODO_dump_func | |
387 | | TODO_ggc_collect | |
388 | | TODO_update_ssa | |
8ddbbcae JH |
389 | | TODO_verify_ssa /* todo_flags_finish */ |
390 | } | |
67514449 | 391 | }; |