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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 | |
fa10beec | 39 | address to make the load source possibly non-addressable and to |
67514449 RG |
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 | ||
fa10beec | 51 | but also handles more complex scenarios like |
67514449 RG |
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; | |
726a989a | 98 | gimple vop_stmt; |
67514449 RG |
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 | { | |
726a989a | 107 | gimple vop_stmt = phivn[SSA_NAME_VERSION (name)].vop_stmt; |
67514449 RG |
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 | { | |
726a989a | 115 | gimple use_stmt; |
67514449 RG |
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. */ | |
726a989a | 122 | if (((is_gimple_assign (use_stmt) |
67514449 | 123 | && !ZERO_SSA_OPERANDS (use_stmt, SSA_OP_VDEF)) |
726a989a RB |
124 | || gimple_code (use_stmt) == GIMPLE_PHI) |
125 | && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb)) | |
67514449 RG |
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 | |
726a989a | 142 | phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt, |
67514449 RG |
143 | struct phiprop_d *phivn, size_t n) |
144 | { | |
726a989a RB |
145 | tree res; |
146 | gimple new_phi; | |
67514449 RG |
147 | edge_iterator ei; |
148 | edge e; | |
149 | ||
726a989a RB |
150 | gcc_assert (is_gimple_assign (use_stmt) |
151 | && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF); | |
152 | ||
67514449 RG |
153 | /* Build a new PHI node to replace the definition of |
154 | the indirect reference lhs. */ | |
726a989a | 155 | res = gimple_assign_lhs (use_stmt); |
67514449 RG |
156 | SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb); |
157 | ||
158 | /* Add PHI arguments for each edge inserting loads of the | |
159 | addressable operands. */ | |
160 | FOR_EACH_EDGE (e, ei, bb->preds) | |
161 | { | |
726a989a RB |
162 | tree old_arg, new_var; |
163 | gimple tmp; | |
67514449 RG |
164 | |
165 | old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); | |
166 | while (TREE_CODE (old_arg) == SSA_NAME | |
167 | && (SSA_NAME_VERSION (old_arg) >= n | |
168 | || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE)) | |
169 | { | |
726a989a RB |
170 | gimple def_stmt = SSA_NAME_DEF_STMT (old_arg); |
171 | old_arg = gimple_assign_rhs1 (def_stmt); | |
67514449 RG |
172 | } |
173 | ||
174 | if (TREE_CODE (old_arg) == SSA_NAME) | |
175 | /* Reuse a formerly created dereference. */ | |
176 | new_var = phivn[SSA_NAME_VERSION (old_arg)].value; | |
177 | else | |
178 | { | |
726a989a | 179 | gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR); |
67514449 RG |
180 | old_arg = TREE_OPERAND (old_arg, 0); |
181 | new_var = create_tmp_var (TREE_TYPE (old_arg), NULL); | |
726a989a | 182 | tmp = gimple_build_assign (new_var, unshare_expr (old_arg)); |
67514449 RG |
183 | if (TREE_CODE (TREE_TYPE (old_arg)) == COMPLEX_TYPE |
184 | || TREE_CODE (TREE_TYPE (old_arg)) == VECTOR_TYPE) | |
185 | DECL_GIMPLE_REG_P (new_var) = 1; | |
726a989a | 186 | gcc_assert (is_gimple_reg (new_var)); |
67514449 RG |
187 | add_referenced_var (new_var); |
188 | new_var = make_ssa_name (new_var, tmp); | |
726a989a | 189 | gimple_assign_set_lhs (tmp, new_var); |
67514449 | 190 | |
726a989a | 191 | gsi_insert_on_edge (e, tmp); |
67514449 RG |
192 | |
193 | update_stmt (tmp); | |
194 | mark_symbols_for_renaming (tmp); | |
195 | } | |
196 | ||
197 | add_phi_arg (new_phi, new_var, e); | |
198 | } | |
199 | ||
200 | update_stmt (new_phi); | |
201 | ||
202 | return res; | |
203 | } | |
204 | ||
205 | /* Propagate between the phi node arguments of PHI in BB and phi result | |
206 | users. For now this matches | |
207 | # p_2 = PHI <&x, &y> | |
208 | <Lx>:; | |
209 | p_3 = p_2; | |
210 | z_2 = *p_3; | |
211 | and converts it to | |
212 | # z_2 = PHI <x, y> | |
213 | <Lx>:; | |
214 | Returns true if a transformation was done and edge insertions | |
215 | need to be committed. Global data PHIVN and N is used to track | |
216 | past transformation results. We need to be especially careful here | |
217 | with aliasing issues as we are moving memory reads. */ | |
218 | ||
219 | static bool | |
726a989a RB |
220 | propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn, |
221 | size_t n) | |
67514449 RG |
222 | { |
223 | tree ptr = PHI_RESULT (phi); | |
726a989a RB |
224 | gimple use_stmt; |
225 | tree res = NULL_TREE; | |
226 | gimple_stmt_iterator gsi; | |
67514449 RG |
227 | imm_use_iterator ui; |
228 | use_operand_p arg_p, use; | |
229 | ssa_op_iter i; | |
230 | bool phi_inserted; | |
231 | ||
232 | if (MTAG_P (SSA_NAME_VAR (ptr)) | |
233 | || !POINTER_TYPE_P (TREE_TYPE (ptr)) | |
234 | || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr)))) | |
235 | return false; | |
236 | ||
237 | /* Check if we can "cheaply" dereference all phi arguments. */ | |
238 | FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE) | |
239 | { | |
240 | tree arg = USE_FROM_PTR (arg_p); | |
241 | /* Walk the ssa chain until we reach a ssa name we already | |
242 | created a value for or we reach a definition of the form | |
243 | ssa_name_n = &var; */ | |
244 | while (TREE_CODE (arg) == SSA_NAME | |
245 | && !SSA_NAME_IS_DEFAULT_DEF (arg) | |
246 | && (SSA_NAME_VERSION (arg) >= n | |
247 | || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE)) | |
248 | { | |
726a989a RB |
249 | gimple def_stmt = SSA_NAME_DEF_STMT (arg); |
250 | if (gimple_code (def_stmt) != GIMPLE_ASSIGN) | |
67514449 | 251 | return false; |
726a989a | 252 | arg = gimple_assign_rhs1 (def_stmt); |
67514449 RG |
253 | } |
254 | if ((TREE_CODE (arg) != ADDR_EXPR | |
255 | /* Avoid to have to decay *&a to a[0] later. */ | |
256 | || !is_gimple_reg_type (TREE_TYPE (TREE_OPERAND (arg, 0)))) | |
257 | && !(TREE_CODE (arg) == SSA_NAME | |
258 | && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE | |
259 | && phivn_valid_p (phivn, arg, bb))) | |
260 | return false; | |
261 | } | |
262 | ||
263 | /* Find a dereferencing use. First follow (single use) ssa | |
264 | copy chains for ptr. */ | |
265 | while (single_imm_use (ptr, &use, &use_stmt) | |
726a989a RB |
266 | && gimple_assign_ssa_name_copy_p (use_stmt)) |
267 | ptr = gimple_assign_lhs (use_stmt); | |
67514449 RG |
268 | |
269 | /* Replace the first dereference of *ptr if there is one and if we | |
270 | can move the loads to the place of the ptr phi node. */ | |
271 | phi_inserted = false; | |
272 | FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr) | |
273 | { | |
274 | ssa_op_iter ui2; | |
275 | tree vuse; | |
276 | ||
277 | /* Check whether this is a load of *ptr. */ | |
726a989a RB |
278 | if (!(is_gimple_assign (use_stmt) |
279 | && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME | |
280 | && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF | |
281 | && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr | |
67514449 | 282 | /* We cannot replace a load that may throw or is volatile. */ |
726a989a | 283 | && !stmt_can_throw_internal (use_stmt))) |
67514449 RG |
284 | continue; |
285 | ||
286 | /* Check if we can move the loads. The def stmts of all virtual uses | |
287 | need to be post-dominated by bb. */ | |
288 | FOR_EACH_SSA_TREE_OPERAND (vuse, use_stmt, ui2, SSA_OP_VUSE) | |
289 | { | |
726a989a | 290 | gimple def_stmt = SSA_NAME_DEF_STMT (vuse); |
67514449 | 291 | if (!SSA_NAME_IS_DEFAULT_DEF (vuse) |
726a989a | 292 | && (gimple_bb (def_stmt) == bb |
67514449 | 293 | || !dominated_by_p (CDI_DOMINATORS, |
726a989a | 294 | bb, gimple_bb (def_stmt)))) |
67514449 RG |
295 | goto next; |
296 | } | |
297 | ||
298 | /* Found a proper dereference. Insert a phi node if this | |
299 | is the first load transformation. */ | |
300 | if (!phi_inserted) | |
301 | { | |
302 | res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n); | |
303 | ||
304 | /* Remember the value we created for *ptr. */ | |
305 | phivn[SSA_NAME_VERSION (ptr)].value = res; | |
306 | phivn[SSA_NAME_VERSION (ptr)].vop_stmt = use_stmt; | |
307 | ||
308 | /* Remove old stmt. The phi is taken care of by DCE, if we | |
309 | want to delete it here we also have to delete all intermediate | |
310 | copies. */ | |
726a989a RB |
311 | gsi = gsi_for_stmt (use_stmt); |
312 | gsi_remove (&gsi, false); | |
67514449 RG |
313 | |
314 | phi_inserted = true; | |
315 | } | |
316 | else | |
317 | { | |
318 | /* Further replacements are easy, just make a copy out of the | |
319 | load. */ | |
726a989a | 320 | gimple_assign_set_rhs1 (use_stmt, res); |
67514449 RG |
321 | update_stmt (use_stmt); |
322 | } | |
323 | ||
324 | next:; | |
325 | /* Continue searching for a proper dereference. */ | |
326 | } | |
327 | ||
328 | return phi_inserted; | |
329 | } | |
330 | ||
331 | /* Helper walking the dominator tree starting from BB and processing | |
332 | phi nodes with global data PHIVN and N. */ | |
333 | ||
334 | static bool | |
335 | tree_ssa_phiprop_1 (basic_block bb, struct phiprop_d *phivn, size_t n) | |
336 | { | |
337 | bool did_something = false; | |
338 | basic_block son; | |
726a989a | 339 | gimple_stmt_iterator gsi; |
67514449 | 340 | |
726a989a RB |
341 | for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) |
342 | did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n); | |
67514449 RG |
343 | |
344 | for (son = first_dom_son (CDI_DOMINATORS, bb); | |
345 | son; | |
346 | son = next_dom_son (CDI_DOMINATORS, son)) | |
347 | did_something |= tree_ssa_phiprop_1 (son, phivn, n); | |
348 | ||
349 | return did_something; | |
350 | } | |
351 | ||
352 | /* Main entry for phiprop pass. */ | |
353 | ||
354 | static unsigned int | |
355 | tree_ssa_phiprop (void) | |
356 | { | |
357 | struct phiprop_d *phivn; | |
358 | ||
359 | calculate_dominance_info (CDI_DOMINATORS); | |
360 | ||
361 | phivn = XCNEWVEC (struct phiprop_d, num_ssa_names); | |
362 | ||
363 | if (tree_ssa_phiprop_1 (ENTRY_BLOCK_PTR, phivn, num_ssa_names)) | |
726a989a | 364 | gsi_commit_edge_inserts (); |
67514449 RG |
365 | |
366 | free (phivn); | |
367 | ||
368 | return 0; | |
369 | } | |
370 | ||
371 | static bool | |
372 | gate_phiprop (void) | |
373 | { | |
374 | return 1; | |
375 | } | |
376 | ||
8ddbbcae JH |
377 | struct gimple_opt_pass pass_phiprop = |
378 | { | |
379 | { | |
380 | GIMPLE_PASS, | |
67514449 RG |
381 | "phiprop", /* name */ |
382 | gate_phiprop, /* gate */ | |
383 | tree_ssa_phiprop, /* execute */ | |
384 | NULL, /* sub */ | |
385 | NULL, /* next */ | |
386 | 0, /* static_pass_number */ | |
387 | TV_TREE_PHIPROP, /* tv_id */ | |
388 | PROP_cfg | PROP_ssa, /* properties_required */ | |
389 | 0, /* properties_provided */ | |
390 | 0, /* properties_destroyed */ | |
391 | 0, /* todo_flags_start */ | |
392 | TODO_dump_func | |
393 | | TODO_ggc_collect | |
394 | | TODO_update_ssa | |
8ddbbcae JH |
395 | | TODO_verify_ssa /* todo_flags_finish */ |
396 | } | |
67514449 | 397 | }; |