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comparison gcc/tree-ssa-phiprop.c @ 0:a06113de4d67

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author kent <kent@cr.ie.u-ryukyu.ac.jp>
date Fri, 17 Jul 2009 14:47:48 +0900
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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 possibly 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 scenarios 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 gimple 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 gimple 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 gimple 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 (((is_gimple_assign (use_stmt)
123 && !ZERO_SSA_OPERANDS (use_stmt, SSA_OP_VDEF))
124 || gimple_code (use_stmt) == GIMPLE_PHI)
125 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (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, gimple phi, gimple use_stmt,
143 struct phiprop_d *phivn, size_t n)
144 {
145 tree res;
146 gimple new_phi;
147 edge_iterator ei;
148 edge e;
149
150 gcc_assert (is_gimple_assign (use_stmt)
151 && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF);
152
153 /* Build a new PHI node to replace the definition of
154 the indirect reference lhs. */
155 res = gimple_assign_lhs (use_stmt);
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 {
162 tree old_arg, new_var;
163 gimple tmp;
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 {
170 gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
171 old_arg = gimple_assign_rhs1 (def_stmt);
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 {
179 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
180 old_arg = TREE_OPERAND (old_arg, 0);
181 new_var = create_tmp_var (TREE_TYPE (old_arg), NULL);
182 tmp = gimple_build_assign (new_var, unshare_expr (old_arg));
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;
186 gcc_assert (is_gimple_reg (new_var));
187 add_referenced_var (new_var);
188 new_var = make_ssa_name (new_var, tmp);
189 gimple_assign_set_lhs (tmp, new_var);
190
191 gsi_insert_on_edge (e, tmp);
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
220 propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn,
221 size_t n)
222 {
223 tree ptr = PHI_RESULT (phi);
224 gimple use_stmt;
225 tree res = NULL_TREE;
226 gimple_stmt_iterator gsi;
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 {
249 gimple def_stmt = SSA_NAME_DEF_STMT (arg);
250 if (!gimple_assign_single_p (def_stmt))
251 return false;
252 arg = gimple_assign_rhs1 (def_stmt);
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)
266 && gimple_assign_ssa_name_copy_p (use_stmt))
267 ptr = gimple_assign_lhs (use_stmt);
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. */
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
282 /* We cannot replace a load that may throw or is volatile. */
283 && !stmt_can_throw_internal (use_stmt)))
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 {
290 gimple def_stmt = SSA_NAME_DEF_STMT (vuse);
291 if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
292 && (gimple_bb (def_stmt) == bb
293 || !dominated_by_p (CDI_DOMINATORS,
294 bb, gimple_bb (def_stmt))))
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. */
311 gsi = gsi_for_stmt (use_stmt);
312 gsi_remove (&gsi, false);
313
314 phi_inserted = true;
315 }
316 else
317 {
318 /* Further replacements are easy, just make a copy out of the
319 load. */
320 gimple_assign_set_rhs1 (use_stmt, res);
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;
339 gimple_stmt_iterator gsi;
340
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);
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))
364 gsi_commit_edge_inserts ();
365
366 free (phivn);
367
368 return 0;
369 }
370
371 static bool
372 gate_phiprop (void)
373 {
374 return 1;
375 }
376
377 struct gimple_opt_pass pass_phiprop =
378 {
379 {
380 GIMPLE_PASS,
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
395 | TODO_verify_ssa /* todo_flags_finish */
396 }
397 };