1 /* Backward propagation of indirect loads through PHIs.
2 Copyright (C) 2007-2013 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 "tree.h"
26 #include "tm_p.h"
27 #include "basic-block.h"
28 #include "gimple-pretty-print.h"
29 #include "tree-flow.h"
30 #include "tree-pass.h"
31 #include "langhooks.h"
32 #include "flags.h"
33
34 /* This pass propagates indirect loads through the PHI node for its
35 address to make the load source possibly non-addressable and to
36 allow for PHI optimization to trigger.
37
38 For example the pass changes
39
40 # addr_1 = PHI <&a, &b>
41 tmp_1 = *addr_1;
42
43 to
44
45 # tmp_1 = PHI <a, b>
46
47 but also handles more complex scenarios like
48
49 D.2077_2 = &this_1(D)->a1;
50 ...
51
52 # b_12 = PHI <&c(2), D.2077_2(3)>
53 D.2114_13 = *b_12;
54 ...
55
56 # b_15 = PHI <b_12(4), &b(5)>
57 D.2080_5 = &this_1(D)->a0;
58 ...
59
60 # b_18 = PHI <D.2080_5(6), &c(7)>
61 ...
62
63 # b_21 = PHI <b_15(8), b_18(9)>
64 D.2076_8 = *b_21;
65
66 where the addresses loaded are defined by PHIs itself.
67 The above happens for
68
69 std::max(std::min(a0, c), std::min(std::max(a1, c), b))
70
71 where this pass transforms it to a form later PHI optimization
72 recognizes and transforms it to the simple
73
74 D.2109_10 = this_1(D)->a1;
75 D.2110_11 = c;
76 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
77 D.2115_14 = b;
78 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
79 D.2119_16 = this_1(D)->a0;
80 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
81 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;
82
83 The pass does a dominator walk processing loads using a basic-block
84 local analysis and stores the result for use by transformations on
85 dominated basic-blocks. */
86
87
88 /* Structure to keep track of the value of a dereferenced PHI result
89 and the virtual operand used for that dereference. */
90
91 struct phiprop_d
92 {
93 tree value;
94 tree vuse;
95 };
96
97 /* Verify if the value recorded for NAME in PHIVN is still valid at
98 the start of basic block BB. */
99
100 static bool
phivn_valid_p(struct phiprop_d * phivn,tree name,basic_block bb)101 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
102 {
103 tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;
104 gimple use_stmt;
105 imm_use_iterator ui2;
106 bool ok = true;
107
108 /* The def stmts of the virtual uses need to be dominated by bb. */
109 gcc_assert (vuse != NULL_TREE);
110
111 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
112 {
113 /* If BB does not dominate a VDEF, the value is invalid. */
114 if ((gimple_vdef (use_stmt) != NULL_TREE
115 || gimple_code (use_stmt) == GIMPLE_PHI)
116 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
117 {
118 ok = false;
119 BREAK_FROM_IMM_USE_STMT (ui2);
120 }
121 }
122
123 return ok;
124 }
125
126 /* Insert a new phi node for the dereference of PHI at basic_block
127 BB with the virtual operands from USE_STMT. */
128
129 static tree
phiprop_insert_phi(basic_block bb,gimple phi,gimple use_stmt,struct phiprop_d * phivn,size_t n)130 phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt,
131 struct phiprop_d *phivn, size_t n)
132 {
133 tree res;
134 gimple new_phi;
135 edge_iterator ei;
136 edge e;
137
138 gcc_assert (is_gimple_assign (use_stmt)
139 && gimple_assign_rhs_code (use_stmt) == MEM_REF);
140
141 /* Build a new PHI node to replace the definition of
142 the indirect reference lhs. */
143 res = gimple_assign_lhs (use_stmt);
144 new_phi = create_phi_node (res, bb);
145
146 if (dump_file && (dump_flags & TDF_DETAILS))
147 {
148 fprintf (dump_file, "Inserting PHI for result of load ");
149 print_gimple_stmt (dump_file, use_stmt, 0, 0);
150 }
151
152 /* Add PHI arguments for each edge inserting loads of the
153 addressable operands. */
154 FOR_EACH_EDGE (e, ei, bb->preds)
155 {
156 tree old_arg, new_var;
157 gimple tmp;
158 source_location locus;
159
160 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
161 locus = gimple_phi_arg_location_from_edge (phi, e);
162 while (TREE_CODE (old_arg) == SSA_NAME
163 && (SSA_NAME_VERSION (old_arg) >= n
164 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
165 {
166 gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
167 old_arg = gimple_assign_rhs1 (def_stmt);
168 locus = gimple_location (def_stmt);
169 }
170
171 if (TREE_CODE (old_arg) == SSA_NAME)
172 {
173 if (dump_file && (dump_flags & TDF_DETAILS))
174 {
175 fprintf (dump_file, " for edge defining ");
176 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
177 fprintf (dump_file, " reusing PHI result ");
178 print_generic_expr (dump_file,
179 phivn[SSA_NAME_VERSION (old_arg)].value, 0);
180 fprintf (dump_file, "\n");
181 }
182 /* Reuse a formerly created dereference. */
183 new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
184 }
185 else
186 {
187 tree rhs = gimple_assign_rhs1 (use_stmt);
188 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
189 new_var = make_ssa_name (TREE_TYPE (rhs), NULL);
190 if (!is_gimple_min_invariant (old_arg))
191 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
192 else
193 old_arg = unshare_expr (old_arg);
194 tmp = gimple_build_assign (new_var,
195 fold_build2 (MEM_REF, TREE_TYPE (rhs),
196 old_arg,
197 TREE_OPERAND (rhs, 1)));
198 gimple_set_location (tmp, locus);
199
200 gsi_insert_on_edge (e, tmp);
201 update_stmt (tmp);
202
203 if (dump_file && (dump_flags & TDF_DETAILS))
204 {
205 fprintf (dump_file, " for edge defining ");
206 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
207 fprintf (dump_file, " inserting load ");
208 print_gimple_stmt (dump_file, tmp, 0, 0);
209 }
210 }
211
212 add_phi_arg (new_phi, new_var, e, locus);
213 }
214
215 update_stmt (new_phi);
216
217 if (dump_file && (dump_flags & TDF_DETAILS))
218 print_gimple_stmt (dump_file, new_phi, 0, 0);
219
220 return res;
221 }
222
223 /* Propagate between the phi node arguments of PHI in BB and phi result
224 users. For now this matches
225 # p_2 = PHI <&x, &y>
226 <Lx>:;
227 p_3 = p_2;
228 z_2 = *p_3;
229 and converts it to
230 # z_2 = PHI <x, y>
231 <Lx>:;
232 Returns true if a transformation was done and edge insertions
233 need to be committed. Global data PHIVN and N is used to track
234 past transformation results. We need to be especially careful here
235 with aliasing issues as we are moving memory reads. */
236
237 static bool
propagate_with_phi(basic_block bb,gimple phi,struct phiprop_d * phivn,size_t n)238 propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn,
239 size_t n)
240 {
241 tree ptr = PHI_RESULT (phi);
242 gimple use_stmt;
243 tree res = NULL_TREE;
244 gimple_stmt_iterator gsi;
245 imm_use_iterator ui;
246 use_operand_p arg_p, use;
247 ssa_op_iter i;
248 bool phi_inserted;
249 tree type = NULL_TREE;
250 bool one_invariant = false;
251
252 if (!POINTER_TYPE_P (TREE_TYPE (ptr))
253 || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
254 return false;
255
256 /* Check if we can "cheaply" dereference all phi arguments. */
257 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
258 {
259 tree arg = USE_FROM_PTR (arg_p);
260 /* Walk the ssa chain until we reach a ssa name we already
261 created a value for or we reach a definition of the form
262 ssa_name_n = &var; */
263 while (TREE_CODE (arg) == SSA_NAME
264 && !SSA_NAME_IS_DEFAULT_DEF (arg)
265 && (SSA_NAME_VERSION (arg) >= n
266 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
267 {
268 gimple def_stmt = SSA_NAME_DEF_STMT (arg);
269 if (!gimple_assign_single_p (def_stmt))
270 return false;
271 arg = gimple_assign_rhs1 (def_stmt);
272 }
273 if (TREE_CODE (arg) != ADDR_EXPR
274 && !(TREE_CODE (arg) == SSA_NAME
275 && SSA_NAME_VERSION (arg) < n
276 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
277 && (!type
278 || types_compatible_p
279 (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value)))
280 && phivn_valid_p (phivn, arg, bb)))
281 return false;
282 if (!type
283 && TREE_CODE (arg) == SSA_NAME)
284 type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value);
285 if (TREE_CODE (arg) == ADDR_EXPR
286 && is_gimple_min_invariant (arg))
287 one_invariant = true;
288 }
289
290 /* If we neither have an address of a decl nor can reuse a previously
291 inserted load, do not hoist anything. */
292 if (!one_invariant
293 && !type)
294 return false;
295
296 /* Find a dereferencing use. First follow (single use) ssa
297 copy chains for ptr. */
298 while (single_imm_use (ptr, &use, &use_stmt)
299 && gimple_assign_ssa_name_copy_p (use_stmt))
300 ptr = gimple_assign_lhs (use_stmt);
301
302 /* Replace the first dereference of *ptr if there is one and if we
303 can move the loads to the place of the ptr phi node. */
304 phi_inserted = false;
305 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
306 {
307 gimple def_stmt;
308 tree vuse;
309
310 /* Only replace loads in blocks that post-dominate the PHI node. That
311 makes sure we don't end up speculating loads. */
312 if (!dominated_by_p (CDI_POST_DOMINATORS,
313 bb, gimple_bb (use_stmt)))
314 continue;
315
316 /* Check whether this is a load of *ptr. */
317 if (!(is_gimple_assign (use_stmt)
318 && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
319 && gimple_assign_rhs_code (use_stmt) == MEM_REF
320 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
321 && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1))
322 && (!type
323 || types_compatible_p
324 (TREE_TYPE (gimple_assign_lhs (use_stmt)), type))
325 /* We cannot replace a load that may throw or is volatile. */
326 && !stmt_can_throw_internal (use_stmt)))
327 continue;
328
329 /* Check if we can move the loads. The def stmt of the virtual use
330 needs to be in a different basic block dominating bb. */
331 vuse = gimple_vuse (use_stmt);
332 def_stmt = SSA_NAME_DEF_STMT (vuse);
333 if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
334 && (gimple_bb (def_stmt) == bb
335 || !dominated_by_p (CDI_DOMINATORS,
336 bb, gimple_bb (def_stmt))))
337 goto next;
338
339 /* Found a proper dereference. Insert a phi node if this
340 is the first load transformation. */
341 if (!phi_inserted)
342 {
343 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
344 type = TREE_TYPE (res);
345
346 /* Remember the value we created for *ptr. */
347 phivn[SSA_NAME_VERSION (ptr)].value = res;
348 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;
349
350 /* Remove old stmt. The phi is taken care of by DCE, if we
351 want to delete it here we also have to delete all intermediate
352 copies. */
353 gsi = gsi_for_stmt (use_stmt);
354 gsi_remove (&gsi, true);
355
356 phi_inserted = true;
357 }
358 else
359 {
360 /* Further replacements are easy, just make a copy out of the
361 load. */
362 gimple_assign_set_rhs1 (use_stmt, res);
363 update_stmt (use_stmt);
364 }
365
366 next:;
367 /* Continue searching for a proper dereference. */
368 }
369
370 return phi_inserted;
371 }
372
373 /* Main entry for phiprop pass. */
374
375 static unsigned int
tree_ssa_phiprop(void)376 tree_ssa_phiprop (void)
377 {
378 vec<basic_block> bbs;
379 struct phiprop_d *phivn;
380 bool did_something = false;
381 basic_block bb;
382 gimple_stmt_iterator gsi;
383 unsigned i;
384 size_t n;
385
386 calculate_dominance_info (CDI_DOMINATORS);
387 calculate_dominance_info (CDI_POST_DOMINATORS);
388
389 n = num_ssa_names;
390 phivn = XCNEWVEC (struct phiprop_d, n);
391
392 /* Walk the dominator tree in preorder. */
393 bbs = get_all_dominated_blocks (CDI_DOMINATORS,
394 single_succ (ENTRY_BLOCK_PTR));
395 FOR_EACH_VEC_ELT (bbs, i, bb)
396 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
397 did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n);
398
399 if (did_something)
400 gsi_commit_edge_inserts ();
401
402 bbs.release ();
403 free (phivn);
404
405 free_dominance_info (CDI_POST_DOMINATORS);
406
407 return 0;
408 }
409
410 static bool
gate_phiprop(void)411 gate_phiprop (void)
412 {
413 return flag_tree_phiprop;
414 }
415
416 struct gimple_opt_pass pass_phiprop =
417 {
418 {
419 GIMPLE_PASS,
420 "phiprop", /* name */
421 OPTGROUP_NONE, /* optinfo_flags */
422 gate_phiprop, /* gate */
423 tree_ssa_phiprop, /* execute */
424 NULL, /* sub */
425 NULL, /* next */
426 0, /* static_pass_number */
427 TV_TREE_PHIPROP, /* tv_id */
428 PROP_cfg | PROP_ssa, /* properties_required */
429 0, /* properties_provided */
430 0, /* properties_destroyed */
431 0, /* todo_flags_start */
432 TODO_ggc_collect
433 | TODO_update_ssa
434 | TODO_verify_ssa /* todo_flags_finish */
435 }
436 };
437