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[official-gcc.git] / gcc / tree-phinodes.c
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1 /* Generic routines for manipulating PHIs
2 Copyright (C) 2003-2021 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3, or (at your option)
9 any later version.
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
20 #include "config.h"
21 #include "system.h"
22 #include "coretypes.h"
23 #include "backend.h"
24 #include "tree.h"
25 #include "gimple.h"
26 #include "ssa.h"
27 #include "fold-const.h"
28 #include "gimple-iterator.h"
29 #include "tree-ssa.h"
31 /* Rewriting a function into SSA form can create a huge number of PHIs
32 many of which may be thrown away shortly after their creation if jumps
33 were threaded through PHI nodes.
35 While our garbage collection mechanisms will handle this situation, it
36 is extremely wasteful to create nodes and throw them away, especially
37 when the nodes can be reused.
39 For PR 8361, we can significantly reduce the number of nodes allocated
40 and thus the total amount of memory allocated by managing PHIs a
41 little. This additionally helps reduce the amount of work done by the
42 garbage collector. Similar results have been seen on a wider variety
43 of tests (such as the compiler itself).
45 PHI nodes have different sizes, so we can't have a single list of all
46 the PHI nodes as it would be too expensive to walk down that list to
47 find a PHI of a suitable size.
49 Instead we have an array of lists of free PHI nodes. The array is
50 indexed by the number of PHI alternatives that PHI node can hold.
51 Except for the last array member, which holds all remaining PHI
52 nodes.
54 So to find a free PHI node, we compute its index into the free PHI
55 node array and see if there are any elements with an exact match.
56 If so, then we are done. Otherwise, we test the next larger size
57 up and continue until we are in the last array element.
59 We do not actually walk members of the last array element. While it
60 might allow us to pick up a few reusable PHI nodes, it could potentially
61 be very expensive if the program has released a bunch of large PHI nodes,
62 but keeps asking for even larger PHI nodes. Experiments have shown that
63 walking the elements of the last array entry would result in finding less
64 than .1% additional reusable PHI nodes.
66 Note that we can never have less than two PHI argument slots. Thus,
67 the -2 on all the calculations below. */
69 #define NUM_BUCKETS 10
70 static GTY ((deletable (""))) vec<gimple *, va_gc> *free_phinodes[NUM_BUCKETS - 2];
71 static unsigned long free_phinode_count;
73 static int ideal_phi_node_len (int);
75 unsigned int phi_nodes_reused;
76 unsigned int phi_nodes_created;
78 /* Dump some simple statistics regarding the re-use of PHI nodes. */
80 void
81 phinodes_print_statistics (void)
83 fprintf (stderr, "%-32s" PRsa (11) "\n", "PHI nodes allocated:",
84 SIZE_AMOUNT (phi_nodes_created));
85 fprintf (stderr, "%-32s" PRsa (11) "\n", "PHI nodes reused:",
86 SIZE_AMOUNT (phi_nodes_reused));
89 /* Allocate a PHI node with at least LEN arguments. If the free list
90 happens to contain a PHI node with LEN arguments or more, return
91 that one. */
93 static inline gphi *
94 allocate_phi_node (size_t len)
96 gphi *phi;
97 size_t bucket = NUM_BUCKETS - 2;
98 size_t size = sizeof (struct gphi)
99 + (len - 1) * sizeof (struct phi_arg_d);
101 if (free_phinode_count)
102 for (bucket = len - 2; bucket < NUM_BUCKETS - 2; bucket++)
103 if (free_phinodes[bucket])
104 break;
106 /* If our free list has an element, then use it. */
107 if (bucket < NUM_BUCKETS - 2
108 && gimple_phi_capacity ((*free_phinodes[bucket])[0]) >= len)
110 free_phinode_count--;
111 phi = as_a <gphi *> (free_phinodes[bucket]->pop ());
112 if (free_phinodes[bucket]->is_empty ())
113 vec_free (free_phinodes[bucket]);
114 if (GATHER_STATISTICS)
115 phi_nodes_reused++;
117 else
119 phi = static_cast <gphi *> (ggc_internal_alloc (size));
120 if (GATHER_STATISTICS)
122 enum gimple_alloc_kind kind = gimple_alloc_kind (GIMPLE_PHI);
123 phi_nodes_created++;
124 gimple_alloc_counts[(int) kind]++;
125 gimple_alloc_sizes[(int) kind] += size;
129 return phi;
132 /* Given LEN, the original number of requested PHI arguments, return
133 a new, "ideal" length for the PHI node. The "ideal" length rounds
134 the total size of the PHI node up to the next power of two bytes.
136 Rounding up will not result in wasting any memory since the size request
137 will be rounded up by the GC system anyway. [ Note this is not entirely
138 true since the original length might have fit on one of the special
139 GC pages. ] By rounding up, we may avoid the need to reallocate the
140 PHI node later if we increase the number of arguments for the PHI. */
142 static int
143 ideal_phi_node_len (int len)
145 size_t size, new_size;
146 int log2, new_len;
148 /* We do not support allocations of less than two PHI argument slots. */
149 if (len < 2)
150 len = 2;
152 /* Compute the number of bytes of the original request. */
153 size = sizeof (struct gphi)
154 + (len - 1) * sizeof (struct phi_arg_d);
156 /* Round it up to the next power of two. */
157 log2 = ceil_log2 (size);
158 new_size = 1 << log2;
160 /* Now compute and return the number of PHI argument slots given an
161 ideal size allocation. */
162 new_len = len + (new_size - size) / sizeof (struct phi_arg_d);
163 return new_len;
166 /* Return a PHI node with LEN argument slots for variable VAR. */
168 static gphi *
169 make_phi_node (tree var, int len)
171 gphi *phi;
172 int capacity, i;
174 capacity = ideal_phi_node_len (len);
176 phi = allocate_phi_node (capacity);
178 /* We need to clear the entire PHI node, including the argument
179 portion, because we represent a "missing PHI argument" by placing
180 NULL_TREE in PHI_ARG_DEF. */
181 memset (phi, 0, (sizeof (struct gphi)
182 - sizeof (struct phi_arg_d)
183 + sizeof (struct phi_arg_d) * len));
184 phi->code = GIMPLE_PHI;
185 gimple_init_singleton (phi);
186 phi->nargs = len;
187 phi->capacity = capacity;
188 if (!var)
190 else if (TREE_CODE (var) == SSA_NAME)
191 gimple_phi_set_result (phi, var);
192 else
193 gimple_phi_set_result (phi, make_ssa_name (var, phi));
195 for (i = 0; i < len; i++)
197 use_operand_p imm;
199 gimple_phi_arg_set_location (phi, i, UNKNOWN_LOCATION);
200 imm = gimple_phi_arg_imm_use_ptr (phi, i);
201 imm->use = gimple_phi_arg_def_ptr (phi, i);
202 imm->prev = NULL;
203 imm->next = NULL;
204 imm->loc.stmt = phi;
207 return phi;
210 /* We no longer need PHI, release it so that it may be reused. */
212 static void
213 release_phi_node (gimple *phi)
215 size_t bucket;
216 size_t len = gimple_phi_capacity (phi);
217 size_t x;
219 for (x = 0; x < gimple_phi_num_args (phi); x++)
221 use_operand_p imm;
222 imm = gimple_phi_arg_imm_use_ptr (phi, x);
223 delink_imm_use (imm);
226 bucket = len > NUM_BUCKETS - 1 ? NUM_BUCKETS - 1 : len;
227 bucket -= 2;
228 vec_safe_push (free_phinodes[bucket], phi);
229 free_phinode_count++;
233 /* Resize an existing PHI node. The only way is up. Return the
234 possibly relocated phi. */
236 static gphi *
237 resize_phi_node (gphi *phi, size_t len)
239 size_t old_size, i;
240 gphi *new_phi;
242 gcc_assert (len > gimple_phi_capacity (phi));
244 /* The garbage collector will not look at the PHI node beyond the
245 first PHI_NUM_ARGS elements. Therefore, all we have to copy is a
246 portion of the PHI node currently in use. */
247 old_size = sizeof (struct gphi)
248 + (gimple_phi_num_args (phi) - 1) * sizeof (struct phi_arg_d);
250 new_phi = allocate_phi_node (len);
252 memcpy (new_phi, phi, old_size);
253 memset ((char *)new_phi + old_size, 0,
254 (sizeof (struct gphi)
255 - sizeof (struct phi_arg_d)
256 + sizeof (struct phi_arg_d) * len) - old_size);
258 for (i = 0; i < gimple_phi_num_args (new_phi); i++)
260 use_operand_p imm, old_imm;
261 imm = gimple_phi_arg_imm_use_ptr (new_phi, i);
262 old_imm = gimple_phi_arg_imm_use_ptr (phi, i);
263 imm->use = gimple_phi_arg_def_ptr (new_phi, i);
264 relink_imm_use_stmt (imm, old_imm, new_phi);
267 new_phi->capacity = len;
269 return new_phi;
272 /* Reserve PHI arguments for a new edge to basic block BB. */
274 void
275 reserve_phi_args_for_new_edge (basic_block bb)
277 size_t len = EDGE_COUNT (bb->preds);
278 size_t cap = ideal_phi_node_len (len + 4);
279 gphi_iterator gsi;
281 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
283 gphi *stmt = gsi.phi ();
285 if (len > gimple_phi_capacity (stmt))
287 gphi *new_phi = resize_phi_node (stmt, cap);
289 /* The result of the PHI is defined by this PHI node. */
290 SSA_NAME_DEF_STMT (gimple_phi_result (new_phi)) = new_phi;
291 gsi_set_stmt (&gsi, new_phi);
293 release_phi_node (stmt);
294 stmt = new_phi;
297 stmt->nargs++;
299 /* We represent a "missing PHI argument" by placing NULL_TREE in
300 the corresponding slot. If PHI arguments were added
301 immediately after an edge is created, this zeroing would not
302 be necessary, but unfortunately this is not the case. For
303 example, the loop optimizer duplicates several basic blocks,
304 redirects edges, and then fixes up PHI arguments later in
305 batch. */
306 use_operand_p imm = gimple_phi_arg_imm_use_ptr (stmt, len - 1);
307 imm->use = gimple_phi_arg_def_ptr (stmt, len - 1);
308 imm->prev = NULL;
309 imm->next = NULL;
310 imm->loc.stmt = stmt;
311 SET_PHI_ARG_DEF (stmt, len - 1, NULL_TREE);
312 gimple_phi_arg_set_location (stmt, len - 1, UNKNOWN_LOCATION);
316 /* Adds PHI to BB. */
318 void
319 add_phi_node_to_bb (gphi *phi, basic_block bb)
321 gimple_seq seq = phi_nodes (bb);
322 /* Add the new PHI node to the list of PHI nodes for block BB. */
323 if (seq == NULL)
324 set_phi_nodes (bb, gimple_seq_alloc_with_stmt (phi));
325 else
327 gimple_seq_add_stmt (&seq, phi);
328 gcc_assert (seq == phi_nodes (bb));
331 /* Associate BB to the PHI node. */
332 gimple_set_bb (phi, bb);
336 /* Create a new PHI node for variable VAR at basic block BB. */
338 gphi *
339 create_phi_node (tree var, basic_block bb)
341 gphi *phi = make_phi_node (var, EDGE_COUNT (bb->preds));
343 add_phi_node_to_bb (phi, bb);
344 return phi;
348 /* Add a new argument to PHI node PHI. DEF is the incoming reaching
349 definition and E is the edge through which DEF reaches PHI. The new
350 argument is added at the end of the argument list.
351 If PHI has reached its maximum capacity, add a few slots. In this case,
352 PHI points to the reallocated phi node when we return. */
354 void
355 add_phi_arg (gphi *phi, tree def, edge e, location_t locus)
357 basic_block bb = e->dest;
359 gcc_assert (bb == gimple_bb (phi));
361 /* We resize PHI nodes upon edge creation. We should always have
362 enough room at this point. */
363 gcc_assert (gimple_phi_num_args (phi) <= gimple_phi_capacity (phi));
365 /* We resize PHI nodes upon edge creation. We should always have
366 enough room at this point. */
367 gcc_assert (e->dest_idx < gimple_phi_num_args (phi));
369 /* Copy propagation needs to know what object occur in abnormal
370 PHI nodes. This is a convenient place to record such information. */
371 if (e->flags & EDGE_ABNORMAL)
373 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def) = 1;
374 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (phi)) = 1;
377 SET_PHI_ARG_DEF (phi, e->dest_idx, def);
378 gimple_phi_arg_set_location (phi, e->dest_idx, locus);
382 /* Remove the Ith argument from PHI's argument list. This routine
383 implements removal by swapping the last alternative with the
384 alternative we want to delete and then shrinking the vector, which
385 is consistent with how we remove an edge from the edge vector. */
387 static void
388 remove_phi_arg_num (gphi *phi, int i)
390 int num_elem = gimple_phi_num_args (phi);
392 gcc_assert (i < num_elem);
394 /* Delink the item which is being removed. */
395 delink_imm_use (gimple_phi_arg_imm_use_ptr (phi, i));
397 /* If it is not the last element, move the last element
398 to the element we want to delete, resetting all the links. */
399 if (i != num_elem - 1)
401 use_operand_p old_p, new_p;
402 old_p = gimple_phi_arg_imm_use_ptr (phi, num_elem - 1);
403 new_p = gimple_phi_arg_imm_use_ptr (phi, i);
404 /* Set use on new node, and link into last element's place. */
405 *(new_p->use) = *(old_p->use);
406 relink_imm_use (new_p, old_p);
407 /* Move the location as well. */
408 gimple_phi_arg_set_location (phi, i,
409 gimple_phi_arg_location (phi, num_elem - 1));
412 /* Shrink the vector and return. Note that we do not have to clear
413 PHI_ARG_DEF because the garbage collector will not look at those
414 elements beyond the first PHI_NUM_ARGS elements of the array. */
415 phi->nargs--;
419 /* Remove all PHI arguments associated with edge E. */
421 void
422 remove_phi_args (edge e)
424 gphi_iterator gsi;
426 for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi))
427 remove_phi_arg_num (gsi.phi (),
428 e->dest_idx);
432 /* Remove the PHI node pointed-to by iterator GSI from basic block BB. After
433 removal, iterator GSI is updated to point to the next PHI node in the
434 sequence. If RELEASE_LHS_P is true, the LHS of this PHI node is released
435 into the free pool of SSA names. */
437 void
438 remove_phi_node (gimple_stmt_iterator *gsi, bool release_lhs_p)
440 gimple *phi = gsi_stmt (*gsi);
442 if (release_lhs_p)
443 insert_debug_temps_for_defs (gsi);
445 gsi_remove (gsi, false);
447 /* If we are deleting the PHI node, then we should release the
448 SSA_NAME node so that it can be reused. */
449 release_phi_node (phi);
450 if (release_lhs_p)
451 release_ssa_name (gimple_phi_result (phi));
454 /* Remove all the phi nodes from BB. */
456 void
457 remove_phi_nodes (basic_block bb)
459 gphi_iterator gsi;
461 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); )
462 remove_phi_node (&gsi, true);
464 set_phi_nodes (bb, NULL);
467 /* Given PHI, return its RHS if the PHI is a degenerate, otherwise return
468 NULL. */
470 tree
471 degenerate_phi_result (gphi *phi)
473 tree lhs = gimple_phi_result (phi);
474 tree val = NULL;
475 size_t i;
477 /* Ignoring arguments which are the same as LHS, if all the remaining
478 arguments are the same, then the PHI is a degenerate and has the
479 value of that common argument. */
480 for (i = 0; i < gimple_phi_num_args (phi); i++)
482 tree arg = gimple_phi_arg_def (phi, i);
484 if (arg == lhs)
485 continue;
486 else if (!arg)
487 break;
488 else if (!val)
489 val = arg;
490 else if (arg == val)
491 continue;
492 /* We bring in some of operand_equal_p not only to speed things
493 up, but also to avoid crashing when dereferencing the type of
494 a released SSA name. */
495 else if (TREE_CODE (val) != TREE_CODE (arg)
496 || TREE_CODE (val) == SSA_NAME
497 || !operand_equal_p (arg, val, 0))
498 break;
500 return (i == gimple_phi_num_args (phi) ? val : NULL);
503 /* Set PHI nodes of a basic block BB to SEQ. */
505 void
506 set_phi_nodes (basic_block bb, gimple_seq seq)
508 gimple_stmt_iterator i;
510 gcc_checking_assert (!(bb->flags & BB_RTL));
511 bb->il.gimple.phi_nodes = seq;
512 if (seq)
513 for (i = gsi_start (seq); !gsi_end_p (i); gsi_next (&i))
514 gimple_set_bb (gsi_stmt (i), bb);
517 #include "gt-tree-phinodes.h"