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1 /* Generic routines for manipulating PHIs
2 Copyright (C) 2003-2013 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)
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/>. */
22 #include "coretypes.h"
26 #include "basic-block.h"
28 #include "gimple-iterator.h"
29 #include "gimple-ssa.h"
30 #include "tree-phinodes.h"
31 #include "ssa-iterators.h"
32 #include "stringpool.h"
33 #include "tree-ssanames.h"
35 #include "diagnostic-core.h"
37 /* Rewriting a function into SSA form can create a huge number of PHIs
38 many of which may be thrown away shortly after their creation if jumps
39 were threaded through PHI nodes.
41 While our garbage collection mechanisms will handle this situation, it
42 is extremely wasteful to create nodes and throw them away, especially
43 when the nodes can be reused.
45 For PR 8361, we can significantly reduce the number of nodes allocated
46 and thus the total amount of memory allocated by managing PHIs a
47 little. This additionally helps reduce the amount of work done by the
48 garbage collector. Similar results have been seen on a wider variety
49 of tests (such as the compiler itself).
51 PHI nodes have different sizes, so we can't have a single list of all
52 the PHI nodes as it would be too expensive to walk down that list to
53 find a PHI of a suitable size.
55 Instead we have an array of lists of free PHI nodes. The array is
56 indexed by the number of PHI alternatives that PHI node can hold.
57 Except for the last array member, which holds all remaining PHI
60 So to find a free PHI node, we compute its index into the free PHI
61 node array and see if there are any elements with an exact match.
62 If so, then we are done. Otherwise, we test the next larger size
63 up and continue until we are in the last array element.
65 We do not actually walk members of the last array element. While it
66 might allow us to pick up a few reusable PHI nodes, it could potentially
67 be very expensive if the program has released a bunch of large PHI nodes,
68 but keeps asking for even larger PHI nodes. Experiments have shown that
69 walking the elements of the last array entry would result in finding less
70 than .1% additional reusable PHI nodes.
72 Note that we can never have less than two PHI argument slots. Thus,
73 the -2 on all the calculations below. */
75 #define NUM_BUCKETS 10
76 static GTY ((deletable (""))) vec
<gimple
, va_gc
> *free_phinodes
[NUM_BUCKETS
- 2];
77 static unsigned long free_phinode_count
;
79 static int ideal_phi_node_len (int);
81 unsigned int phi_nodes_reused
;
82 unsigned int phi_nodes_created
;
84 /* Dump some simple statistics regarding the re-use of PHI nodes. */
87 phinodes_print_statistics (void)
89 fprintf (stderr
, "PHI nodes allocated: %u\n", phi_nodes_created
);
90 fprintf (stderr
, "PHI nodes reused: %u\n", phi_nodes_reused
);
93 /* Allocate a PHI node with at least LEN arguments. If the free list
94 happens to contain a PHI node with LEN arguments or more, return
98 allocate_phi_node (size_t len
)
101 size_t bucket
= NUM_BUCKETS
- 2;
102 size_t size
= sizeof (struct gimple_statement_phi
)
103 + (len
- 1) * sizeof (struct phi_arg_d
);
105 if (free_phinode_count
)
106 for (bucket
= len
- 2; bucket
< NUM_BUCKETS
- 2; bucket
++)
107 if (free_phinodes
[bucket
])
110 /* If our free list has an element, then use it. */
111 if (bucket
< NUM_BUCKETS
- 2
112 && gimple_phi_capacity ((*free_phinodes
[bucket
])[0]) >= len
)
114 free_phinode_count
--;
115 phi
= free_phinodes
[bucket
]->pop ();
116 if (free_phinodes
[bucket
]->is_empty ())
117 vec_free (free_phinodes
[bucket
]);
118 if (GATHER_STATISTICS
)
123 phi
= ggc_alloc_gimple_statement_d (size
);
124 if (GATHER_STATISTICS
)
126 enum gimple_alloc_kind kind
= gimple_alloc_kind (GIMPLE_PHI
);
128 gimple_alloc_counts
[(int) kind
]++;
129 gimple_alloc_sizes
[(int) kind
] += size
;
136 /* Given LEN, the original number of requested PHI arguments, return
137 a new, "ideal" length for the PHI node. The "ideal" length rounds
138 the total size of the PHI node up to the next power of two bytes.
140 Rounding up will not result in wasting any memory since the size request
141 will be rounded up by the GC system anyway. [ Note this is not entirely
142 true since the original length might have fit on one of the special
143 GC pages. ] By rounding up, we may avoid the need to reallocate the
144 PHI node later if we increase the number of arguments for the PHI. */
147 ideal_phi_node_len (int len
)
149 size_t size
, new_size
;
152 /* We do not support allocations of less than two PHI argument slots. */
156 /* Compute the number of bytes of the original request. */
157 size
= sizeof (struct gimple_statement_phi
)
158 + (len
- 1) * sizeof (struct phi_arg_d
);
160 /* Round it up to the next power of two. */
161 log2
= ceil_log2 (size
);
162 new_size
= 1 << log2
;
164 /* Now compute and return the number of PHI argument slots given an
165 ideal size allocation. */
166 new_len
= len
+ (new_size
- size
) / sizeof (struct phi_arg_d
);
170 /* Return a PHI node with LEN argument slots for variable VAR. */
173 make_phi_node (tree var
, int len
)
178 capacity
= ideal_phi_node_len (len
);
180 phi
= allocate_phi_node (capacity
);
182 /* We need to clear the entire PHI node, including the argument
183 portion, because we represent a "missing PHI argument" by placing
184 NULL_TREE in PHI_ARG_DEF. */
185 memset (phi
, 0, (sizeof (struct gimple_statement_phi
)
186 - sizeof (struct phi_arg_d
)
187 + sizeof (struct phi_arg_d
) * len
));
188 phi
->gsbase
.code
= GIMPLE_PHI
;
189 gimple_init_singleton (phi
);
190 phi
->gimple_phi
.nargs
= len
;
191 phi
->gimple_phi
.capacity
= capacity
;
194 else if (TREE_CODE (var
) == SSA_NAME
)
195 gimple_phi_set_result (phi
, var
);
197 gimple_phi_set_result (phi
, make_ssa_name (var
, phi
));
199 for (i
= 0; i
< capacity
; i
++)
203 gimple_phi_arg_set_location (phi
, i
, UNKNOWN_LOCATION
);
204 imm
= gimple_phi_arg_imm_use_ptr (phi
, i
);
205 imm
->use
= gimple_phi_arg_def_ptr (phi
, i
);
214 /* We no longer need PHI, release it so that it may be reused. */
217 release_phi_node (gimple phi
)
220 size_t len
= gimple_phi_capacity (phi
);
223 for (x
= 0; x
< gimple_phi_num_args (phi
); x
++)
226 imm
= gimple_phi_arg_imm_use_ptr (phi
, x
);
227 delink_imm_use (imm
);
230 bucket
= len
> NUM_BUCKETS
- 1 ? NUM_BUCKETS
- 1 : len
;
232 vec_safe_push (free_phinodes
[bucket
], phi
);
233 free_phinode_count
++;
237 /* Resize an existing PHI node. The only way is up. Return the
238 possibly relocated phi. */
241 resize_phi_node (gimple phi
, size_t len
)
246 gcc_assert (len
> gimple_phi_capacity (phi
));
248 /* The garbage collector will not look at the PHI node beyond the
249 first PHI_NUM_ARGS elements. Therefore, all we have to copy is a
250 portion of the PHI node currently in use. */
251 old_size
= sizeof (struct gimple_statement_phi
)
252 + (gimple_phi_num_args (phi
) - 1) * sizeof (struct phi_arg_d
);
254 new_phi
= allocate_phi_node (len
);
256 memcpy (new_phi
, phi
, 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
->gimple_phi
.capacity
= len
;
269 for (i
= gimple_phi_num_args (new_phi
); i
< len
; i
++)
273 gimple_phi_arg_set_location (new_phi
, i
, UNKNOWN_LOCATION
);
274 imm
= gimple_phi_arg_imm_use_ptr (new_phi
, i
);
275 imm
->use
= gimple_phi_arg_def_ptr (new_phi
, i
);
278 imm
->loc
.stmt
= new_phi
;
284 /* Reserve PHI arguments for a new edge to basic block BB. */
287 reserve_phi_args_for_new_edge (basic_block bb
)
289 size_t len
= EDGE_COUNT (bb
->preds
);
290 size_t cap
= ideal_phi_node_len (len
+ 4);
291 gimple_stmt_iterator gsi
;
293 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
295 gimple stmt
= gsi_stmt (gsi
);
297 if (len
> gimple_phi_capacity (stmt
))
299 gimple new_phi
= resize_phi_node (stmt
, cap
);
301 /* The result of the PHI is defined by this PHI node. */
302 SSA_NAME_DEF_STMT (gimple_phi_result (new_phi
)) = new_phi
;
303 gsi_set_stmt (&gsi
, new_phi
);
305 release_phi_node (stmt
);
309 /* We represent a "missing PHI argument" by placing NULL_TREE in
310 the corresponding slot. If PHI arguments were added
311 immediately after an edge is created, this zeroing would not
312 be necessary, but unfortunately this is not the case. For
313 example, the loop optimizer duplicates several basic blocks,
314 redirects edges, and then fixes up PHI arguments later in
316 SET_PHI_ARG_DEF (stmt
, len
- 1, NULL_TREE
);
317 gimple_phi_arg_set_location (stmt
, len
- 1, UNKNOWN_LOCATION
);
319 stmt
->gimple_phi
.nargs
++;
323 /* Adds PHI to BB. */
326 add_phi_node_to_bb (gimple phi
, basic_block bb
)
328 gimple_seq seq
= phi_nodes (bb
);
329 /* Add the new PHI node to the list of PHI nodes for block BB. */
331 set_phi_nodes (bb
, gimple_seq_alloc_with_stmt (phi
));
334 gimple_seq_add_stmt (&seq
, phi
);
335 gcc_assert (seq
== phi_nodes (bb
));
338 /* Associate BB to the PHI node. */
339 gimple_set_bb (phi
, bb
);
343 /* Create a new PHI node for variable VAR at basic block BB. */
346 create_phi_node (tree var
, basic_block bb
)
348 gimple phi
= make_phi_node (var
, EDGE_COUNT (bb
->preds
));
350 add_phi_node_to_bb (phi
, bb
);
355 /* Add a new argument to PHI node PHI. DEF is the incoming reaching
356 definition and E is the edge through which DEF reaches PHI. The new
357 argument is added at the end of the argument list.
358 If PHI has reached its maximum capacity, add a few slots. In this case,
359 PHI points to the reallocated phi node when we return. */
362 add_phi_arg (gimple phi
, tree def
, edge e
, source_location locus
)
364 basic_block bb
= e
->dest
;
366 gcc_assert (bb
== gimple_bb (phi
));
368 /* We resize PHI nodes upon edge creation. We should always have
369 enough room at this point. */
370 gcc_assert (gimple_phi_num_args (phi
) <= gimple_phi_capacity (phi
));
372 /* We resize PHI nodes upon edge creation. We should always have
373 enough room at this point. */
374 gcc_assert (e
->dest_idx
< gimple_phi_num_args (phi
));
376 /* Copy propagation needs to know what object occur in abnormal
377 PHI nodes. This is a convenient place to record such information. */
378 if (e
->flags
& EDGE_ABNORMAL
)
380 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def
) = 1;
381 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (phi
)) = 1;
384 SET_PHI_ARG_DEF (phi
, e
->dest_idx
, def
);
385 gimple_phi_arg_set_location (phi
, e
->dest_idx
, locus
);
389 /* Remove the Ith argument from PHI's argument list. This routine
390 implements removal by swapping the last alternative with the
391 alternative we want to delete and then shrinking the vector, which
392 is consistent with how we remove an edge from the edge vector. */
395 remove_phi_arg_num (gimple phi
, int i
)
397 int num_elem
= gimple_phi_num_args (phi
);
399 gcc_assert (i
< num_elem
);
401 /* Delink the item which is being removed. */
402 delink_imm_use (gimple_phi_arg_imm_use_ptr (phi
, i
));
404 /* If it is not the last element, move the last element
405 to the element we want to delete, resetting all the links. */
406 if (i
!= num_elem
- 1)
408 use_operand_p old_p
, new_p
;
409 old_p
= gimple_phi_arg_imm_use_ptr (phi
, num_elem
- 1);
410 new_p
= gimple_phi_arg_imm_use_ptr (phi
, i
);
411 /* Set use on new node, and link into last element's place. */
412 *(new_p
->use
) = *(old_p
->use
);
413 relink_imm_use (new_p
, old_p
);
414 /* Move the location as well. */
415 gimple_phi_arg_set_location (phi
, i
,
416 gimple_phi_arg_location (phi
, num_elem
- 1));
419 /* Shrink the vector and return. Note that we do not have to clear
420 PHI_ARG_DEF because the garbage collector will not look at those
421 elements beyond the first PHI_NUM_ARGS elements of the array. */
422 phi
->gimple_phi
.nargs
--;
426 /* Remove all PHI arguments associated with edge E. */
429 remove_phi_args (edge e
)
431 gimple_stmt_iterator gsi
;
433 for (gsi
= gsi_start_phis (e
->dest
); !gsi_end_p (gsi
); gsi_next (&gsi
))
434 remove_phi_arg_num (gsi_stmt (gsi
), e
->dest_idx
);
438 /* Remove the PHI node pointed-to by iterator GSI from basic block BB. After
439 removal, iterator GSI is updated to point to the next PHI node in the
440 sequence. If RELEASE_LHS_P is true, the LHS of this PHI node is released
441 into the free pool of SSA names. */
444 remove_phi_node (gimple_stmt_iterator
*gsi
, bool release_lhs_p
)
446 gimple phi
= gsi_stmt (*gsi
);
449 insert_debug_temps_for_defs (gsi
);
451 gsi_remove (gsi
, false);
453 /* If we are deleting the PHI node, then we should release the
454 SSA_NAME node so that it can be reused. */
455 release_phi_node (phi
);
457 release_ssa_name (gimple_phi_result (phi
));
460 /* Remove all the phi nodes from BB. */
463 remove_phi_nodes (basic_block bb
)
465 gimple_stmt_iterator gsi
;
467 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); )
468 remove_phi_node (&gsi
, true);
470 set_phi_nodes (bb
, NULL
);
473 /* Given PHI, return its RHS if the PHI is a degenerate, otherwise return
477 degenerate_phi_result (gimple phi
)
479 tree lhs
= gimple_phi_result (phi
);
483 /* Ignoring arguments which are the same as LHS, if all the remaining
484 arguments are the same, then the PHI is a degenerate and has the
485 value of that common argument. */
486 for (i
= 0; i
< gimple_phi_num_args (phi
); i
++)
488 tree arg
= gimple_phi_arg_def (phi
, i
);
498 /* We bring in some of operand_equal_p not only to speed things
499 up, but also to avoid crashing when dereferencing the type of
500 a released SSA name. */
501 else if (TREE_CODE (val
) != TREE_CODE (arg
)
502 || TREE_CODE (val
) == SSA_NAME
503 || !operand_equal_p (arg
, val
, 0))
506 return (i
== gimple_phi_num_args (phi
) ? val
: NULL
);
509 /* Set PHI nodes of a basic block BB to SEQ. */
512 set_phi_nodes (basic_block bb
, gimple_seq seq
)
514 gimple_stmt_iterator i
;
516 gcc_checking_assert (!(bb
->flags
& BB_RTL
));
517 bb
->il
.gimple
.phi_nodes
= seq
;
519 for (i
= gsi_start (seq
); !gsi_end_p (i
); gsi_next (&i
))
520 gimple_set_bb (gsi_stmt (i
), bb
);
523 #include "gt-tree-phinodes.h"