1 /* Generic routines for manipulating SSA_NAME expressions
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 "tree-pass.h"
28 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
29 many of which may be thrown away shortly after their creation if jumps
30 were threaded through PHI nodes.
32 While our garbage collection mechanisms will handle this situation, it
33 is extremely wasteful to create nodes and throw them away, especially
34 when the nodes can be reused.
36 For PR 8361, we can significantly reduce the number of nodes allocated
37 and thus the total amount of memory allocated by managing SSA_NAMEs a
38 little. This additionally helps reduce the amount of work done by the
39 garbage collector. Similar results have been seen on a wider variety
40 of tests (such as the compiler itself).
42 Right now we maintain our free list on a per-function basis. It may
43 or may not make sense to maintain the free list for the duration of
46 External code should rely solely upon HIGHEST_SSA_VERSION and the
47 externally defined functions. External code should not know about
48 the details of the free list management.
50 External code should also not assume the version number on nodes is
51 monotonically increasing. We reuse the version number when we
52 reuse an SSA_NAME expression. This helps keep arrays and bitmaps
56 /* Version numbers with special meanings. We start allocating new version
57 numbers after the special ones. */
58 #define UNUSED_NAME_VERSION 0
60 unsigned int ssa_name_nodes_reused
;
61 unsigned int ssa_name_nodes_created
;
63 #define FREE_SSANAMES(fun) (fun)->gimple_df->free_ssanames
66 /* Initialize management of SSA_NAMEs to default SIZE. If SIZE is
70 init_ssanames (struct function
*fn
, int size
)
75 vec_alloc (SSANAMES (fn
), size
);
77 /* Version 0 is special, so reserve the first slot in the table. Though
78 currently unused, we may use version 0 in alias analysis as part of
79 the heuristics used to group aliases when the alias sets are too
82 We use vec::quick_push here because we know that SSA_NAMES has at
83 least 50 elements reserved in it. */
84 SSANAMES (fn
)->quick_push (NULL_TREE
);
85 FREE_SSANAMES (fn
) = NULL
;
87 fn
->gimple_df
->ssa_renaming_needed
= 0;
88 fn
->gimple_df
->rename_vops
= 0;
91 /* Finalize management of SSA_NAMEs. */
96 vec_free (SSANAMES (cfun
));
97 vec_free (FREE_SSANAMES (cfun
));
100 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes. */
103 ssanames_print_statistics (void)
105 fprintf (stderr
, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created
);
106 fprintf (stderr
, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused
);
109 /* Return an SSA_NAME node for variable VAR defined in statement STMT
110 in function FN. STMT may be an empty statement for artificial
111 references (e.g., default definitions created when a variable is
112 used without a preceding definition). */
115 make_ssa_name_fn (struct function
*fn
, tree var
, gimple stmt
)
120 gcc_assert (TREE_CODE (var
) == VAR_DECL
121 || TREE_CODE (var
) == PARM_DECL
122 || TREE_CODE (var
) == RESULT_DECL
123 || (TYPE_P (var
) && is_gimple_reg_type (var
)));
125 /* If our free list has an element, then use it. */
126 if (!vec_safe_is_empty (FREE_SSANAMES (fn
)))
128 t
= FREE_SSANAMES (fn
)->pop ();
129 if (GATHER_STATISTICS
)
130 ssa_name_nodes_reused
++;
132 /* The node was cleared out when we put it on the free list, so
133 there is no need to do so again here. */
134 gcc_assert (ssa_name (SSA_NAME_VERSION (t
)) == NULL
);
135 (*SSANAMES (fn
))[SSA_NAME_VERSION (t
)] = t
;
139 t
= make_node (SSA_NAME
);
140 SSA_NAME_VERSION (t
) = SSANAMES (fn
)->length ();
141 vec_safe_push (SSANAMES (fn
), t
);
142 if (GATHER_STATISTICS
)
143 ssa_name_nodes_created
++;
149 SET_SSA_NAME_VAR_OR_IDENTIFIER (t
, NULL_TREE
);
153 TREE_TYPE (t
) = TREE_TYPE (var
);
154 SET_SSA_NAME_VAR_OR_IDENTIFIER (t
, var
);
156 SSA_NAME_DEF_STMT (t
) = stmt
;
157 if (POINTER_TYPE_P (TREE_TYPE (t
)))
158 SSA_NAME_PTR_INFO (t
) = NULL
;
160 SSA_NAME_RANGE_INFO (t
) = NULL
;
162 SSA_NAME_IN_FREE_LIST (t
) = 0;
163 SSA_NAME_IS_DEFAULT_DEF (t
) = 0;
164 imm
= &(SSA_NAME_IMM_USE_NODE (t
));
168 imm
->loc
.ssa_name
= t
;
173 /* Store range information MIN, and MAX to tree ssa_name NAME. */
176 set_range_info (tree name
, double_int min
, double_int max
)
178 gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name
)));
179 range_info_def
*ri
= SSA_NAME_RANGE_INFO (name
);
181 /* Allocate if not available. */
184 ri
= ggc_alloc_cleared_range_info_def ();
185 SSA_NAME_RANGE_INFO (name
) = ri
;
188 /* Set the values. */
194 /* Gets range information MIN, MAX and returns enum value_range_type
195 corresponding to tree ssa_name NAME. enum value_range_type returned
196 is used to determine if MIN and MAX are valid values. */
198 enum value_range_type
199 get_range_info (tree name
, double_int
*min
, double_int
*max
)
201 enum value_range_type range_type
;
202 gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name
)));
203 gcc_assert (min
&& max
);
204 range_info_def
*ri
= SSA_NAME_RANGE_INFO (name
);
206 /* Return VR_VARYING for SSA_NAMEs with NULL RANGE_INFO or SSA_NAMEs
207 with integral types width > 2 * HOST_BITS_PER_WIDE_INT precision. */
208 if (!ri
|| (GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (name
)))
209 > 2 * HOST_BITS_PER_WIDE_INT
))
212 /* If min > max, it is VR_ANTI_RANGE. */
213 if (ri
->min
.cmp (ri
->max
, TYPE_UNSIGNED (TREE_TYPE (name
))) == 1)
215 /* VR_ANTI_RANGE ~[min, max] is encoded as [max + 1, min - 1]. */
216 range_type
= VR_ANTI_RANGE
;
217 *min
= ri
->max
+ double_int_one
;
218 *max
= ri
->min
- double_int_one
;
222 /* Otherwise (when min <= max), it is VR_RANGE. */
223 range_type
= VR_RANGE
;
230 /* We no longer need the SSA_NAME expression VAR, release it so that
233 Note it is assumed that no calls to make_ssa_name will be made
234 until all uses of the ssa name are released and that the only
235 use of the SSA_NAME expression is to check its SSA_NAME_VAR. All
236 other fields must be assumed clobbered. */
239 release_ssa_name (tree var
)
244 /* Never release the default definition for a symbol. It's a
245 special SSA name that should always exist once it's created. */
246 if (SSA_NAME_IS_DEFAULT_DEF (var
))
249 /* If VAR has been registered for SSA updating, don't remove it.
250 After update_ssa has run, the name will be released. */
251 if (name_registered_for_update_p (var
))
253 release_ssa_name_after_update_ssa (var
);
257 /* release_ssa_name can be called multiple times on a single SSA_NAME.
258 However, it should only end up on our free list one time. We
259 keep a status bit in the SSA_NAME node itself to indicate it has
260 been put on the free list.
262 Note that once on the freelist you can not reference the SSA_NAME's
263 defining statement. */
264 if (! SSA_NAME_IN_FREE_LIST (var
))
266 tree saved_ssa_name_var
= SSA_NAME_VAR (var
);
267 int saved_ssa_name_version
= SSA_NAME_VERSION (var
);
268 use_operand_p imm
= &(SSA_NAME_IMM_USE_NODE (var
));
270 if (MAY_HAVE_DEBUG_STMTS
)
271 insert_debug_temp_for_var_def (NULL
, var
);
273 #ifdef ENABLE_CHECKING
274 verify_imm_links (stderr
, var
);
276 while (imm
->next
!= imm
)
277 delink_imm_use (imm
->next
);
279 (*SSANAMES (cfun
))[SSA_NAME_VERSION (var
)] = NULL_TREE
;
280 memset (var
, 0, tree_size (var
));
284 imm
->loc
.ssa_name
= var
;
286 /* First put back the right tree node so that the tree checking
287 macros do not complain. */
288 TREE_SET_CODE (var
, SSA_NAME
);
290 /* Restore the version number. */
291 SSA_NAME_VERSION (var
) = saved_ssa_name_version
;
293 /* Hopefully this can go away once we have the new incremental
294 SSA updating code installed. */
295 SET_SSA_NAME_VAR_OR_IDENTIFIER (var
, saved_ssa_name_var
);
297 /* Note this SSA_NAME is now in the first list. */
298 SSA_NAME_IN_FREE_LIST (var
) = 1;
300 /* And finally put it on the free list. */
301 vec_safe_push (FREE_SSANAMES (cfun
), var
);
305 /* If the alignment of the pointer described by PI is known, return true and
306 store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
307 respectively. Otherwise return false. */
310 get_ptr_info_alignment (struct ptr_info_def
*pi
, unsigned int *alignp
,
311 unsigned int *misalignp
)
316 *misalignp
= pi
->misalign
;
323 /* State that the pointer described by PI has unknown alignment. */
326 mark_ptr_info_alignment_unknown (struct ptr_info_def
*pi
)
332 /* Store the the power-of-two byte alignment and the deviation from that
333 alignment of pointer described by PI to ALIOGN and MISALIGN
337 set_ptr_info_alignment (struct ptr_info_def
*pi
, unsigned int align
,
338 unsigned int misalign
)
340 gcc_checking_assert (align
!= 0);
341 gcc_assert ((align
& (align
- 1)) == 0);
342 gcc_assert ((misalign
& ~(align
- 1)) == 0);
345 pi
->misalign
= misalign
;
348 /* If pointer described by PI has known alignment, increase its known
349 misalignment by INCREMENT modulo its current alignment. */
352 adjust_ptr_info_misalignment (struct ptr_info_def
*pi
,
353 unsigned int increment
)
357 pi
->misalign
+= increment
;
358 pi
->misalign
&= (pi
->align
- 1);
362 /* Return the alias information associated with pointer T. It creates a
363 new instance if none existed. */
365 struct ptr_info_def
*
366 get_ptr_info (tree t
)
368 struct ptr_info_def
*pi
;
370 gcc_assert (POINTER_TYPE_P (TREE_TYPE (t
)));
372 pi
= SSA_NAME_PTR_INFO (t
);
375 pi
= ggc_alloc_cleared_ptr_info_def ();
376 pt_solution_reset (&pi
->pt
);
377 mark_ptr_info_alignment_unknown (pi
);
378 SSA_NAME_PTR_INFO (t
) = pi
;
385 /* Creates a new SSA name using the template NAME tobe defined by
386 statement STMT in function FN. */
389 copy_ssa_name_fn (struct function
*fn
, tree name
, gimple stmt
)
393 if (SSA_NAME_VAR (name
))
394 new_name
= make_ssa_name_fn (fn
, SSA_NAME_VAR (name
), stmt
);
397 new_name
= make_ssa_name_fn (fn
, TREE_TYPE (name
), stmt
);
398 SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name
, SSA_NAME_IDENTIFIER (name
));
405 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
406 the SSA name NAME. */
409 duplicate_ssa_name_ptr_info (tree name
, struct ptr_info_def
*ptr_info
)
411 struct ptr_info_def
*new_ptr_info
;
413 gcc_assert (POINTER_TYPE_P (TREE_TYPE (name
)));
414 gcc_assert (!SSA_NAME_PTR_INFO (name
));
419 new_ptr_info
= ggc_alloc_ptr_info_def ();
420 *new_ptr_info
= *ptr_info
;
422 SSA_NAME_PTR_INFO (name
) = new_ptr_info
;
425 /* Creates a duplicate of the range_info_def at RANGE_INFO for use by
426 the SSA name NAME. */
428 duplicate_ssa_name_range_info (tree name
, struct range_info_def
*range_info
)
430 struct range_info_def
*new_range_info
;
432 gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name
)));
433 gcc_assert (!SSA_NAME_RANGE_INFO (name
));
438 new_range_info
= ggc_alloc_range_info_def ();
439 *new_range_info
= *range_info
;
441 SSA_NAME_RANGE_INFO (name
) = new_range_info
;
446 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
450 duplicate_ssa_name_fn (struct function
*fn
, tree name
, gimple stmt
)
452 tree new_name
= copy_ssa_name_fn (fn
, name
, stmt
);
453 if (POINTER_TYPE_P (TREE_TYPE (name
)))
455 struct ptr_info_def
*old_ptr_info
= SSA_NAME_PTR_INFO (name
);
458 duplicate_ssa_name_ptr_info (new_name
, old_ptr_info
);
462 struct range_info_def
*old_range_info
= SSA_NAME_RANGE_INFO (name
);
465 duplicate_ssa_name_range_info (new_name
, old_range_info
);
472 /* Release all the SSA_NAMEs created by STMT. */
475 release_defs (gimple stmt
)
480 /* Make sure that we are in SSA. Otherwise, operand cache may point
482 gcc_assert (gimple_in_ssa_p (cfun
));
484 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter
, SSA_OP_ALL_DEFS
)
485 if (TREE_CODE (def
) == SSA_NAME
)
486 release_ssa_name (def
);
490 /* Replace the symbol associated with SSA_NAME with SYM. */
493 replace_ssa_name_symbol (tree ssa_name
, tree sym
)
495 SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name
, sym
);
496 TREE_TYPE (ssa_name
) = TREE_TYPE (sym
);
499 /* Return SSA names that are unused to GGC memory and compact the SSA
500 version namespace. This is used to keep footprint of compiler during
501 interprocedural optimization. */
503 release_dead_ssa_names (void)
506 int n
= vec_safe_length (FREE_SSANAMES (cfun
));
508 /* Now release the freelist. */
509 vec_free (FREE_SSANAMES (cfun
));
511 /* And compact the SSA number space. We make sure to not change the
512 relative order of SSA versions. */
513 for (i
= 1, j
= 1; i
< cfun
->gimple_df
->ssa_names
->length (); ++i
)
515 tree name
= ssa_name (i
);
520 SSA_NAME_VERSION (name
) = j
;
521 (*cfun
->gimple_df
->ssa_names
)[j
] = name
;
526 cfun
->gimple_df
->ssa_names
->truncate (j
);
528 statistics_counter_event (cfun
, "SSA names released", n
);
529 statistics_counter_event (cfun
, "SSA name holes removed", i
- j
);
531 fprintf (dump_file
, "Released %i names, %.2f%%, removed %i holes\n",
532 n
, n
* 100.0 / num_ssa_names
, i
- j
);
538 const pass_data pass_data_release_ssa_names
=
540 GIMPLE_PASS
, /* type */
541 "release_ssa", /* name */
542 OPTGROUP_NONE
, /* optinfo_flags */
543 false, /* has_gate */
544 true, /* has_execute */
545 TV_TREE_SSA_OTHER
, /* tv_id */
546 PROP_ssa
, /* properties_required */
547 0, /* properties_provided */
548 0, /* properties_destroyed */
549 TODO_remove_unused_locals
, /* todo_flags_start */
550 0, /* todo_flags_finish */
553 class pass_release_ssa_names
: public gimple_opt_pass
556 pass_release_ssa_names (gcc::context
*ctxt
)
557 : gimple_opt_pass (pass_data_release_ssa_names
, ctxt
)
560 /* opt_pass methods: */
561 unsigned int execute () { return release_dead_ssa_names (); }
563 }; // class pass_release_ssa_names
568 make_pass_release_ssa_names (gcc::context
*ctxt
)
570 return new pass_release_ssa_names (ctxt
);