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1 : // Function-related RTL SSA classes -*- C++ -*-
2 : // Copyright (C) 2020-2026 Free Software Foundation, Inc.
3 : //
4 : // This file is part of GCC.
5 : //
6 : // GCC is free software; you can redistribute it and/or modify it under
7 : // the terms of the GNU General Public License as published by the Free
8 : // Software Foundation; either version 3, or (at your option) any later
9 : // version.
10 : //
11 : // GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 : // WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 : // FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 : // for more details.
15 : //
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/>.
19 :
20 : namespace rtl_ssa {
21 :
22 : // SSA-related information about a function. It contains three levels
23 : // of information, each in reverse postorder:
24 : //
25 : // - a list of extended basic blocks
26 : // - a list of basic blocks
27 : // - a list of instructions
28 : //
29 : // It also maintains a list of definitions of memory, and a list of
30 : // definitions of each register.
31 : //
32 : // See doc/rtl.texi for more details about the way this information
33 : // is organized and how changes to it are made.
34 : class function_info
35 : {
36 : // The default obstack alignment takes long double into account.
37 : // Since we have no use for that here, and since we allocate many
38 : // relatively small objects, it's better to specify an alignment
39 : // explicitly. The allocation routines assert that the alignment
40 : // is enough for the objects being allocated.
41 : //
42 : // Because various structures use pointer_mux, we need at least 2 bytes
43 : // of alignment.
44 : static const size_t obstack_alignment = sizeof (void *);
45 :
46 : public:
47 : // Construct SSA form for function FN.
48 : function_info (function *fn);
49 : ~function_info ();
50 :
51 : // Return a list of all the extended basic blocks in the function, in reverse
52 : // postorder. The list includes the entry and exit blocks.
53 : iterator_range<ebb_iterator> ebbs () const;
54 :
55 : // Like ebbs (), but in the reverse order.
56 : iterator_range<reverse_ebb_iterator> reverse_ebbs () const;
57 :
58 : // Return a list of all the basic blocks in the function, in reverse
59 : // postorder. The list includes the entry and exit blocks.
60 : iterator_range<bb_iterator> bbs () const;
61 :
62 : // Like bbs (), but in the reverse order.
63 : iterator_range<reverse_bb_iterator> reverse_bbs () const;
64 :
65 : // Return the SSA information for the basic block with index INDEX.
66 : bb_info *bb (unsigned int index) const { return m_bbs[index]; }
67 :
68 : // Return the SSA information for CFG_BB.
69 279144036 : bb_info *bb (basic_block cfg_bb) const { return m_bbs[cfg_bb->index]; }
70 :
71 : // Create a temporary def.
72 : set_info *create_set (obstack_watermark &watermark,
73 : insn_info *insn,
74 : resource_info resource);
75 :
76 : // Create a temporary use of SET as part of a change to INSN.
77 : // SET can be a pre-existing definition or one that is being created
78 : // as part of the same change group.
79 : use_info *create_use (obstack_watermark &watermark,
80 : insn_info *insn,
81 : set_info *set);
82 :
83 : // Create a temporary insn with code INSN_CODE and pattern PAT.
84 : insn_info *create_insn (obstack_watermark &watermark,
85 : rtx_code insn_code,
86 : rtx pat);
87 :
88 : // Return a list of all the instructions in the function, in reverse
89 : // postorder. The list includes both real and artificial instructions.
90 : //
91 : // Iterations over the list will pick up any new instructions that are
92 : // inserted after the iterator's current instruction.
93 : iterator_range<any_insn_iterator> all_insns () const;
94 :
95 : // Like all_insns (), but in the reverse order.
96 : //
97 : // Iterations over the list will pick up any new instructions that are
98 : // inserted before the iterator's current instruction.
99 : iterator_range<reverse_any_insn_iterator> reverse_all_insns () const;
100 :
101 : // Like all_insns (), but without the debug instructions.
102 : iterator_range<nondebug_insn_iterator> nondebug_insns () const;
103 :
104 : // Like reverse_all_insns (), but without the debug instructions.
105 : iterator_range<reverse_nondebug_insn_iterator>
106 : reverse_nondebug_insns () const;
107 :
108 : // Return the first and last instructions in insns ().
109 2087216 : insn_info *first_insn () const { return m_first_insn; }
110 : insn_info *last_insn () const { return m_last_insn; }
111 :
112 : // Return a list of all definitions of memory, in reverse postorder.
113 : // This includes both real stores by instructions and artificial
114 : // definitions by things like phi nodes.
115 : iterator_range<def_iterator> mem_defs () const;
116 :
117 : // Return a list of all definitions of register REGNO, in reverse postorder.
118 : // This includes both real stores by instructions and artificial
119 : // definitions by things like phi nodes.
120 : iterator_range<def_iterator> reg_defs (unsigned int regno) const;
121 :
122 : // Return true if SET is the only set of SET->resource () and if it
123 : // dominates all uses (excluding uses of SET->resource () at points
124 : // where SET->resource () is always undefined).
125 : bool is_single_dominating_def (const set_info *set) const;
126 :
127 : // Check if all uses of register REGNO are either unconditionally undefined
128 : // or use the same single dominating definition. Return the definition
129 : // if so, otherwise return null.
130 : set_info *single_dominating_def (unsigned int regno) const;
131 :
132 : // Look for a definition of RESOURCE at INSN. Return the result of the
133 : // search as a def_lookup; see the comments there for more details.
134 : //
135 : // NOTE: This is not the function to use if INSN is known to be a real
136 : // instruction (one with an RTL pattern) and if the caller is only
137 : // interested in definitions within INSN itself. In those cases
138 : // it is better to use find_access.
139 : def_lookup find_def (resource_info resource, insn_info *insn);
140 :
141 : // Search for a use of DEF around non-debug instruction INSN and return the
142 : // result of the search as a use_lookup. See the comment above the class
143 : // for more details about the result means.
144 : //
145 : // NOTE: This is not the function to use if INSN is known to be a real
146 : // instruction (one with an RTL pattern) and if the caller is only
147 : // interested in uses within INSN itself. In those cases it is better
148 : // to use find_access.
149 : use_lookup find_use (set_info *def, insn_info *insn);
150 :
151 : // Return an RAII object that owns all temporary RTL SSA memory
152 : // allocated during a change attempt. The object should remain in
153 : // scope until the change has been aborted or successfully completed.
154 79632591 : obstack_watermark new_change_attempt () { return &m_temp_obstack; }
155 :
156 : // SET and INSN belong to the same EBB, with SET occuring before INSN.
157 : // Return true if SET is still available at INSN.
158 : bool remains_available_at_insn (const set_info *set, insn_info *insn);
159 :
160 : // SET either occurs in BB or is known to be available on entry to BB.
161 : // Return true if it is also available on exit from BB. (The value
162 : // might or might not be live.)
163 : bool remains_available_on_exit (const set_info *set, bb_info *bb);
164 :
165 : // Make a best attempt to check whether the values used by USES are
166 : // available on entry to BB, without solving a full dataflow problem.
167 : // If all the values are already live on entry to BB or can be made
168 : // available there, return a use_array that describes the uses as
169 : // if they occured at the start of BB. These uses are purely temporary,
170 : // and will not become permanent unless applied using change_insns.
171 : //
172 : // If the operation fails, return an invalid use_array.
173 : //
174 : // WATERMARK is a watermark returned by new_change_attempt ().
175 : // WILL_BE_DEBUG_USES is true if the returned use_array will be
176 : // used only for debug instructions.
177 : use_array make_uses_available (obstack_watermark &watermark,
178 : use_array uses, bb_info *bb,
179 : bool will_be_debug_uses);
180 :
181 : // If CHANGE doesn't already clobber REGNO, try to add such a clobber,
182 : // limiting the movement range in order to make the clobber valid.
183 : // Use IGNORE to guide this process, where IGNORE is an object that
184 : // provides the same interface as ignore_nothing.
185 : //
186 : // That is, when determining whether REGNO is live, ignore accesses made
187 : // by an instruction I if IGNORE says that I should be ignored. The caller
188 : // then assumes the responsibility of ensuring that CHANGE and I are placed
189 : // in a valid order. Similarly, ignore live ranges associated with a
190 : // definition of REGNO if IGNORE says that that definition should be
191 : // ignored.
192 : //
193 : // Return true on success. Leave CHANGE unmodified when returning false.
194 : //
195 : // WATERMARK is a watermark returned by new_change_attempt ().
196 : template<typename IgnorePredicates>
197 : bool add_regno_clobber (obstack_watermark &watermark, insn_change &change,
198 : unsigned int regno, IgnorePredicates ignore);
199 :
200 : // Return true if change_insns will be able to perform the changes
201 : // described by CHANGES.
202 : bool verify_insn_changes (array_slice<insn_change *const> changes);
203 :
204 : // Perform all the changes in CHANGES, keeping the instructions in the
205 : // order specified by the CHANGES array. On return, the SSA information
206 : // remains up-to-date. The same is true for instruction-level DF
207 : // information, although the block-level DF information might be
208 : // marked dirty.
209 : void change_insns (array_slice<insn_change *> changes);
210 :
211 : // Like change_insns, but for a single change CHANGE.
212 : void change_insn (insn_change &change);
213 :
214 : // Given a use USE, re-parent it to get its def from NEW_DEF.
215 : void reparent_use (use_info *use, set_info *new_def);
216 :
217 : // If the changes that have been made to instructions require updates
218 : // to the CFG, perform those updates now. Return true if something changed.
219 : // If it did:
220 : //
221 : // - The SSA information is now invalid and needs to be recomputed.
222 : //
223 : // - Dominance information is no longer available (in either direction).
224 : //
225 : // - The caller will need to call cleanup_cfg at some point.
226 : //
227 : // ??? We could probably update the SSA information for simple updates,
228 : // but currently nothing would benefit. These late CFG changes are
229 : // relatively rare anyway, since gimple optimisers should remove most
230 : // unnecessary control flow.
231 : bool perform_pending_updates ();
232 :
233 : // Print the contents of the function to PP.
234 : void print (pretty_printer *pp) const;
235 :
236 : // Allocate an object of type T above the obstack watermark WM.
237 : template<typename T, typename... Ts>
238 : T *change_alloc (obstack_watermark &wm, Ts... args);
239 :
240 : private:
241 : class bb_phi_info;
242 : class build_info;
243 : class bb_walker;
244 :
245 : // Return an RAII object that owns all objects allocated by
246 : // allocate_temp during its lifetime.
247 26782891 : obstack_watermark temp_watermark () { return &m_temp_obstack; }
248 :
249 : template<typename T, typename... Ts>
250 : T *allocate (Ts... args);
251 :
252 : template<typename T, typename... Ts>
253 : T *allocate_temp (Ts... args);
254 :
255 : access_array temp_access_array (access_array accesses);
256 :
257 : clobber_group *need_clobber_group (clobber_info *);
258 : def_node *need_def_node (def_info *);
259 : def_splay_tree need_def_splay_tree (def_info *);
260 :
261 : use_info *make_use_available (use_info *, bb_info *, bool);
262 : def_array insert_temp_clobber (obstack_watermark &, insn_info *,
263 : unsigned int, def_array);
264 :
265 : void insert_def_before (def_info *, def_info *);
266 : void insert_def_after (def_info *, def_info *);
267 : void remove_def_from_list (def_info *);
268 :
269 : void add_clobber (clobber_info *, clobber_group *);
270 : void remove_clobber (clobber_info *, clobber_group *);
271 : void prepend_clobber_to_group (clobber_info *, clobber_group *);
272 : void append_clobber_to_group (clobber_info *, clobber_group *);
273 : void merge_clobber_groups (clobber_info *, clobber_info *,
274 : def_info *);
275 : std::array<clobber_group *, 2> split_clobber_group (clobber_group *,
276 : insn_info *);
277 :
278 : void append_def (def_info *);
279 : void add_def (def_info *);
280 : void remove_def (def_info *);
281 :
282 : void need_use_splay_tree (set_info *);
283 :
284 : static void insert_use_before (use_info *, use_info *);
285 : static void insert_use_after (use_info *, use_info *);
286 :
287 : void add_use (use_info *);
288 : void remove_use (use_info *);
289 :
290 : insn_info::order_node *need_order_node (insn_info *);
291 :
292 : void add_insn_after (insn_info *, insn_info *);
293 : void replace_nondebug_insn (insn_info *, insn_info *);
294 : void append_insn (insn_info *);
295 : void remove_insn (insn_info *);
296 :
297 : insn_info *append_artificial_insn (bb_info *, rtx_insn * = nullptr);
298 :
299 : void start_insn_accesses ();
300 : void finish_insn_accesses (insn_info *);
301 :
302 : use_info *create_reg_use (build_info &, insn_info *, resource_info);
303 : void record_use (build_info &, insn_info *, rtx_obj_reference);
304 : void record_call_clobbers (build_info &, insn_info *, rtx_call_insn *);
305 : void record_def (build_info &, insn_info *, rtx_obj_reference);
306 : void add_insn_to_block (build_info &, rtx_insn *);
307 :
308 : void add_reg_unused_notes (insn_info *);
309 :
310 : void add_live_out_use (bb_info *, set_info *);
311 : set_info *live_out_value (bb_info *, set_info *);
312 : void commit_make_use_available (use_info *);
313 :
314 : void append_phi (ebb_info *, phi_info *);
315 : void remove_phi (phi_info *);
316 : void delete_phi (phi_info *);
317 : void replace_phi (phi_info *, set_info *);
318 : phi_info *create_phi (ebb_info *, resource_info, access_info **,
319 : unsigned int);
320 : phi_info *create_degenerate_phi (ebb_info *, set_info *);
321 :
322 : bb_info *create_bb_info (basic_block);
323 : void append_bb (bb_info *);
324 :
325 : void process_uses_of_deleted_def (set_info *);
326 : insn_info *add_placeholder_after (insn_info *);
327 : void possibly_queue_changes (insn_change &);
328 : void finalize_new_accesses (insn_change &, insn_info *,
329 : hash_set<def_info *> &);
330 : void apply_changes_to_insn (insn_change &,
331 : hash_set<def_info *> &);
332 :
333 : void init_function_data ();
334 : void calculate_potential_phi_regs (build_info &);
335 : void place_phis (build_info &);
336 : void create_ebbs (build_info &);
337 : void add_entry_block_defs (build_info &);
338 : void calculate_ebb_live_in_for_debug (build_info &);
339 : void add_phi_nodes (build_info &);
340 : void add_artificial_accesses (build_info &, df_ref_flags);
341 : void add_block_contents (build_info &);
342 : void record_block_live_out (build_info &);
343 : void start_block (build_info &, bb_info *);
344 : void end_block (build_info &, bb_info *);
345 : void populate_phi_inputs (build_info &);
346 : void process_all_blocks ();
347 :
348 : void simplify_phi_setup (phi_info *, set_info **, bitmap);
349 : void simplify_phi_propagate (phi_info *, set_info **, bitmap, bitmap);
350 : void simplify_phis ();
351 :
352 : // The function that this object describes.
353 : function *m_fn;
354 :
355 : // The lowest (negative) in-use artificial insn uid minus one.
356 : int m_next_artificial_uid;
357 :
358 : // The highest in-use phi uid plus one.
359 : unsigned int m_next_phi_uid;
360 :
361 : // The highest in-use register number plus one.
362 : unsigned int m_num_regs;
363 :
364 : // M_DEFS[R] is the first definition of register R - 1 in a reverse
365 : // postorder traversal of the function, or null if the function has
366 : // no definition of R. Applying last () gives the last definition of R.
367 : //
368 : // M_DEFS[0] is for memory; MEM_REGNO + 1 == 0.
369 : auto_vec<def_info *> m_defs;
370 :
371 : // M_BBS[BI] gives the SSA information about the block with index BI.
372 : auto_vec<bb_info *> m_bbs;
373 :
374 : // An obstack used to allocate the main RTL SSA information.
375 : obstack m_obstack;
376 :
377 : // An obstack used for temporary work, such as while building up a list
378 : // of possible instruction changes.
379 : obstack m_temp_obstack;
380 :
381 : // The start of each obstack, so that all memory in them can be freed.
382 : char *m_obstack_start;
383 : char *m_temp_obstack_start;
384 :
385 : // The entry and exit blocks.
386 : bb_info *m_first_bb;
387 : bb_info *m_last_bb;
388 :
389 : // The first and last instructions in a reverse postorder traversal
390 : // of the function.
391 : insn_info *m_first_insn;
392 : insn_info *m_last_insn;
393 :
394 : // The last nondebug instruction in the list of instructions.
395 : // This is only different from m_last_insn when building the initial
396 : // SSA information; after that, the last instruction is always a
397 : // BB end instruction.
398 : insn_info *m_last_nondebug_insn;
399 :
400 : // Temporary working state when building up lists of definitions and uses.
401 : // Keeping them around should reduce the number of unnecessary reallocations.
402 : auto_vec<access_info *> m_temp_defs;
403 : auto_vec<access_info *> m_temp_uses;
404 :
405 : // A list of phis that are no longer in use. Their uids are still unique
406 : // and so can be recycled.
407 : phi_info *m_free_phis;
408 :
409 : // A list of instructions that have been changed in ways that need
410 : // further processing later, such as removing dead instructions or
411 : // altering the CFG.
412 : auto_vec<insn_info *> m_queued_insn_updates;
413 :
414 : // The INSN_UIDs of all instructions in M_QUEUED_INSN_UPDATES.
415 : auto_bitmap m_queued_insn_update_uids;
416 :
417 : // A basic_block is in this bitmap if we need to call purge_dead_edges
418 : // on it. As with M_QUEUED_INSN_UPDATES, these updates are queued until
419 : // a convenient point.
420 : auto_bitmap m_need_to_purge_dead_edges;
421 :
422 : // The set of hard registers that are fully or partially clobbered
423 : // by at least one insn_call_clobbers_note.
424 : HARD_REG_SET m_clobbered_by_calls;
425 : };
426 :
427 : void pp_function (pretty_printer *, const function_info *);
428 : }
429 :
430 : void dump (FILE *, const rtl_ssa::function_info *);
431 :
432 : void DEBUG_FUNCTION debug (const rtl_ssa::function_info *);
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