1 /* SSA Dominator optimizations for trees
2 Copyright (C) 2001-2018 Free Software Foundation, Inc.
3 Contributed by Diego Novillo <dnovillo@redhat.com>
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 "backend.h"
25 #include "tree.h"
26 #include "gimple.h"
27 #include "tree-pass.h"
28 #include "ssa.h"
29 #include "gimple-pretty-print.h"
30 #include "fold-const.h"
31 #include "cfganal.h"
32 #include "cfgloop.h"
33 #include "gimple-fold.h"
34 #include "tree-eh.h"
35 #include "tree-inline.h"
36 #include "gimple-iterator.h"
37 #include "tree-cfg.h"
38 #include "tree-into-ssa.h"
39 #include "domwalk.h"
40 #include "tree-ssa-propagate.h"
41 #include "tree-ssa-threadupdate.h"
42 #include "params.h"
43 #include "tree-ssa-scopedtables.h"
44 #include "tree-ssa-threadedge.h"
45 #include "tree-ssa-dom.h"
46 #include "gimplify.h"
47 #include "tree-cfgcleanup.h"
48 #include "dbgcnt.h"
49 #include "alloc-pool.h"
50 #include "tree-vrp.h"
51 #include "vr-values.h"
52 #include "gimple-ssa-evrp-analyze.h"
53
54 /* This file implements optimizations on the dominator tree. */
55
56 /* Structure for recording edge equivalences.
57
58 Computing and storing the edge equivalences instead of creating
59 them on-demand can save significant amounts of time, particularly
60 for pathological cases involving switch statements.
61
62 These structures live for a single iteration of the dominator
63 optimizer in the edge's AUX field. At the end of an iteration we
64 free each of these structures. */
65 class edge_info
66 {
67 public:
68 typedef std::pair <tree, tree> equiv_pair;
69 edge_info (edge);
70 ~edge_info ();
71
72 /* Record a simple LHS = RHS equivalence. This may trigger
73 calls to derive_equivalences. */
74 void record_simple_equiv (tree, tree);
75
76 /* If traversing this edge creates simple equivalences, we store
77 them as LHS/RHS pairs within this vector. */
78 vec<equiv_pair> simple_equivalences;
79
80 /* Traversing an edge may also indicate one or more particular conditions
81 are true or false. */
82 vec<cond_equivalence> cond_equivalences;
83
84 private:
85 /* Derive equivalences by walking the use-def chains. */
86 void derive_equivalences (tree, tree, int);
87 };
88
89 /* Track whether or not we have changed the control flow graph. */
90 static bool cfg_altered;
91
92 /* Bitmap of blocks that have had EH statements cleaned. We should
93 remove their dead edges eventually. */
94 static bitmap need_eh_cleanup;
95 static vec<gimple *> need_noreturn_fixup;
96
97 /* Statistics for dominator optimizations. */
98 struct opt_stats_d
99 {
100 long num_stmts;
101 long num_exprs_considered;
102 long num_re;
103 long num_const_prop;
104 long num_copy_prop;
105 };
106
107 static struct opt_stats_d opt_stats;
108
109 /* Local functions. */
110 static void record_equality (tree, tree, class const_and_copies *);
111 static void record_equivalences_from_phis (basic_block);
112 static void record_equivalences_from_incoming_edge (basic_block,
113 class const_and_copies *,
114 class avail_exprs_stack *);
115 static void eliminate_redundant_computations (gimple_stmt_iterator *,
116 class const_and_copies *,
117 class avail_exprs_stack *);
118 static void record_equivalences_from_stmt (gimple *, int,
119 class avail_exprs_stack *);
120 static void dump_dominator_optimization_stats (FILE *file,
121 hash_table<expr_elt_hasher> *);
122
123 /* Constructor for EDGE_INFO. An EDGE_INFO instance is always
124 associated with an edge E. */
125
edge_info(edge e)126 edge_info::edge_info (edge e)
127 {
128 /* Free the old one associated with E, if it exists and
129 associate our new object with E. */
130 free_dom_edge_info (e);
131 e->aux = this;
132
133 /* And initialize the embedded vectors. */
134 simple_equivalences = vNULL;
135 cond_equivalences = vNULL;
136 }
137
138 /* Destructor just needs to release the vectors. */
139
~edge_info(void)140 edge_info::~edge_info (void)
141 {
142 this->cond_equivalences.release ();
143 this->simple_equivalences.release ();
144 }
145
146 /* NAME is known to have the value VALUE, which must be a constant.
147
148 Walk through its use-def chain to see if there are other equivalences
149 we might be able to derive.
150
151 RECURSION_LIMIT controls how far back we recurse through the use-def
152 chains. */
153
154 void
derive_equivalences(tree name,tree value,int recursion_limit)155 edge_info::derive_equivalences (tree name, tree value, int recursion_limit)
156 {
157 if (TREE_CODE (name) != SSA_NAME || TREE_CODE (value) != INTEGER_CST)
158 return;
159
160 /* This records the equivalence for the toplevel object. Do
161 this before checking the recursion limit. */
162 simple_equivalences.safe_push (equiv_pair (name, value));
163
164 /* Limit how far up the use-def chains we are willing to walk. */
165 if (recursion_limit == 0)
166 return;
167
168 /* We can walk up the use-def chains to potentially find more
169 equivalences. */
170 gimple *def_stmt = SSA_NAME_DEF_STMT (name);
171 if (is_gimple_assign (def_stmt))
172 {
173 enum tree_code code = gimple_assign_rhs_code (def_stmt);
174 switch (code)
175 {
176 /* If the result of an OR is zero, then its operands are, too. */
177 case BIT_IOR_EXPR:
178 if (integer_zerop (value))
179 {
180 tree rhs1 = gimple_assign_rhs1 (def_stmt);
181 tree rhs2 = gimple_assign_rhs2 (def_stmt);
182
183 value = build_zero_cst (TREE_TYPE (rhs1));
184 derive_equivalences (rhs1, value, recursion_limit - 1);
185 value = build_zero_cst (TREE_TYPE (rhs2));
186 derive_equivalences (rhs2, value, recursion_limit - 1);
187 }
188 break;
189
190 /* If the result of an AND is nonzero, then its operands are, too. */
191 case BIT_AND_EXPR:
192 if (!integer_zerop (value))
193 {
194 tree rhs1 = gimple_assign_rhs1 (def_stmt);
195 tree rhs2 = gimple_assign_rhs2 (def_stmt);
196
197 /* If either operand has a boolean range, then we
198 know its value must be one, otherwise we just know it
199 is nonzero. The former is clearly useful, I haven't
200 seen cases where the latter is helpful yet. */
201 if (TREE_CODE (rhs1) == SSA_NAME)
202 {
203 if (ssa_name_has_boolean_range (rhs1))
204 {
205 value = build_one_cst (TREE_TYPE (rhs1));
206 derive_equivalences (rhs1, value, recursion_limit - 1);
207 }
208 }
209 if (TREE_CODE (rhs2) == SSA_NAME)
210 {
211 if (ssa_name_has_boolean_range (rhs2))
212 {
213 value = build_one_cst (TREE_TYPE (rhs2));
214 derive_equivalences (rhs2, value, recursion_limit - 1);
215 }
216 }
217 }
218 break;
219
220 /* If LHS is an SSA_NAME and RHS is a constant integer and LHS was
221 set via a widening type conversion, then we may be able to record
222 additional equivalences. */
223 case NOP_EXPR:
224 case CONVERT_EXPR:
225 {
226 tree rhs = gimple_assign_rhs1 (def_stmt);
227 tree rhs_type = TREE_TYPE (rhs);
228 if (INTEGRAL_TYPE_P (rhs_type)
229 && (TYPE_PRECISION (TREE_TYPE (name))
230 >= TYPE_PRECISION (rhs_type))
231 && int_fits_type_p (value, rhs_type))
232 derive_equivalences (rhs,
233 fold_convert (rhs_type, value),
234 recursion_limit - 1);
235 break;
236 }
237
238 /* We can invert the operation of these codes trivially if
239 one of the RHS operands is a constant to produce a known
240 value for the other RHS operand. */
241 case POINTER_PLUS_EXPR:
242 case PLUS_EXPR:
243 {
244 tree rhs1 = gimple_assign_rhs1 (def_stmt);
245 tree rhs2 = gimple_assign_rhs2 (def_stmt);
246
247 /* If either argument is a constant, then we can compute
248 a constant value for the nonconstant argument. */
249 if (TREE_CODE (rhs1) == INTEGER_CST
250 && TREE_CODE (rhs2) == SSA_NAME)
251 derive_equivalences (rhs2,
252 fold_binary (MINUS_EXPR, TREE_TYPE (rhs1),
253 value, rhs1),
254 recursion_limit - 1);
255 else if (TREE_CODE (rhs2) == INTEGER_CST
256 && TREE_CODE (rhs1) == SSA_NAME)
257 derive_equivalences (rhs1,
258 fold_binary (MINUS_EXPR, TREE_TYPE (rhs1),
259 value, rhs2),
260 recursion_limit - 1);
261 break;
262 }
263
264 /* If one of the operands is a constant, then we can compute
265 the value of the other operand. If both operands are
266 SSA_NAMEs, then they must be equal if the result is zero. */
267 case MINUS_EXPR:
268 {
269 tree rhs1 = gimple_assign_rhs1 (def_stmt);
270 tree rhs2 = gimple_assign_rhs2 (def_stmt);
271
272 /* If either argument is a constant, then we can compute
273 a constant value for the nonconstant argument. */
274 if (TREE_CODE (rhs1) == INTEGER_CST
275 && TREE_CODE (rhs2) == SSA_NAME)
276 derive_equivalences (rhs2,
277 fold_binary (MINUS_EXPR, TREE_TYPE (rhs1),
278 rhs1, value),
279 recursion_limit - 1);
280 else if (TREE_CODE (rhs2) == INTEGER_CST
281 && TREE_CODE (rhs1) == SSA_NAME)
282 derive_equivalences (rhs1,
283 fold_binary (PLUS_EXPR, TREE_TYPE (rhs1),
284 value, rhs2),
285 recursion_limit - 1);
286 else if (integer_zerop (value))
287 {
288 tree cond = build2 (EQ_EXPR, boolean_type_node,
289 gimple_assign_rhs1 (def_stmt),
290 gimple_assign_rhs2 (def_stmt));
291 tree inverted = invert_truthvalue (cond);
292 record_conditions (&this->cond_equivalences, cond, inverted);
293 }
294 break;
295 }
296
297 case EQ_EXPR:
298 case NE_EXPR:
299 {
300 if ((code == EQ_EXPR && integer_onep (value))
301 || (code == NE_EXPR && integer_zerop (value)))
302 {
303 tree rhs1 = gimple_assign_rhs1 (def_stmt);
304 tree rhs2 = gimple_assign_rhs2 (def_stmt);
305
306 /* If either argument is a constant, then record the
307 other argument as being the same as that constant.
308
309 If neither operand is a constant, then we have a
310 conditional name == name equivalence. */
311 if (TREE_CODE (rhs1) == INTEGER_CST)
312 derive_equivalences (rhs2, rhs1, recursion_limit - 1);
313 else if (TREE_CODE (rhs2) == INTEGER_CST)
314 derive_equivalences (rhs1, rhs2, recursion_limit - 1);
315 }
316 else
317 {
318 tree cond = build2 (code, boolean_type_node,
319 gimple_assign_rhs1 (def_stmt),
320 gimple_assign_rhs2 (def_stmt));
321 tree inverted = invert_truthvalue (cond);
322 if (integer_zerop (value))
323 std::swap (cond, inverted);
324 record_conditions (&this->cond_equivalences, cond, inverted);
325 }
326 break;
327 }
328
329 /* For BIT_NOT and NEGATE, we can just apply the operation to the
330 VALUE to get the new equivalence. It will always be a constant
331 so we can recurse. */
332 case BIT_NOT_EXPR:
333 case NEGATE_EXPR:
334 {
335 tree rhs = gimple_assign_rhs1 (def_stmt);
336 tree res;
337 /* If this is a NOT and the operand has a boolean range, then we
338 know its value must be zero or one. We are not supposed to
339 have a BIT_NOT_EXPR for boolean types with precision > 1 in
340 the general case, see e.g. the handling of TRUTH_NOT_EXPR in
341 the gimplifier, but it can be generated by match.pd out of
342 a BIT_XOR_EXPR wrapped in a BIT_AND_EXPR. Now the handling
343 of BIT_AND_EXPR above already forces a specific semantics for
344 boolean types with precision > 1 so we must do the same here,
345 otherwise we could change the semantics of TRUTH_NOT_EXPR for
346 boolean types with precision > 1. */
347 if (code == BIT_NOT_EXPR
348 && TREE_CODE (rhs) == SSA_NAME
349 && ssa_name_has_boolean_range (rhs))
350 {
351 if ((TREE_INT_CST_LOW (value) & 1) == 0)
352 res = build_one_cst (TREE_TYPE (rhs));
353 else
354 res = build_zero_cst (TREE_TYPE (rhs));
355 }
356 else
357 res = fold_build1 (code, TREE_TYPE (rhs), value);
358 derive_equivalences (rhs, res, recursion_limit - 1);
359 break;
360 }
361
362 default:
363 {
364 if (TREE_CODE_CLASS (code) == tcc_comparison)
365 {
366 tree cond = build2 (code, boolean_type_node,
367 gimple_assign_rhs1 (def_stmt),
368 gimple_assign_rhs2 (def_stmt));
369 tree inverted = invert_truthvalue (cond);
370 if (integer_zerop (value))
371 std::swap (cond, inverted);
372 record_conditions (&this->cond_equivalences, cond, inverted);
373 break;
374 }
375 break;
376 }
377 }
378 }
379 }
380
381 void
record_simple_equiv(tree lhs,tree rhs)382 edge_info::record_simple_equiv (tree lhs, tree rhs)
383 {
384 /* If the RHS is a constant, then we may be able to derive
385 further equivalences. Else just record the name = name
386 equivalence. */
387 if (TREE_CODE (rhs) == INTEGER_CST)
388 derive_equivalences (lhs, rhs, 4);
389 else
390 simple_equivalences.safe_push (equiv_pair (lhs, rhs));
391 }
392
393 /* Free the edge_info data attached to E, if it exists. */
394
395 void
free_dom_edge_info(edge e)396 free_dom_edge_info (edge e)
397 {
398 class edge_info *edge_info = (struct edge_info *)e->aux;
399
400 if (edge_info)
401 delete edge_info;
402 }
403
404 /* Free all EDGE_INFO structures associated with edges in the CFG.
405 If a particular edge can be threaded, copy the redirection
406 target from the EDGE_INFO structure into the edge's AUX field
407 as required by code to update the CFG and SSA graph for
408 jump threading. */
409
410 static void
free_all_edge_infos(void)411 free_all_edge_infos (void)
412 {
413 basic_block bb;
414 edge_iterator ei;
415 edge e;
416
417 FOR_EACH_BB_FN (bb, cfun)
418 {
419 FOR_EACH_EDGE (e, ei, bb->preds)
420 {
421 free_dom_edge_info (e);
422 e->aux = NULL;
423 }
424 }
425 }
426
427 /* We have finished optimizing BB, record any information implied by
428 taking a specific outgoing edge from BB. */
429
430 static void
record_edge_info(basic_block bb)431 record_edge_info (basic_block bb)
432 {
433 gimple_stmt_iterator gsi = gsi_last_bb (bb);
434 class edge_info *edge_info;
435
436 if (! gsi_end_p (gsi))
437 {
438 gimple *stmt = gsi_stmt (gsi);
439 location_t loc = gimple_location (stmt);
440
441 if (gimple_code (stmt) == GIMPLE_SWITCH)
442 {
443 gswitch *switch_stmt = as_a <gswitch *> (stmt);
444 tree index = gimple_switch_index (switch_stmt);
445
446 if (TREE_CODE (index) == SSA_NAME)
447 {
448 int i;
449 int n_labels = gimple_switch_num_labels (switch_stmt);
450 tree *info = XCNEWVEC (tree, last_basic_block_for_fn (cfun));
451 edge e;
452 edge_iterator ei;
453
454 for (i = 0; i < n_labels; i++)
455 {
456 tree label = gimple_switch_label (switch_stmt, i);
457 basic_block target_bb = label_to_block (CASE_LABEL (label));
458 if (CASE_HIGH (label)
459 || !CASE_LOW (label)
460 || info[target_bb->index])
461 info[target_bb->index] = error_mark_node;
462 else
463 info[target_bb->index] = label;
464 }
465
466 FOR_EACH_EDGE (e, ei, bb->succs)
467 {
468 basic_block target_bb = e->dest;
469 tree label = info[target_bb->index];
470
471 if (label != NULL && label != error_mark_node)
472 {
473 tree x = fold_convert_loc (loc, TREE_TYPE (index),
474 CASE_LOW (label));
475 edge_info = new class edge_info (e);
476 edge_info->record_simple_equiv (index, x);
477 }
478 }
479 free (info);
480 }
481 }
482
483 /* A COND_EXPR may create equivalences too. */
484 if (gimple_code (stmt) == GIMPLE_COND)
485 {
486 edge true_edge;
487 edge false_edge;
488
489 tree op0 = gimple_cond_lhs (stmt);
490 tree op1 = gimple_cond_rhs (stmt);
491 enum tree_code code = gimple_cond_code (stmt);
492
493 extract_true_false_edges_from_block (bb, &true_edge, &false_edge);
494
495 /* Special case comparing booleans against a constant as we
496 know the value of OP0 on both arms of the branch. i.e., we
497 can record an equivalence for OP0 rather than COND.
498
499 However, don't do this if the constant isn't zero or one.
500 Such conditionals will get optimized more thoroughly during
501 the domwalk. */
502 if ((code == EQ_EXPR || code == NE_EXPR)
503 && TREE_CODE (op0) == SSA_NAME
504 && ssa_name_has_boolean_range (op0)
505 && is_gimple_min_invariant (op1)
506 && (integer_zerop (op1) || integer_onep (op1)))
507 {
508 tree true_val = constant_boolean_node (true, TREE_TYPE (op0));
509 tree false_val = constant_boolean_node (false, TREE_TYPE (op0));
510
511 if (code == EQ_EXPR)
512 {
513 edge_info = new class edge_info (true_edge);
514 edge_info->record_simple_equiv (op0,
515 (integer_zerop (op1)
516 ? false_val : true_val));
517 edge_info = new class edge_info (false_edge);
518 edge_info->record_simple_equiv (op0,
519 (integer_zerop (op1)
520 ? true_val : false_val));
521 }
522 else
523 {
524 edge_info = new class edge_info (true_edge);
525 edge_info->record_simple_equiv (op0,
526 (integer_zerop (op1)
527 ? true_val : false_val));
528 edge_info = new class edge_info (false_edge);
529 edge_info->record_simple_equiv (op0,
530 (integer_zerop (op1)
531 ? false_val : true_val));
532 }
533 }
534 /* This can show up in the IL as a result of copy propagation
535 it will eventually be canonicalized, but we have to cope
536 with this case within the pass. */
537 else if (is_gimple_min_invariant (op0)
538 && TREE_CODE (op1) == SSA_NAME)
539 {
540 tree cond = build2 (code, boolean_type_node, op0, op1);
541 tree inverted = invert_truthvalue_loc (loc, cond);
542 bool can_infer_simple_equiv
543 = !(HONOR_SIGNED_ZEROS (op0)
544 && real_zerop (op0));
545 struct edge_info *edge_info;
546
547 edge_info = new class edge_info (true_edge);
548 record_conditions (&edge_info->cond_equivalences, cond, inverted);
549
550 if (can_infer_simple_equiv && code == EQ_EXPR)
551 edge_info->record_simple_equiv (op1, op0);
552
553 edge_info = new class edge_info (false_edge);
554 record_conditions (&edge_info->cond_equivalences, inverted, cond);
555
556 if (can_infer_simple_equiv && TREE_CODE (inverted) == EQ_EXPR)
557 edge_info->record_simple_equiv (op1, op0);
558 }
559
560 else if (TREE_CODE (op0) == SSA_NAME
561 && (TREE_CODE (op1) == SSA_NAME
562 || is_gimple_min_invariant (op1)))
563 {
564 tree cond = build2 (code, boolean_type_node, op0, op1);
565 tree inverted = invert_truthvalue_loc (loc, cond);
566 bool can_infer_simple_equiv
567 = !(HONOR_SIGNED_ZEROS (op1)
568 && (TREE_CODE (op1) == SSA_NAME || real_zerop (op1)));
569 struct edge_info *edge_info;
570
571 edge_info = new class edge_info (true_edge);
572 record_conditions (&edge_info->cond_equivalences, cond, inverted);
573
574 if (can_infer_simple_equiv && code == EQ_EXPR)
575 edge_info->record_simple_equiv (op0, op1);
576
577 edge_info = new class edge_info (false_edge);
578 record_conditions (&edge_info->cond_equivalences, inverted, cond);
579
580 if (can_infer_simple_equiv && TREE_CODE (inverted) == EQ_EXPR)
581 edge_info->record_simple_equiv (op0, op1);
582 }
583 }
584 }
585 }
586
587
588 class dom_opt_dom_walker : public dom_walker
589 {
590 public:
dom_opt_dom_walker(cdi_direction direction,class const_and_copies * const_and_copies,class avail_exprs_stack * avail_exprs_stack,gcond * dummy_cond)591 dom_opt_dom_walker (cdi_direction direction,
592 class const_and_copies *const_and_copies,
593 class avail_exprs_stack *avail_exprs_stack,
594 gcond *dummy_cond)
595 : dom_walker (direction, REACHABLE_BLOCKS),
596 m_const_and_copies (const_and_copies),
597 m_avail_exprs_stack (avail_exprs_stack),
598 m_dummy_cond (dummy_cond) { }
599
600 virtual edge before_dom_children (basic_block);
601 virtual void after_dom_children (basic_block);
602
603 private:
604
605 /* Unwindable equivalences, both const/copy and expression varieties. */
606 class const_and_copies *m_const_and_copies;
607 class avail_exprs_stack *m_avail_exprs_stack;
608
609 /* VRP data. */
610 class evrp_range_analyzer evrp_range_analyzer;
611
612 /* Dummy condition to avoid creating lots of throw away statements. */
613 gcond *m_dummy_cond;
614
615 /* Optimize a single statement within a basic block using the
616 various tables mantained by DOM. Returns the taken edge if
617 the statement is a conditional with a statically determined
618 value. */
619 edge optimize_stmt (basic_block, gimple_stmt_iterator);
620 };
621
622 /* Jump threading, redundancy elimination and const/copy propagation.
623
624 This pass may expose new symbols that need to be renamed into SSA. For
625 every new symbol exposed, its corresponding bit will be set in
626 VARS_TO_RENAME. */
627
628 namespace {
629
630 const pass_data pass_data_dominator =
631 {
632 GIMPLE_PASS, /* type */
633 "dom", /* name */
634 OPTGROUP_NONE, /* optinfo_flags */
635 TV_TREE_SSA_DOMINATOR_OPTS, /* tv_id */
636 ( PROP_cfg | PROP_ssa ), /* properties_required */
637 0, /* properties_provided */
638 0, /* properties_destroyed */
639 0, /* todo_flags_start */
640 ( TODO_cleanup_cfg | TODO_update_ssa ), /* todo_flags_finish */
641 };
642
643 class pass_dominator : public gimple_opt_pass
644 {
645 public:
pass_dominator(gcc::context * ctxt)646 pass_dominator (gcc::context *ctxt)
647 : gimple_opt_pass (pass_data_dominator, ctxt),
648 may_peel_loop_headers_p (false)
649 {}
650
651 /* opt_pass methods: */
clone()652 opt_pass * clone () { return new pass_dominator (m_ctxt); }
set_pass_param(unsigned int n,bool param)653 void set_pass_param (unsigned int n, bool param)
654 {
655 gcc_assert (n == 0);
656 may_peel_loop_headers_p = param;
657 }
gate(function *)658 virtual bool gate (function *) { return flag_tree_dom != 0; }
659 virtual unsigned int execute (function *);
660
661 private:
662 /* This flag is used to prevent loops from being peeled repeatedly in jump
663 threading; it will be removed once we preserve loop structures throughout
664 the compilation -- we will be able to mark the affected loops directly in
665 jump threading, and avoid peeling them next time. */
666 bool may_peel_loop_headers_p;
667 }; // class pass_dominator
668
669 unsigned int
execute(function * fun)670 pass_dominator::execute (function *fun)
671 {
672 memset (&opt_stats, 0, sizeof (opt_stats));
673
674 /* Create our hash tables. */
675 hash_table<expr_elt_hasher> *avail_exprs
676 = new hash_table<expr_elt_hasher> (1024);
677 class avail_exprs_stack *avail_exprs_stack
678 = new class avail_exprs_stack (avail_exprs);
679 class const_and_copies *const_and_copies = new class const_and_copies ();
680 need_eh_cleanup = BITMAP_ALLOC (NULL);
681 need_noreturn_fixup.create (0);
682
683 calculate_dominance_info (CDI_DOMINATORS);
684 cfg_altered = false;
685
686 /* We need to know loop structures in order to avoid destroying them
687 in jump threading. Note that we still can e.g. thread through loop
688 headers to an exit edge, or through loop header to the loop body, assuming
689 that we update the loop info.
690
691 TODO: We don't need to set LOOPS_HAVE_PREHEADERS generally, but due
692 to several overly conservative bail-outs in jump threading, case
693 gcc.dg/tree-ssa/pr21417.c can't be threaded if loop preheader is
694 missing. We should improve jump threading in future then
695 LOOPS_HAVE_PREHEADERS won't be needed here. */
696 loop_optimizer_init (LOOPS_HAVE_PREHEADERS | LOOPS_HAVE_SIMPLE_LATCHES);
697
698 /* Initialize the value-handle array. */
699 threadedge_initialize_values ();
700
701 /* We need accurate information regarding back edges in the CFG
702 for jump threading; this may include back edges that are not part of
703 a single loop. */
704 mark_dfs_back_edges ();
705
706 /* We want to create the edge info structures before the dominator walk
707 so that they'll be in place for the jump threader, particularly when
708 threading through a join block.
709
710 The conditions will be lazily updated with global equivalences as
711 we reach them during the dominator walk. */
712 basic_block bb;
713 FOR_EACH_BB_FN (bb, fun)
714 record_edge_info (bb);
715
716 gcond *dummy_cond = gimple_build_cond (NE_EXPR, integer_zero_node,
717 integer_zero_node, NULL, NULL);
718
719 /* Recursively walk the dominator tree optimizing statements. */
720 dom_opt_dom_walker walker (CDI_DOMINATORS, const_and_copies,
721 avail_exprs_stack, dummy_cond);
722 walker.walk (fun->cfg->x_entry_block_ptr);
723
724 /* Look for blocks where we cleared EDGE_EXECUTABLE on an outgoing
725 edge. When found, remove jump threads which contain any outgoing
726 edge from the affected block. */
727 if (cfg_altered)
728 {
729 FOR_EACH_BB_FN (bb, fun)
730 {
731 edge_iterator ei;
732 edge e;
733
734 /* First see if there are any edges without EDGE_EXECUTABLE
735 set. */
736 bool found = false;
737 FOR_EACH_EDGE (e, ei, bb->succs)
738 {
739 if ((e->flags & EDGE_EXECUTABLE) == 0)
740 {
741 found = true;
742 break;
743 }
744 }
745
746 /* If there were any such edges found, then remove jump threads
747 containing any edge leaving BB. */
748 if (found)
749 FOR_EACH_EDGE (e, ei, bb->succs)
750 remove_jump_threads_including (e);
751 }
752 }
753
754 {
755 gimple_stmt_iterator gsi;
756 basic_block bb;
757 FOR_EACH_BB_FN (bb, fun)
758 {
759 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
760 update_stmt_if_modified (gsi_stmt (gsi));
761 }
762 }
763
764 /* If we exposed any new variables, go ahead and put them into
765 SSA form now, before we handle jump threading. This simplifies
766 interactions between rewriting of _DECL nodes into SSA form
767 and rewriting SSA_NAME nodes into SSA form after block
768 duplication and CFG manipulation. */
769 update_ssa (TODO_update_ssa);
770
771 free_all_edge_infos ();
772
773 /* Thread jumps, creating duplicate blocks as needed. */
774 cfg_altered |= thread_through_all_blocks (may_peel_loop_headers_p);
775
776 if (cfg_altered)
777 free_dominance_info (CDI_DOMINATORS);
778
779 /* Removal of statements may make some EH edges dead. Purge
780 such edges from the CFG as needed. */
781 if (!bitmap_empty_p (need_eh_cleanup))
782 {
783 unsigned i;
784 bitmap_iterator bi;
785
786 /* Jump threading may have created forwarder blocks from blocks
787 needing EH cleanup; the new successor of these blocks, which
788 has inherited from the original block, needs the cleanup.
789 Don't clear bits in the bitmap, as that can break the bitmap
790 iterator. */
791 EXECUTE_IF_SET_IN_BITMAP (need_eh_cleanup, 0, i, bi)
792 {
793 basic_block bb = BASIC_BLOCK_FOR_FN (fun, i);
794 if (bb == NULL)
795 continue;
796 while (single_succ_p (bb)
797 && (single_succ_edge (bb)->flags
798 & (EDGE_EH|EDGE_DFS_BACK)) == 0)
799 bb = single_succ (bb);
800 if (bb == EXIT_BLOCK_PTR_FOR_FN (fun))
801 continue;
802 if ((unsigned) bb->index != i)
803 bitmap_set_bit (need_eh_cleanup, bb->index);
804 }
805
806 gimple_purge_all_dead_eh_edges (need_eh_cleanup);
807 bitmap_clear (need_eh_cleanup);
808 }
809
810 /* Fixup stmts that became noreturn calls. This may require splitting
811 blocks and thus isn't possible during the dominator walk or before
812 jump threading finished. Do this in reverse order so we don't
813 inadvertedly remove a stmt we want to fixup by visiting a dominating
814 now noreturn call first. */
815 while (!need_noreturn_fixup.is_empty ())
816 {
817 gimple *stmt = need_noreturn_fixup.pop ();
818 if (dump_file && dump_flags & TDF_DETAILS)
819 {
820 fprintf (dump_file, "Fixing up noreturn call ");
821 print_gimple_stmt (dump_file, stmt, 0);
822 fprintf (dump_file, "\n");
823 }
824 fixup_noreturn_call (stmt);
825 }
826
827 statistics_counter_event (fun, "Redundant expressions eliminated",
828 opt_stats.num_re);
829 statistics_counter_event (fun, "Constants propagated",
830 opt_stats.num_const_prop);
831 statistics_counter_event (fun, "Copies propagated",
832 opt_stats.num_copy_prop);
833
834 /* Debugging dumps. */
835 if (dump_file && (dump_flags & TDF_STATS))
836 dump_dominator_optimization_stats (dump_file, avail_exprs);
837
838 loop_optimizer_finalize ();
839
840 /* Delete our main hashtable. */
841 delete avail_exprs;
842 avail_exprs = NULL;
843
844 /* Free asserted bitmaps and stacks. */
845 BITMAP_FREE (need_eh_cleanup);
846 need_noreturn_fixup.release ();
847 delete avail_exprs_stack;
848 delete const_and_copies;
849
850 /* Free the value-handle array. */
851 threadedge_finalize_values ();
852
853 return 0;
854 }
855
856 } // anon namespace
857
858 gimple_opt_pass *
make_pass_dominator(gcc::context * ctxt)859 make_pass_dominator (gcc::context *ctxt)
860 {
861 return new pass_dominator (ctxt);
862 }
863
864 /* A hack until we remove threading from tree-vrp.c and bring the
865 simplification routine into the dom_opt_dom_walker class. */
866 static class vr_values *x_vr_values;
867
868 /* A trivial wrapper so that we can present the generic jump
869 threading code with a simple API for simplifying statements. */
870 static tree
simplify_stmt_for_jump_threading(gimple * stmt,gimple * within_stmt ATTRIBUTE_UNUSED,class avail_exprs_stack * avail_exprs_stack,basic_block bb ATTRIBUTE_UNUSED)871 simplify_stmt_for_jump_threading (gimple *stmt,
872 gimple *within_stmt ATTRIBUTE_UNUSED,
873 class avail_exprs_stack *avail_exprs_stack,
874 basic_block bb ATTRIBUTE_UNUSED)
875 {
876 /* First query our hash table to see if the the expression is available
877 there. A non-NULL return value will be either a constant or another
878 SSA_NAME. */
879 tree cached_lhs = avail_exprs_stack->lookup_avail_expr (stmt, false, true);
880 if (cached_lhs)
881 return cached_lhs;
882
883 /* If the hash table query failed, query VRP information. This is
884 essentially the same as tree-vrp's simplification routine. The
885 copy in tree-vrp is scheduled for removal in gcc-9. */
886 if (gcond *cond_stmt = dyn_cast <gcond *> (stmt))
887 {
888 cached_lhs
889 = x_vr_values->vrp_evaluate_conditional (gimple_cond_code (cond_stmt),
890 gimple_cond_lhs (cond_stmt),
891 gimple_cond_rhs (cond_stmt),
892 within_stmt);
893 return cached_lhs;
894 }
895
896 if (gswitch *switch_stmt = dyn_cast <gswitch *> (stmt))
897 {
898 tree op = gimple_switch_index (switch_stmt);
899 if (TREE_CODE (op) != SSA_NAME)
900 return NULL_TREE;
901
902 value_range *vr = x_vr_values->get_value_range (op);
903 if ((vr->type != VR_RANGE && vr->type != VR_ANTI_RANGE)
904 || symbolic_range_p (vr))
905 return NULL_TREE;
906
907 if (vr->type == VR_RANGE)
908 {
909 size_t i, j;
910
911 find_case_label_range (switch_stmt, vr->min, vr->max, &i, &j);
912
913 if (i == j)
914 {
915 tree label = gimple_switch_label (switch_stmt, i);
916
917 if (CASE_HIGH (label) != NULL_TREE
918 ? (tree_int_cst_compare (CASE_LOW (label), vr->min) <= 0
919 && tree_int_cst_compare (CASE_HIGH (label), vr->max) >= 0)
920 : (tree_int_cst_equal (CASE_LOW (label), vr->min)
921 && tree_int_cst_equal (vr->min, vr->max)))
922 return label;
923
924 if (i > j)
925 return gimple_switch_label (switch_stmt, 0);
926 }
927 }
928
929 if (vr->type == VR_ANTI_RANGE)
930 {
931 unsigned n = gimple_switch_num_labels (switch_stmt);
932 tree min_label = gimple_switch_label (switch_stmt, 1);
933 tree max_label = gimple_switch_label (switch_stmt, n - 1);
934
935 /* The default label will be taken only if the anti-range of the
936 operand is entirely outside the bounds of all the (non-default)
937 case labels. */
938 if (tree_int_cst_compare (vr->min, CASE_LOW (min_label)) <= 0
939 && (CASE_HIGH (max_label) != NULL_TREE
940 ? tree_int_cst_compare (vr->max, CASE_HIGH (max_label)) >= 0
941 : tree_int_cst_compare (vr->max, CASE_LOW (max_label)) >= 0))
942 return gimple_switch_label (switch_stmt, 0);
943 }
944 return NULL_TREE;
945 }
946
947 if (gassign *assign_stmt = dyn_cast <gassign *> (stmt))
948 {
949 tree lhs = gimple_assign_lhs (assign_stmt);
950 if (TREE_CODE (lhs) == SSA_NAME
951 && (INTEGRAL_TYPE_P (TREE_TYPE (lhs))
952 || POINTER_TYPE_P (TREE_TYPE (lhs)))
953 && stmt_interesting_for_vrp (stmt))
954 {
955 edge dummy_e;
956 tree dummy_tree;
957 value_range new_vr = VR_INITIALIZER;
958 x_vr_values->extract_range_from_stmt (stmt, &dummy_e,
959 &dummy_tree, &new_vr);
960 if (range_int_cst_singleton_p (&new_vr))
961 return new_vr.min;
962 }
963 }
964 return NULL;
965 }
966
967 /* Valueize hook for gimple_fold_stmt_to_constant_1. */
968
969 static tree
dom_valueize(tree t)970 dom_valueize (tree t)
971 {
972 if (TREE_CODE (t) == SSA_NAME)
973 {
974 tree tem = SSA_NAME_VALUE (t);
975 if (tem)
976 return tem;
977 }
978 return t;
979 }
980
981 /* We have just found an equivalence for LHS on an edge E.
982 Look backwards to other uses of LHS and see if we can derive
983 additional equivalences that are valid on edge E. */
984 static void
back_propagate_equivalences(tree lhs,edge e,class const_and_copies * const_and_copies)985 back_propagate_equivalences (tree lhs, edge e,
986 class const_and_copies *const_and_copies)
987 {
988 use_operand_p use_p;
989 imm_use_iterator iter;
990 bitmap domby = NULL;
991 basic_block dest = e->dest;
992
993 /* Iterate over the uses of LHS to see if any dominate E->dest.
994 If so, they may create useful equivalences too.
995
996 ??? If the code gets re-organized to a worklist to catch more
997 indirect opportunities and it is made to handle PHIs then this
998 should only consider use_stmts in basic-blocks we have already visited. */
999 FOR_EACH_IMM_USE_FAST (use_p, iter, lhs)
1000 {
1001 gimple *use_stmt = USE_STMT (use_p);
1002
1003 /* Often the use is in DEST, which we trivially know we can't use.
1004 This is cheaper than the dominator set tests below. */
1005 if (dest == gimple_bb (use_stmt))
1006 continue;
1007
1008 /* Filter out statements that can never produce a useful
1009 equivalence. */
1010 tree lhs2 = gimple_get_lhs (use_stmt);
1011 if (!lhs2 || TREE_CODE (lhs2) != SSA_NAME)
1012 continue;
1013
1014 /* Profiling has shown the domination tests here can be fairly
1015 expensive. We get significant improvements by building the
1016 set of blocks that dominate BB. We can then just test
1017 for set membership below.
1018
1019 We also initialize the set lazily since often the only uses
1020 are going to be in the same block as DEST. */
1021 if (!domby)
1022 {
1023 domby = BITMAP_ALLOC (NULL);
1024 basic_block bb = get_immediate_dominator (CDI_DOMINATORS, dest);
1025 while (bb)
1026 {
1027 bitmap_set_bit (domby, bb->index);
1028 bb = get_immediate_dominator (CDI_DOMINATORS, bb);
1029 }
1030 }
1031
1032 /* This tests if USE_STMT does not dominate DEST. */
1033 if (!bitmap_bit_p (domby, gimple_bb (use_stmt)->index))
1034 continue;
1035
1036 /* At this point USE_STMT dominates DEST and may result in a
1037 useful equivalence. Try to simplify its RHS to a constant
1038 or SSA_NAME. */
1039 tree res = gimple_fold_stmt_to_constant_1 (use_stmt, dom_valueize,
1040 no_follow_ssa_edges);
1041 if (res && (TREE_CODE (res) == SSA_NAME || is_gimple_min_invariant (res)))
1042 record_equality (lhs2, res, const_and_copies);
1043 }
1044
1045 if (domby)
1046 BITMAP_FREE (domby);
1047 }
1048
1049 /* Record into CONST_AND_COPIES and AVAIL_EXPRS_STACK any equivalences implied
1050 by traversing edge E (which are cached in E->aux).
1051
1052 Callers are responsible for managing the unwinding markers. */
1053 void
record_temporary_equivalences(edge e,class const_and_copies * const_and_copies,class avail_exprs_stack * avail_exprs_stack)1054 record_temporary_equivalences (edge e,
1055 class const_and_copies *const_and_copies,
1056 class avail_exprs_stack *avail_exprs_stack)
1057 {
1058 int i;
1059 class edge_info *edge_info = (class edge_info *) e->aux;
1060
1061 /* If we have info associated with this edge, record it into
1062 our equivalence tables. */
1063 if (edge_info)
1064 {
1065 cond_equivalence *eq;
1066 /* If we have 0 = COND or 1 = COND equivalences, record them
1067 into our expression hash tables. */
1068 for (i = 0; edge_info->cond_equivalences.iterate (i, &eq); ++i)
1069 avail_exprs_stack->record_cond (eq);
1070
1071 edge_info::equiv_pair *seq;
1072 for (i = 0; edge_info->simple_equivalences.iterate (i, &seq); ++i)
1073 {
1074 tree lhs = seq->first;
1075 if (!lhs || TREE_CODE (lhs) != SSA_NAME)
1076 continue;
1077
1078 /* Record the simple NAME = VALUE equivalence. */
1079 tree rhs = seq->second;
1080
1081 /* If this is a SSA_NAME = SSA_NAME equivalence and one operand is
1082 cheaper to compute than the other, then set up the equivalence
1083 such that we replace the expensive one with the cheap one.
1084
1085 If they are the same cost to compute, then do not record
1086 anything. */
1087 if (TREE_CODE (lhs) == SSA_NAME && TREE_CODE (rhs) == SSA_NAME)
1088 {
1089 gimple *rhs_def = SSA_NAME_DEF_STMT (rhs);
1090 int rhs_cost = estimate_num_insns (rhs_def, &eni_size_weights);
1091
1092 gimple *lhs_def = SSA_NAME_DEF_STMT (lhs);
1093 int lhs_cost = estimate_num_insns (lhs_def, &eni_size_weights);
1094
1095 if (rhs_cost > lhs_cost)
1096 record_equality (rhs, lhs, const_and_copies);
1097 else if (rhs_cost < lhs_cost)
1098 record_equality (lhs, rhs, const_and_copies);
1099 }
1100 else
1101 record_equality (lhs, rhs, const_and_copies);
1102
1103
1104 /* Any equivalence found for LHS may result in additional
1105 equivalences for other uses of LHS that we have already
1106 processed. */
1107 back_propagate_equivalences (lhs, e, const_and_copies);
1108 }
1109 }
1110 }
1111
1112 /* PHI nodes can create equivalences too.
1113
1114 Ignoring any alternatives which are the same as the result, if
1115 all the alternatives are equal, then the PHI node creates an
1116 equivalence. */
1117
1118 static void
record_equivalences_from_phis(basic_block bb)1119 record_equivalences_from_phis (basic_block bb)
1120 {
1121 gphi_iterator gsi;
1122
1123 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
1124 {
1125 gphi *phi = gsi.phi ();
1126
1127 tree lhs = gimple_phi_result (phi);
1128 tree rhs = NULL;
1129 size_t i;
1130
1131 for (i = 0; i < gimple_phi_num_args (phi); i++)
1132 {
1133 tree t = gimple_phi_arg_def (phi, i);
1134
1135 /* Ignore alternatives which are the same as our LHS. Since
1136 LHS is a PHI_RESULT, it is known to be a SSA_NAME, so we
1137 can simply compare pointers. */
1138 if (lhs == t)
1139 continue;
1140
1141 /* If the associated edge is not marked as executable, then it
1142 can be ignored. */
1143 if ((gimple_phi_arg_edge (phi, i)->flags & EDGE_EXECUTABLE) == 0)
1144 continue;
1145
1146 t = dom_valueize (t);
1147
1148 /* If T is an SSA_NAME and its associated edge is a backedge,
1149 then quit as we can not utilize this equivalence. */
1150 if (TREE_CODE (t) == SSA_NAME
1151 && (gimple_phi_arg_edge (phi, i)->flags & EDGE_DFS_BACK))
1152 break;
1153
1154 /* If we have not processed an alternative yet, then set
1155 RHS to this alternative. */
1156 if (rhs == NULL)
1157 rhs = t;
1158 /* If we have processed an alternative (stored in RHS), then
1159 see if it is equal to this one. If it isn't, then stop
1160 the search. */
1161 else if (! operand_equal_for_phi_arg_p (rhs, t))
1162 break;
1163 }
1164
1165 /* If we had no interesting alternatives, then all the RHS alternatives
1166 must have been the same as LHS. */
1167 if (!rhs)
1168 rhs = lhs;
1169
1170 /* If we managed to iterate through each PHI alternative without
1171 breaking out of the loop, then we have a PHI which may create
1172 a useful equivalence. We do not need to record unwind data for
1173 this, since this is a true assignment and not an equivalence
1174 inferred from a comparison. All uses of this ssa name are dominated
1175 by this assignment, so unwinding just costs time and space. */
1176 if (i == gimple_phi_num_args (phi)
1177 && may_propagate_copy (lhs, rhs))
1178 set_ssa_name_value (lhs, rhs);
1179 }
1180 }
1181
1182 /* Record any equivalences created by the incoming edge to BB into
1183 CONST_AND_COPIES and AVAIL_EXPRS_STACK. If BB has more than one
1184 incoming edge, then no equivalence is created. */
1185
1186 static void
record_equivalences_from_incoming_edge(basic_block bb,class const_and_copies * const_and_copies,class avail_exprs_stack * avail_exprs_stack)1187 record_equivalences_from_incoming_edge (basic_block bb,
1188 class const_and_copies *const_and_copies,
1189 class avail_exprs_stack *avail_exprs_stack)
1190 {
1191 edge e;
1192 basic_block parent;
1193
1194 /* If our parent block ended with a control statement, then we may be
1195 able to record some equivalences based on which outgoing edge from
1196 the parent was followed. */
1197 parent = get_immediate_dominator (CDI_DOMINATORS, bb);
1198
1199 e = single_pred_edge_ignoring_loop_edges (bb, true);
1200
1201 /* If we had a single incoming edge from our parent block, then enter
1202 any data associated with the edge into our tables. */
1203 if (e && e->src == parent)
1204 record_temporary_equivalences (e, const_and_copies, avail_exprs_stack);
1205 }
1206
1207 /* Dump statistics for the hash table HTAB. */
1208
1209 static void
htab_statistics(FILE * file,const hash_table<expr_elt_hasher> & htab)1210 htab_statistics (FILE *file, const hash_table<expr_elt_hasher> &htab)
1211 {
1212 fprintf (file, "size %ld, %ld elements, %f collision/search ratio\n",
1213 (long) htab.size (),
1214 (long) htab.elements (),
1215 htab.collisions ());
1216 }
1217
1218 /* Dump SSA statistics on FILE. */
1219
1220 static void
dump_dominator_optimization_stats(FILE * file,hash_table<expr_elt_hasher> * avail_exprs)1221 dump_dominator_optimization_stats (FILE *file,
1222 hash_table<expr_elt_hasher> *avail_exprs)
1223 {
1224 fprintf (file, "Total number of statements: %6ld\n\n",
1225 opt_stats.num_stmts);
1226 fprintf (file, "Exprs considered for dominator optimizations: %6ld\n",
1227 opt_stats.num_exprs_considered);
1228
1229 fprintf (file, "\nHash table statistics:\n");
1230
1231 fprintf (file, " avail_exprs: ");
1232 htab_statistics (file, *avail_exprs);
1233 }
1234
1235
1236 /* Similarly, but assume that X and Y are the two operands of an EQ_EXPR.
1237 This constrains the cases in which we may treat this as assignment. */
1238
1239 static void
record_equality(tree x,tree y,class const_and_copies * const_and_copies)1240 record_equality (tree x, tree y, class const_and_copies *const_and_copies)
1241 {
1242 tree prev_x = NULL, prev_y = NULL;
1243
1244 if (tree_swap_operands_p (x, y))
1245 std::swap (x, y);
1246
1247 /* Most of the time tree_swap_operands_p does what we want. But there
1248 are cases where we know one operand is better for copy propagation than
1249 the other. Given no other code cares about ordering of equality
1250 comparison operators for that purpose, we just handle the special cases
1251 here. */
1252 if (TREE_CODE (x) == SSA_NAME && TREE_CODE (y) == SSA_NAME)
1253 {
1254 /* If one operand is a single use operand, then make it
1255 X. This will preserve its single use properly and if this
1256 conditional is eliminated, the computation of X can be
1257 eliminated as well. */
1258 if (has_single_use (y) && ! has_single_use (x))
1259 std::swap (x, y);
1260 }
1261 if (TREE_CODE (x) == SSA_NAME)
1262 prev_x = SSA_NAME_VALUE (x);
1263 if (TREE_CODE (y) == SSA_NAME)
1264 prev_y = SSA_NAME_VALUE (y);
1265
1266 /* If one of the previous values is invariant, or invariant in more loops
1267 (by depth), then use that.
1268 Otherwise it doesn't matter which value we choose, just so
1269 long as we canonicalize on one value. */
1270 if (is_gimple_min_invariant (y))
1271 ;
1272 else if (is_gimple_min_invariant (x))
1273 prev_x = x, x = y, y = prev_x, prev_x = prev_y;
1274 else if (prev_x && is_gimple_min_invariant (prev_x))
1275 x = y, y = prev_x, prev_x = prev_y;
1276 else if (prev_y)
1277 y = prev_y;
1278
1279 /* After the swapping, we must have one SSA_NAME. */
1280 if (TREE_CODE (x) != SSA_NAME)
1281 return;
1282
1283 /* For IEEE, -0.0 == 0.0, so we don't necessarily know the sign of a
1284 variable compared against zero. If we're honoring signed zeros,
1285 then we cannot record this value unless we know that the value is
1286 nonzero. */
1287 if (HONOR_SIGNED_ZEROS (x)
1288 && (TREE_CODE (y) != REAL_CST
1289 || real_equal (&dconst0, &TREE_REAL_CST (y))))
1290 return;
1291
1292 const_and_copies->record_const_or_copy (x, y, prev_x);
1293 }
1294
1295 /* Returns true when STMT is a simple iv increment. It detects the
1296 following situation:
1297
1298 i_1 = phi (..., i_k)
1299 [...]
1300 i_j = i_{j-1} for each j : 2 <= j <= k-1
1301 [...]
1302 i_k = i_{k-1} +/- ... */
1303
1304 bool
simple_iv_increment_p(gimple * stmt)1305 simple_iv_increment_p (gimple *stmt)
1306 {
1307 enum tree_code code;
1308 tree lhs, preinc;
1309 gimple *phi;
1310 size_t i;
1311
1312 if (gimple_code (stmt) != GIMPLE_ASSIGN)
1313 return false;
1314
1315 lhs = gimple_assign_lhs (stmt);
1316 if (TREE_CODE (lhs) != SSA_NAME)
1317 return false;
1318
1319 code = gimple_assign_rhs_code (stmt);
1320 if (code != PLUS_EXPR
1321 && code != MINUS_EXPR
1322 && code != POINTER_PLUS_EXPR)
1323 return false;
1324
1325 preinc = gimple_assign_rhs1 (stmt);
1326 if (TREE_CODE (preinc) != SSA_NAME)
1327 return false;
1328
1329 phi = SSA_NAME_DEF_STMT (preinc);
1330 while (gimple_code (phi) != GIMPLE_PHI)
1331 {
1332 /* Follow trivial copies, but not the DEF used in a back edge,
1333 so that we don't prevent coalescing. */
1334 if (!gimple_assign_ssa_name_copy_p (phi))
1335 return false;
1336 preinc = gimple_assign_rhs1 (phi);
1337 phi = SSA_NAME_DEF_STMT (preinc);
1338 }
1339
1340 for (i = 0; i < gimple_phi_num_args (phi); i++)
1341 if (gimple_phi_arg_def (phi, i) == lhs)
1342 return true;
1343
1344 return false;
1345 }
1346
1347 /* Propagate know values from SSA_NAME_VALUE into the PHI nodes of the
1348 successors of BB. */
1349
1350 static void
cprop_into_successor_phis(basic_block bb,class const_and_copies * const_and_copies)1351 cprop_into_successor_phis (basic_block bb,
1352 class const_and_copies *const_and_copies)
1353 {
1354 edge e;
1355 edge_iterator ei;
1356
1357 FOR_EACH_EDGE (e, ei, bb->succs)
1358 {
1359 int indx;
1360 gphi_iterator gsi;
1361
1362 /* If this is an abnormal edge, then we do not want to copy propagate
1363 into the PHI alternative associated with this edge. */
1364 if (e->flags & EDGE_ABNORMAL)
1365 continue;
1366
1367 gsi = gsi_start_phis (e->dest);
1368 if (gsi_end_p (gsi))
1369 continue;
1370
1371 /* We may have an equivalence associated with this edge. While
1372 we can not propagate it into non-dominated blocks, we can
1373 propagate them into PHIs in non-dominated blocks. */
1374
1375 /* Push the unwind marker so we can reset the const and copies
1376 table back to its original state after processing this edge. */
1377 const_and_copies->push_marker ();
1378
1379 /* Extract and record any simple NAME = VALUE equivalences.
1380
1381 Don't bother with [01] = COND equivalences, they're not useful
1382 here. */
1383 class edge_info *edge_info = (class edge_info *) e->aux;
1384
1385 if (edge_info)
1386 {
1387 edge_info::equiv_pair *seq;
1388 for (int i = 0; edge_info->simple_equivalences.iterate (i, &seq); ++i)
1389 {
1390 tree lhs = seq->first;
1391 tree rhs = seq->second;
1392
1393 if (lhs && TREE_CODE (lhs) == SSA_NAME)
1394 const_and_copies->record_const_or_copy (lhs, rhs);
1395 }
1396
1397 }
1398
1399 indx = e->dest_idx;
1400 for ( ; !gsi_end_p (gsi); gsi_next (&gsi))
1401 {
1402 tree new_val;
1403 use_operand_p orig_p;
1404 tree orig_val;
1405 gphi *phi = gsi.phi ();
1406
1407 /* The alternative may be associated with a constant, so verify
1408 it is an SSA_NAME before doing anything with it. */
1409 orig_p = gimple_phi_arg_imm_use_ptr (phi, indx);
1410 orig_val = get_use_from_ptr (orig_p);
1411 if (TREE_CODE (orig_val) != SSA_NAME)
1412 continue;
1413
1414 /* If we have *ORIG_P in our constant/copy table, then replace
1415 ORIG_P with its value in our constant/copy table. */
1416 new_val = SSA_NAME_VALUE (orig_val);
1417 if (new_val
1418 && new_val != orig_val
1419 && may_propagate_copy (orig_val, new_val))
1420 propagate_value (orig_p, new_val);
1421 }
1422
1423 const_and_copies->pop_to_marker ();
1424 }
1425 }
1426
1427 edge
before_dom_children(basic_block bb)1428 dom_opt_dom_walker::before_dom_children (basic_block bb)
1429 {
1430 gimple_stmt_iterator gsi;
1431
1432 if (dump_file && (dump_flags & TDF_DETAILS))
1433 fprintf (dump_file, "\n\nOptimizing block #%d\n\n", bb->index);
1434
1435 evrp_range_analyzer.enter (bb);
1436
1437 /* Push a marker on the stacks of local information so that we know how
1438 far to unwind when we finalize this block. */
1439 m_avail_exprs_stack->push_marker ();
1440 m_const_and_copies->push_marker ();
1441
1442 record_equivalences_from_incoming_edge (bb, m_const_and_copies,
1443 m_avail_exprs_stack);
1444
1445 /* PHI nodes can create equivalences too. */
1446 record_equivalences_from_phis (bb);
1447
1448 /* Create equivalences from redundant PHIs. PHIs are only truly
1449 redundant when they exist in the same block, so push another
1450 marker and unwind right afterwards. */
1451 m_avail_exprs_stack->push_marker ();
1452 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
1453 eliminate_redundant_computations (&gsi, m_const_and_copies,
1454 m_avail_exprs_stack);
1455 m_avail_exprs_stack->pop_to_marker ();
1456
1457 edge taken_edge = NULL;
1458 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
1459 {
1460 evrp_range_analyzer.record_ranges_from_stmt (gsi_stmt (gsi), false);
1461 taken_edge = this->optimize_stmt (bb, gsi);
1462 }
1463
1464 /* Now prepare to process dominated blocks. */
1465 record_edge_info (bb);
1466 cprop_into_successor_phis (bb, m_const_and_copies);
1467 if (taken_edge && !dbg_cnt (dom_unreachable_edges))
1468 return NULL;
1469
1470 return taken_edge;
1471 }
1472
1473 /* We have finished processing the dominator children of BB, perform
1474 any finalization actions in preparation for leaving this node in
1475 the dominator tree. */
1476
1477 void
after_dom_children(basic_block bb)1478 dom_opt_dom_walker::after_dom_children (basic_block bb)
1479 {
1480 x_vr_values = evrp_range_analyzer.get_vr_values ();
1481 thread_outgoing_edges (bb, m_dummy_cond, m_const_and_copies,
1482 m_avail_exprs_stack,
1483 &evrp_range_analyzer,
1484 simplify_stmt_for_jump_threading);
1485 x_vr_values = NULL;
1486
1487 /* These remove expressions local to BB from the tables. */
1488 m_avail_exprs_stack->pop_to_marker ();
1489 m_const_and_copies->pop_to_marker ();
1490 evrp_range_analyzer.leave (bb);
1491 }
1492
1493 /* Search for redundant computations in STMT. If any are found, then
1494 replace them with the variable holding the result of the computation.
1495
1496 If safe, record this expression into AVAIL_EXPRS_STACK and
1497 CONST_AND_COPIES. */
1498
1499 static void
eliminate_redundant_computations(gimple_stmt_iterator * gsi,class const_and_copies * const_and_copies,class avail_exprs_stack * avail_exprs_stack)1500 eliminate_redundant_computations (gimple_stmt_iterator* gsi,
1501 class const_and_copies *const_and_copies,
1502 class avail_exprs_stack *avail_exprs_stack)
1503 {
1504 tree expr_type;
1505 tree cached_lhs;
1506 tree def;
1507 bool insert = true;
1508 bool assigns_var_p = false;
1509
1510 gimple *stmt = gsi_stmt (*gsi);
1511
1512 if (gimple_code (stmt) == GIMPLE_PHI)
1513 def = gimple_phi_result (stmt);
1514 else
1515 def = gimple_get_lhs (stmt);
1516
1517 /* Certain expressions on the RHS can be optimized away, but can not
1518 themselves be entered into the hash tables. */
1519 if (! def
1520 || TREE_CODE (def) != SSA_NAME
1521 || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def)
1522 || gimple_vdef (stmt)
1523 /* Do not record equivalences for increments of ivs. This would create
1524 overlapping live ranges for a very questionable gain. */
1525 || simple_iv_increment_p (stmt))
1526 insert = false;
1527
1528 /* Check if the expression has been computed before. */
1529 cached_lhs = avail_exprs_stack->lookup_avail_expr (stmt, insert, true);
1530
1531 opt_stats.num_exprs_considered++;
1532
1533 /* Get the type of the expression we are trying to optimize. */
1534 if (is_gimple_assign (stmt))
1535 {
1536 expr_type = TREE_TYPE (gimple_assign_lhs (stmt));
1537 assigns_var_p = true;
1538 }
1539 else if (gimple_code (stmt) == GIMPLE_COND)
1540 expr_type = boolean_type_node;
1541 else if (is_gimple_call (stmt))
1542 {
1543 gcc_assert (gimple_call_lhs (stmt));
1544 expr_type = TREE_TYPE (gimple_call_lhs (stmt));
1545 assigns_var_p = true;
1546 }
1547 else if (gswitch *swtch_stmt = dyn_cast <gswitch *> (stmt))
1548 expr_type = TREE_TYPE (gimple_switch_index (swtch_stmt));
1549 else if (gimple_code (stmt) == GIMPLE_PHI)
1550 /* We can't propagate into a phi, so the logic below doesn't apply.
1551 Instead record an equivalence between the cached LHS and the
1552 PHI result of this statement, provided they are in the same block.
1553 This should be sufficient to kill the redundant phi. */
1554 {
1555 if (def && cached_lhs)
1556 const_and_copies->record_const_or_copy (def, cached_lhs);
1557 return;
1558 }
1559 else
1560 gcc_unreachable ();
1561
1562 if (!cached_lhs)
1563 return;
1564
1565 /* It is safe to ignore types here since we have already done
1566 type checking in the hashing and equality routines. In fact
1567 type checking here merely gets in the way of constant
1568 propagation. Also, make sure that it is safe to propagate
1569 CACHED_LHS into the expression in STMT. */
1570 if ((TREE_CODE (cached_lhs) != SSA_NAME
1571 && (assigns_var_p
1572 || useless_type_conversion_p (expr_type, TREE_TYPE (cached_lhs))))
1573 || may_propagate_copy_into_stmt (stmt, cached_lhs))
1574 {
1575 gcc_checking_assert (TREE_CODE (cached_lhs) == SSA_NAME
1576 || is_gimple_min_invariant (cached_lhs));
1577
1578 if (dump_file && (dump_flags & TDF_DETAILS))
1579 {
1580 fprintf (dump_file, " Replaced redundant expr '");
1581 print_gimple_expr (dump_file, stmt, 0, dump_flags);
1582 fprintf (dump_file, "' with '");
1583 print_generic_expr (dump_file, cached_lhs, dump_flags);
1584 fprintf (dump_file, "'\n");
1585 }
1586
1587 opt_stats.num_re++;
1588
1589 if (assigns_var_p
1590 && !useless_type_conversion_p (expr_type, TREE_TYPE (cached_lhs)))
1591 cached_lhs = fold_convert (expr_type, cached_lhs);
1592
1593 propagate_tree_value_into_stmt (gsi, cached_lhs);
1594
1595 /* Since it is always necessary to mark the result as modified,
1596 perhaps we should move this into propagate_tree_value_into_stmt
1597 itself. */
1598 gimple_set_modified (gsi_stmt (*gsi), true);
1599 }
1600 }
1601
1602 /* STMT, a GIMPLE_ASSIGN, may create certain equivalences, in either
1603 the available expressions table or the const_and_copies table.
1604 Detect and record those equivalences into AVAIL_EXPRS_STACK.
1605
1606 We handle only very simple copy equivalences here. The heavy
1607 lifing is done by eliminate_redundant_computations. */
1608
1609 static void
record_equivalences_from_stmt(gimple * stmt,int may_optimize_p,class avail_exprs_stack * avail_exprs_stack)1610 record_equivalences_from_stmt (gimple *stmt, int may_optimize_p,
1611 class avail_exprs_stack *avail_exprs_stack)
1612 {
1613 tree lhs;
1614 enum tree_code lhs_code;
1615
1616 gcc_assert (is_gimple_assign (stmt));
1617
1618 lhs = gimple_assign_lhs (stmt);
1619 lhs_code = TREE_CODE (lhs);
1620
1621 if (lhs_code == SSA_NAME
1622 && gimple_assign_single_p (stmt))
1623 {
1624 tree rhs = gimple_assign_rhs1 (stmt);
1625
1626 /* If the RHS of the assignment is a constant or another variable that
1627 may be propagated, register it in the CONST_AND_COPIES table. We
1628 do not need to record unwind data for this, since this is a true
1629 assignment and not an equivalence inferred from a comparison. All
1630 uses of this ssa name are dominated by this assignment, so unwinding
1631 just costs time and space. */
1632 if (may_optimize_p
1633 && (TREE_CODE (rhs) == SSA_NAME
1634 || is_gimple_min_invariant (rhs)))
1635 {
1636 rhs = dom_valueize (rhs);
1637
1638 if (dump_file && (dump_flags & TDF_DETAILS))
1639 {
1640 fprintf (dump_file, "==== ASGN ");
1641 print_generic_expr (dump_file, lhs);
1642 fprintf (dump_file, " = ");
1643 print_generic_expr (dump_file, rhs);
1644 fprintf (dump_file, "\n");
1645 }
1646
1647 set_ssa_name_value (lhs, rhs);
1648 }
1649 }
1650
1651 /* Make sure we can propagate &x + CST. */
1652 if (lhs_code == SSA_NAME
1653 && gimple_assign_rhs_code (stmt) == POINTER_PLUS_EXPR
1654 && TREE_CODE (gimple_assign_rhs1 (stmt)) == ADDR_EXPR
1655 && TREE_CODE (gimple_assign_rhs2 (stmt)) == INTEGER_CST)
1656 {
1657 tree op0 = gimple_assign_rhs1 (stmt);
1658 tree op1 = gimple_assign_rhs2 (stmt);
1659 tree new_rhs
1660 = build_fold_addr_expr (fold_build2 (MEM_REF,
1661 TREE_TYPE (TREE_TYPE (op0)),
1662 unshare_expr (op0),
1663 fold_convert (ptr_type_node,
1664 op1)));
1665 if (dump_file && (dump_flags & TDF_DETAILS))
1666 {
1667 fprintf (dump_file, "==== ASGN ");
1668 print_generic_expr (dump_file, lhs);
1669 fprintf (dump_file, " = ");
1670 print_generic_expr (dump_file, new_rhs);
1671 fprintf (dump_file, "\n");
1672 }
1673
1674 set_ssa_name_value (lhs, new_rhs);
1675 }
1676
1677 /* A memory store, even an aliased store, creates a useful
1678 equivalence. By exchanging the LHS and RHS, creating suitable
1679 vops and recording the result in the available expression table,
1680 we may be able to expose more redundant loads. */
1681 if (!gimple_has_volatile_ops (stmt)
1682 && gimple_references_memory_p (stmt)
1683 && gimple_assign_single_p (stmt)
1684 && (TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME
1685 || is_gimple_min_invariant (gimple_assign_rhs1 (stmt)))
1686 && !is_gimple_reg (lhs))
1687 {
1688 tree rhs = gimple_assign_rhs1 (stmt);
1689 gassign *new_stmt;
1690
1691 /* Build a new statement with the RHS and LHS exchanged. */
1692 if (TREE_CODE (rhs) == SSA_NAME)
1693 {
1694 /* NOTE tuples. The call to gimple_build_assign below replaced
1695 a call to build_gimple_modify_stmt, which did not set the
1696 SSA_NAME_DEF_STMT on the LHS of the assignment. Doing so
1697 may cause an SSA validation failure, as the LHS may be a
1698 default-initialized name and should have no definition. I'm
1699 a bit dubious of this, as the artificial statement that we
1700 generate here may in fact be ill-formed, but it is simply
1701 used as an internal device in this pass, and never becomes
1702 part of the CFG. */
1703 gimple *defstmt = SSA_NAME_DEF_STMT (rhs);
1704 new_stmt = gimple_build_assign (rhs, lhs);
1705 SSA_NAME_DEF_STMT (rhs) = defstmt;
1706 }
1707 else
1708 new_stmt = gimple_build_assign (rhs, lhs);
1709
1710 gimple_set_vuse (new_stmt, gimple_vdef (stmt));
1711
1712 /* Finally enter the statement into the available expression
1713 table. */
1714 avail_exprs_stack->lookup_avail_expr (new_stmt, true, true);
1715 }
1716 }
1717
1718 /* Replace *OP_P in STMT with any known equivalent value for *OP_P from
1719 CONST_AND_COPIES. */
1720
1721 static void
cprop_operand(gimple * stmt,use_operand_p op_p)1722 cprop_operand (gimple *stmt, use_operand_p op_p)
1723 {
1724 tree val;
1725 tree op = USE_FROM_PTR (op_p);
1726
1727 /* If the operand has a known constant value or it is known to be a
1728 copy of some other variable, use the value or copy stored in
1729 CONST_AND_COPIES. */
1730 val = SSA_NAME_VALUE (op);
1731 if (val && val != op)
1732 {
1733 /* Do not replace hard register operands in asm statements. */
1734 if (gimple_code (stmt) == GIMPLE_ASM
1735 && !may_propagate_copy_into_asm (op))
1736 return;
1737
1738 /* Certain operands are not allowed to be copy propagated due
1739 to their interaction with exception handling and some GCC
1740 extensions. */
1741 if (!may_propagate_copy (op, val))
1742 return;
1743
1744 /* Do not propagate copies into BIVs.
1745 See PR23821 and PR62217 for how this can disturb IV and
1746 number of iteration analysis. */
1747 if (TREE_CODE (val) != INTEGER_CST)
1748 {
1749 gimple *def = SSA_NAME_DEF_STMT (op);
1750 if (gimple_code (def) == GIMPLE_PHI
1751 && gimple_bb (def)->loop_father->header == gimple_bb (def))
1752 return;
1753 }
1754
1755 /* Dump details. */
1756 if (dump_file && (dump_flags & TDF_DETAILS))
1757 {
1758 fprintf (dump_file, " Replaced '");
1759 print_generic_expr (dump_file, op, dump_flags);
1760 fprintf (dump_file, "' with %s '",
1761 (TREE_CODE (val) != SSA_NAME ? "constant" : "variable"));
1762 print_generic_expr (dump_file, val, dump_flags);
1763 fprintf (dump_file, "'\n");
1764 }
1765
1766 if (TREE_CODE (val) != SSA_NAME)
1767 opt_stats.num_const_prop++;
1768 else
1769 opt_stats.num_copy_prop++;
1770
1771 propagate_value (op_p, val);
1772
1773 /* And note that we modified this statement. This is now
1774 safe, even if we changed virtual operands since we will
1775 rescan the statement and rewrite its operands again. */
1776 gimple_set_modified (stmt, true);
1777 }
1778 }
1779
1780 /* CONST_AND_COPIES is a table which maps an SSA_NAME to the current
1781 known value for that SSA_NAME (or NULL if no value is known).
1782
1783 Propagate values from CONST_AND_COPIES into the uses, vuses and
1784 vdef_ops of STMT. */
1785
1786 static void
cprop_into_stmt(gimple * stmt)1787 cprop_into_stmt (gimple *stmt)
1788 {
1789 use_operand_p op_p;
1790 ssa_op_iter iter;
1791 tree last_copy_propagated_op = NULL;
1792
1793 FOR_EACH_SSA_USE_OPERAND (op_p, stmt, iter, SSA_OP_USE)
1794 {
1795 tree old_op = USE_FROM_PTR (op_p);
1796
1797 /* If we have A = B and B = A in the copy propagation tables
1798 (due to an equality comparison), avoid substituting B for A
1799 then A for B in the trivially discovered cases. This allows
1800 optimization of statements were A and B appear as input
1801 operands. */
1802 if (old_op != last_copy_propagated_op)
1803 {
1804 cprop_operand (stmt, op_p);
1805
1806 tree new_op = USE_FROM_PTR (op_p);
1807 if (new_op != old_op && TREE_CODE (new_op) == SSA_NAME)
1808 last_copy_propagated_op = new_op;
1809 }
1810 }
1811 }
1812
1813 /* If STMT contains a relational test, try to convert it into an
1814 equality test if there is only a single value which can ever
1815 make the test true.
1816
1817 For example, if the expression hash table contains:
1818
1819 TRUE = (i <= 1)
1820
1821 And we have a test within statement of i >= 1, then we can safely
1822 rewrite the test as i == 1 since there only a single value where
1823 the test is true.
1824
1825 This is similar to code in VRP. */
1826
1827 static void
test_for_singularity(gimple * stmt,gcond * dummy_cond,avail_exprs_stack * avail_exprs_stack)1828 test_for_singularity (gimple *stmt, gcond *dummy_cond,
1829 avail_exprs_stack *avail_exprs_stack)
1830 {
1831 /* We want to support gimple conditionals as well as assignments
1832 where the RHS contains a conditional. */
1833 if (is_gimple_assign (stmt) || gimple_code (stmt) == GIMPLE_COND)
1834 {
1835 enum tree_code code = ERROR_MARK;
1836 tree lhs, rhs;
1837
1838 /* Extract the condition of interest from both forms we support. */
1839 if (is_gimple_assign (stmt))
1840 {
1841 code = gimple_assign_rhs_code (stmt);
1842 lhs = gimple_assign_rhs1 (stmt);
1843 rhs = gimple_assign_rhs2 (stmt);
1844 }
1845 else if (gimple_code (stmt) == GIMPLE_COND)
1846 {
1847 code = gimple_cond_code (as_a <gcond *> (stmt));
1848 lhs = gimple_cond_lhs (as_a <gcond *> (stmt));
1849 rhs = gimple_cond_rhs (as_a <gcond *> (stmt));
1850 }
1851
1852 /* We're looking for a relational test using LE/GE. Also note we can
1853 canonicalize LT/GT tests against constants into LE/GT tests. */
1854 if (code == LE_EXPR || code == GE_EXPR
1855 || ((code == LT_EXPR || code == GT_EXPR)
1856 && TREE_CODE (rhs) == INTEGER_CST))
1857 {
1858 /* For LT_EXPR and GT_EXPR, canonicalize to LE_EXPR and GE_EXPR. */
1859 if (code == LT_EXPR)
1860 rhs = fold_build2 (MINUS_EXPR, TREE_TYPE (rhs),
1861 rhs, build_int_cst (TREE_TYPE (rhs), 1));
1862
1863 if (code == GT_EXPR)
1864 rhs = fold_build2 (PLUS_EXPR, TREE_TYPE (rhs),
1865 rhs, build_int_cst (TREE_TYPE (rhs), 1));
1866
1867 /* Determine the code we want to check for in the hash table. */
1868 enum tree_code test_code;
1869 if (code == GE_EXPR || code == GT_EXPR)
1870 test_code = LE_EXPR;
1871 else
1872 test_code = GE_EXPR;
1873
1874 /* Update the dummy statement so we can query the hash tables. */
1875 gimple_cond_set_code (dummy_cond, test_code);
1876 gimple_cond_set_lhs (dummy_cond, lhs);
1877 gimple_cond_set_rhs (dummy_cond, rhs);
1878 tree cached_lhs
1879 = avail_exprs_stack->lookup_avail_expr (dummy_cond, false, false);
1880
1881 /* If the lookup returned 1 (true), then the expression we
1882 queried was in the hash table. As a result there is only
1883 one value that makes the original conditional true. Update
1884 STMT accordingly. */
1885 if (cached_lhs && integer_onep (cached_lhs))
1886 {
1887 if (is_gimple_assign (stmt))
1888 {
1889 gimple_assign_set_rhs_code (stmt, EQ_EXPR);
1890 gimple_assign_set_rhs2 (stmt, rhs);
1891 gimple_set_modified (stmt, true);
1892 }
1893 else
1894 {
1895 gimple_set_modified (stmt, true);
1896 gimple_cond_set_code (as_a <gcond *> (stmt), EQ_EXPR);
1897 gimple_cond_set_rhs (as_a <gcond *> (stmt), rhs);
1898 gimple_set_modified (stmt, true);
1899 }
1900 }
1901 }
1902 }
1903 }
1904
1905 /* Optimize the statement in block BB pointed to by iterator SI.
1906
1907 We try to perform some simplistic global redundancy elimination and
1908 constant propagation:
1909
1910 1- To detect global redundancy, we keep track of expressions that have
1911 been computed in this block and its dominators. If we find that the
1912 same expression is computed more than once, we eliminate repeated
1913 computations by using the target of the first one.
1914
1915 2- Constant values and copy assignments. This is used to do very
1916 simplistic constant and copy propagation. When a constant or copy
1917 assignment is found, we map the value on the RHS of the assignment to
1918 the variable in the LHS in the CONST_AND_COPIES table.
1919
1920 3- Very simple redundant store elimination is performed.
1921
1922 4- We can simpify a condition to a constant or from a relational
1923 condition to an equality condition. */
1924
1925 edge
optimize_stmt(basic_block bb,gimple_stmt_iterator si)1926 dom_opt_dom_walker::optimize_stmt (basic_block bb, gimple_stmt_iterator si)
1927 {
1928 gimple *stmt, *old_stmt;
1929 bool may_optimize_p;
1930 bool modified_p = false;
1931 bool was_noreturn;
1932 edge retval = NULL;
1933
1934 old_stmt = stmt = gsi_stmt (si);
1935 was_noreturn = is_gimple_call (stmt) && gimple_call_noreturn_p (stmt);
1936
1937 if (dump_file && (dump_flags & TDF_DETAILS))
1938 {
1939 fprintf (dump_file, "Optimizing statement ");
1940 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1941 }
1942
1943 update_stmt_if_modified (stmt);
1944 opt_stats.num_stmts++;
1945
1946 /* Const/copy propagate into USES, VUSES and the RHS of VDEFs. */
1947 cprop_into_stmt (stmt);
1948
1949 /* If the statement has been modified with constant replacements,
1950 fold its RHS before checking for redundant computations. */
1951 if (gimple_modified_p (stmt))
1952 {
1953 tree rhs = NULL;
1954
1955 /* Try to fold the statement making sure that STMT is kept
1956 up to date. */
1957 if (fold_stmt (&si))
1958 {
1959 stmt = gsi_stmt (si);
1960 gimple_set_modified (stmt, true);
1961
1962 if (dump_file && (dump_flags & TDF_DETAILS))
1963 {
1964 fprintf (dump_file, " Folded to: ");
1965 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1966 }
1967 }
1968
1969 /* We only need to consider cases that can yield a gimple operand. */
1970 if (gimple_assign_single_p (stmt))
1971 rhs = gimple_assign_rhs1 (stmt);
1972 else if (gimple_code (stmt) == GIMPLE_GOTO)
1973 rhs = gimple_goto_dest (stmt);
1974 else if (gswitch *swtch_stmt = dyn_cast <gswitch *> (stmt))
1975 /* This should never be an ADDR_EXPR. */
1976 rhs = gimple_switch_index (swtch_stmt);
1977
1978 if (rhs && TREE_CODE (rhs) == ADDR_EXPR)
1979 recompute_tree_invariant_for_addr_expr (rhs);
1980
1981 /* Indicate that maybe_clean_or_replace_eh_stmt needs to be called,
1982 even if fold_stmt updated the stmt already and thus cleared
1983 gimple_modified_p flag on it. */
1984 modified_p = true;
1985 }
1986
1987 /* Check for redundant computations. Do this optimization only
1988 for assignments that have no volatile ops and conditionals. */
1989 may_optimize_p = (!gimple_has_side_effects (stmt)
1990 && (is_gimple_assign (stmt)
1991 || (is_gimple_call (stmt)
1992 && gimple_call_lhs (stmt) != NULL_TREE)
1993 || gimple_code (stmt) == GIMPLE_COND
1994 || gimple_code (stmt) == GIMPLE_SWITCH));
1995
1996 if (may_optimize_p)
1997 {
1998 if (gimple_code (stmt) == GIMPLE_CALL)
1999 {
2000 /* Resolve __builtin_constant_p. If it hasn't been
2001 folded to integer_one_node by now, it's fairly
2002 certain that the value simply isn't constant. */
2003 tree callee = gimple_call_fndecl (stmt);
2004 if (callee
2005 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL
2006 && DECL_FUNCTION_CODE (callee) == BUILT_IN_CONSTANT_P)
2007 {
2008 propagate_tree_value_into_stmt (&si, integer_zero_node);
2009 stmt = gsi_stmt (si);
2010 }
2011 }
2012
2013 if (gimple_code (stmt) == GIMPLE_COND)
2014 {
2015 tree lhs = gimple_cond_lhs (stmt);
2016 tree rhs = gimple_cond_rhs (stmt);
2017
2018 /* If the LHS has a range [0..1] and the RHS has a range ~[0..1],
2019 then this conditional is computable at compile time. We can just
2020 shove either 0 or 1 into the LHS, mark the statement as modified
2021 and all the right things will just happen below.
2022
2023 Note this would apply to any case where LHS has a range
2024 narrower than its type implies and RHS is outside that
2025 narrower range. Future work. */
2026 if (TREE_CODE (lhs) == SSA_NAME
2027 && ssa_name_has_boolean_range (lhs)
2028 && TREE_CODE (rhs) == INTEGER_CST
2029 && ! (integer_zerop (rhs) || integer_onep (rhs)))
2030 {
2031 gimple_cond_set_lhs (as_a <gcond *> (stmt),
2032 fold_convert (TREE_TYPE (lhs),
2033 integer_zero_node));
2034 gimple_set_modified (stmt, true);
2035 }
2036 else if (TREE_CODE (lhs) == SSA_NAME)
2037 {
2038 /* Exploiting EVRP data is not yet fully integrated into DOM
2039 but we need to do something for this case to avoid regressing
2040 udr4.f90 and new1.C which have unexecutable blocks with
2041 undefined behavior that get diagnosed if they're left in the
2042 IL because we've attached range information to new
2043 SSA_NAMES. */
2044 update_stmt_if_modified (stmt);
2045 edge taken_edge = NULL;
2046 evrp_range_analyzer.vrp_visit_cond_stmt (as_a <gcond *> (stmt),
2047 &taken_edge);
2048 if (taken_edge)
2049 {
2050 if (taken_edge->flags & EDGE_TRUE_VALUE)
2051 gimple_cond_make_true (as_a <gcond *> (stmt));
2052 else if (taken_edge->flags & EDGE_FALSE_VALUE)
2053 gimple_cond_make_false (as_a <gcond *> (stmt));
2054 else
2055 gcc_unreachable ();
2056 gimple_set_modified (stmt, true);
2057 update_stmt (stmt);
2058 cfg_altered = true;
2059 return taken_edge;
2060 }
2061 }
2062 }
2063
2064 update_stmt_if_modified (stmt);
2065 eliminate_redundant_computations (&si, m_const_and_copies,
2066 m_avail_exprs_stack);
2067 stmt = gsi_stmt (si);
2068
2069 /* Perform simple redundant store elimination. */
2070 if (gimple_assign_single_p (stmt)
2071 && TREE_CODE (gimple_assign_lhs (stmt)) != SSA_NAME)
2072 {
2073 tree lhs = gimple_assign_lhs (stmt);
2074 tree rhs = gimple_assign_rhs1 (stmt);
2075 tree cached_lhs;
2076 gassign *new_stmt;
2077 rhs = dom_valueize (rhs);
2078 /* Build a new statement with the RHS and LHS exchanged. */
2079 if (TREE_CODE (rhs) == SSA_NAME)
2080 {
2081 gimple *defstmt = SSA_NAME_DEF_STMT (rhs);
2082 new_stmt = gimple_build_assign (rhs, lhs);
2083 SSA_NAME_DEF_STMT (rhs) = defstmt;
2084 }
2085 else
2086 new_stmt = gimple_build_assign (rhs, lhs);
2087 gimple_set_vuse (new_stmt, gimple_vuse (stmt));
2088 cached_lhs = m_avail_exprs_stack->lookup_avail_expr (new_stmt, false,
2089 false);
2090 if (cached_lhs && operand_equal_p (rhs, cached_lhs, 0))
2091 {
2092 basic_block bb = gimple_bb (stmt);
2093 unlink_stmt_vdef (stmt);
2094 if (gsi_remove (&si, true))
2095 {
2096 bitmap_set_bit (need_eh_cleanup, bb->index);
2097 if (dump_file && (dump_flags & TDF_DETAILS))
2098 fprintf (dump_file, " Flagged to clear EH edges.\n");
2099 }
2100 release_defs (stmt);
2101 return retval;
2102 }
2103 }
2104
2105 /* If this statement was not redundant, we may still be able to simplify
2106 it, which may in turn allow other part of DOM or other passes to do
2107 a better job. */
2108 test_for_singularity (stmt, m_dummy_cond, m_avail_exprs_stack);
2109 }
2110
2111 /* Record any additional equivalences created by this statement. */
2112 if (is_gimple_assign (stmt))
2113 record_equivalences_from_stmt (stmt, may_optimize_p, m_avail_exprs_stack);
2114
2115 /* If STMT is a COND_EXPR or SWITCH_EXPR and it was modified, then we may
2116 know where it goes. */
2117 if (gimple_modified_p (stmt) || modified_p)
2118 {
2119 tree val = NULL;
2120
2121 if (gimple_code (stmt) == GIMPLE_COND)
2122 val = fold_binary_loc (gimple_location (stmt),
2123 gimple_cond_code (stmt), boolean_type_node,
2124 gimple_cond_lhs (stmt),
2125 gimple_cond_rhs (stmt));
2126 else if (gswitch *swtch_stmt = dyn_cast <gswitch *> (stmt))
2127 val = gimple_switch_index (swtch_stmt);
2128
2129 if (val && TREE_CODE (val) == INTEGER_CST)
2130 {
2131 retval = find_taken_edge (bb, val);
2132 if (retval)
2133 {
2134 /* Fix the condition to be either true or false. */
2135 if (gimple_code (stmt) == GIMPLE_COND)
2136 {
2137 if (integer_zerop (val))
2138 gimple_cond_make_false (as_a <gcond *> (stmt));
2139 else if (integer_onep (val))
2140 gimple_cond_make_true (as_a <gcond *> (stmt));
2141 else
2142 gcc_unreachable ();
2143
2144 gimple_set_modified (stmt, true);
2145 }
2146
2147 /* Further simplifications may be possible. */
2148 cfg_altered = true;
2149 }
2150 }
2151
2152 update_stmt_if_modified (stmt);
2153
2154 /* If we simplified a statement in such a way as to be shown that it
2155 cannot trap, update the eh information and the cfg to match. */
2156 if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt))
2157 {
2158 bitmap_set_bit (need_eh_cleanup, bb->index);
2159 if (dump_file && (dump_flags & TDF_DETAILS))
2160 fprintf (dump_file, " Flagged to clear EH edges.\n");
2161 }
2162
2163 if (!was_noreturn
2164 && is_gimple_call (stmt) && gimple_call_noreturn_p (stmt))
2165 need_noreturn_fixup.safe_push (stmt);
2166 }
2167 return retval;
2168 }
2169