1 /* Generic SSA value propagation engine.
2 Copyright (C) 2004, 2005, 2006, 2007 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 it
8 under the terms of the GNU General Public License as published by the
9 Free Software Foundation; either version 2, or (at your option) any
10 later version.
11
12 GCC is distributed in the hope that it will be useful, but WITHOUT
13 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING. If not, write to the Free
19 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
20 02110-1301, USA. */
21
22 #include "config.h"
23 #include "system.h"
24 #include "coretypes.h"
25 #include "tm.h"
26 #include "tree.h"
27 #include "flags.h"
28 #include "rtl.h"
29 #include "tm_p.h"
30 #include "ggc.h"
31 #include "basic-block.h"
32 #include "output.h"
33 #include "expr.h"
34 #include "function.h"
35 #include "diagnostic.h"
36 #include "timevar.h"
37 #include "tree-dump.h"
38 #include "tree-flow.h"
39 #include "tree-pass.h"
40 #include "tree-ssa-propagate.h"
41 #include "langhooks.h"
42 #include "varray.h"
43 #include "vec.h"
44
45 /* This file implements a generic value propagation engine based on
46 the same propagation used by the SSA-CCP algorithm [1].
47
48 Propagation is performed by simulating the execution of every
49 statement that produces the value being propagated. Simulation
50 proceeds as follows:
51
52 1- Initially, all edges of the CFG are marked not executable and
53 the CFG worklist is seeded with all the statements in the entry
54 basic block (block 0).
55
56 2- Every statement S is simulated with a call to the call-back
57 function SSA_PROP_VISIT_STMT. This evaluation may produce 3
58 results:
59
60 SSA_PROP_NOT_INTERESTING: Statement S produces nothing of
61 interest and does not affect any of the work lists.
62
63 SSA_PROP_VARYING: The value produced by S cannot be determined
64 at compile time. Further simulation of S is not required.
65 If S is a conditional jump, all the outgoing edges for the
66 block are considered executable and added to the work
67 list.
68
69 SSA_PROP_INTERESTING: S produces a value that can be computed
70 at compile time. Its result can be propagated into the
71 statements that feed from S. Furthermore, if S is a
72 conditional jump, only the edge known to be taken is added
73 to the work list. Edges that are known not to execute are
74 never simulated.
75
76 3- PHI nodes are simulated with a call to SSA_PROP_VISIT_PHI. The
77 return value from SSA_PROP_VISIT_PHI has the same semantics as
78 described in #2.
79
80 4- Three work lists are kept. Statements are only added to these
81 lists if they produce one of SSA_PROP_INTERESTING or
82 SSA_PROP_VARYING.
83
84 CFG_BLOCKS contains the list of blocks to be simulated.
85 Blocks are added to this list if their incoming edges are
86 found executable.
87
88 VARYING_SSA_EDGES contains the list of statements that feed
89 from statements that produce an SSA_PROP_VARYING result.
90 These are simulated first to speed up processing.
91
92 INTERESTING_SSA_EDGES contains the list of statements that
93 feed from statements that produce an SSA_PROP_INTERESTING
94 result.
95
96 5- Simulation terminates when all three work lists are drained.
97
98 Before calling ssa_propagate, it is important to clear
99 DONT_SIMULATE_AGAIN for all the statements in the program that
100 should be simulated. This initialization allows an implementation
101 to specify which statements should never be simulated.
102
103 It is also important to compute def-use information before calling
104 ssa_propagate.
105
106 References:
107
108 [1] Constant propagation with conditional branches,
109 Wegman and Zadeck, ACM TOPLAS 13(2):181-210.
110
111 [2] Building an Optimizing Compiler,
112 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
113
114 [3] Advanced Compiler Design and Implementation,
115 Steven Muchnick, Morgan Kaufmann, 1997, Section 12.6 */
116
117 /* Function pointers used to parameterize the propagation engine. */
118 static ssa_prop_visit_stmt_fn ssa_prop_visit_stmt;
119 static ssa_prop_visit_phi_fn ssa_prop_visit_phi;
120
121 /* Use the TREE_DEPRECATED bitflag to mark statements that have been
122 added to one of the SSA edges worklists. This flag is used to
123 avoid visiting statements unnecessarily when draining an SSA edge
124 worklist. If while simulating a basic block, we find a statement with
125 STMT_IN_SSA_EDGE_WORKLIST set, we clear it to prevent SSA edge
126 processing from visiting it again. */
127 #define STMT_IN_SSA_EDGE_WORKLIST(T) TREE_DEPRECATED (T)
128
129 /* A bitmap to keep track of executable blocks in the CFG. */
130 static sbitmap executable_blocks;
131
132 /* Array of control flow edges on the worklist. */
133 static VEC(basic_block,heap) *cfg_blocks;
134
135 static unsigned int cfg_blocks_num = 0;
136 static int cfg_blocks_tail;
137 static int cfg_blocks_head;
138
139 static sbitmap bb_in_list;
140
141 /* Worklist of SSA edges which will need reexamination as their
142 definition has changed. SSA edges are def-use edges in the SSA
143 web. For each D-U edge, we store the target statement or PHI node
144 U. */
145 static GTY(()) VEC(tree,gc) *interesting_ssa_edges;
146
147 /* Identical to INTERESTING_SSA_EDGES. For performance reasons, the
148 list of SSA edges is split into two. One contains all SSA edges
149 who need to be reexamined because their lattice value changed to
150 varying (this worklist), and the other contains all other SSA edges
151 to be reexamined (INTERESTING_SSA_EDGES).
152
153 Since most values in the program are VARYING, the ideal situation
154 is to move them to that lattice value as quickly as possible.
155 Thus, it doesn't make sense to process any other type of lattice
156 value until all VARYING values are propagated fully, which is one
157 thing using the VARYING worklist achieves. In addition, if we
158 don't use a separate worklist for VARYING edges, we end up with
159 situations where lattice values move from
160 UNDEFINED->INTERESTING->VARYING instead of UNDEFINED->VARYING. */
161 static GTY(()) VEC(tree,gc) *varying_ssa_edges;
162
163
164 /* Return true if the block worklist empty. */
165
166 static inline bool
cfg_blocks_empty_p(void)167 cfg_blocks_empty_p (void)
168 {
169 return (cfg_blocks_num == 0);
170 }
171
172
173 /* Add a basic block to the worklist. The block must not be already
174 in the worklist, and it must not be the ENTRY or EXIT block. */
175
176 static void
cfg_blocks_add(basic_block bb)177 cfg_blocks_add (basic_block bb)
178 {
179 bool head = false;
180
181 gcc_assert (bb != ENTRY_BLOCK_PTR && bb != EXIT_BLOCK_PTR);
182 gcc_assert (!TEST_BIT (bb_in_list, bb->index));
183
184 if (cfg_blocks_empty_p ())
185 {
186 cfg_blocks_tail = cfg_blocks_head = 0;
187 cfg_blocks_num = 1;
188 }
189 else
190 {
191 cfg_blocks_num++;
192 if (cfg_blocks_num > VEC_length (basic_block, cfg_blocks))
193 {
194 /* We have to grow the array now. Adjust to queue to occupy
195 the full space of the original array. We do not need to
196 initialize the newly allocated portion of the array
197 because we keep track of CFG_BLOCKS_HEAD and
198 CFG_BLOCKS_HEAD. */
199 cfg_blocks_tail = VEC_length (basic_block, cfg_blocks);
200 cfg_blocks_head = 0;
201 VEC_safe_grow (basic_block, heap, cfg_blocks, 2 * cfg_blocks_tail);
202 }
203 /* Minor optimization: we prefer to see blocks with more
204 predecessors later, because there is more of a chance that
205 the incoming edges will be executable. */
206 else if (EDGE_COUNT (bb->preds)
207 >= EDGE_COUNT (VEC_index (basic_block, cfg_blocks,
208 cfg_blocks_head)->preds))
209 cfg_blocks_tail = ((cfg_blocks_tail + 1)
210 % VEC_length (basic_block, cfg_blocks));
211 else
212 {
213 if (cfg_blocks_head == 0)
214 cfg_blocks_head = VEC_length (basic_block, cfg_blocks);
215 --cfg_blocks_head;
216 head = true;
217 }
218 }
219
220 VEC_replace (basic_block, cfg_blocks,
221 head ? cfg_blocks_head : cfg_blocks_tail,
222 bb);
223 SET_BIT (bb_in_list, bb->index);
224 }
225
226
227 /* Remove a block from the worklist. */
228
229 static basic_block
cfg_blocks_get(void)230 cfg_blocks_get (void)
231 {
232 basic_block bb;
233
234 bb = VEC_index (basic_block, cfg_blocks, cfg_blocks_head);
235
236 gcc_assert (!cfg_blocks_empty_p ());
237 gcc_assert (bb);
238
239 cfg_blocks_head = ((cfg_blocks_head + 1)
240 % VEC_length (basic_block, cfg_blocks));
241 --cfg_blocks_num;
242 RESET_BIT (bb_in_list, bb->index);
243
244 return bb;
245 }
246
247
248 /* We have just defined a new value for VAR. If IS_VARYING is true,
249 add all immediate uses of VAR to VARYING_SSA_EDGES, otherwise add
250 them to INTERESTING_SSA_EDGES. */
251
252 static void
add_ssa_edge(tree var,bool is_varying)253 add_ssa_edge (tree var, bool is_varying)
254 {
255 imm_use_iterator iter;
256 use_operand_p use_p;
257
258 FOR_EACH_IMM_USE_FAST (use_p, iter, var)
259 {
260 tree use_stmt = USE_STMT (use_p);
261
262 if (!DONT_SIMULATE_AGAIN (use_stmt)
263 && !STMT_IN_SSA_EDGE_WORKLIST (use_stmt))
264 {
265 STMT_IN_SSA_EDGE_WORKLIST (use_stmt) = 1;
266 if (is_varying)
267 VEC_safe_push (tree, gc, varying_ssa_edges, use_stmt);
268 else
269 VEC_safe_push (tree, gc, interesting_ssa_edges, use_stmt);
270 }
271 }
272 }
273
274
275 /* Add edge E to the control flow worklist. */
276
277 static void
add_control_edge(edge e)278 add_control_edge (edge e)
279 {
280 basic_block bb = e->dest;
281 if (bb == EXIT_BLOCK_PTR)
282 return;
283
284 /* If the edge had already been executed, skip it. */
285 if (e->flags & EDGE_EXECUTABLE)
286 return;
287
288 e->flags |= EDGE_EXECUTABLE;
289
290 /* If the block is already in the list, we're done. */
291 if (TEST_BIT (bb_in_list, bb->index))
292 return;
293
294 cfg_blocks_add (bb);
295
296 if (dump_file && (dump_flags & TDF_DETAILS))
297 fprintf (dump_file, "Adding Destination of edge (%d -> %d) to worklist\n\n",
298 e->src->index, e->dest->index);
299 }
300
301
302 /* Simulate the execution of STMT and update the work lists accordingly. */
303
304 static void
simulate_stmt(tree stmt)305 simulate_stmt (tree stmt)
306 {
307 enum ssa_prop_result val = SSA_PROP_NOT_INTERESTING;
308 edge taken_edge = NULL;
309 tree output_name = NULL_TREE;
310
311 /* Don't bother visiting statements that are already
312 considered varying by the propagator. */
313 if (DONT_SIMULATE_AGAIN (stmt))
314 return;
315
316 if (TREE_CODE (stmt) == PHI_NODE)
317 {
318 val = ssa_prop_visit_phi (stmt);
319 output_name = PHI_RESULT (stmt);
320 }
321 else
322 val = ssa_prop_visit_stmt (stmt, &taken_edge, &output_name);
323
324 if (val == SSA_PROP_VARYING)
325 {
326 DONT_SIMULATE_AGAIN (stmt) = 1;
327
328 /* If the statement produced a new varying value, add the SSA
329 edges coming out of OUTPUT_NAME. */
330 if (output_name)
331 add_ssa_edge (output_name, true);
332
333 /* If STMT transfers control out of its basic block, add
334 all outgoing edges to the work list. */
335 if (stmt_ends_bb_p (stmt))
336 {
337 edge e;
338 edge_iterator ei;
339 basic_block bb = bb_for_stmt (stmt);
340 FOR_EACH_EDGE (e, ei, bb->succs)
341 add_control_edge (e);
342 }
343 }
344 else if (val == SSA_PROP_INTERESTING)
345 {
346 /* If the statement produced new value, add the SSA edges coming
347 out of OUTPUT_NAME. */
348 if (output_name)
349 add_ssa_edge (output_name, false);
350
351 /* If we know which edge is going to be taken out of this block,
352 add it to the CFG work list. */
353 if (taken_edge)
354 add_control_edge (taken_edge);
355 }
356 }
357
358 /* Process an SSA edge worklist. WORKLIST is the SSA edge worklist to
359 drain. This pops statements off the given WORKLIST and processes
360 them until there are no more statements on WORKLIST.
361 We take a pointer to WORKLIST because it may be reallocated when an
362 SSA edge is added to it in simulate_stmt. */
363
364 static void
process_ssa_edge_worklist(VEC (tree,gc)** worklist)365 process_ssa_edge_worklist (VEC(tree,gc) **worklist)
366 {
367 /* Drain the entire worklist. */
368 while (VEC_length (tree, *worklist) > 0)
369 {
370 basic_block bb;
371
372 /* Pull the statement to simulate off the worklist. */
373 tree stmt = VEC_pop (tree, *worklist);
374
375 /* If this statement was already visited by simulate_block, then
376 we don't need to visit it again here. */
377 if (!STMT_IN_SSA_EDGE_WORKLIST (stmt))
378 continue;
379
380 /* STMT is no longer in a worklist. */
381 STMT_IN_SSA_EDGE_WORKLIST (stmt) = 0;
382
383 if (dump_file && (dump_flags & TDF_DETAILS))
384 {
385 fprintf (dump_file, "\nSimulating statement (from ssa_edges): ");
386 print_generic_stmt (dump_file, stmt, dump_flags);
387 }
388
389 bb = bb_for_stmt (stmt);
390
391 /* PHI nodes are always visited, regardless of whether or not
392 the destination block is executable. Otherwise, visit the
393 statement only if its block is marked executable. */
394 if (TREE_CODE (stmt) == PHI_NODE
395 || TEST_BIT (executable_blocks, bb->index))
396 simulate_stmt (stmt);
397 }
398 }
399
400
401 /* Simulate the execution of BLOCK. Evaluate the statement associated
402 with each variable reference inside the block. */
403
404 static void
simulate_block(basic_block block)405 simulate_block (basic_block block)
406 {
407 tree phi;
408
409 /* There is nothing to do for the exit block. */
410 if (block == EXIT_BLOCK_PTR)
411 return;
412
413 if (dump_file && (dump_flags & TDF_DETAILS))
414 fprintf (dump_file, "\nSimulating block %d\n", block->index);
415
416 /* Always simulate PHI nodes, even if we have simulated this block
417 before. */
418 for (phi = phi_nodes (block); phi; phi = PHI_CHAIN (phi))
419 simulate_stmt (phi);
420
421 /* If this is the first time we've simulated this block, then we
422 must simulate each of its statements. */
423 if (!TEST_BIT (executable_blocks, block->index))
424 {
425 block_stmt_iterator j;
426 unsigned int normal_edge_count;
427 edge e, normal_edge;
428 edge_iterator ei;
429
430 /* Note that we have simulated this block. */
431 SET_BIT (executable_blocks, block->index);
432
433 for (j = bsi_start (block); !bsi_end_p (j); bsi_next (&j))
434 {
435 tree stmt = bsi_stmt (j);
436
437 /* If this statement is already in the worklist then
438 "cancel" it. The reevaluation implied by the worklist
439 entry will produce the same value we generate here and
440 thus reevaluating it again from the worklist is
441 pointless. */
442 if (STMT_IN_SSA_EDGE_WORKLIST (stmt))
443 STMT_IN_SSA_EDGE_WORKLIST (stmt) = 0;
444
445 simulate_stmt (stmt);
446 }
447
448 /* We can not predict when abnormal edges will be executed, so
449 once a block is considered executable, we consider any
450 outgoing abnormal edges as executable.
451
452 At the same time, if this block has only one successor that is
453 reached by non-abnormal edges, then add that successor to the
454 worklist. */
455 normal_edge_count = 0;
456 normal_edge = NULL;
457 FOR_EACH_EDGE (e, ei, block->succs)
458 {
459 if (e->flags & EDGE_ABNORMAL)
460 add_control_edge (e);
461 else
462 {
463 normal_edge_count++;
464 normal_edge = e;
465 }
466 }
467
468 if (normal_edge_count == 1)
469 add_control_edge (normal_edge);
470 }
471 }
472
473
474 /* Initialize local data structures and work lists. */
475
476 static void
ssa_prop_init(void)477 ssa_prop_init (void)
478 {
479 edge e;
480 edge_iterator ei;
481 basic_block bb;
482 size_t i;
483
484 /* Worklists of SSA edges. */
485 interesting_ssa_edges = VEC_alloc (tree, gc, 20);
486 varying_ssa_edges = VEC_alloc (tree, gc, 20);
487
488 executable_blocks = sbitmap_alloc (last_basic_block);
489 sbitmap_zero (executable_blocks);
490
491 bb_in_list = sbitmap_alloc (last_basic_block);
492 sbitmap_zero (bb_in_list);
493
494 if (dump_file && (dump_flags & TDF_DETAILS))
495 dump_immediate_uses (dump_file);
496
497 cfg_blocks = VEC_alloc (basic_block, heap, 20);
498 VEC_safe_grow (basic_block, heap, cfg_blocks, 20);
499
500 /* Initialize the values for every SSA_NAME. */
501 for (i = 1; i < num_ssa_names; i++)
502 if (ssa_name (i))
503 SSA_NAME_VALUE (ssa_name (i)) = NULL_TREE;
504
505 /* Initially assume that every edge in the CFG is not executable.
506 (including the edges coming out of ENTRY_BLOCK_PTR). */
507 FOR_ALL_BB (bb)
508 {
509 block_stmt_iterator si;
510
511 for (si = bsi_start (bb); !bsi_end_p (si); bsi_next (&si))
512 STMT_IN_SSA_EDGE_WORKLIST (bsi_stmt (si)) = 0;
513
514 FOR_EACH_EDGE (e, ei, bb->succs)
515 e->flags &= ~EDGE_EXECUTABLE;
516 }
517
518 /* Seed the algorithm by adding the successors of the entry block to the
519 edge worklist. */
520 FOR_EACH_EDGE (e, ei, ENTRY_BLOCK_PTR->succs)
521 add_control_edge (e);
522 }
523
524
525 /* Free allocated storage. */
526
527 static void
ssa_prop_fini(void)528 ssa_prop_fini (void)
529 {
530 VEC_free (tree, gc, interesting_ssa_edges);
531 VEC_free (tree, gc, varying_ssa_edges);
532 VEC_free (basic_block, heap, cfg_blocks);
533 cfg_blocks = NULL;
534 sbitmap_free (bb_in_list);
535 sbitmap_free (executable_blocks);
536 }
537
538
539 /* Get the main expression from statement STMT. */
540
541 tree
get_rhs(tree stmt)542 get_rhs (tree stmt)
543 {
544 enum tree_code code = TREE_CODE (stmt);
545
546 switch (code)
547 {
548 case RETURN_EXPR:
549 stmt = TREE_OPERAND (stmt, 0);
550 if (!stmt || TREE_CODE (stmt) != MODIFY_EXPR)
551 return stmt;
552 /* FALLTHRU */
553
554 case MODIFY_EXPR:
555 stmt = TREE_OPERAND (stmt, 1);
556 if (TREE_CODE (stmt) == WITH_SIZE_EXPR)
557 return TREE_OPERAND (stmt, 0);
558 else
559 return stmt;
560
561 case COND_EXPR:
562 return COND_EXPR_COND (stmt);
563 case SWITCH_EXPR:
564 return SWITCH_COND (stmt);
565 case GOTO_EXPR:
566 return GOTO_DESTINATION (stmt);
567 case LABEL_EXPR:
568 return LABEL_EXPR_LABEL (stmt);
569
570 default:
571 return stmt;
572 }
573 }
574
575
576 /* Set the main expression of *STMT_P to EXPR. If EXPR is not a valid
577 GIMPLE expression no changes are done and the function returns
578 false. */
579
580 bool
set_rhs(tree * stmt_p,tree expr)581 set_rhs (tree *stmt_p, tree expr)
582 {
583 tree stmt = *stmt_p, op;
584 enum tree_code code = TREE_CODE (expr);
585 stmt_ann_t ann;
586 tree var;
587 ssa_op_iter iter;
588
589 /* Verify the constant folded result is valid gimple. */
590 if (TREE_CODE_CLASS (code) == tcc_binary)
591 {
592 if (!is_gimple_val (TREE_OPERAND (expr, 0))
593 || !is_gimple_val (TREE_OPERAND (expr, 1)))
594 return false;
595 }
596 else if (TREE_CODE_CLASS (code) == tcc_unary)
597 {
598 if (!is_gimple_val (TREE_OPERAND (expr, 0)))
599 return false;
600 }
601 else if (code == ADDR_EXPR)
602 {
603 if (TREE_CODE (TREE_OPERAND (expr, 0)) == ARRAY_REF
604 && !is_gimple_val (TREE_OPERAND (TREE_OPERAND (expr, 0), 1)))
605 return false;
606 }
607 else if (code == COMPOUND_EXPR
608 || code == MODIFY_EXPR)
609 return false;
610
611 if (EXPR_HAS_LOCATION (stmt)
612 && EXPR_P (expr)
613 && ! EXPR_HAS_LOCATION (expr)
614 && TREE_SIDE_EFFECTS (expr)
615 && TREE_CODE (expr) != LABEL_EXPR)
616 SET_EXPR_LOCATION (expr, EXPR_LOCATION (stmt));
617
618 switch (TREE_CODE (stmt))
619 {
620 case RETURN_EXPR:
621 op = TREE_OPERAND (stmt, 0);
622 if (TREE_CODE (op) != MODIFY_EXPR)
623 {
624 TREE_OPERAND (stmt, 0) = expr;
625 break;
626 }
627 stmt = op;
628 /* FALLTHRU */
629
630 case MODIFY_EXPR:
631 op = TREE_OPERAND (stmt, 1);
632 if (TREE_CODE (op) == WITH_SIZE_EXPR)
633 stmt = op;
634 TREE_OPERAND (stmt, 1) = expr;
635 break;
636
637 case COND_EXPR:
638 if (!is_gimple_condexpr (expr))
639 return false;
640 COND_EXPR_COND (stmt) = expr;
641 break;
642 case SWITCH_EXPR:
643 SWITCH_COND (stmt) = expr;
644 break;
645 case GOTO_EXPR:
646 GOTO_DESTINATION (stmt) = expr;
647 break;
648 case LABEL_EXPR:
649 LABEL_EXPR_LABEL (stmt) = expr;
650 break;
651
652 default:
653 /* Replace the whole statement with EXPR. If EXPR has no side
654 effects, then replace *STMT_P with an empty statement. */
655 ann = stmt_ann (stmt);
656 *stmt_p = TREE_SIDE_EFFECTS (expr) ? expr : build_empty_stmt ();
657 (*stmt_p)->common.ann = (tree_ann_t) ann;
658
659 if (in_ssa_p
660 && TREE_SIDE_EFFECTS (expr))
661 {
662 /* Fix all the SSA_NAMEs created by *STMT_P to point to its new
663 replacement. */
664 FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_ALL_DEFS)
665 {
666 if (TREE_CODE (var) == SSA_NAME)
667 SSA_NAME_DEF_STMT (var) = *stmt_p;
668 }
669 }
670 break;
671 }
672
673 return true;
674 }
675
676
677 /* Entry point to the propagation engine.
678
679 VISIT_STMT is called for every statement visited.
680 VISIT_PHI is called for every PHI node visited. */
681
682 void
ssa_propagate(ssa_prop_visit_stmt_fn visit_stmt,ssa_prop_visit_phi_fn visit_phi)683 ssa_propagate (ssa_prop_visit_stmt_fn visit_stmt,
684 ssa_prop_visit_phi_fn visit_phi)
685 {
686 ssa_prop_visit_stmt = visit_stmt;
687 ssa_prop_visit_phi = visit_phi;
688
689 ssa_prop_init ();
690
691 /* Iterate until the worklists are empty. */
692 while (!cfg_blocks_empty_p ()
693 || VEC_length (tree, interesting_ssa_edges) > 0
694 || VEC_length (tree, varying_ssa_edges) > 0)
695 {
696 if (!cfg_blocks_empty_p ())
697 {
698 /* Pull the next block to simulate off the worklist. */
699 basic_block dest_block = cfg_blocks_get ();
700 simulate_block (dest_block);
701 }
702
703 /* In order to move things to varying as quickly as
704 possible,process the VARYING_SSA_EDGES worklist first. */
705 process_ssa_edge_worklist (&varying_ssa_edges);
706
707 /* Now process the INTERESTING_SSA_EDGES worklist. */
708 process_ssa_edge_worklist (&interesting_ssa_edges);
709 }
710
711 ssa_prop_fini ();
712 }
713
714
715 /* Return the first V_MAY_DEF or V_MUST_DEF operand for STMT. */
716
717 tree
first_vdef(tree stmt)718 first_vdef (tree stmt)
719 {
720 ssa_op_iter iter;
721 tree op;
722
723 /* Simply return the first operand we arrive at. */
724 FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_VIRTUAL_DEFS)
725 return (op);
726
727 gcc_unreachable ();
728 }
729
730
731 /* Return true if STMT is of the form 'LHS = mem_ref', where 'mem_ref'
732 is a non-volatile pointer dereference, a structure reference or a
733 reference to a single _DECL. Ignore volatile memory references
734 because they are not interesting for the optimizers. */
735
736 bool
stmt_makes_single_load(tree stmt)737 stmt_makes_single_load (tree stmt)
738 {
739 tree rhs;
740
741 if (TREE_CODE (stmt) != MODIFY_EXPR)
742 return false;
743
744 if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VMAYDEF|SSA_OP_VUSE))
745 return false;
746
747 rhs = TREE_OPERAND (stmt, 1);
748 STRIP_NOPS (rhs);
749
750 return (!TREE_THIS_VOLATILE (rhs)
751 && (DECL_P (rhs)
752 || REFERENCE_CLASS_P (rhs)));
753 }
754
755
756 /* Return true if STMT is of the form 'mem_ref = RHS', where 'mem_ref'
757 is a non-volatile pointer dereference, a structure reference or a
758 reference to a single _DECL. Ignore volatile memory references
759 because they are not interesting for the optimizers. */
760
761 bool
stmt_makes_single_store(tree stmt)762 stmt_makes_single_store (tree stmt)
763 {
764 tree lhs;
765
766 if (TREE_CODE (stmt) != MODIFY_EXPR)
767 return false;
768
769 if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VMAYDEF|SSA_OP_VMUSTDEF))
770 return false;
771
772 lhs = TREE_OPERAND (stmt, 0);
773 STRIP_NOPS (lhs);
774
775 return (!TREE_THIS_VOLATILE (lhs)
776 && (DECL_P (lhs)
777 || REFERENCE_CLASS_P (lhs)));
778 }
779
780
781 /* If STMT makes a single memory load and all the virtual use operands
782 have the same value in array VALUES, return it. Otherwise, return
783 NULL. */
784
785 prop_value_t *
get_value_loaded_by(tree stmt,prop_value_t * values)786 get_value_loaded_by (tree stmt, prop_value_t *values)
787 {
788 ssa_op_iter i;
789 tree vuse;
790 prop_value_t *prev_val = NULL;
791 prop_value_t *val = NULL;
792
793 FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, i, SSA_OP_VIRTUAL_USES)
794 {
795 val = &values[SSA_NAME_VERSION (vuse)];
796 if (prev_val && prev_val->value != val->value)
797 return NULL;
798 prev_val = val;
799 }
800
801 return val;
802 }
803
804
805 /* Propagation statistics. */
806 struct prop_stats_d
807 {
808 long num_const_prop;
809 long num_copy_prop;
810 long num_pred_folded;
811 };
812
813 static struct prop_stats_d prop_stats;
814
815 /* Replace USE references in statement STMT with the values stored in
816 PROP_VALUE. Return true if at least one reference was replaced. If
817 REPLACED_ADDRESSES_P is given, it will be set to true if an address
818 constant was replaced. */
819
820 bool
replace_uses_in(tree stmt,bool * replaced_addresses_p,prop_value_t * prop_value)821 replace_uses_in (tree stmt, bool *replaced_addresses_p,
822 prop_value_t *prop_value)
823 {
824 bool replaced = false;
825 use_operand_p use;
826 ssa_op_iter iter;
827
828 FOR_EACH_SSA_USE_OPERAND (use, stmt, iter, SSA_OP_USE)
829 {
830 tree tuse = USE_FROM_PTR (use);
831 tree val = prop_value[SSA_NAME_VERSION (tuse)].value;
832
833 if (val == tuse || val == NULL_TREE)
834 continue;
835
836 if (TREE_CODE (stmt) == ASM_EXPR
837 && !may_propagate_copy_into_asm (tuse))
838 continue;
839
840 if (!may_propagate_copy (tuse, val))
841 continue;
842
843 if (TREE_CODE (val) != SSA_NAME)
844 prop_stats.num_const_prop++;
845 else
846 prop_stats.num_copy_prop++;
847
848 propagate_value (use, val);
849
850 replaced = true;
851 if (POINTER_TYPE_P (TREE_TYPE (tuse)) && replaced_addresses_p)
852 *replaced_addresses_p = true;
853 }
854
855 return replaced;
856 }
857
858
859 /* Replace the VUSE references in statement STMT with the values
860 stored in PROP_VALUE. Return true if a reference was replaced. If
861 REPLACED_ADDRESSES_P is given, it will be set to true if an address
862 constant was replaced.
863
864 Replacing VUSE operands is slightly more complex than replacing
865 regular USEs. We are only interested in two types of replacements
866 here:
867
868 1- If the value to be replaced is a constant or an SSA name for a
869 GIMPLE register, then we are making a copy/constant propagation
870 from a memory store. For instance,
871
872 # a_3 = V_MAY_DEF <a_2>
873 a.b = x_1;
874 ...
875 # VUSE <a_3>
876 y_4 = a.b;
877
878 This replacement is only possible iff STMT is an assignment
879 whose RHS is identical to the LHS of the statement that created
880 the VUSE(s) that we are replacing. Otherwise, we may do the
881 wrong replacement:
882
883 # a_3 = V_MAY_DEF <a_2>
884 # b_5 = V_MAY_DEF <b_4>
885 *p = 10;
886 ...
887 # VUSE <b_5>
888 x_8 = b;
889
890 Even though 'b_5' acquires the value '10' during propagation,
891 there is no way for the propagator to tell whether the
892 replacement is correct in every reached use, because values are
893 computed at definition sites. Therefore, when doing final
894 substitution of propagated values, we have to check each use
895 site. Since the RHS of STMT ('b') is different from the LHS of
896 the originating statement ('*p'), we cannot replace 'b' with
897 '10'.
898
899 Similarly, when merging values from PHI node arguments,
900 propagators need to take care not to merge the same values
901 stored in different locations:
902
903 if (...)
904 # a_3 = V_MAY_DEF <a_2>
905 a.b = 3;
906 else
907 # a_4 = V_MAY_DEF <a_2>
908 a.c = 3;
909 # a_5 = PHI <a_3, a_4>
910
911 It would be wrong to propagate '3' into 'a_5' because that
912 operation merges two stores to different memory locations.
913
914
915 2- If the value to be replaced is an SSA name for a virtual
916 register, then we simply replace each VUSE operand with its
917 value from PROP_VALUE. This is the same replacement done by
918 replace_uses_in. */
919
920 static bool
replace_vuses_in(tree stmt,bool * replaced_addresses_p,prop_value_t * prop_value)921 replace_vuses_in (tree stmt, bool *replaced_addresses_p,
922 prop_value_t *prop_value)
923 {
924 bool replaced = false;
925 ssa_op_iter iter;
926 use_operand_p vuse;
927
928 if (stmt_makes_single_load (stmt))
929 {
930 /* If STMT is an assignment whose RHS is a single memory load,
931 see if we are trying to propagate a constant or a GIMPLE
932 register (case #1 above). */
933 prop_value_t *val = get_value_loaded_by (stmt, prop_value);
934 tree rhs = TREE_OPERAND (stmt, 1);
935
936 if (val
937 && val->value
938 && (is_gimple_reg (val->value)
939 || is_gimple_min_invariant (val->value))
940 && simple_cst_equal (rhs, val->mem_ref) == 1)
941
942 {
943 /* If we are replacing a constant address, inform our
944 caller. */
945 if (TREE_CODE (val->value) != SSA_NAME
946 && POINTER_TYPE_P (TREE_TYPE (TREE_OPERAND (stmt, 1)))
947 && replaced_addresses_p)
948 *replaced_addresses_p = true;
949
950 /* We can only perform the substitution if the load is done
951 from the same memory location as the original store.
952 Since we already know that there are no intervening
953 stores between DEF_STMT and STMT, we only need to check
954 that the RHS of STMT is the same as the memory reference
955 propagated together with the value. */
956 TREE_OPERAND (stmt, 1) = val->value;
957
958 if (TREE_CODE (val->value) != SSA_NAME)
959 prop_stats.num_const_prop++;
960 else
961 prop_stats.num_copy_prop++;
962
963 /* Since we have replaced the whole RHS of STMT, there
964 is no point in checking the other VUSEs, as they will
965 all have the same value. */
966 return true;
967 }
968 }
969
970 /* Otherwise, the values for every VUSE operand must be other
971 SSA_NAMEs that can be propagated into STMT. */
972 FOR_EACH_SSA_USE_OPERAND (vuse, stmt, iter, SSA_OP_VIRTUAL_USES)
973 {
974 tree var = USE_FROM_PTR (vuse);
975 tree val = prop_value[SSA_NAME_VERSION (var)].value;
976
977 if (val == NULL_TREE || var == val)
978 continue;
979
980 /* Constants and copies propagated between real and virtual
981 operands are only possible in the cases handled above. They
982 should be ignored in any other context. */
983 if (is_gimple_min_invariant (val) || is_gimple_reg (val))
984 continue;
985
986 propagate_value (vuse, val);
987 prop_stats.num_copy_prop++;
988 replaced = true;
989 }
990
991 return replaced;
992 }
993
994
995 /* Replace propagated values into all the arguments for PHI using the
996 values from PROP_VALUE. */
997
998 static void
replace_phi_args_in(tree phi,prop_value_t * prop_value)999 replace_phi_args_in (tree phi, prop_value_t *prop_value)
1000 {
1001 int i;
1002 bool replaced = false;
1003 tree prev_phi = NULL;
1004
1005 if (dump_file && (dump_flags & TDF_DETAILS))
1006 prev_phi = unshare_expr (phi);
1007
1008 for (i = 0; i < PHI_NUM_ARGS (phi); i++)
1009 {
1010 tree arg = PHI_ARG_DEF (phi, i);
1011
1012 if (TREE_CODE (arg) == SSA_NAME)
1013 {
1014 tree val = prop_value[SSA_NAME_VERSION (arg)].value;
1015
1016 if (val && val != arg && may_propagate_copy (arg, val))
1017 {
1018 if (TREE_CODE (val) != SSA_NAME)
1019 prop_stats.num_const_prop++;
1020 else
1021 prop_stats.num_copy_prop++;
1022
1023 propagate_value (PHI_ARG_DEF_PTR (phi, i), val);
1024 replaced = true;
1025
1026 /* If we propagated a copy and this argument flows
1027 through an abnormal edge, update the replacement
1028 accordingly. */
1029 if (TREE_CODE (val) == SSA_NAME
1030 && PHI_ARG_EDGE (phi, i)->flags & EDGE_ABNORMAL)
1031 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (val) = 1;
1032 }
1033 }
1034 }
1035
1036 if (replaced && dump_file && (dump_flags & TDF_DETAILS))
1037 {
1038 fprintf (dump_file, "Folded PHI node: ");
1039 print_generic_stmt (dump_file, prev_phi, TDF_SLIM);
1040 fprintf (dump_file, " into: ");
1041 print_generic_stmt (dump_file, phi, TDF_SLIM);
1042 fprintf (dump_file, "\n");
1043 }
1044 }
1045
1046
1047 /* If STMT has a predicate whose value can be computed using the value
1048 range information computed by VRP, compute its value and return true.
1049 Otherwise, return false. */
1050
1051 static bool
fold_predicate_in(tree stmt)1052 fold_predicate_in (tree stmt)
1053 {
1054 tree *pred_p = NULL;
1055 bool modify_expr_p = false;
1056 tree val;
1057
1058 if (TREE_CODE (stmt) == MODIFY_EXPR
1059 && COMPARISON_CLASS_P (TREE_OPERAND (stmt, 1)))
1060 {
1061 modify_expr_p = true;
1062 pred_p = &TREE_OPERAND (stmt, 1);
1063 }
1064 else if (TREE_CODE (stmt) == COND_EXPR)
1065 pred_p = &COND_EXPR_COND (stmt);
1066 else
1067 return false;
1068
1069 val = vrp_evaluate_conditional (*pred_p, stmt);
1070 if (val)
1071 {
1072 if (modify_expr_p)
1073 val = fold_convert (TREE_TYPE (*pred_p), val);
1074
1075 if (dump_file)
1076 {
1077 fprintf (dump_file, "Folding predicate ");
1078 print_generic_expr (dump_file, *pred_p, 0);
1079 fprintf (dump_file, " to ");
1080 print_generic_expr (dump_file, val, 0);
1081 fprintf (dump_file, "\n");
1082 }
1083
1084 prop_stats.num_pred_folded++;
1085 *pred_p = val;
1086 return true;
1087 }
1088
1089 return false;
1090 }
1091
1092
1093 /* Perform final substitution and folding of propagated values.
1094
1095 PROP_VALUE[I] contains the single value that should be substituted
1096 at every use of SSA name N_I. If PROP_VALUE is NULL, no values are
1097 substituted.
1098
1099 If USE_RANGES_P is true, statements that contain predicate
1100 expressions are evaluated with a call to vrp_evaluate_conditional.
1101 This will only give meaningful results when called from tree-vrp.c
1102 (the information used by vrp_evaluate_conditional is built by the
1103 VRP pass). */
1104
1105 void
substitute_and_fold(prop_value_t * prop_value,bool use_ranges_p)1106 substitute_and_fold (prop_value_t *prop_value, bool use_ranges_p)
1107 {
1108 basic_block bb;
1109
1110 if (prop_value == NULL && !use_ranges_p)
1111 return;
1112
1113 if (dump_file && (dump_flags & TDF_DETAILS))
1114 fprintf (dump_file, "\nSubstituing values and folding statements\n\n");
1115
1116 memset (&prop_stats, 0, sizeof (prop_stats));
1117
1118 /* Substitute values in every statement of every basic block. */
1119 FOR_EACH_BB (bb)
1120 {
1121 block_stmt_iterator i;
1122 tree phi;
1123
1124 /* Propagate known values into PHI nodes. */
1125 if (prop_value)
1126 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
1127 replace_phi_args_in (phi, prop_value);
1128
1129 for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
1130 {
1131 bool replaced_address, did_replace;
1132 tree prev_stmt = NULL;
1133 tree stmt = bsi_stmt (i);
1134
1135 /* Ignore ASSERT_EXPRs. They are used by VRP to generate
1136 range information for names and they are discarded
1137 afterwards. */
1138 if (TREE_CODE (stmt) == MODIFY_EXPR
1139 && TREE_CODE (TREE_OPERAND (stmt, 1)) == ASSERT_EXPR)
1140 continue;
1141
1142 /* Replace the statement with its folded version and mark it
1143 folded. */
1144 did_replace = false;
1145 replaced_address = false;
1146 if (dump_file && (dump_flags & TDF_DETAILS))
1147 prev_stmt = unshare_expr (stmt);
1148
1149 /* If we have range information, see if we can fold
1150 predicate expressions. */
1151 if (use_ranges_p)
1152 did_replace = fold_predicate_in (stmt);
1153
1154 if (prop_value)
1155 {
1156 /* Only replace real uses if we couldn't fold the
1157 statement using value range information (value range
1158 information is not collected on virtuals, so we only
1159 need to check this for real uses). */
1160 if (!did_replace)
1161 did_replace |= replace_uses_in (stmt, &replaced_address,
1162 prop_value);
1163
1164 did_replace |= replace_vuses_in (stmt, &replaced_address,
1165 prop_value);
1166 }
1167
1168 /* If we made a replacement, fold and cleanup the statement. */
1169 if (did_replace)
1170 {
1171 tree old_stmt = stmt;
1172 tree rhs;
1173
1174 fold_stmt (bsi_stmt_ptr (i));
1175 stmt = bsi_stmt (i);
1176
1177 /* If we folded a builtin function, we'll likely
1178 need to rename VDEFs. */
1179 mark_new_vars_to_rename (stmt);
1180
1181 /* If we cleaned up EH information from the statement,
1182 remove EH edges. */
1183 if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt))
1184 tree_purge_dead_eh_edges (bb);
1185
1186 rhs = get_rhs (stmt);
1187 if (TREE_CODE (rhs) == ADDR_EXPR)
1188 recompute_tree_invariant_for_addr_expr (rhs);
1189
1190 if (dump_file && (dump_flags & TDF_DETAILS))
1191 {
1192 fprintf (dump_file, "Folded statement: ");
1193 print_generic_stmt (dump_file, prev_stmt, TDF_SLIM);
1194 fprintf (dump_file, " into: ");
1195 print_generic_stmt (dump_file, stmt, TDF_SLIM);
1196 fprintf (dump_file, "\n");
1197 }
1198 }
1199
1200 /* Some statements may be simplified using ranges. For
1201 example, division may be replaced by shifts, modulo
1202 replaced with bitwise and, etc. Do this after
1203 substituting constants, folding, etc so that we're
1204 presented with a fully propagated, canonicalized
1205 statement. */
1206 if (use_ranges_p)
1207 simplify_stmt_using_ranges (stmt);
1208
1209 }
1210 }
1211
1212 if (dump_file && (dump_flags & TDF_STATS))
1213 {
1214 fprintf (dump_file, "Constants propagated: %6ld\n",
1215 prop_stats.num_const_prop);
1216 fprintf (dump_file, "Copies propagated: %6ld\n",
1217 prop_stats.num_copy_prop);
1218 fprintf (dump_file, "Predicates folded: %6ld\n",
1219 prop_stats.num_pred_folded);
1220 }
1221 }
1222
1223 #include "gt-tree-ssa-propagate.h"
1224