2014-07-31 Robert Dewar <dewar@adacore.com>
[official-gcc.git] / gcc / tree-ssa-copy.c
blob06d98df00fc115220549e7e62c1ca7c2b82dec43
1 /* Copy propagation and SSA_NAME replacement support routines.
2 Copyright (C) 2004-2014 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3, or (at your option)
9 any later version.
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
20 #include "config.h"
21 #include "system.h"
22 #include "coretypes.h"
23 #include "tm.h"
24 #include "tree.h"
25 #include "flags.h"
26 #include "tm_p.h"
27 #include "basic-block.h"
28 #include "function.h"
29 #include "gimple-pretty-print.h"
30 #include "tree-ssa-alias.h"
31 #include "internal-fn.h"
32 #include "gimple-expr.h"
33 #include "is-a.h"
34 #include "gimple.h"
35 #include "gimple-iterator.h"
36 #include "gimple-ssa.h"
37 #include "tree-cfg.h"
38 #include "tree-phinodes.h"
39 #include "ssa-iterators.h"
40 #include "stringpool.h"
41 #include "tree-ssanames.h"
42 #include "tree-pass.h"
43 #include "tree-ssa-propagate.h"
44 #include "langhooks.h"
45 #include "cfgloop.h"
46 #include "tree-scalar-evolution.h"
47 #include "tree-ssa-dom.h"
48 #include "tree-ssa-loop-niter.h"
51 /* This file implements the copy propagation pass and provides a
52 handful of interfaces for performing const/copy propagation and
53 simple expression replacement which keep variable annotations
54 up-to-date.
56 We require that for any copy operation where the RHS and LHS have
57 a non-null memory tag the memory tag be the same. It is OK
58 for one or both of the memory tags to be NULL.
60 We also require tracking if a variable is dereferenced in a load or
61 store operation.
63 We enforce these requirements by having all copy propagation and
64 replacements of one SSA_NAME with a different SSA_NAME to use the
65 APIs defined in this file. */
67 /*---------------------------------------------------------------------------
68 Copy propagation
69 ---------------------------------------------------------------------------*/
70 /* Lattice for copy-propagation. The lattice is initialized to
71 UNDEFINED (value == NULL) for SSA names that can become a copy
72 of something or VARYING (value == self) if not (see get_copy_of_val
73 and stmt_may_generate_copy). Other values make the name a COPY
74 of that value.
76 When visiting a statement or PHI node the lattice value for an
77 SSA name can transition from UNDEFINED to COPY to VARYING. */
79 struct prop_value_d {
80 /* Copy-of value. */
81 tree value;
83 typedef struct prop_value_d prop_value_t;
85 static prop_value_t *copy_of;
86 static unsigned n_copy_of;
89 /* Return true if this statement may generate a useful copy. */
91 static bool
92 stmt_may_generate_copy (gimple stmt)
94 if (gimple_code (stmt) == GIMPLE_PHI)
95 return !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (gimple_phi_result (stmt));
97 if (gimple_code (stmt) != GIMPLE_ASSIGN)
98 return false;
100 /* If the statement has volatile operands, it won't generate a
101 useful copy. */
102 if (gimple_has_volatile_ops (stmt))
103 return false;
105 /* Statements with loads and/or stores will never generate a useful copy. */
106 if (gimple_vuse (stmt))
107 return false;
109 /* Otherwise, the only statements that generate useful copies are
110 assignments whose RHS is just an SSA name that doesn't flow
111 through abnormal edges. */
112 return ((gimple_assign_rhs_code (stmt) == SSA_NAME
113 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (gimple_assign_rhs1 (stmt)))
114 || is_gimple_min_invariant (gimple_assign_rhs1 (stmt)));
118 /* Return the copy-of value for VAR. */
120 static inline prop_value_t *
121 get_copy_of_val (tree var)
123 prop_value_t *val = &copy_of[SSA_NAME_VERSION (var)];
125 if (val->value == NULL_TREE
126 && !stmt_may_generate_copy (SSA_NAME_DEF_STMT (var)))
128 /* If the variable will never generate a useful copy relation,
129 make it its own copy. */
130 val->value = var;
133 return val;
136 /* Return the variable VAR is a copy of or VAR if VAR isn't the result
137 of a copy. */
139 static inline tree
140 valueize_val (tree var)
142 if (TREE_CODE (var) == SSA_NAME)
144 tree val = get_copy_of_val (var)->value;
145 if (val)
146 return val;
148 return var;
151 /* Set VAL to be the copy of VAR. If that changed return true. */
153 static inline bool
154 set_copy_of_val (tree var, tree val)
156 unsigned int ver = SSA_NAME_VERSION (var);
157 tree old;
159 /* Set FIRST to be the first link in COPY_OF[DEST]. If that
160 changed, return true. */
161 old = copy_of[ver].value;
162 copy_of[ver].value = val;
164 if (old != val
165 || (val && !operand_equal_p (old, val, 0)))
166 return true;
168 return false;
172 /* Dump the copy-of value for variable VAR to FILE. */
174 static void
175 dump_copy_of (FILE *file, tree var)
177 tree val;
179 print_generic_expr (file, var, dump_flags);
180 if (TREE_CODE (var) != SSA_NAME)
181 return;
183 val = copy_of[SSA_NAME_VERSION (var)].value;
184 fprintf (file, " copy-of chain: ");
185 print_generic_expr (file, var, 0);
186 fprintf (file, " ");
187 if (!val)
188 fprintf (file, "[UNDEFINED]");
189 else if (val == var)
190 fprintf (file, "[NOT A COPY]");
191 else
193 fprintf (file, "-> ");
194 print_generic_expr (file, val, 0);
195 fprintf (file, " ");
196 fprintf (file, "[COPY]");
201 /* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS
202 value and store the LHS into *RESULT_P. */
204 static enum ssa_prop_result
205 copy_prop_visit_assignment (gimple stmt, tree *result_p)
207 tree lhs, rhs;
209 lhs = gimple_assign_lhs (stmt);
210 rhs = valueize_val (gimple_assign_rhs1 (stmt));
212 if (TREE_CODE (lhs) == SSA_NAME)
214 /* Straight copy between two SSA names. First, make sure that
215 we can propagate the RHS into uses of LHS. */
216 if (!may_propagate_copy (lhs, rhs))
217 return SSA_PROP_VARYING;
219 *result_p = lhs;
220 if (set_copy_of_val (*result_p, rhs))
221 return SSA_PROP_INTERESTING;
222 else
223 return SSA_PROP_NOT_INTERESTING;
226 return SSA_PROP_VARYING;
230 /* Visit the GIMPLE_COND STMT. Return SSA_PROP_INTERESTING
231 if it can determine which edge will be taken. Otherwise, return
232 SSA_PROP_VARYING. */
234 static enum ssa_prop_result
235 copy_prop_visit_cond_stmt (gimple stmt, edge *taken_edge_p)
237 enum ssa_prop_result retval = SSA_PROP_VARYING;
238 location_t loc = gimple_location (stmt);
240 tree op0 = valueize_val (gimple_cond_lhs (stmt));
241 tree op1 = valueize_val (gimple_cond_rhs (stmt));
243 /* See if we can determine the predicate's value. */
244 if (dump_file && (dump_flags & TDF_DETAILS))
246 fprintf (dump_file, "Trying to determine truth value of ");
247 fprintf (dump_file, "predicate ");
248 print_gimple_stmt (dump_file, stmt, 0, 0);
251 /* Fold COND and see whether we get a useful result. */
252 tree folded_cond = fold_binary_loc (loc, gimple_cond_code (stmt),
253 boolean_type_node, op0, op1);
254 if (folded_cond)
256 basic_block bb = gimple_bb (stmt);
257 *taken_edge_p = find_taken_edge (bb, folded_cond);
258 if (*taken_edge_p)
259 retval = SSA_PROP_INTERESTING;
262 if (dump_file && (dump_flags & TDF_DETAILS) && *taken_edge_p)
263 fprintf (dump_file, "\nConditional will always take edge %d->%d\n",
264 (*taken_edge_p)->src->index, (*taken_edge_p)->dest->index);
266 return retval;
270 /* Evaluate statement STMT. If the statement produces a new output
271 value, return SSA_PROP_INTERESTING and store the SSA_NAME holding
272 the new value in *RESULT_P.
274 If STMT is a conditional branch and we can determine its truth
275 value, set *TAKEN_EDGE_P accordingly.
277 If the new value produced by STMT is varying, return
278 SSA_PROP_VARYING. */
280 static enum ssa_prop_result
281 copy_prop_visit_stmt (gimple stmt, edge *taken_edge_p, tree *result_p)
283 enum ssa_prop_result retval;
285 if (dump_file && (dump_flags & TDF_DETAILS))
287 fprintf (dump_file, "\nVisiting statement:\n");
288 print_gimple_stmt (dump_file, stmt, 0, dump_flags);
289 fprintf (dump_file, "\n");
292 if (gimple_assign_single_p (stmt)
293 && TREE_CODE (gimple_assign_lhs (stmt)) == SSA_NAME
294 && (TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME
295 || is_gimple_min_invariant (gimple_assign_rhs1 (stmt))))
297 /* If the statement is a copy assignment, evaluate its RHS to
298 see if the lattice value of its output has changed. */
299 retval = copy_prop_visit_assignment (stmt, result_p);
301 else if (gimple_code (stmt) == GIMPLE_COND)
303 /* See if we can determine which edge goes out of a conditional
304 jump. */
305 retval = copy_prop_visit_cond_stmt (stmt, taken_edge_p);
307 else
308 retval = SSA_PROP_VARYING;
310 if (retval == SSA_PROP_VARYING)
312 tree def;
313 ssa_op_iter i;
315 /* Any other kind of statement is not interesting for constant
316 propagation and, therefore, not worth simulating. */
317 if (dump_file && (dump_flags & TDF_DETAILS))
318 fprintf (dump_file, "No interesting values produced.\n");
320 /* The assignment is not a copy operation. Don't visit this
321 statement again and mark all the definitions in the statement
322 to be copies of nothing. */
323 FOR_EACH_SSA_TREE_OPERAND (def, stmt, i, SSA_OP_ALL_DEFS)
324 set_copy_of_val (def, def);
327 return retval;
331 /* Visit PHI node PHI. If all the arguments produce the same value,
332 set it to be the value of the LHS of PHI. */
334 static enum ssa_prop_result
335 copy_prop_visit_phi_node (gimple phi)
337 enum ssa_prop_result retval;
338 unsigned i;
339 prop_value_t phi_val = { NULL_TREE };
341 tree lhs = gimple_phi_result (phi);
343 if (dump_file && (dump_flags & TDF_DETAILS))
345 fprintf (dump_file, "\nVisiting PHI node: ");
346 print_gimple_stmt (dump_file, phi, 0, dump_flags);
349 for (i = 0; i < gimple_phi_num_args (phi); i++)
351 prop_value_t *arg_val;
352 tree arg_value;
353 tree arg = gimple_phi_arg_def (phi, i);
354 edge e = gimple_phi_arg_edge (phi, i);
356 /* We don't care about values flowing through non-executable
357 edges. */
358 if (!(e->flags & EDGE_EXECUTABLE))
359 continue;
361 /* Names that flow through abnormal edges cannot be used to
362 derive copies. */
363 if (TREE_CODE (arg) == SSA_NAME && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg))
365 phi_val.value = lhs;
366 break;
369 if (dump_file && (dump_flags & TDF_DETAILS))
371 fprintf (dump_file, "\tArgument #%d: ", i);
372 dump_copy_of (dump_file, arg);
373 fprintf (dump_file, "\n");
376 if (TREE_CODE (arg) == SSA_NAME)
378 arg_val = get_copy_of_val (arg);
380 /* If we didn't visit the definition of arg yet treat it as
381 UNDEFINED. This also handles PHI arguments that are the
382 same as lhs. We'll come here again. */
383 if (!arg_val->value)
384 continue;
386 arg_value = arg_val->value;
388 else
389 arg_value = valueize_val (arg);
391 /* In loop-closed SSA form do not copy-propagate SSA-names across
392 loop exit edges. */
393 if (loops_state_satisfies_p (LOOP_CLOSED_SSA)
394 && TREE_CODE (arg_value) == SSA_NAME
395 && loop_exit_edge_p (e->src->loop_father, e))
397 phi_val.value = lhs;
398 break;
401 /* If the LHS didn't have a value yet, make it a copy of the
402 first argument we find. */
403 if (phi_val.value == NULL_TREE)
405 phi_val.value = arg_value;
406 continue;
409 /* If PHI_VAL and ARG don't have a common copy-of chain, then
410 this PHI node cannot be a copy operation. */
411 if (phi_val.value != arg_value
412 && !operand_equal_p (phi_val.value, arg_value, 0))
414 phi_val.value = lhs;
415 break;
419 if (phi_val.value
420 && may_propagate_copy (lhs, phi_val.value)
421 && set_copy_of_val (lhs, phi_val.value))
422 retval = (phi_val.value != lhs) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING;
423 else
424 retval = SSA_PROP_NOT_INTERESTING;
426 if (dump_file && (dump_flags & TDF_DETAILS))
428 fprintf (dump_file, "PHI node ");
429 dump_copy_of (dump_file, lhs);
430 fprintf (dump_file, "\nTelling the propagator to ");
431 if (retval == SSA_PROP_INTERESTING)
432 fprintf (dump_file, "add SSA edges out of this PHI and continue.");
433 else if (retval == SSA_PROP_VARYING)
434 fprintf (dump_file, "add SSA edges out of this PHI and never visit again.");
435 else
436 fprintf (dump_file, "do nothing with SSA edges and keep iterating.");
437 fprintf (dump_file, "\n\n");
440 return retval;
444 /* Initialize structures used for copy propagation. */
446 static void
447 init_copy_prop (void)
449 basic_block bb;
451 n_copy_of = num_ssa_names;
452 copy_of = XCNEWVEC (prop_value_t, n_copy_of);
454 FOR_EACH_BB_FN (bb, cfun)
456 gimple_stmt_iterator si;
458 for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si))
460 gimple stmt = gsi_stmt (si);
461 ssa_op_iter iter;
462 tree def;
464 /* The only statements that we care about are those that may
465 generate useful copies. We also need to mark conditional
466 jumps so that their outgoing edges are added to the work
467 lists of the propagator. */
468 if (stmt_ends_bb_p (stmt))
469 prop_set_simulate_again (stmt, true);
470 else if (stmt_may_generate_copy (stmt))
471 prop_set_simulate_again (stmt, true);
472 else
473 prop_set_simulate_again (stmt, false);
475 /* Mark all the outputs of this statement as not being
476 the copy of anything. */
477 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
478 if (!prop_simulate_again_p (stmt))
479 set_copy_of_val (def, def);
482 for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si))
484 gimple phi = gsi_stmt (si);
485 tree def;
487 def = gimple_phi_result (phi);
488 if (virtual_operand_p (def))
489 prop_set_simulate_again (phi, false);
490 else
491 prop_set_simulate_again (phi, true);
493 if (!prop_simulate_again_p (phi))
494 set_copy_of_val (def, def);
499 /* Callback for substitute_and_fold to get at the final copy-of values. */
501 static tree
502 get_value (tree name)
504 tree val;
505 if (SSA_NAME_VERSION (name) >= n_copy_of)
506 return NULL_TREE;
507 val = copy_of[SSA_NAME_VERSION (name)].value;
508 if (val && val != name)
509 return val;
510 return NULL_TREE;
513 /* Deallocate memory used in copy propagation and do final
514 substitution. */
516 static bool
517 fini_copy_prop (void)
519 unsigned i;
521 /* Set the final copy-of value for each variable by traversing the
522 copy-of chains. */
523 for (i = 1; i < num_ssa_names; i++)
525 tree var = ssa_name (i);
526 if (!var
527 || !copy_of[i].value
528 || copy_of[i].value == var)
529 continue;
531 /* In theory the points-to solution of all members of the
532 copy chain is their intersection. For now we do not bother
533 to compute this but only make sure we do not lose points-to
534 information completely by setting the points-to solution
535 of the representative to the first solution we find if
536 it doesn't have one already. */
537 if (copy_of[i].value != var
538 && TREE_CODE (copy_of[i].value) == SSA_NAME)
540 basic_block copy_of_bb
541 = gimple_bb (SSA_NAME_DEF_STMT (copy_of[i].value));
542 basic_block var_bb = gimple_bb (SSA_NAME_DEF_STMT (var));
543 if (POINTER_TYPE_P (TREE_TYPE (var))
544 && SSA_NAME_PTR_INFO (var)
545 && !SSA_NAME_PTR_INFO (copy_of[i].value))
547 duplicate_ssa_name_ptr_info (copy_of[i].value,
548 SSA_NAME_PTR_INFO (var));
549 /* Points-to information is cfg insensitive,
550 but alignment info might be cfg sensitive, if it
551 e.g. is derived from VRP derived non-zero bits.
552 So, do not copy alignment info if the two SSA_NAMEs
553 aren't defined in the same basic block. */
554 if (var_bb != copy_of_bb)
555 mark_ptr_info_alignment_unknown
556 (SSA_NAME_PTR_INFO (copy_of[i].value));
558 else if (!POINTER_TYPE_P (TREE_TYPE (var))
559 && SSA_NAME_RANGE_INFO (var)
560 && !SSA_NAME_RANGE_INFO (copy_of[i].value)
561 && var_bb == copy_of_bb)
562 duplicate_ssa_name_range_info (copy_of[i].value,
563 SSA_NAME_RANGE_TYPE (var),
564 SSA_NAME_RANGE_INFO (var));
568 bool changed = substitute_and_fold (get_value, NULL, true);
569 if (changed)
571 free_numbers_of_iterations_estimates ();
572 if (scev_initialized_p ())
573 scev_reset ();
576 free (copy_of);
578 return changed;
582 /* Main entry point to the copy propagator.
584 PHIS_ONLY is true if we should only consider PHI nodes as generating
585 copy propagation opportunities.
587 The algorithm propagates the value COPY-OF using ssa_propagate. For
588 every variable X_i, COPY-OF(X_i) indicates which variable is X_i created
589 from. The following example shows how the algorithm proceeds at a
590 high level:
592 1 a_24 = x_1
593 2 a_2 = PHI <a_24, x_1>
594 3 a_5 = PHI <a_2>
595 4 x_1 = PHI <x_298, a_5, a_2>
597 The end result should be that a_2, a_5, a_24 and x_1 are a copy of
598 x_298. Propagation proceeds as follows.
600 Visit #1: a_24 is copy-of x_1. Value changed.
601 Visit #2: a_2 is copy-of x_1. Value changed.
602 Visit #3: a_5 is copy-of x_1. Value changed.
603 Visit #4: x_1 is copy-of x_298. Value changed.
604 Visit #1: a_24 is copy-of x_298. Value changed.
605 Visit #2: a_2 is copy-of x_298. Value changed.
606 Visit #3: a_5 is copy-of x_298. Value changed.
607 Visit #4: x_1 is copy-of x_298. Stable state reached.
609 When visiting PHI nodes, we only consider arguments that flow
610 through edges marked executable by the propagation engine. So,
611 when visiting statement #2 for the first time, we will only look at
612 the first argument (a_24) and optimistically assume that its value
613 is the copy of a_24 (x_1). */
615 static unsigned int
616 execute_copy_prop (void)
618 init_copy_prop ();
619 ssa_propagate (copy_prop_visit_stmt, copy_prop_visit_phi_node);
620 if (fini_copy_prop ())
621 return TODO_cleanup_cfg;
622 return 0;
625 namespace {
627 const pass_data pass_data_copy_prop =
629 GIMPLE_PASS, /* type */
630 "copyprop", /* name */
631 OPTGROUP_NONE, /* optinfo_flags */
632 TV_TREE_COPY_PROP, /* tv_id */
633 ( PROP_ssa | PROP_cfg ), /* properties_required */
634 0, /* properties_provided */
635 0, /* properties_destroyed */
636 0, /* todo_flags_start */
637 0, /* todo_flags_finish */
640 class pass_copy_prop : public gimple_opt_pass
642 public:
643 pass_copy_prop (gcc::context *ctxt)
644 : gimple_opt_pass (pass_data_copy_prop, ctxt)
647 /* opt_pass methods: */
648 opt_pass * clone () { return new pass_copy_prop (m_ctxt); }
649 virtual bool gate (function *) { return flag_tree_copy_prop != 0; }
650 virtual unsigned int execute (function *) { return execute_copy_prop (); }
652 }; // class pass_copy_prop
654 } // anon namespace
656 gimple_opt_pass *
657 make_pass_copy_prop (gcc::context *ctxt)
659 return new pass_copy_prop (ctxt);