1 /* Copy propagation and SSA_NAME replacement support routines.
2 Copyright (C) 2004, 2005 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 2, or (at your option)
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING. If not, write to
18 the Free Software Foundation, 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
23 #include "coretypes.h"
30 #include "basic-block.h"
34 #include "diagnostic.h"
36 #include "tree-dump.h"
37 #include "tree-flow.h"
38 #include "tree-pass.h"
39 #include "tree-ssa-propagate.h"
40 #include "langhooks.h"
42 /* This file implements the copy propagation pass and provides a
43 handful of interfaces for performing const/copy propagation and
44 simple expression replacement which keep variable annotations
47 We require that for any copy operation where the RHS and LHS have
48 a non-null memory tag the memory tag be the same. It is OK
49 for one or both of the memory tags to be NULL.
51 We also require tracking if a variable is dereferenced in a load or
54 We enforce these requirements by having all copy propagation and
55 replacements of one SSA_NAME with a different SSA_NAME to use the
56 APIs defined in this file. */
58 /* Return true if we may propagate ORIG into DEST, false otherwise. */
61 may_propagate_copy (tree dest, tree orig)
63 tree type_d = TREE_TYPE (dest);
64 tree type_o = TREE_TYPE (orig);
66 /* Do not copy between types for which we *do* need a conversion. */
67 if (!tree_ssa_useless_type_conversion_1 (type_d, type_o))
70 /* FIXME. GIMPLE is allowing pointer assignments and comparisons of
71 pointers that have different alias sets. This means that these
72 pointers will have different memory tags associated to them.
74 If we allow copy propagation in these cases, statements de-referencing
75 the new pointer will now have a reference to a different memory tag
76 with potentially incorrect SSA information.
78 This was showing up in libjava/java/util/zip/ZipFile.java with code
81 struct java.io.BufferedInputStream *T.660;
82 struct java.io.BufferedInputStream *T.647;
83 struct java.io.InputStream *is;
84 struct java.io.InputStream *is.662;
87 is = T.660; <-- This ought to be type-casted
90 Also, f/name.c exposed a similar problem with a COND_EXPR predicate
91 that was causing DOM to generate and equivalence with two pointers of
92 alias-incompatible types:
94 struct _ffename_space *n;
103 I think that GIMPLE should emit the appropriate type-casts. For the
104 time being, blocking copy-propagation in these cases is the safe thing
106 if (TREE_CODE (dest) == SSA_NAME
107 && TREE_CODE (orig) == SSA_NAME
108 && POINTER_TYPE_P (type_d)
109 && POINTER_TYPE_P (type_o))
111 tree mt_dest = var_ann (SSA_NAME_VAR (dest))->type_mem_tag;
112 tree mt_orig = var_ann (SSA_NAME_VAR (orig))->type_mem_tag;
113 if (mt_dest && mt_orig && mt_dest != mt_orig)
115 else if (!lang_hooks.types_compatible_p (type_d, type_o))
117 else if (get_alias_set (TREE_TYPE (type_d)) !=
118 get_alias_set (TREE_TYPE (type_o)))
122 /* If the destination is a SSA_NAME for a virtual operand, then we have
123 some special cases to handle. */
124 if (TREE_CODE (dest) == SSA_NAME && !is_gimple_reg (dest))
126 /* If both operands are SSA_NAMEs referring to virtual operands, then
127 we can always propagate. */
128 if (TREE_CODE (orig) == SSA_NAME
129 && !is_gimple_reg (orig))
132 /* We have a "copy" from something like a constant into a virtual
133 operand. Reject these. */
137 /* If ORIG flows in from an abnormal edge, it cannot be propagated. */
138 if (TREE_CODE (orig) == SSA_NAME
139 && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig))
142 /* If DEST is an SSA_NAME that flows from an abnormal edge, then it
143 cannot be replaced. */
144 if (TREE_CODE (dest) == SSA_NAME
145 && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest))
148 /* Anything else is OK. */
152 /* Similarly, but we know that we're propagating into an ASM_EXPR. */
155 may_propagate_copy_into_asm (tree dest)
157 /* Hard register operands of asms are special. Do not bypass. */
158 return !(TREE_CODE (dest) == SSA_NAME
159 && TREE_CODE (SSA_NAME_VAR (dest)) == VAR_DECL
160 && DECL_HARD_REGISTER (SSA_NAME_VAR (dest)));
164 /* Given two SSA_NAMEs pointers ORIG and NEW such that we are copy
165 propagating NEW into ORIG, consolidate aliasing information so that
166 they both share the same memory tags. */
169 merge_alias_info (tree orig, tree new)
171 tree new_sym = SSA_NAME_VAR (new);
172 tree orig_sym = SSA_NAME_VAR (orig);
173 var_ann_t new_ann = var_ann (new_sym);
174 var_ann_t orig_ann = var_ann (orig_sym);
176 gcc_assert (POINTER_TYPE_P (TREE_TYPE (orig)));
177 gcc_assert (POINTER_TYPE_P (TREE_TYPE (new)));
179 #if defined ENABLE_CHECKING
180 gcc_assert (lang_hooks.types_compatible_p (TREE_TYPE (orig),
183 /* If the pointed-to alias sets are different, these two pointers
184 would never have the same memory tag. In this case, NEW should
185 not have been propagated into ORIG. */
186 gcc_assert (get_alias_set (TREE_TYPE (TREE_TYPE (new_sym)))
187 == get_alias_set (TREE_TYPE (TREE_TYPE (orig_sym))));
190 /* Synchronize the type tags. If both pointers had a tag and they
191 are different, then something has gone wrong. */
192 if (new_ann->type_mem_tag == NULL_TREE)
193 new_ann->type_mem_tag = orig_ann->type_mem_tag;
194 else if (orig_ann->type_mem_tag == NULL_TREE)
195 orig_ann->type_mem_tag = new_ann->type_mem_tag;
197 gcc_assert (new_ann->type_mem_tag == orig_ann->type_mem_tag);
199 /* Synchronize the name tags. If NEW did not have a name tag, get
200 it from ORIG. This happens when NEW is a compiler generated
201 temporary which still hasn't had its points-to information filled
203 if (SSA_NAME_PTR_INFO (orig))
205 struct ptr_info_def *orig_ptr_info = SSA_NAME_PTR_INFO (orig);
206 struct ptr_info_def *new_ptr_info = SSA_NAME_PTR_INFO (new);
208 if (new_ptr_info == NULL)
209 duplicate_ssa_name_ptr_info (new, orig_ptr_info);
210 else if (orig_ptr_info->name_mem_tag
211 && new_ptr_info->name_mem_tag
212 && orig_ptr_info->pt_vars
213 && new_ptr_info->pt_vars)
215 /* Note that pointer NEW may actually have a different set
216 of pointed-to variables. However, since NEW is being
217 copy-propagated into ORIG, it must always be true that
218 the pointed-to set for pointer NEW is the same, or a
219 subset, of the pointed-to set for pointer ORIG. If this
220 isn't the case, we shouldn't have been able to do the
221 propagation of NEW into ORIG. */
222 gcc_assert (bitmap_intersect_p (new_ptr_info->pt_vars,
223 orig_ptr_info->pt_vars));
229 /* Common code for propagate_value and replace_exp.
231 Replace use operand OP_P with VAL. FOR_PROPAGATION indicates if the
232 replacement is done to propagate a value or not. */
235 replace_exp_1 (use_operand_p op_p, tree val,
236 bool for_propagation ATTRIBUTE_UNUSED)
238 tree op = USE_FROM_PTR (op_p);
240 #if defined ENABLE_CHECKING
241 gcc_assert (!(for_propagation
242 && TREE_CODE (op) == SSA_NAME
243 && TREE_CODE (val) == SSA_NAME
244 && !may_propagate_copy (op, val)));
247 if (TREE_CODE (val) == SSA_NAME)
249 if (TREE_CODE (op) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (op)))
250 merge_alias_info (op, val);
254 SET_USE (op_p, unsave_expr_now (val));
258 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
259 into the operand pointed by OP_P.
261 Use this version for const/copy propagation as it will perform additional
262 checks to ensure validity of the const/copy propagation. */
265 propagate_value (use_operand_p op_p, tree val)
267 replace_exp_1 (op_p, val, true);
271 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
272 into the tree pointed by OP_P.
274 Use this version for const/copy propagation when SSA operands are not
275 available. It will perform the additional checks to ensure validity of
276 the const/copy propagation, but will not update any operand information.
277 Be sure to mark the stmt as modified. */
280 propagate_tree_value (tree *op_p, tree val)
282 #if defined ENABLE_CHECKING
283 gcc_assert (!(TREE_CODE (val) == SSA_NAME
284 && TREE_CODE (*op_p) == SSA_NAME
285 && !may_propagate_copy (*op_p, val)));
288 if (TREE_CODE (val) == SSA_NAME)
290 if (TREE_CODE (*op_p) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (*op_p)))
291 merge_alias_info (*op_p, val);
295 *op_p = unsave_expr_now (val);
299 /* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).
301 Use this version when not const/copy propagating values. For example,
302 PRE uses this version when building expressions as they would appear
303 in specific blocks taking into account actions of PHI nodes. */
306 replace_exp (use_operand_p op_p, tree val)
308 replace_exp_1 (op_p, val, false);
312 /*---------------------------------------------------------------------------
314 ---------------------------------------------------------------------------*/
315 /* During propagation, we keep chains of variables that are copies of
316 one another. If variable X_i is a copy of X_j and X_j is a copy of
317 X_k, COPY_OF will contain:
319 COPY_OF[i].VALUE = X_j
320 COPY_OF[j].VALUE = X_k
321 COPY_OF[k].VALUE = X_k
323 After propagation, the copy-of value for each variable X_i is
324 converted into the final value by walking the copy-of chains and
325 updating COPY_OF[i].VALUE to be the last element of the chain. */
326 static prop_value_t *copy_of;
328 /* Used in set_copy_of_val to determine if the last link of a copy-of
329 chain has changed. */
330 static tree *cached_last_copy_of;
332 /* True if we are doing copy propagation on loads and stores. */
333 static bool do_store_copy_prop;
336 /* Return true if this statement may generate a useful copy. */
339 stmt_may_generate_copy (tree stmt)
344 if (TREE_CODE (stmt) == PHI_NODE)
345 return !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (stmt));
347 if (TREE_CODE (stmt) != MODIFY_EXPR)
350 lhs = TREE_OPERAND (stmt, 0);
351 rhs = TREE_OPERAND (stmt, 1);
352 ann = stmt_ann (stmt);
354 /* If the statement has volatile operands, it won't generate a
356 if (ann->has_volatile_ops)
359 /* If we are not doing store copy-prop, statements with loads and/or
360 stores will never generate a useful copy. */
361 if (!do_store_copy_prop
362 && !ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS))
365 /* Otherwise, the only statements that generate useful copies are
366 assignments whose RHS is just an SSA name that doesn't flow
367 through abnormal edges. */
368 return TREE_CODE (rhs) == SSA_NAME && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs);
372 /* Return the copy-of value for VAR. */
374 static inline prop_value_t *
375 get_copy_of_val (tree var)
377 prop_value_t *val = ©_of[SSA_NAME_VERSION (var)];
379 if (val->value == NULL_TREE
380 && !stmt_may_generate_copy (SSA_NAME_DEF_STMT (var)))
382 /* If the variable will never generate a useful copy relation,
383 make it its own copy. */
385 val->mem_ref = NULL_TREE;
392 /* Return last link in the copy-of chain for VAR. */
395 get_last_copy_of (tree var)
400 /* Traverse COPY_OF starting at VAR until we get to the last
401 link in the chain. Since it is possible to have cycles in PHI
402 nodes, the copy-of chain may also contain cycles.
404 To avoid infinite loops and to avoid traversing lengthy copy-of
405 chains, we artificially limit the maximum number of chains we are
408 The value 5 was taken from a compiler and runtime library
409 bootstrap and a mixture of C and C++ code from various sources.
410 More than 82% of all copy-of chains were shorter than 5 links. */
414 for (i = 0; i < LIMIT; i++)
416 tree copy = copy_of[SSA_NAME_VERSION (last)].value;
417 if (copy == NULL_TREE || copy == last)
422 /* If we have reached the limit, then we are either in a copy-of
423 cycle or the copy-of chain is too long. In this case, just
424 return VAR so that it is not considered a copy of anything. */
425 return (i < LIMIT ? last : var);
429 /* Set FIRST to be the first variable in the copy-of chain for DEST.
430 If DEST's copy-of value or its copy-of chain has changed, return
433 MEM_REF is the memory reference where FIRST is stored. This is
434 used when DEST is a non-register and we are copy propagating loads
438 set_copy_of_val (tree dest, tree first, tree mem_ref)
440 unsigned int dest_ver = SSA_NAME_VERSION (dest);
441 tree old_first, old_last, new_last;
443 /* Set FIRST to be the first link in COPY_OF[DEST]. If that
444 changed, return true. */
445 old_first = copy_of[dest_ver].value;
446 copy_of[dest_ver].value = first;
447 copy_of[dest_ver].mem_ref = mem_ref;
449 if (old_first != first)
452 /* If FIRST and OLD_FIRST are the same, we need to check whether the
453 copy-of chain starting at FIRST ends in a different variable. If
454 the copy-of chain starting at FIRST ends up in a different
455 variable than the last cached value we had for DEST, then return
456 true because DEST is now a copy of a different variable.
458 This test is necessary because even though the first link in the
459 copy-of chain may not have changed, if any of the variables in
460 the copy-of chain changed its final value, DEST will now be the
461 copy of a different variable, so we have to do another round of
462 propagation for everything that depends on DEST. */
463 old_last = cached_last_copy_of[dest_ver];
464 new_last = get_last_copy_of (dest);
465 cached_last_copy_of[dest_ver] = new_last;
467 return (old_last != new_last);
471 /* Dump the copy-of value for variable VAR to DUMP_FILE. */
474 dump_copy_of (FILE *dump_file, tree var)
479 print_generic_expr (dump_file, var, dump_flags);
481 if (TREE_CODE (var) != SSA_NAME)
484 visited = sbitmap_alloc (num_ssa_names);
485 SET_BIT (visited, SSA_NAME_VERSION (var));
487 fprintf (dump_file, " copy-of chain: ");
490 print_generic_expr (dump_file, val, 0);
491 fprintf (dump_file, " ");
492 while (copy_of[SSA_NAME_VERSION (val)].value)
494 fprintf (dump_file, "-> ");
495 val = copy_of[SSA_NAME_VERSION (val)].value;
496 print_generic_expr (dump_file, val, 0);
497 fprintf (dump_file, " ");
498 if (TEST_BIT (visited, SSA_NAME_VERSION (val)))
500 SET_BIT (visited, SSA_NAME_VERSION (val));
503 val = get_copy_of_val (var)->value;
504 if (val == NULL_TREE)
505 fprintf (dump_file, "[UNDEFINED]");
507 fprintf (dump_file, "[COPY]");
509 fprintf (dump_file, "[NOT A COPY]");
511 sbitmap_free (visited);
515 /* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS
516 value and store the LHS into *RESULT_P. If STMT generates more
517 than one name (i.e., STMT is an aliased store), it is enough to
518 store the first name in the V_MAY_DEF list into *RESULT_P. After
519 all, the names generated will be VUSEd in the same statements. */
521 static enum ssa_prop_result
522 copy_prop_visit_assignment (tree stmt, tree *result_p)
525 prop_value_t *rhs_val;
527 lhs = TREE_OPERAND (stmt, 0);
528 rhs = TREE_OPERAND (stmt, 1);
530 gcc_assert (TREE_CODE (rhs) == SSA_NAME);
532 rhs_val = get_copy_of_val (rhs);
534 if (TREE_CODE (lhs) == SSA_NAME)
536 /* Straight copy between two SSA names. First, make sure that
537 we can propagate the RHS into uses of LHS. */
538 if (!may_propagate_copy (lhs, rhs))
539 return SSA_PROP_VARYING;
541 /* Avoid copy propagation from an inner into an outer loop.
542 Otherwise, this may move loop variant variables outside of
543 their loops and prevent coalescing opportunities. If the
544 value was loop invariant, it will be hoisted by LICM and
545 exposed for copy propagation. */
546 if (loop_depth_of_name (rhs) > loop_depth_of_name (lhs))
547 return SSA_PROP_VARYING;
549 /* Notice that in the case of assignments, we make the LHS be a
550 copy of RHS's value, not of RHS itself. This avoids keeping
551 unnecessary copy-of chains (assignments cannot be in a cycle
552 like PHI nodes), speeding up the propagation process.
553 This is different from what we do in copy_prop_visit_phi_node.
554 In those cases, we are interested in the copy-of chains. */
556 if (set_copy_of_val (*result_p, rhs_val->value, rhs_val->mem_ref))
557 return SSA_PROP_INTERESTING;
559 return SSA_PROP_NOT_INTERESTING;
561 else if (stmt_makes_single_store (stmt))
563 /* Otherwise, set the names in V_MAY_DEF/V_MUST_DEF operands
564 to be a copy of RHS. */
569 /* This should only be executed when doing store copy-prop. */
570 gcc_assert (do_store_copy_prop);
572 /* Set the value of every VDEF to RHS_VAL. */
574 FOR_EACH_SSA_TREE_OPERAND (vdef, stmt, i, SSA_OP_VIRTUAL_DEFS)
575 changed |= set_copy_of_val (vdef, rhs_val->value, lhs);
577 /* Note that for propagation purposes, we are only interested in
578 visiting statements that load the exact same memory reference
579 stored here. Those statements will have the exact same list
580 of virtual uses, so it is enough to set the output of this
581 statement to be its first virtual definition. */
582 *result_p = first_vdef (stmt);
585 return SSA_PROP_INTERESTING;
587 return SSA_PROP_NOT_INTERESTING;
591 return SSA_PROP_VARYING;
595 /* Visit the COND_EXPR STMT. Return SSA_PROP_INTERESTING
596 if it can determine which edge will be taken. Otherwise, return
599 static enum ssa_prop_result
600 copy_prop_visit_cond_stmt (tree stmt, edge *taken_edge_p)
602 enum ssa_prop_result retval;
605 cond = COND_EXPR_COND (stmt);
606 retval = SSA_PROP_VARYING;
608 /* The only conditionals that we may be able to compute statically
609 are predicates involving two SSA_NAMEs. */
610 if (COMPARISON_CLASS_P (cond)
611 && TREE_CODE (TREE_OPERAND (cond, 0)) == SSA_NAME
612 && TREE_CODE (TREE_OPERAND (cond, 1)) == SSA_NAME)
614 tree op0 = get_last_copy_of (TREE_OPERAND (cond, 0));
615 tree op1 = get_last_copy_of (TREE_OPERAND (cond, 1));
617 /* See if we can determine the predicate's value. */
618 if (dump_file && (dump_flags & TDF_DETAILS))
620 fprintf (dump_file, "Trying to determine truth value of ");
621 fprintf (dump_file, "predicate ");
622 print_generic_stmt (dump_file, cond, 0);
625 /* We can fold COND and get a useful result only when we have
626 the same SSA_NAME on both sides of a comparison operator. */
629 tree folded_cond = fold_binary (TREE_CODE (cond), boolean_type_node,
633 basic_block bb = bb_for_stmt (stmt);
634 *taken_edge_p = find_taken_edge (bb, folded_cond);
636 retval = SSA_PROP_INTERESTING;
641 if (dump_file && (dump_flags & TDF_DETAILS) && *taken_edge_p)
642 fprintf (dump_file, "\nConditional will always take edge %d->%d\n",
643 (*taken_edge_p)->src->index, (*taken_edge_p)->dest->index);
649 /* Evaluate statement STMT. If the statement produces a new output
650 value, return SSA_PROP_INTERESTING and store the SSA_NAME holding
651 the new value in *RESULT_P.
653 If STMT is a conditional branch and we can determine its truth
654 value, set *TAKEN_EDGE_P accordingly.
656 If the new value produced by STMT is varying, return
659 static enum ssa_prop_result
660 copy_prop_visit_stmt (tree stmt, edge *taken_edge_p, tree *result_p)
663 enum ssa_prop_result retval;
665 if (dump_file && (dump_flags & TDF_DETAILS))
667 fprintf (dump_file, "\nVisiting statement:\n");
668 print_generic_stmt (dump_file, stmt, dump_flags);
669 fprintf (dump_file, "\n");
672 ann = stmt_ann (stmt);
674 if (TREE_CODE (stmt) == MODIFY_EXPR
675 && TREE_CODE (TREE_OPERAND (stmt, 1)) == SSA_NAME
676 && (do_store_copy_prop
677 || TREE_CODE (TREE_OPERAND (stmt, 0)) == SSA_NAME))
679 /* If the statement is a copy assignment, evaluate its RHS to
680 see if the lattice value of its output has changed. */
681 retval = copy_prop_visit_assignment (stmt, result_p);
683 else if (TREE_CODE (stmt) == COND_EXPR)
685 /* See if we can determine which edge goes out of a conditional
687 retval = copy_prop_visit_cond_stmt (stmt, taken_edge_p);
690 retval = SSA_PROP_VARYING;
692 if (retval == SSA_PROP_VARYING)
697 /* Any other kind of statement is not interesting for constant
698 propagation and, therefore, not worth simulating. */
699 if (dump_file && (dump_flags & TDF_DETAILS))
700 fprintf (dump_file, "No interesting values produced.\n");
702 /* The assignment is not a copy operation. Don't visit this
703 statement again and mark all the definitions in the statement
704 to be copies of nothing. */
705 FOR_EACH_SSA_TREE_OPERAND (def, stmt, i, SSA_OP_ALL_DEFS)
706 set_copy_of_val (def, def, NULL_TREE);
713 /* Visit PHI node PHI. If all the arguments produce the same value,
714 set it to be the value of the LHS of PHI. */
716 static enum ssa_prop_result
717 copy_prop_visit_phi_node (tree phi)
719 enum ssa_prop_result retval;
722 prop_value_t phi_val = { 0, NULL_TREE, NULL_TREE };
724 lhs = PHI_RESULT (phi);
726 if (dump_file && (dump_flags & TDF_DETAILS))
728 fprintf (dump_file, "\nVisiting PHI node: ");
729 print_generic_expr (dump_file, phi, dump_flags);
730 fprintf (dump_file, "\n\n");
733 for (i = 0; i < PHI_NUM_ARGS (phi); i++)
735 prop_value_t *arg_val;
736 tree arg = PHI_ARG_DEF (phi, i);
737 edge e = PHI_ARG_EDGE (phi, i);
739 /* We don't care about values flowing through non-executable
741 if (!(e->flags & EDGE_EXECUTABLE))
744 /* Constants in the argument list never generate a useful copy.
745 Similarly, names that flow through abnormal edges cannot be
746 used to derive copies. */
747 if (TREE_CODE (arg) != SSA_NAME || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg))
753 /* Avoid copy propagation from an inner into an outer loop.
754 Otherwise, this may move loop variant variables outside of
755 their loops and prevent coalescing opportunities. If the
756 value was loop invariant, it will be hoisted by LICM and
757 exposed for copy propagation. */
758 if (loop_depth_of_name (arg) > loop_depth_of_name (lhs))
764 /* If the LHS appears in the argument list, ignore it. It is
765 irrelevant as a copy. */
766 if (arg == lhs || get_last_copy_of (arg) == lhs)
769 if (dump_file && (dump_flags & TDF_DETAILS))
771 fprintf (dump_file, "\tArgument #%d: ", i);
772 dump_copy_of (dump_file, arg);
773 fprintf (dump_file, "\n");
776 arg_val = get_copy_of_val (arg);
778 /* If the LHS didn't have a value yet, make it a copy of the
779 first argument we find. Notice that while we make the LHS be
780 a copy of the argument itself, we take the memory reference
781 from the argument's value so that we can compare it to the
782 memory reference of all the other arguments. */
783 if (phi_val.value == NULL_TREE)
786 phi_val.mem_ref = arg_val->mem_ref;
790 /* If PHI_VAL and ARG don't have a common copy-of chain, then
791 this PHI node cannot be a copy operation. Also, if we are
792 copy propagating stores and these two arguments came from
793 different memory references, they cannot be considered
795 if (get_last_copy_of (phi_val.value) != get_last_copy_of (arg)
796 || (do_store_copy_prop
799 && simple_cst_equal (phi_val.mem_ref, arg_val->mem_ref) != 1))
806 if (phi_val.value && set_copy_of_val (lhs, phi_val.value, phi_val.mem_ref))
807 retval = (phi_val.value != lhs) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING;
809 retval = SSA_PROP_NOT_INTERESTING;
811 if (dump_file && (dump_flags & TDF_DETAILS))
813 fprintf (dump_file, "\nPHI node ");
814 dump_copy_of (dump_file, lhs);
815 fprintf (dump_file, "\nTelling the propagator to ");
816 if (retval == SSA_PROP_INTERESTING)
817 fprintf (dump_file, "add SSA edges out of this PHI and continue.");
818 else if (retval == SSA_PROP_VARYING)
819 fprintf (dump_file, "add SSA edges out of this PHI and never visit again.");
821 fprintf (dump_file, "do nothing with SSA edges and keep iterating.");
822 fprintf (dump_file, "\n\n");
829 /* Initialize structures used for copy propagation. */
832 init_copy_prop (void)
836 copy_of = xmalloc (num_ssa_names * sizeof (*copy_of));
837 memset (copy_of, 0, num_ssa_names * sizeof (*copy_of));
839 cached_last_copy_of = xmalloc (num_ssa_names * sizeof (*cached_last_copy_of));
840 memset (cached_last_copy_of, 0, num_ssa_names * sizeof (*cached_last_copy_of));
844 block_stmt_iterator si;
847 for (si = bsi_start (bb); !bsi_end_p (si); bsi_next (&si))
849 tree stmt = bsi_stmt (si);
851 /* The only statements that we care about are those that may
852 generate useful copies. We also need to mark conditional
853 jumps so that their outgoing edges are added to the work
854 lists of the propagator. */
855 if (stmt_ends_bb_p (stmt))
856 DONT_SIMULATE_AGAIN (stmt) = false;
857 else if (stmt_may_generate_copy (stmt))
858 DONT_SIMULATE_AGAIN (stmt) = false;
864 /* No need to simulate this statement anymore. */
865 DONT_SIMULATE_AGAIN (stmt) = true;
867 /* Mark all the outputs of this statement as not being
868 the copy of anything. */
869 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
870 set_copy_of_val (def, def, NULL_TREE);
874 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
875 DONT_SIMULATE_AGAIN (phi) = false;
880 /* Deallocate memory used in copy propagation and do final
884 fini_copy_prop (void)
888 /* Set the final copy-of value for each variable by traversing the
890 for (i = 1; i < num_ssa_names; i++)
892 tree var = ssa_name (i);
893 if (var && copy_of[i].value && copy_of[i].value != var)
894 copy_of[i].value = get_last_copy_of (var);
897 substitute_and_fold (copy_of);
899 free (cached_last_copy_of);
904 /* Main entry point to the copy propagator. The algorithm propagates
905 the value COPY-OF using ssa_propagate. For every variable X_i,
906 COPY-OF(X_i) indicates which variable is X_i created from. The
907 following example shows how the algorithm proceeds at a high level:
910 2 a_2 = PHI <a_24, x_1>
912 4 x_1 = PHI <x_298, a_5, a_2>
914 The end result should be that a_2, a_5, a_24 and x_1 are a copy of
915 x_298. Propagation proceeds as follows.
917 Visit #1: a_24 is copy-of x_1. Value changed.
918 Visit #2: a_2 is copy-of x_1. Value changed.
919 Visit #3: a_5 is copy-of x_1. Value changed.
920 Visit #4: x_1 is copy-of x_298. Value changed.
921 Visit #1: a_24 is copy-of x_298. Value changed.
922 Visit #2: a_2 is copy-of x_298. Value changed.
923 Visit #3: a_5 is copy-of x_298. Value changed.
924 Visit #4: x_1 is copy-of x_298. Stable state reached.
926 When visiting PHI nodes, we only consider arguments that flow
927 through edges marked executable by the propagation engine. So,
928 when visiting statement #2 for the first time, we will only look at
929 the first argument (a_24) and optimistically assume that its value
930 is the copy of a_24 (x_1).
932 The problem with this approach is that it may fail to discover copy
933 relations in PHI cycles. Instead of propagating copy-of
934 values, we actually propagate copy-of chains. For instance:
941 In this code fragment, COPY-OF (X_i) = { D_4, C_9, A_3, B_1 }.
942 Obviously, we are only really interested in the last value of the
943 chain, however the propagator needs to access the copy-of chain
944 when visiting PHI nodes.
946 To represent the copy-of chain, we use the array COPY_CHAINS, which
947 holds the first link in the copy-of chain for every variable.
948 If variable X_i is a copy of X_j, which in turn is a copy of X_k,
949 the array will contain:
955 Keeping copy-of chains instead of copy-of values directly becomes
956 important when visiting PHI nodes. Suppose that we had the
957 following PHI cycle, such that x_52 is already considered a copy of
960 1 x_54 = PHI <x_53, x_52>
961 2 x_53 = PHI <x_898, x_54>
963 Visit #1: x_54 is copy-of x_53 (because x_52 is copy-of x_53)
964 Visit #2: x_53 is copy-of x_898 (because x_54 is a copy of x_53,
965 so it is considered irrelevant
967 Visit #1: x_54 is copy-of nothing (x_53 is a copy-of x_898 and
968 x_52 is a copy of x_53, so
970 Visit #2: x_53 is copy-of nothing
972 This problem is avoided by keeping a chain of copies, instead of
973 the final copy-of value. Propagation will now only keep the first
974 element of a variable's copy-of chain. When visiting PHI nodes,
975 arguments are considered equal if their copy-of chains end in the
976 same variable. So, as long as their copy-of chains overlap, we
977 know that they will be a copy of the same variable, regardless of
978 which variable that may be).
980 Propagation would then proceed as follows (the notation a -> b
981 means that a is a copy-of b):
983 Visit #1: x_54 = PHI <x_53, x_52>
986 Result: x_54 -> x_53. Value changed. Add SSA edges.
988 Visit #1: x_53 = PHI <x_898, x_54>
991 Result: x_53 -> x_898. Value changed. Add SSA edges.
993 Visit #2: x_54 = PHI <x_53, x_52>
995 x_52 -> x_53 -> x_898
996 Result: x_54 -> x_898. Value changed. Add SSA edges.
998 Visit #2: x_53 = PHI <x_898, x_54>
1001 Result: x_53 -> x_898. Value didn't change. Stable state
1003 Once the propagator stabilizes, we end up with the desired result
1004 x_53 and x_54 are both copies of x_898. */
1007 execute_copy_prop (bool store_copy_prop)
1009 do_store_copy_prop = store_copy_prop;
1011 ssa_propagate (copy_prop_visit_stmt, copy_prop_visit_phi_node);
1017 gate_copy_prop (void)
1019 return flag_tree_copy_prop != 0;
1025 execute_copy_prop (false);
1028 struct tree_opt_pass pass_copy_prop =
1030 "copyprop", /* name */
1031 gate_copy_prop, /* gate */
1032 do_copy_prop, /* execute */
1035 0, /* static_pass_number */
1036 TV_TREE_COPY_PROP, /* tv_id */
1037 PROP_ssa | PROP_alias | PROP_cfg, /* properties_required */
1038 0, /* properties_provided */
1039 0, /* properties_destroyed */
1040 0, /* todo_flags_start */
1045 | TODO_update_ssa, /* todo_flags_finish */
1051 gate_store_copy_prop (void)
1053 /* STORE-COPY-PROP is enabled only with -ftree-store-copy-prop, but
1054 when -fno-tree-store-copy-prop is specified, we should run
1055 regular COPY-PROP. That's why the pass is enabled with either
1057 return flag_tree_store_copy_prop != 0 || flag_tree_copy_prop != 0;
1061 store_copy_prop (void)
1063 /* If STORE-COPY-PROP is not enabled, we just run regular COPY-PROP. */
1064 execute_copy_prop (flag_tree_store_copy_prop != 0);
1067 struct tree_opt_pass pass_store_copy_prop =
1069 "store_copyprop", /* name */
1070 gate_store_copy_prop, /* gate */
1071 store_copy_prop, /* execute */
1074 0, /* static_pass_number */
1075 TV_TREE_STORE_COPY_PROP, /* tv_id */
1076 PROP_ssa | PROP_alias | PROP_cfg, /* properties_required */
1077 0, /* properties_provided */
1078 0, /* properties_destroyed */
1079 0, /* todo_flags_start */
1084 | TODO_update_ssa, /* todo_flags_finish */