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, 51 Franklin Street, Fifth Floor,
19 Boston, MA 02110-1301, 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))->symbol_mem_tag;
112 tree mt_orig = var_ann (SSA_NAME_VAR (orig))->symbol_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 symbol tags. If both pointers had a tag and they
191 are different, then something has gone wrong. Symbol tags can
192 always be merged because they are flow insensitive, all the SSA
193 names of the same base DECL share the same symbol tag. */
194 if (new_ann->symbol_mem_tag == NULL_TREE)
195 new_ann->symbol_mem_tag = orig_ann->symbol_mem_tag;
196 else if (orig_ann->symbol_mem_tag == NULL_TREE)
197 orig_ann->symbol_mem_tag = new_ann->symbol_mem_tag;
199 gcc_assert (new_ann->symbol_mem_tag == orig_ann->symbol_mem_tag);
201 /* Check that flow-sensitive information is compatible. Notice that
202 we may not merge flow-sensitive information here. This function
203 is called when propagating equivalences dictated by the IL, like
204 a copy operation P_i = Q_j, and from equivalences dictated by
205 control-flow, like if (P_i == Q_j).
207 In the former case, P_i and Q_j are equivalent in every block
208 dominated by the assignment, so their flow-sensitive information
209 is always the same. However, in the latter case, the pointers
210 P_i and Q_j are only equivalent in one of the sub-graphs out of
211 the predicate, so their flow-sensitive information is not the
212 same in every block dominated by the predicate.
214 Since we cannot distinguish one case from another in this
215 function, we can only make sure that if P_i and Q_j have
216 flow-sensitive information, they should be compatible. */
217 if (SSA_NAME_PTR_INFO (orig) && SSA_NAME_PTR_INFO (new))
219 struct ptr_info_def *orig_ptr_info = SSA_NAME_PTR_INFO (orig);
220 struct ptr_info_def *new_ptr_info = SSA_NAME_PTR_INFO (new);
222 /* Note that pointer NEW and ORIG may actually have different
223 pointed-to variables (e.g., PR 18291 represented in
224 testsuite/gcc.c-torture/compile/pr18291.c). However, since
225 NEW is being copy-propagated into ORIG, it must always be
226 true that the pointed-to set for pointer NEW is the same, or
227 a subset, of the pointed-to set for pointer ORIG. If this
228 isn't the case, we shouldn't have been able to do the
229 propagation of NEW into ORIG. */
230 if (orig_ptr_info->name_mem_tag
231 && new_ptr_info->name_mem_tag
232 && orig_ptr_info->pt_vars
233 && new_ptr_info->pt_vars)
234 gcc_assert (bitmap_intersect_p (new_ptr_info->pt_vars,
235 orig_ptr_info->pt_vars));
240 /* Common code for propagate_value and replace_exp.
242 Replace use operand OP_P with VAL. FOR_PROPAGATION indicates if the
243 replacement is done to propagate a value or not. */
246 replace_exp_1 (use_operand_p op_p, tree val,
247 bool for_propagation ATTRIBUTE_UNUSED)
249 tree op = USE_FROM_PTR (op_p);
251 #if defined ENABLE_CHECKING
252 gcc_assert (!(for_propagation
253 && TREE_CODE (op) == SSA_NAME
254 && TREE_CODE (val) == SSA_NAME
255 && !may_propagate_copy (op, val)));
258 if (TREE_CODE (val) == SSA_NAME)
260 if (TREE_CODE (op) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (op)))
261 merge_alias_info (op, val);
265 SET_USE (op_p, unsave_expr_now (val));
269 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
270 into the operand pointed to by OP_P.
272 Use this version for const/copy propagation as it will perform additional
273 checks to ensure validity of the const/copy propagation. */
276 propagate_value (use_operand_p op_p, tree val)
278 replace_exp_1 (op_p, val, true);
282 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
283 into the tree pointed to by OP_P.
285 Use this version for const/copy propagation when SSA operands are not
286 available. It will perform the additional checks to ensure validity of
287 the const/copy propagation, but will not update any operand information.
288 Be sure to mark the stmt as modified. */
291 propagate_tree_value (tree *op_p, tree val)
293 #if defined ENABLE_CHECKING
294 gcc_assert (!(TREE_CODE (val) == SSA_NAME
295 && TREE_CODE (*op_p) == SSA_NAME
296 && !may_propagate_copy (*op_p, val)));
299 if (TREE_CODE (val) == SSA_NAME)
301 if (TREE_CODE (*op_p) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (*op_p)))
302 merge_alias_info (*op_p, val);
306 *op_p = unsave_expr_now (val);
310 /* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).
312 Use this version when not const/copy propagating values. For example,
313 PRE uses this version when building expressions as they would appear
314 in specific blocks taking into account actions of PHI nodes. */
317 replace_exp (use_operand_p op_p, tree val)
319 replace_exp_1 (op_p, val, false);
323 /*---------------------------------------------------------------------------
325 ---------------------------------------------------------------------------*/
326 /* During propagation, we keep chains of variables that are copies of
327 one another. If variable X_i is a copy of X_j and X_j is a copy of
328 X_k, COPY_OF will contain:
330 COPY_OF[i].VALUE = X_j
331 COPY_OF[j].VALUE = X_k
332 COPY_OF[k].VALUE = X_k
334 After propagation, the copy-of value for each variable X_i is
335 converted into the final value by walking the copy-of chains and
336 updating COPY_OF[i].VALUE to be the last element of the chain. */
337 static prop_value_t *copy_of;
339 /* Used in set_copy_of_val to determine if the last link of a copy-of
340 chain has changed. */
341 static tree *cached_last_copy_of;
343 /* True if we are doing copy propagation on loads and stores. */
344 static bool do_store_copy_prop;
347 /* Return true if this statement may generate a useful copy. */
350 stmt_may_generate_copy (tree stmt)
355 if (TREE_CODE (stmt) == PHI_NODE)
356 return !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (stmt));
358 if (TREE_CODE (stmt) != MODIFY_EXPR)
361 lhs = TREE_OPERAND (stmt, 0);
362 rhs = TREE_OPERAND (stmt, 1);
363 ann = stmt_ann (stmt);
365 /* If the statement has volatile operands, it won't generate a
367 if (ann->has_volatile_ops)
370 /* If we are not doing store copy-prop, statements with loads and/or
371 stores will never generate a useful copy. */
372 if (!do_store_copy_prop
373 && !ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS))
376 /* Otherwise, the only statements that generate useful copies are
377 assignments whose RHS is just an SSA name that doesn't flow
378 through abnormal edges. */
379 return TREE_CODE (rhs) == SSA_NAME && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs);
383 /* Return the copy-of value for VAR. */
385 static inline prop_value_t *
386 get_copy_of_val (tree var)
388 prop_value_t *val = ©_of[SSA_NAME_VERSION (var)];
390 if (val->value == NULL_TREE
391 && !stmt_may_generate_copy (SSA_NAME_DEF_STMT (var)))
393 /* If the variable will never generate a useful copy relation,
394 make it its own copy. */
396 val->mem_ref = NULL_TREE;
403 /* Return last link in the copy-of chain for VAR. */
406 get_last_copy_of (tree var)
411 /* Traverse COPY_OF starting at VAR until we get to the last
412 link in the chain. Since it is possible to have cycles in PHI
413 nodes, the copy-of chain may also contain cycles.
415 To avoid infinite loops and to avoid traversing lengthy copy-of
416 chains, we artificially limit the maximum number of chains we are
419 The value 5 was taken from a compiler and runtime library
420 bootstrap and a mixture of C and C++ code from various sources.
421 More than 82% of all copy-of chains were shorter than 5 links. */
425 for (i = 0; i < LIMIT; i++)
427 tree copy = copy_of[SSA_NAME_VERSION (last)].value;
428 if (copy == NULL_TREE || copy == last)
433 /* If we have reached the limit, then we are either in a copy-of
434 cycle or the copy-of chain is too long. In this case, just
435 return VAR so that it is not considered a copy of anything. */
436 return (i < LIMIT ? last : var);
440 /* Set FIRST to be the first variable in the copy-of chain for DEST.
441 If DEST's copy-of value or its copy-of chain has changed, return
444 MEM_REF is the memory reference where FIRST is stored. This is
445 used when DEST is a non-register and we are copy propagating loads
449 set_copy_of_val (tree dest, tree first, tree mem_ref)
451 unsigned int dest_ver = SSA_NAME_VERSION (dest);
452 tree old_first, old_last, new_last;
454 /* Set FIRST to be the first link in COPY_OF[DEST]. If that
455 changed, return true. */
456 old_first = copy_of[dest_ver].value;
457 copy_of[dest_ver].value = first;
458 copy_of[dest_ver].mem_ref = mem_ref;
460 if (old_first != first)
463 /* If FIRST and OLD_FIRST are the same, we need to check whether the
464 copy-of chain starting at FIRST ends in a different variable. If
465 the copy-of chain starting at FIRST ends up in a different
466 variable than the last cached value we had for DEST, then return
467 true because DEST is now a copy of a different variable.
469 This test is necessary because even though the first link in the
470 copy-of chain may not have changed, if any of the variables in
471 the copy-of chain changed its final value, DEST will now be the
472 copy of a different variable, so we have to do another round of
473 propagation for everything that depends on DEST. */
474 old_last = cached_last_copy_of[dest_ver];
475 new_last = get_last_copy_of (dest);
476 cached_last_copy_of[dest_ver] = new_last;
478 return (old_last != new_last);
482 /* Dump the copy-of value for variable VAR to FILE. */
485 dump_copy_of (FILE *file, tree var)
490 print_generic_expr (file, var, dump_flags);
492 if (TREE_CODE (var) != SSA_NAME)
495 visited = sbitmap_alloc (num_ssa_names);
496 sbitmap_zero (visited);
497 SET_BIT (visited, SSA_NAME_VERSION (var));
499 fprintf (file, " copy-of chain: ");
502 print_generic_expr (file, val, 0);
504 while (copy_of[SSA_NAME_VERSION (val)].value)
506 fprintf (file, "-> ");
507 val = copy_of[SSA_NAME_VERSION (val)].value;
508 print_generic_expr (file, val, 0);
510 if (TEST_BIT (visited, SSA_NAME_VERSION (val)))
512 SET_BIT (visited, SSA_NAME_VERSION (val));
515 val = get_copy_of_val (var)->value;
516 if (val == NULL_TREE)
517 fprintf (file, "[UNDEFINED]");
519 fprintf (file, "[COPY]");
521 fprintf (file, "[NOT A COPY]");
523 sbitmap_free (visited);
527 /* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS
528 value and store the LHS into *RESULT_P. If STMT generates more
529 than one name (i.e., STMT is an aliased store), it is enough to
530 store the first name in the V_MAY_DEF list into *RESULT_P. After
531 all, the names generated will be VUSEd in the same statements. */
533 static enum ssa_prop_result
534 copy_prop_visit_assignment (tree stmt, tree *result_p)
537 prop_value_t *rhs_val;
539 lhs = TREE_OPERAND (stmt, 0);
540 rhs = TREE_OPERAND (stmt, 1);
542 gcc_assert (TREE_CODE (rhs) == SSA_NAME);
544 rhs_val = get_copy_of_val (rhs);
546 if (TREE_CODE (lhs) == SSA_NAME)
548 /* Straight copy between two SSA names. First, make sure that
549 we can propagate the RHS into uses of LHS. */
550 if (!may_propagate_copy (lhs, rhs))
551 return SSA_PROP_VARYING;
553 /* Notice that in the case of assignments, we make the LHS be a
554 copy of RHS's value, not of RHS itself. This avoids keeping
555 unnecessary copy-of chains (assignments cannot be in a cycle
556 like PHI nodes), speeding up the propagation process.
557 This is different from what we do in copy_prop_visit_phi_node.
558 In those cases, we are interested in the copy-of chains. */
560 if (set_copy_of_val (*result_p, rhs_val->value, rhs_val->mem_ref))
561 return SSA_PROP_INTERESTING;
563 return SSA_PROP_NOT_INTERESTING;
565 else if (stmt_makes_single_store (stmt))
567 /* Otherwise, set the names in V_MAY_DEF/V_MUST_DEF operands
568 to be a copy of RHS. */
573 /* This should only be executed when doing store copy-prop. */
574 gcc_assert (do_store_copy_prop);
576 /* Set the value of every VDEF to RHS_VAL. */
578 FOR_EACH_SSA_TREE_OPERAND (vdef, stmt, i, SSA_OP_VIRTUAL_DEFS)
579 changed |= set_copy_of_val (vdef, rhs_val->value, lhs);
581 /* Note that for propagation purposes, we are only interested in
582 visiting statements that load the exact same memory reference
583 stored here. Those statements will have the exact same list
584 of virtual uses, so it is enough to set the output of this
585 statement to be its first virtual definition. */
586 *result_p = first_vdef (stmt);
589 return SSA_PROP_INTERESTING;
591 return SSA_PROP_NOT_INTERESTING;
595 return SSA_PROP_VARYING;
599 /* Visit the COND_EXPR STMT. Return SSA_PROP_INTERESTING
600 if it can determine which edge will be taken. Otherwise, return
603 static enum ssa_prop_result
604 copy_prop_visit_cond_stmt (tree stmt, edge *taken_edge_p)
606 enum ssa_prop_result retval;
609 cond = COND_EXPR_COND (stmt);
610 retval = SSA_PROP_VARYING;
612 /* The only conditionals that we may be able to compute statically
613 are predicates involving two SSA_NAMEs. */
614 if (COMPARISON_CLASS_P (cond)
615 && TREE_CODE (TREE_OPERAND (cond, 0)) == SSA_NAME
616 && TREE_CODE (TREE_OPERAND (cond, 1)) == SSA_NAME)
618 tree op0 = get_last_copy_of (TREE_OPERAND (cond, 0));
619 tree op1 = get_last_copy_of (TREE_OPERAND (cond, 1));
621 /* See if we can determine the predicate's value. */
622 if (dump_file && (dump_flags & TDF_DETAILS))
624 fprintf (dump_file, "Trying to determine truth value of ");
625 fprintf (dump_file, "predicate ");
626 print_generic_stmt (dump_file, cond, 0);
629 /* We can fold COND and get a useful result only when we have
630 the same SSA_NAME on both sides of a comparison operator. */
633 tree folded_cond = fold_binary (TREE_CODE (cond), boolean_type_node,
637 basic_block bb = bb_for_stmt (stmt);
638 *taken_edge_p = find_taken_edge (bb, folded_cond);
640 retval = SSA_PROP_INTERESTING;
645 if (dump_file && (dump_flags & TDF_DETAILS) && *taken_edge_p)
646 fprintf (dump_file, "\nConditional will always take edge %d->%d\n",
647 (*taken_edge_p)->src->index, (*taken_edge_p)->dest->index);
653 /* Evaluate statement STMT. If the statement produces a new output
654 value, return SSA_PROP_INTERESTING and store the SSA_NAME holding
655 the new value in *RESULT_P.
657 If STMT is a conditional branch and we can determine its truth
658 value, set *TAKEN_EDGE_P accordingly.
660 If the new value produced by STMT is varying, return
663 static enum ssa_prop_result
664 copy_prop_visit_stmt (tree stmt, edge *taken_edge_p, tree *result_p)
666 enum ssa_prop_result retval;
668 if (dump_file && (dump_flags & TDF_DETAILS))
670 fprintf (dump_file, "\nVisiting statement:\n");
671 print_generic_stmt (dump_file, stmt, dump_flags);
672 fprintf (dump_file, "\n");
675 if (TREE_CODE (stmt) == MODIFY_EXPR
676 && TREE_CODE (TREE_OPERAND (stmt, 1)) == SSA_NAME
677 && (do_store_copy_prop
678 || TREE_CODE (TREE_OPERAND (stmt, 0)) == SSA_NAME))
680 /* If the statement is a copy assignment, evaluate its RHS to
681 see if the lattice value of its output has changed. */
682 retval = copy_prop_visit_assignment (stmt, result_p);
684 else if (TREE_CODE (stmt) == COND_EXPR)
686 /* See if we can determine which edge goes out of a conditional
688 retval = copy_prop_visit_cond_stmt (stmt, taken_edge_p);
691 retval = SSA_PROP_VARYING;
693 if (retval == SSA_PROP_VARYING)
698 /* Any other kind of statement is not interesting for constant
699 propagation and, therefore, not worth simulating. */
700 if (dump_file && (dump_flags & TDF_DETAILS))
701 fprintf (dump_file, "No interesting values produced.\n");
703 /* The assignment is not a copy operation. Don't visit this
704 statement again and mark all the definitions in the statement
705 to be copies of nothing. */
706 FOR_EACH_SSA_TREE_OPERAND (def, stmt, i, SSA_OP_ALL_DEFS)
707 set_copy_of_val (def, def, NULL_TREE);
714 /* Visit PHI node PHI. If all the arguments produce the same value,
715 set it to be the value of the LHS of PHI. */
717 static enum ssa_prop_result
718 copy_prop_visit_phi_node (tree phi)
720 enum ssa_prop_result retval;
723 prop_value_t phi_val = { 0, NULL_TREE, NULL_TREE };
725 lhs = PHI_RESULT (phi);
727 if (dump_file && (dump_flags & TDF_DETAILS))
729 fprintf (dump_file, "\nVisiting PHI node: ");
730 print_generic_expr (dump_file, phi, dump_flags);
731 fprintf (dump_file, "\n\n");
734 for (i = 0; i < PHI_NUM_ARGS (phi); i++)
736 prop_value_t *arg_val;
737 tree arg = PHI_ARG_DEF (phi, i);
738 edge e = PHI_ARG_EDGE (phi, i);
740 /* We don't care about values flowing through non-executable
742 if (!(e->flags & EDGE_EXECUTABLE))
745 /* Constants in the argument list never generate a useful copy.
746 Similarly, names that flow through abnormal edges cannot be
747 used to derive copies. */
748 if (TREE_CODE (arg) != SSA_NAME || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg))
754 /* Avoid copy propagation from an inner into an outer loop.
755 Otherwise, this may move loop variant variables outside of
756 their loops and prevent coalescing opportunities. If the
757 value was loop invariant, it will be hoisted by LICM and
758 exposed for copy propagation. */
759 if (loop_depth_of_name (arg) > loop_depth_of_name (lhs))
765 /* If the LHS appears in the argument list, ignore it. It is
766 irrelevant as a copy. */
767 if (arg == lhs || get_last_copy_of (arg) == lhs)
770 if (dump_file && (dump_flags & TDF_DETAILS))
772 fprintf (dump_file, "\tArgument #%d: ", i);
773 dump_copy_of (dump_file, arg);
774 fprintf (dump_file, "\n");
777 arg_val = get_copy_of_val (arg);
779 /* If the LHS didn't have a value yet, make it a copy of the
780 first argument we find. Notice that while we make the LHS be
781 a copy of the argument itself, we take the memory reference
782 from the argument's value so that we can compare it to the
783 memory reference of all the other arguments. */
784 if (phi_val.value == NULL_TREE)
787 phi_val.mem_ref = arg_val->mem_ref;
791 /* If PHI_VAL and ARG don't have a common copy-of chain, then
792 this PHI node cannot be a copy operation. Also, if we are
793 copy propagating stores and these two arguments came from
794 different memory references, they cannot be considered
796 if (get_last_copy_of (phi_val.value) != get_last_copy_of (arg)
797 || (do_store_copy_prop
800 && simple_cst_equal (phi_val.mem_ref, arg_val->mem_ref) != 1))
807 if (phi_val.value && set_copy_of_val (lhs, phi_val.value, phi_val.mem_ref))
808 retval = (phi_val.value != lhs) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING;
810 retval = SSA_PROP_NOT_INTERESTING;
812 if (dump_file && (dump_flags & TDF_DETAILS))
814 fprintf (dump_file, "\nPHI node ");
815 dump_copy_of (dump_file, lhs);
816 fprintf (dump_file, "\nTelling the propagator to ");
817 if (retval == SSA_PROP_INTERESTING)
818 fprintf (dump_file, "add SSA edges out of this PHI and continue.");
819 else if (retval == SSA_PROP_VARYING)
820 fprintf (dump_file, "add SSA edges out of this PHI and never visit again.");
822 fprintf (dump_file, "do nothing with SSA edges and keep iterating.");
823 fprintf (dump_file, "\n\n");
830 /* Initialize structures used for copy propagation. PHIS_ONLY is true
831 if we should only consider PHI nodes as generating copy propagation
835 init_copy_prop (void)
839 copy_of = XNEWVEC (prop_value_t, num_ssa_names);
840 memset (copy_of, 0, num_ssa_names * sizeof (*copy_of));
842 cached_last_copy_of = XNEWVEC (tree, num_ssa_names);
843 memset (cached_last_copy_of, 0, num_ssa_names * sizeof (*cached_last_copy_of));
847 block_stmt_iterator si;
849 int depth = bb->loop_depth;
851 for (si = bsi_start (bb); !bsi_end_p (si); bsi_next (&si))
853 tree stmt = bsi_stmt (si);
856 /* The only statements that we care about are those that may
857 generate useful copies. We also need to mark conditional
858 jumps so that their outgoing edges are added to the work
859 lists of the propagator.
861 Avoid copy propagation from an inner into an outer loop.
862 Otherwise, this may move loop variant variables outside of
863 their loops and prevent coalescing opportunities. If the
864 value was loop invariant, it will be hoisted by LICM and
865 exposed for copy propagation. */
866 if (stmt_ends_bb_p (stmt))
867 DONT_SIMULATE_AGAIN (stmt) = false;
868 else if (stmt_may_generate_copy (stmt)
869 && loop_depth_of_name (TREE_OPERAND (stmt, 1)) <= depth)
870 DONT_SIMULATE_AGAIN (stmt) = false;
872 DONT_SIMULATE_AGAIN (stmt) = true;
874 /* Mark all the outputs of this statement as not being
875 the copy of anything. */
876 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
877 if (DONT_SIMULATE_AGAIN (stmt))
878 set_copy_of_val (def, def, NULL_TREE);
880 cached_last_copy_of[SSA_NAME_VERSION (def)] = def;
883 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
885 def = PHI_RESULT (phi);
886 if (!do_store_copy_prop && !is_gimple_reg (def))
887 DONT_SIMULATE_AGAIN (phi) = true;
889 DONT_SIMULATE_AGAIN (phi) = false;
891 if (DONT_SIMULATE_AGAIN (phi))
892 set_copy_of_val (def, def, NULL_TREE);
894 cached_last_copy_of[SSA_NAME_VERSION (def)] = def;
900 /* Deallocate memory used in copy propagation and do final
904 fini_copy_prop (void)
909 /* Set the final copy-of value for each variable by traversing the
911 tmp = XNEWVEC (prop_value_t, num_ssa_names);
912 memset (tmp, 0, num_ssa_names * sizeof (*tmp));
913 for (i = 1; i < num_ssa_names; i++)
915 tree var = ssa_name (i);
916 if (var && copy_of[i].value && copy_of[i].value != var)
917 tmp[i].value = get_last_copy_of (var);
920 substitute_and_fold (tmp, false);
922 free (cached_last_copy_of);
928 /* Main entry point to the copy propagator.
930 PHIS_ONLY is true if we should only consider PHI nodes as generating
931 copy propagation opportunities.
933 The algorithm propagates the value COPY-OF using ssa_propagate. For
934 every variable X_i, COPY-OF(X_i) indicates which variable is X_i created
935 from. The following example shows how the algorithm proceeds at a
939 2 a_2 = PHI <a_24, x_1>
941 4 x_1 = PHI <x_298, a_5, a_2>
943 The end result should be that a_2, a_5, a_24 and x_1 are a copy of
944 x_298. Propagation proceeds as follows.
946 Visit #1: a_24 is copy-of x_1. Value changed.
947 Visit #2: a_2 is copy-of x_1. Value changed.
948 Visit #3: a_5 is copy-of x_1. Value changed.
949 Visit #4: x_1 is copy-of x_298. Value changed.
950 Visit #1: a_24 is copy-of x_298. Value changed.
951 Visit #2: a_2 is copy-of x_298. Value changed.
952 Visit #3: a_5 is copy-of x_298. Value changed.
953 Visit #4: x_1 is copy-of x_298. Stable state reached.
955 When visiting PHI nodes, we only consider arguments that flow
956 through edges marked executable by the propagation engine. So,
957 when visiting statement #2 for the first time, we will only look at
958 the first argument (a_24) and optimistically assume that its value
959 is the copy of a_24 (x_1).
961 The problem with this approach is that it may fail to discover copy
962 relations in PHI cycles. Instead of propagating copy-of
963 values, we actually propagate copy-of chains. For instance:
970 In this code fragment, COPY-OF (X_i) = { D_4, C_9, A_3, B_1 }.
971 Obviously, we are only really interested in the last value of the
972 chain, however the propagator needs to access the copy-of chain
973 when visiting PHI nodes.
975 To represent the copy-of chain, we use the array COPY_CHAINS, which
976 holds the first link in the copy-of chain for every variable.
977 If variable X_i is a copy of X_j, which in turn is a copy of X_k,
978 the array will contain:
984 Keeping copy-of chains instead of copy-of values directly becomes
985 important when visiting PHI nodes. Suppose that we had the
986 following PHI cycle, such that x_52 is already considered a copy of
989 1 x_54 = PHI <x_53, x_52>
990 2 x_53 = PHI <x_898, x_54>
992 Visit #1: x_54 is copy-of x_53 (because x_52 is copy-of x_53)
993 Visit #2: x_53 is copy-of x_898 (because x_54 is a copy of x_53,
994 so it is considered irrelevant
996 Visit #1: x_54 is copy-of nothing (x_53 is a copy-of x_898 and
997 x_52 is a copy of x_53, so
999 Visit #2: x_53 is copy-of nothing
1001 This problem is avoided by keeping a chain of copies, instead of
1002 the final copy-of value. Propagation will now only keep the first
1003 element of a variable's copy-of chain. When visiting PHI nodes,
1004 arguments are considered equal if their copy-of chains end in the
1005 same variable. So, as long as their copy-of chains overlap, we
1006 know that they will be a copy of the same variable, regardless of
1007 which variable that may be).
1009 Propagation would then proceed as follows (the notation a -> b
1010 means that a is a copy-of b):
1012 Visit #1: x_54 = PHI <x_53, x_52>
1015 Result: x_54 -> x_53. Value changed. Add SSA edges.
1017 Visit #1: x_53 = PHI <x_898, x_54>
1020 Result: x_53 -> x_898. Value changed. Add SSA edges.
1022 Visit #2: x_54 = PHI <x_53, x_52>
1024 x_52 -> x_53 -> x_898
1025 Result: x_54 -> x_898. Value changed. Add SSA edges.
1027 Visit #2: x_53 = PHI <x_898, x_54>
1030 Result: x_53 -> x_898. Value didn't change. Stable state
1032 Once the propagator stabilizes, we end up with the desired result
1033 x_53 and x_54 are both copies of x_898. */
1036 execute_copy_prop (bool store_copy_prop)
1038 do_store_copy_prop = store_copy_prop;
1040 ssa_propagate (copy_prop_visit_stmt, copy_prop_visit_phi_node);
1046 gate_copy_prop (void)
1048 return flag_tree_copy_prop != 0;
1054 execute_copy_prop (false);
1058 struct tree_opt_pass pass_copy_prop =
1060 "copyprop", /* name */
1061 gate_copy_prop, /* gate */
1062 do_copy_prop, /* execute */
1065 0, /* static_pass_number */
1066 TV_TREE_COPY_PROP, /* tv_id */
1067 PROP_ssa | PROP_alias | PROP_cfg, /* properties_required */
1068 0, /* properties_provided */
1069 0, /* properties_destroyed */
1070 0, /* todo_flags_start */
1075 | TODO_update_ssa, /* todo_flags_finish */
1080 gate_store_copy_prop (void)
1082 /* STORE-COPY-PROP is enabled only with -ftree-store-copy-prop, but
1083 when -fno-tree-store-copy-prop is specified, we should run
1084 regular COPY-PROP. That's why the pass is enabled with either
1086 return flag_tree_store_copy_prop != 0 || flag_tree_copy_prop != 0;
1090 store_copy_prop (void)
1092 /* If STORE-COPY-PROP is not enabled, we just run regular COPY-PROP. */
1093 execute_copy_prop (flag_tree_store_copy_prop != 0);
1097 struct tree_opt_pass pass_store_copy_prop =
1099 "store_copyprop", /* name */
1100 gate_store_copy_prop, /* gate */
1101 store_copy_prop, /* execute */
1104 0, /* static_pass_number */
1105 TV_TREE_STORE_COPY_PROP, /* tv_id */
1106 PROP_ssa | PROP_alias | PROP_cfg, /* properties_required */
1107 0, /* properties_provided */
1108 0, /* properties_destroyed */
1109 0, /* todo_flags_start */
1114 | TODO_update_ssa, /* todo_flags_finish */