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 /* For memory partitions, copies are OK as long as the memory symbol
67 belongs to the partition. */
68 if (TREE_CODE (dest
) == SSA_NAME
69 && TREE_CODE (SSA_NAME_VAR (dest
)) == MEMORY_PARTITION_TAG
)
70 return (TREE_CODE (orig
) == SSA_NAME
71 && !is_gimple_reg (orig
)
72 && (SSA_NAME_VAR (dest
) == SSA_NAME_VAR (orig
)
73 || bitmap_bit_p (MPT_SYMBOLS (SSA_NAME_VAR (dest
)),
74 DECL_UID (SSA_NAME_VAR (orig
)))));
76 if (TREE_CODE (orig
) == SSA_NAME
77 && TREE_CODE (SSA_NAME_VAR (orig
)) == MEMORY_PARTITION_TAG
)
78 return (TREE_CODE (dest
) == SSA_NAME
79 && !is_gimple_reg (dest
)
80 && (SSA_NAME_VAR (dest
) == SSA_NAME_VAR (orig
)
81 || bitmap_bit_p (MPT_SYMBOLS (SSA_NAME_VAR (orig
)),
82 DECL_UID (SSA_NAME_VAR (dest
)))));
84 /* Do not copy between types for which we *do* need a conversion. */
85 if (!tree_ssa_useless_type_conversion_1 (type_d
, type_o
))
88 /* FIXME. GIMPLE is allowing pointer assignments and comparisons of
89 pointers that have different alias sets. This means that these
90 pointers will have different memory tags associated to them.
92 If we allow copy propagation in these cases, statements de-referencing
93 the new pointer will now have a reference to a different memory tag
94 with potentially incorrect SSA information.
96 This was showing up in libjava/java/util/zip/ZipFile.java with code
99 struct java.io.BufferedInputStream *T.660;
100 struct java.io.BufferedInputStream *T.647;
101 struct java.io.InputStream *is;
102 struct java.io.InputStream *is.662;
105 is = T.660; <-- This ought to be type-casted
108 Also, f/name.c exposed a similar problem with a COND_EXPR predicate
109 that was causing DOM to generate and equivalence with two pointers of
110 alias-incompatible types:
112 struct _ffename_space *n;
121 I think that GIMPLE should emit the appropriate type-casts. For the
122 time being, blocking copy-propagation in these cases is the safe thing
124 if (TREE_CODE (dest
) == SSA_NAME
125 && TREE_CODE (orig
) == SSA_NAME
126 && POINTER_TYPE_P (type_d
)
127 && POINTER_TYPE_P (type_o
))
129 tree mt_dest
= symbol_mem_tag (SSA_NAME_VAR (dest
));
130 tree mt_orig
= symbol_mem_tag (SSA_NAME_VAR (orig
));
131 if (mt_dest
&& mt_orig
&& mt_dest
!= mt_orig
)
133 else if (!lang_hooks
.types_compatible_p (type_d
, type_o
))
135 else if (get_alias_set (TREE_TYPE (type_d
)) !=
136 get_alias_set (TREE_TYPE (type_o
)))
139 /* Also verify flow-sensitive information is compatible. */
140 if (SSA_NAME_PTR_INFO (orig
) && SSA_NAME_PTR_INFO (dest
))
142 struct ptr_info_def
*orig_ptr_info
= SSA_NAME_PTR_INFO (orig
);
143 struct ptr_info_def
*dest_ptr_info
= SSA_NAME_PTR_INFO (dest
);
145 if (orig_ptr_info
->name_mem_tag
146 && dest_ptr_info
->name_mem_tag
147 && orig_ptr_info
->pt_vars
148 && dest_ptr_info
->pt_vars
149 && !bitmap_intersect_p (dest_ptr_info
->pt_vars
,
150 orig_ptr_info
->pt_vars
))
155 /* If the destination is a SSA_NAME for a virtual operand, then we have
156 some special cases to handle. */
157 if (TREE_CODE (dest
) == SSA_NAME
&& !is_gimple_reg (dest
))
159 /* If both operands are SSA_NAMEs referring to virtual operands, then
160 we can always propagate. */
161 if (TREE_CODE (orig
) == SSA_NAME
162 && !is_gimple_reg (orig
))
165 /* We have a "copy" from something like a constant into a virtual
166 operand. Reject these. */
170 /* If ORIG flows in from an abnormal edge, it cannot be propagated. */
171 if (TREE_CODE (orig
) == SSA_NAME
172 && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig
))
175 /* If DEST is an SSA_NAME that flows from an abnormal edge, then it
176 cannot be replaced. */
177 if (TREE_CODE (dest
) == SSA_NAME
178 && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest
))
181 /* Anything else is OK. */
185 /* Similarly, but we know that we're propagating into an ASM_EXPR. */
188 may_propagate_copy_into_asm (tree dest
)
190 /* Hard register operands of asms are special. Do not bypass. */
191 return !(TREE_CODE (dest
) == SSA_NAME
192 && TREE_CODE (SSA_NAME_VAR (dest
)) == VAR_DECL
193 && DECL_HARD_REGISTER (SSA_NAME_VAR (dest
)));
197 /* Given two SSA_NAMEs pointers ORIG and NEW such that we are copy
198 propagating NEW into ORIG, consolidate aliasing information so that
199 they both share the same memory tags. */
202 merge_alias_info (tree orig_name
, tree new_name
)
204 tree new_sym
= SSA_NAME_VAR (new_name
);
205 tree orig_sym
= SSA_NAME_VAR (orig_name
);
206 var_ann_t new_ann
= var_ann (new_sym
);
207 var_ann_t orig_ann
= var_ann (orig_sym
);
209 /* No merging necessary when memory partitions are involved. */
210 if (factoring_name_p (new_name
))
212 gcc_assert (!is_gimple_reg (orig_sym
));
215 else if (factoring_name_p (orig_name
))
217 gcc_assert (!is_gimple_reg (new_sym
));
221 gcc_assert (POINTER_TYPE_P (TREE_TYPE (orig_name
)));
222 gcc_assert (POINTER_TYPE_P (TREE_TYPE (new_name
)));
224 #if defined ENABLE_CHECKING
225 gcc_assert (lang_hooks
.types_compatible_p (TREE_TYPE (orig_name
),
226 TREE_TYPE (new_name
)));
228 /* If the pointed-to alias sets are different, these two pointers
229 would never have the same memory tag. In this case, NEW should
230 not have been propagated into ORIG. */
231 gcc_assert (get_alias_set (TREE_TYPE (TREE_TYPE (new_sym
)))
232 == get_alias_set (TREE_TYPE (TREE_TYPE (orig_sym
))));
235 /* Synchronize the symbol tags. If both pointers had a tag and they
236 are different, then something has gone wrong. Symbol tags can
237 always be merged because they are flow insensitive, all the SSA
238 names of the same base DECL share the same symbol tag. */
239 if (new_ann
->symbol_mem_tag
== NULL_TREE
)
240 new_ann
->symbol_mem_tag
= orig_ann
->symbol_mem_tag
;
241 else if (orig_ann
->symbol_mem_tag
== NULL_TREE
)
242 orig_ann
->symbol_mem_tag
= new_ann
->symbol_mem_tag
;
244 gcc_assert (new_ann
->symbol_mem_tag
== orig_ann
->symbol_mem_tag
);
246 /* Check that flow-sensitive information is compatible. Notice that
247 we may not merge flow-sensitive information here. This function
248 is called when propagating equivalences dictated by the IL, like
249 a copy operation P_i = Q_j, and from equivalences dictated by
250 control-flow, like if (P_i == Q_j).
252 In the former case, P_i and Q_j are equivalent in every block
253 dominated by the assignment, so their flow-sensitive information
254 is always the same. However, in the latter case, the pointers
255 P_i and Q_j are only equivalent in one of the sub-graphs out of
256 the predicate, so their flow-sensitive information is not the
257 same in every block dominated by the predicate.
259 Since we cannot distinguish one case from another in this
260 function, we can only make sure that if P_i and Q_j have
261 flow-sensitive information, they should be compatible. */
262 if (SSA_NAME_PTR_INFO (orig_name
) && SSA_NAME_PTR_INFO (new_name
))
264 struct ptr_info_def
*orig_ptr_info
= SSA_NAME_PTR_INFO (orig_name
);
265 struct ptr_info_def
*new_ptr_info
= SSA_NAME_PTR_INFO (new_name
);
267 /* Note that pointer NEW and ORIG may actually have different
268 pointed-to variables (e.g., PR 18291 represented in
269 testsuite/gcc.c-torture/compile/pr18291.c). However, since
270 NEW is being copy-propagated into ORIG, it must always be
271 true that the pointed-to set for pointer NEW is the same, or
272 a subset, of the pointed-to set for pointer ORIG. If this
273 isn't the case, we shouldn't have been able to do the
274 propagation of NEW into ORIG. */
275 if (orig_ptr_info
->name_mem_tag
276 && new_ptr_info
->name_mem_tag
277 && orig_ptr_info
->pt_vars
278 && new_ptr_info
->pt_vars
)
279 gcc_assert (bitmap_intersect_p (new_ptr_info
->pt_vars
,
280 orig_ptr_info
->pt_vars
));
285 /* Common code for propagate_value and replace_exp.
287 Replace use operand OP_P with VAL. FOR_PROPAGATION indicates if the
288 replacement is done to propagate a value or not. */
291 replace_exp_1 (use_operand_p op_p
, tree val
,
292 bool for_propagation ATTRIBUTE_UNUSED
)
294 tree op
= USE_FROM_PTR (op_p
);
296 #if defined ENABLE_CHECKING
297 gcc_assert (!(for_propagation
298 && TREE_CODE (op
) == SSA_NAME
299 && TREE_CODE (val
) == SSA_NAME
300 && !may_propagate_copy (op
, val
)));
303 if (TREE_CODE (val
) == SSA_NAME
)
305 if (TREE_CODE (op
) == SSA_NAME
&& POINTER_TYPE_P (TREE_TYPE (op
)))
306 merge_alias_info (op
, val
);
310 SET_USE (op_p
, unsave_expr_now (val
));
314 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
315 into the operand pointed to by OP_P.
317 Use this version for const/copy propagation as it will perform additional
318 checks to ensure validity of the const/copy propagation. */
321 propagate_value (use_operand_p op_p
, tree val
)
323 replace_exp_1 (op_p
, val
, true);
327 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
328 into the tree pointed to by OP_P.
330 Use this version for const/copy propagation when SSA operands are not
331 available. It will perform the additional checks to ensure validity of
332 the const/copy propagation, but will not update any operand information.
333 Be sure to mark the stmt as modified. */
336 propagate_tree_value (tree
*op_p
, tree val
)
338 #if defined ENABLE_CHECKING
339 gcc_assert (!(TREE_CODE (val
) == SSA_NAME
340 && TREE_CODE (*op_p
) == SSA_NAME
341 && !may_propagate_copy (*op_p
, val
)));
344 if (TREE_CODE (val
) == SSA_NAME
)
346 if (TREE_CODE (*op_p
) == SSA_NAME
&& POINTER_TYPE_P (TREE_TYPE (*op_p
)))
347 merge_alias_info (*op_p
, val
);
351 *op_p
= unsave_expr_now (val
);
355 /* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).
357 Use this version when not const/copy propagating values. For example,
358 PRE uses this version when building expressions as they would appear
359 in specific blocks taking into account actions of PHI nodes. */
362 replace_exp (use_operand_p op_p
, tree val
)
364 replace_exp_1 (op_p
, val
, false);
368 /*---------------------------------------------------------------------------
370 ---------------------------------------------------------------------------*/
371 /* During propagation, we keep chains of variables that are copies of
372 one another. If variable X_i is a copy of X_j and X_j is a copy of
373 X_k, COPY_OF will contain:
375 COPY_OF[i].VALUE = X_j
376 COPY_OF[j].VALUE = X_k
377 COPY_OF[k].VALUE = X_k
379 After propagation, the copy-of value for each variable X_i is
380 converted into the final value by walking the copy-of chains and
381 updating COPY_OF[i].VALUE to be the last element of the chain. */
382 static prop_value_t
*copy_of
;
384 /* Used in set_copy_of_val to determine if the last link of a copy-of
385 chain has changed. */
386 static tree
*cached_last_copy_of
;
388 /* True if we are doing copy propagation on loads and stores. */
389 static bool do_store_copy_prop
;
392 /* Return true if this statement may generate a useful copy. */
395 stmt_may_generate_copy (tree stmt
)
400 if (TREE_CODE (stmt
) == PHI_NODE
)
401 return !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (stmt
));
403 if (TREE_CODE (stmt
) != GIMPLE_MODIFY_STMT
)
406 lhs
= GIMPLE_STMT_OPERAND (stmt
, 0);
407 rhs
= GIMPLE_STMT_OPERAND (stmt
, 1);
408 ann
= stmt_ann (stmt
);
410 /* If the statement has volatile operands, it won't generate a
412 if (ann
->has_volatile_ops
)
415 /* If we are not doing store copy-prop, statements with loads and/or
416 stores will never generate a useful copy. */
417 if (!do_store_copy_prop
418 && !ZERO_SSA_OPERANDS (stmt
, SSA_OP_ALL_VIRTUALS
))
421 /* Otherwise, the only statements that generate useful copies are
422 assignments whose RHS is just an SSA name that doesn't flow
423 through abnormal edges. */
424 return (do_store_copy_prop
425 && TREE_CODE (lhs
) == SSA_NAME
)
426 || (TREE_CODE (rhs
) == SSA_NAME
427 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs
));
431 /* Return the copy-of value for VAR. */
433 static inline prop_value_t
*
434 get_copy_of_val (tree var
)
436 prop_value_t
*val
= ©_of
[SSA_NAME_VERSION (var
)];
438 if (val
->value
== NULL_TREE
439 && !stmt_may_generate_copy (SSA_NAME_DEF_STMT (var
)))
441 /* If the variable will never generate a useful copy relation,
442 make it its own copy. */
444 val
->mem_ref
= NULL_TREE
;
451 /* Return last link in the copy-of chain for VAR. */
454 get_last_copy_of (tree var
)
459 /* Traverse COPY_OF starting at VAR until we get to the last
460 link in the chain. Since it is possible to have cycles in PHI
461 nodes, the copy-of chain may also contain cycles.
463 To avoid infinite loops and to avoid traversing lengthy copy-of
464 chains, we artificially limit the maximum number of chains we are
467 The value 5 was taken from a compiler and runtime library
468 bootstrap and a mixture of C and C++ code from various sources.
469 More than 82% of all copy-of chains were shorter than 5 links. */
473 for (i
= 0; i
< LIMIT
; i
++)
475 tree copy
= copy_of
[SSA_NAME_VERSION (last
)].value
;
476 if (copy
== NULL_TREE
|| copy
== last
)
481 /* If we have reached the limit, then we are either in a copy-of
482 cycle or the copy-of chain is too long. In this case, just
483 return VAR so that it is not considered a copy of anything. */
484 return (i
< LIMIT
? last
: var
);
488 /* Set FIRST to be the first variable in the copy-of chain for DEST.
489 If DEST's copy-of value or its copy-of chain has changed, return
492 MEM_REF is the memory reference where FIRST is stored. This is
493 used when DEST is a non-register and we are copy propagating loads
497 set_copy_of_val (tree dest
, tree first
, tree mem_ref
)
499 unsigned int dest_ver
= SSA_NAME_VERSION (dest
);
500 tree old_first
, old_last
, new_last
;
502 /* Set FIRST to be the first link in COPY_OF[DEST]. If that
503 changed, return true. */
504 old_first
= copy_of
[dest_ver
].value
;
505 copy_of
[dest_ver
].value
= first
;
506 copy_of
[dest_ver
].mem_ref
= mem_ref
;
508 if (old_first
!= first
)
511 /* If FIRST and OLD_FIRST are the same, we need to check whether the
512 copy-of chain starting at FIRST ends in a different variable. If
513 the copy-of chain starting at FIRST ends up in a different
514 variable than the last cached value we had for DEST, then return
515 true because DEST is now a copy of a different variable.
517 This test is necessary because even though the first link in the
518 copy-of chain may not have changed, if any of the variables in
519 the copy-of chain changed its final value, DEST will now be the
520 copy of a different variable, so we have to do another round of
521 propagation for everything that depends on DEST. */
522 old_last
= cached_last_copy_of
[dest_ver
];
523 new_last
= get_last_copy_of (dest
);
524 cached_last_copy_of
[dest_ver
] = new_last
;
526 return (old_last
!= new_last
);
530 /* Dump the copy-of value for variable VAR to FILE. */
533 dump_copy_of (FILE *file
, tree var
)
538 print_generic_expr (file
, var
, dump_flags
);
540 if (TREE_CODE (var
) != SSA_NAME
)
543 visited
= sbitmap_alloc (num_ssa_names
);
544 sbitmap_zero (visited
);
545 SET_BIT (visited
, SSA_NAME_VERSION (var
));
547 fprintf (file
, " copy-of chain: ");
550 print_generic_expr (file
, val
, 0);
552 while (copy_of
[SSA_NAME_VERSION (val
)].value
)
554 fprintf (file
, "-> ");
555 val
= copy_of
[SSA_NAME_VERSION (val
)].value
;
556 print_generic_expr (file
, val
, 0);
558 if (TEST_BIT (visited
, SSA_NAME_VERSION (val
)))
560 SET_BIT (visited
, SSA_NAME_VERSION (val
));
563 val
= get_copy_of_val (var
)->value
;
564 if (val
== NULL_TREE
)
565 fprintf (file
, "[UNDEFINED]");
567 fprintf (file
, "[COPY]");
569 fprintf (file
, "[NOT A COPY]");
571 sbitmap_free (visited
);
575 /* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS
576 value and store the LHS into *RESULT_P. If STMT generates more
577 than one name (i.e., STMT is an aliased store), it is enough to
578 store the first name in the VDEF list into *RESULT_P. After
579 all, the names generated will be VUSEd in the same statements. */
581 static enum ssa_prop_result
582 copy_prop_visit_assignment (tree stmt
, tree
*result_p
)
585 prop_value_t
*rhs_val
;
587 lhs
= GIMPLE_STMT_OPERAND (stmt
, 0);
588 rhs
= GIMPLE_STMT_OPERAND (stmt
, 1);
590 gcc_assert (TREE_CODE (rhs
) == SSA_NAME
);
592 rhs_val
= get_copy_of_val (rhs
);
594 if (TREE_CODE (lhs
) == SSA_NAME
)
596 /* Straight copy between two SSA names. First, make sure that
597 we can propagate the RHS into uses of LHS. */
598 if (!may_propagate_copy (lhs
, rhs
))
599 return SSA_PROP_VARYING
;
601 /* Notice that in the case of assignments, we make the LHS be a
602 copy of RHS's value, not of RHS itself. This avoids keeping
603 unnecessary copy-of chains (assignments cannot be in a cycle
604 like PHI nodes), speeding up the propagation process.
605 This is different from what we do in copy_prop_visit_phi_node.
606 In those cases, we are interested in the copy-of chains. */
608 if (set_copy_of_val (*result_p
, rhs_val
->value
, rhs_val
->mem_ref
))
609 return SSA_PROP_INTERESTING
;
611 return SSA_PROP_NOT_INTERESTING
;
613 else if (stmt_makes_single_store (stmt
))
615 /* Otherwise, set the names in VDEF operands to be a copy
621 /* This should only be executed when doing store copy-prop. */
622 gcc_assert (do_store_copy_prop
);
624 /* Set the value of every VDEF to RHS_VAL. */
626 FOR_EACH_SSA_TREE_OPERAND (vdef
, stmt
, i
, SSA_OP_VIRTUAL_DEFS
)
627 changed
|= set_copy_of_val (vdef
, rhs_val
->value
, lhs
);
629 /* Note that for propagation purposes, we are only interested in
630 visiting statements that load the exact same memory reference
631 stored here. Those statements will have the exact same list
632 of virtual uses, so it is enough to set the output of this
633 statement to be its first virtual definition. */
634 *result_p
= first_vdef (stmt
);
637 return SSA_PROP_INTERESTING
;
639 return SSA_PROP_NOT_INTERESTING
;
643 return SSA_PROP_VARYING
;
647 /* Visit the COND_EXPR STMT. Return SSA_PROP_INTERESTING
648 if it can determine which edge will be taken. Otherwise, return
651 static enum ssa_prop_result
652 copy_prop_visit_cond_stmt (tree stmt
, edge
*taken_edge_p
)
654 enum ssa_prop_result retval
;
657 cond
= COND_EXPR_COND (stmt
);
658 retval
= SSA_PROP_VARYING
;
660 /* The only conditionals that we may be able to compute statically
661 are predicates involving two SSA_NAMEs. */
662 if (COMPARISON_CLASS_P (cond
)
663 && TREE_CODE (TREE_OPERAND (cond
, 0)) == SSA_NAME
664 && TREE_CODE (TREE_OPERAND (cond
, 1)) == SSA_NAME
)
666 tree op0
= get_last_copy_of (TREE_OPERAND (cond
, 0));
667 tree op1
= get_last_copy_of (TREE_OPERAND (cond
, 1));
669 /* See if we can determine the predicate's value. */
670 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
672 fprintf (dump_file
, "Trying to determine truth value of ");
673 fprintf (dump_file
, "predicate ");
674 print_generic_stmt (dump_file
, cond
, 0);
677 /* We can fold COND and get a useful result only when we have
678 the same SSA_NAME on both sides of a comparison operator. */
681 tree folded_cond
= fold_binary (TREE_CODE (cond
), boolean_type_node
,
685 basic_block bb
= bb_for_stmt (stmt
);
686 *taken_edge_p
= find_taken_edge (bb
, folded_cond
);
688 retval
= SSA_PROP_INTERESTING
;
693 if (dump_file
&& (dump_flags
& TDF_DETAILS
) && *taken_edge_p
)
694 fprintf (dump_file
, "\nConditional will always take edge %d->%d\n",
695 (*taken_edge_p
)->src
->index
, (*taken_edge_p
)->dest
->index
);
701 /* Evaluate statement STMT. If the statement produces a new output
702 value, return SSA_PROP_INTERESTING and store the SSA_NAME holding
703 the new value in *RESULT_P.
705 If STMT is a conditional branch and we can determine its truth
706 value, set *TAKEN_EDGE_P accordingly.
708 If the new value produced by STMT is varying, return
711 static enum ssa_prop_result
712 copy_prop_visit_stmt (tree stmt
, edge
*taken_edge_p
, tree
*result_p
)
714 enum ssa_prop_result retval
;
716 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
718 fprintf (dump_file
, "\nVisiting statement:\n");
719 print_generic_stmt (dump_file
, stmt
, dump_flags
);
720 fprintf (dump_file
, "\n");
723 if (TREE_CODE (stmt
) == GIMPLE_MODIFY_STMT
724 && TREE_CODE (GIMPLE_STMT_OPERAND (stmt
, 1)) == SSA_NAME
725 && (do_store_copy_prop
726 || TREE_CODE (GIMPLE_STMT_OPERAND (stmt
, 0)) == SSA_NAME
))
728 /* If the statement is a copy assignment, evaluate its RHS to
729 see if the lattice value of its output has changed. */
730 retval
= copy_prop_visit_assignment (stmt
, result_p
);
732 else if (TREE_CODE (stmt
) == GIMPLE_MODIFY_STMT
733 && TREE_CODE (GIMPLE_STMT_OPERAND (stmt
, 0)) == SSA_NAME
734 && do_store_copy_prop
735 && stmt_makes_single_load (stmt
))
737 /* If the statement is a copy assignment with a memory load
738 on the RHS, see if we know the value of this load and
739 update the lattice accordingly. */
740 prop_value_t
*val
= get_value_loaded_by (stmt
, copy_of
);
743 && is_gimple_reg (val
->value
)
744 && operand_equal_p (val
->mem_ref
, GIMPLE_STMT_OPERAND (stmt
, 1), 0))
747 changed
= set_copy_of_val (GIMPLE_STMT_OPERAND (stmt
, 0),
748 val
->value
, val
->mem_ref
);
751 *result_p
= GIMPLE_STMT_OPERAND (stmt
, 0);
752 retval
= SSA_PROP_INTERESTING
;
755 retval
= SSA_PROP_NOT_INTERESTING
;
758 retval
= SSA_PROP_VARYING
;
760 else if (TREE_CODE (stmt
) == COND_EXPR
)
762 /* See if we can determine which edge goes out of a conditional
764 retval
= copy_prop_visit_cond_stmt (stmt
, taken_edge_p
);
767 retval
= SSA_PROP_VARYING
;
769 if (retval
== SSA_PROP_VARYING
)
774 /* Any other kind of statement is not interesting for constant
775 propagation and, therefore, not worth simulating. */
776 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
777 fprintf (dump_file
, "No interesting values produced.\n");
779 /* The assignment is not a copy operation. Don't visit this
780 statement again and mark all the definitions in the statement
781 to be copies of nothing. */
782 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, i
, SSA_OP_ALL_DEFS
)
783 set_copy_of_val (def
, def
, NULL_TREE
);
790 /* Visit PHI node PHI. If all the arguments produce the same value,
791 set it to be the value of the LHS of PHI. */
793 static enum ssa_prop_result
794 copy_prop_visit_phi_node (tree phi
)
796 enum ssa_prop_result retval
;
799 prop_value_t phi_val
= { 0, NULL_TREE
, NULL_TREE
};
801 lhs
= PHI_RESULT (phi
);
803 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
805 fprintf (dump_file
, "\nVisiting PHI node: ");
806 print_generic_expr (dump_file
, phi
, dump_flags
);
807 fprintf (dump_file
, "\n\n");
810 for (i
= 0; i
< PHI_NUM_ARGS (phi
); i
++)
812 prop_value_t
*arg_val
;
813 tree arg
= PHI_ARG_DEF (phi
, i
);
814 edge e
= PHI_ARG_EDGE (phi
, i
);
816 /* We don't care about values flowing through non-executable
818 if (!(e
->flags
& EDGE_EXECUTABLE
))
821 /* Constants in the argument list never generate a useful copy.
822 Similarly, names that flow through abnormal edges cannot be
823 used to derive copies. */
824 if (TREE_CODE (arg
) != SSA_NAME
|| SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg
))
830 /* Avoid copy propagation from an inner into an outer loop.
831 Otherwise, this may move loop variant variables outside of
832 their loops and prevent coalescing opportunities. If the
833 value was loop invariant, it will be hoisted by LICM and
834 exposed for copy propagation. */
835 if (loop_depth_of_name (arg
) > loop_depth_of_name (lhs
))
841 /* If the LHS appears in the argument list, ignore it. It is
842 irrelevant as a copy. */
843 if (arg
== lhs
|| get_last_copy_of (arg
) == lhs
)
846 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
848 fprintf (dump_file
, "\tArgument #%d: ", i
);
849 dump_copy_of (dump_file
, arg
);
850 fprintf (dump_file
, "\n");
853 arg_val
= get_copy_of_val (arg
);
855 /* If the LHS didn't have a value yet, make it a copy of the
856 first argument we find. Notice that while we make the LHS be
857 a copy of the argument itself, we take the memory reference
858 from the argument's value so that we can compare it to the
859 memory reference of all the other arguments. */
860 if (phi_val
.value
== NULL_TREE
)
863 phi_val
.mem_ref
= arg_val
->mem_ref
;
867 /* If PHI_VAL and ARG don't have a common copy-of chain, then
868 this PHI node cannot be a copy operation. Also, if we are
869 copy propagating stores and these two arguments came from
870 different memory references, they cannot be considered
872 if (get_last_copy_of (phi_val
.value
) != get_last_copy_of (arg
)
873 || (do_store_copy_prop
876 && simple_cst_equal (phi_val
.mem_ref
, arg_val
->mem_ref
) != 1))
883 if (phi_val
.value
&& set_copy_of_val (lhs
, phi_val
.value
, phi_val
.mem_ref
))
884 retval
= (phi_val
.value
!= lhs
) ? SSA_PROP_INTERESTING
: SSA_PROP_VARYING
;
886 retval
= SSA_PROP_NOT_INTERESTING
;
888 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
890 fprintf (dump_file
, "\nPHI node ");
891 dump_copy_of (dump_file
, lhs
);
892 fprintf (dump_file
, "\nTelling the propagator to ");
893 if (retval
== SSA_PROP_INTERESTING
)
894 fprintf (dump_file
, "add SSA edges out of this PHI and continue.");
895 else if (retval
== SSA_PROP_VARYING
)
896 fprintf (dump_file
, "add SSA edges out of this PHI and never visit again.");
898 fprintf (dump_file
, "do nothing with SSA edges and keep iterating.");
899 fprintf (dump_file
, "\n\n");
906 /* Initialize structures used for copy propagation. PHIS_ONLY is true
907 if we should only consider PHI nodes as generating copy propagation
911 init_copy_prop (void)
915 copy_of
= XCNEWVEC (prop_value_t
, num_ssa_names
);
917 cached_last_copy_of
= XCNEWVEC (tree
, num_ssa_names
);
921 block_stmt_iterator si
;
923 int depth
= bb
->loop_depth
;
925 for (si
= bsi_start (bb
); !bsi_end_p (si
); bsi_next (&si
))
927 tree stmt
= bsi_stmt (si
);
930 /* The only statements that we care about are those that may
931 generate useful copies. We also need to mark conditional
932 jumps so that their outgoing edges are added to the work
933 lists of the propagator.
935 Avoid copy propagation from an inner into an outer loop.
936 Otherwise, this may move loop variant variables outside of
937 their loops and prevent coalescing opportunities. If the
938 value was loop invariant, it will be hoisted by LICM and
939 exposed for copy propagation. */
940 if (stmt_ends_bb_p (stmt
))
941 DONT_SIMULATE_AGAIN (stmt
) = false;
942 else if (stmt_may_generate_copy (stmt
)
943 && loop_depth_of_name (GIMPLE_STMT_OPERAND (stmt
, 1)) <= depth
)
944 DONT_SIMULATE_AGAIN (stmt
) = false;
946 DONT_SIMULATE_AGAIN (stmt
) = true;
948 /* Mark all the outputs of this statement as not being
949 the copy of anything. */
950 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter
, SSA_OP_ALL_DEFS
)
951 if (DONT_SIMULATE_AGAIN (stmt
))
952 set_copy_of_val (def
, def
, NULL_TREE
);
954 cached_last_copy_of
[SSA_NAME_VERSION (def
)] = def
;
957 for (phi
= phi_nodes (bb
); phi
; phi
= PHI_CHAIN (phi
))
959 def
= PHI_RESULT (phi
);
960 if (!do_store_copy_prop
&& !is_gimple_reg (def
))
961 DONT_SIMULATE_AGAIN (phi
) = true;
963 DONT_SIMULATE_AGAIN (phi
) = false;
965 if (DONT_SIMULATE_AGAIN (phi
))
966 set_copy_of_val (def
, def
, NULL_TREE
);
968 cached_last_copy_of
[SSA_NAME_VERSION (def
)] = def
;
974 /* Deallocate memory used in copy propagation and do final
978 fini_copy_prop (void)
983 /* Set the final copy-of value for each variable by traversing the
985 tmp
= XCNEWVEC (prop_value_t
, num_ssa_names
);
986 for (i
= 1; i
< num_ssa_names
; i
++)
988 tree var
= ssa_name (i
);
989 if (var
&& copy_of
[i
].value
&& copy_of
[i
].value
!= var
)
990 tmp
[i
].value
= get_last_copy_of (var
);
993 substitute_and_fold (tmp
, false);
995 free (cached_last_copy_of
);
1001 /* Main entry point to the copy propagator.
1003 PHIS_ONLY is true if we should only consider PHI nodes as generating
1004 copy propagation opportunities.
1006 The algorithm propagates the value COPY-OF using ssa_propagate. For
1007 every variable X_i, COPY-OF(X_i) indicates which variable is X_i created
1008 from. The following example shows how the algorithm proceeds at a
1012 2 a_2 = PHI <a_24, x_1>
1014 4 x_1 = PHI <x_298, a_5, a_2>
1016 The end result should be that a_2, a_5, a_24 and x_1 are a copy of
1017 x_298. Propagation proceeds as follows.
1019 Visit #1: a_24 is copy-of x_1. Value changed.
1020 Visit #2: a_2 is copy-of x_1. Value changed.
1021 Visit #3: a_5 is copy-of x_1. Value changed.
1022 Visit #4: x_1 is copy-of x_298. Value changed.
1023 Visit #1: a_24 is copy-of x_298. Value changed.
1024 Visit #2: a_2 is copy-of x_298. Value changed.
1025 Visit #3: a_5 is copy-of x_298. Value changed.
1026 Visit #4: x_1 is copy-of x_298. Stable state reached.
1028 When visiting PHI nodes, we only consider arguments that flow
1029 through edges marked executable by the propagation engine. So,
1030 when visiting statement #2 for the first time, we will only look at
1031 the first argument (a_24) and optimistically assume that its value
1032 is the copy of a_24 (x_1).
1034 The problem with this approach is that it may fail to discover copy
1035 relations in PHI cycles. Instead of propagating copy-of
1036 values, we actually propagate copy-of chains. For instance:
1043 In this code fragment, COPY-OF (X_i) = { D_4, C_9, A_3, B_1 }.
1044 Obviously, we are only really interested in the last value of the
1045 chain, however the propagator needs to access the copy-of chain
1046 when visiting PHI nodes.
1048 To represent the copy-of chain, we use the array COPY_CHAINS, which
1049 holds the first link in the copy-of chain for every variable.
1050 If variable X_i is a copy of X_j, which in turn is a copy of X_k,
1051 the array will contain:
1053 COPY_CHAINS[i] = X_j
1054 COPY_CHAINS[j] = X_k
1055 COPY_CHAINS[k] = X_k
1057 Keeping copy-of chains instead of copy-of values directly becomes
1058 important when visiting PHI nodes. Suppose that we had the
1059 following PHI cycle, such that x_52 is already considered a copy of
1062 1 x_54 = PHI <x_53, x_52>
1063 2 x_53 = PHI <x_898, x_54>
1065 Visit #1: x_54 is copy-of x_53 (because x_52 is copy-of x_53)
1066 Visit #2: x_53 is copy-of x_898 (because x_54 is a copy of x_53,
1067 so it is considered irrelevant
1069 Visit #1: x_54 is copy-of nothing (x_53 is a copy-of x_898 and
1070 x_52 is a copy of x_53, so
1072 Visit #2: x_53 is copy-of nothing
1074 This problem is avoided by keeping a chain of copies, instead of
1075 the final copy-of value. Propagation will now only keep the first
1076 element of a variable's copy-of chain. When visiting PHI nodes,
1077 arguments are considered equal if their copy-of chains end in the
1078 same variable. So, as long as their copy-of chains overlap, we
1079 know that they will be a copy of the same variable, regardless of
1080 which variable that may be).
1082 Propagation would then proceed as follows (the notation a -> b
1083 means that a is a copy-of b):
1085 Visit #1: x_54 = PHI <x_53, x_52>
1088 Result: x_54 -> x_53. Value changed. Add SSA edges.
1090 Visit #1: x_53 = PHI <x_898, x_54>
1093 Result: x_53 -> x_898. Value changed. Add SSA edges.
1095 Visit #2: x_54 = PHI <x_53, x_52>
1097 x_52 -> x_53 -> x_898
1098 Result: x_54 -> x_898. Value changed. Add SSA edges.
1100 Visit #2: x_53 = PHI <x_898, x_54>
1103 Result: x_53 -> x_898. Value didn't change. Stable state
1105 Once the propagator stabilizes, we end up with the desired result
1106 x_53 and x_54 are both copies of x_898. */
1109 execute_copy_prop (bool store_copy_prop
)
1111 do_store_copy_prop
= store_copy_prop
;
1113 ssa_propagate (copy_prop_visit_stmt
, copy_prop_visit_phi_node
);
1119 gate_copy_prop (void)
1121 return flag_tree_copy_prop
!= 0;
1127 execute_copy_prop (false);
1131 struct tree_opt_pass pass_copy_prop
=
1133 "copyprop", /* name */
1134 gate_copy_prop
, /* gate */
1135 do_copy_prop
, /* execute */
1138 0, /* static_pass_number */
1139 TV_TREE_COPY_PROP
, /* tv_id */
1140 PROP_ssa
| PROP_cfg
, /* properties_required */
1141 0, /* properties_provided */
1142 0, /* properties_destroyed */
1143 0, /* todo_flags_start */
1148 | TODO_update_ssa
, /* todo_flags_finish */
1153 gate_store_copy_prop (void)
1155 /* STORE-COPY-PROP is enabled only with -ftree-store-copy-prop, but
1156 when -fno-tree-store-copy-prop is specified, we should run
1157 regular COPY-PROP. That's why the pass is enabled with either
1159 return flag_tree_store_copy_prop
!= 0 || flag_tree_copy_prop
!= 0;
1163 store_copy_prop (void)
1165 /* If STORE-COPY-PROP is not enabled, we just run regular COPY-PROP. */
1166 execute_copy_prop (flag_tree_store_copy_prop
!= 0);
1170 struct tree_opt_pass pass_store_copy_prop
=
1172 "store_copyprop", /* name */
1173 gate_store_copy_prop
, /* gate */
1174 store_copy_prop
, /* execute */
1177 0, /* static_pass_number */
1178 TV_TREE_STORE_COPY_PROP
, /* tv_id */
1179 PROP_ssa
| PROP_alias
| PROP_cfg
, /* properties_required */
1180 0, /* properties_provided */
1181 0, /* properties_destroyed */
1182 0, /* todo_flags_start */
1187 | TODO_update_ssa
, /* todo_flags_finish */