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 (do_store_copy_prop
380 && TREE_CODE (lhs
) == SSA_NAME
)
381 || (TREE_CODE (rhs
) == SSA_NAME
382 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs
));
386 /* Return the copy-of value for VAR. */
388 static inline prop_value_t
*
389 get_copy_of_val (tree var
)
391 prop_value_t
*val
= ©_of
[SSA_NAME_VERSION (var
)];
393 if (val
->value
== NULL_TREE
394 && !stmt_may_generate_copy (SSA_NAME_DEF_STMT (var
)))
396 /* If the variable will never generate a useful copy relation,
397 make it its own copy. */
399 val
->mem_ref
= NULL_TREE
;
406 /* Return last link in the copy-of chain for VAR. */
409 get_last_copy_of (tree var
)
414 /* Traverse COPY_OF starting at VAR until we get to the last
415 link in the chain. Since it is possible to have cycles in PHI
416 nodes, the copy-of chain may also contain cycles.
418 To avoid infinite loops and to avoid traversing lengthy copy-of
419 chains, we artificially limit the maximum number of chains we are
422 The value 5 was taken from a compiler and runtime library
423 bootstrap and a mixture of C and C++ code from various sources.
424 More than 82% of all copy-of chains were shorter than 5 links. */
428 for (i
= 0; i
< LIMIT
; i
++)
430 tree copy
= copy_of
[SSA_NAME_VERSION (last
)].value
;
431 if (copy
== NULL_TREE
|| copy
== last
)
436 /* If we have reached the limit, then we are either in a copy-of
437 cycle or the copy-of chain is too long. In this case, just
438 return VAR so that it is not considered a copy of anything. */
439 return (i
< LIMIT
? last
: var
);
443 /* Set FIRST to be the first variable in the copy-of chain for DEST.
444 If DEST's copy-of value or its copy-of chain has changed, return
447 MEM_REF is the memory reference where FIRST is stored. This is
448 used when DEST is a non-register and we are copy propagating loads
452 set_copy_of_val (tree dest
, tree first
, tree mem_ref
)
454 unsigned int dest_ver
= SSA_NAME_VERSION (dest
);
455 tree old_first
, old_last
, new_last
;
457 /* Set FIRST to be the first link in COPY_OF[DEST]. If that
458 changed, return true. */
459 old_first
= copy_of
[dest_ver
].value
;
460 copy_of
[dest_ver
].value
= first
;
461 copy_of
[dest_ver
].mem_ref
= mem_ref
;
463 if (old_first
!= first
)
466 /* If FIRST and OLD_FIRST are the same, we need to check whether the
467 copy-of chain starting at FIRST ends in a different variable. If
468 the copy-of chain starting at FIRST ends up in a different
469 variable than the last cached value we had for DEST, then return
470 true because DEST is now a copy of a different variable.
472 This test is necessary because even though the first link in the
473 copy-of chain may not have changed, if any of the variables in
474 the copy-of chain changed its final value, DEST will now be the
475 copy of a different variable, so we have to do another round of
476 propagation for everything that depends on DEST. */
477 old_last
= cached_last_copy_of
[dest_ver
];
478 new_last
= get_last_copy_of (dest
);
479 cached_last_copy_of
[dest_ver
] = new_last
;
481 return (old_last
!= new_last
);
485 /* Dump the copy-of value for variable VAR to FILE. */
488 dump_copy_of (FILE *file
, tree var
)
493 print_generic_expr (file
, var
, dump_flags
);
495 if (TREE_CODE (var
) != SSA_NAME
)
498 visited
= sbitmap_alloc (num_ssa_names
);
499 sbitmap_zero (visited
);
500 SET_BIT (visited
, SSA_NAME_VERSION (var
));
502 fprintf (file
, " copy-of chain: ");
505 print_generic_expr (file
, val
, 0);
507 while (copy_of
[SSA_NAME_VERSION (val
)].value
)
509 fprintf (file
, "-> ");
510 val
= copy_of
[SSA_NAME_VERSION (val
)].value
;
511 print_generic_expr (file
, val
, 0);
513 if (TEST_BIT (visited
, SSA_NAME_VERSION (val
)))
515 SET_BIT (visited
, SSA_NAME_VERSION (val
));
518 val
= get_copy_of_val (var
)->value
;
519 if (val
== NULL_TREE
)
520 fprintf (file
, "[UNDEFINED]");
522 fprintf (file
, "[COPY]");
524 fprintf (file
, "[NOT A COPY]");
526 sbitmap_free (visited
);
530 /* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS
531 value and store the LHS into *RESULT_P. If STMT generates more
532 than one name (i.e., STMT is an aliased store), it is enough to
533 store the first name in the V_MAY_DEF list into *RESULT_P. After
534 all, the names generated will be VUSEd in the same statements. */
536 static enum ssa_prop_result
537 copy_prop_visit_assignment (tree stmt
, tree
*result_p
)
540 prop_value_t
*rhs_val
;
542 lhs
= TREE_OPERAND (stmt
, 0);
543 rhs
= TREE_OPERAND (stmt
, 1);
545 gcc_assert (TREE_CODE (rhs
) == SSA_NAME
);
547 rhs_val
= get_copy_of_val (rhs
);
549 if (TREE_CODE (lhs
) == SSA_NAME
)
551 /* Straight copy between two SSA names. First, make sure that
552 we can propagate the RHS into uses of LHS. */
553 if (!may_propagate_copy (lhs
, rhs
))
554 return SSA_PROP_VARYING
;
556 /* Notice that in the case of assignments, we make the LHS be a
557 copy of RHS's value, not of RHS itself. This avoids keeping
558 unnecessary copy-of chains (assignments cannot be in a cycle
559 like PHI nodes), speeding up the propagation process.
560 This is different from what we do in copy_prop_visit_phi_node.
561 In those cases, we are interested in the copy-of chains. */
563 if (set_copy_of_val (*result_p
, rhs_val
->value
, rhs_val
->mem_ref
))
564 return SSA_PROP_INTERESTING
;
566 return SSA_PROP_NOT_INTERESTING
;
568 else if (stmt_makes_single_store (stmt
))
570 /* Otherwise, set the names in V_MAY_DEF/V_MUST_DEF operands
571 to be a copy of RHS. */
576 /* This should only be executed when doing store copy-prop. */
577 gcc_assert (do_store_copy_prop
);
579 /* Set the value of every VDEF to RHS_VAL. */
581 FOR_EACH_SSA_TREE_OPERAND (vdef
, stmt
, i
, SSA_OP_VIRTUAL_DEFS
)
582 changed
|= set_copy_of_val (vdef
, rhs_val
->value
, lhs
);
584 /* Note that for propagation purposes, we are only interested in
585 visiting statements that load the exact same memory reference
586 stored here. Those statements will have the exact same list
587 of virtual uses, so it is enough to set the output of this
588 statement to be its first virtual definition. */
589 *result_p
= first_vdef (stmt
);
592 return SSA_PROP_INTERESTING
;
594 return SSA_PROP_NOT_INTERESTING
;
598 return SSA_PROP_VARYING
;
602 /* Visit the COND_EXPR STMT. Return SSA_PROP_INTERESTING
603 if it can determine which edge will be taken. Otherwise, return
606 static enum ssa_prop_result
607 copy_prop_visit_cond_stmt (tree stmt
, edge
*taken_edge_p
)
609 enum ssa_prop_result retval
;
612 cond
= COND_EXPR_COND (stmt
);
613 retval
= SSA_PROP_VARYING
;
615 /* The only conditionals that we may be able to compute statically
616 are predicates involving two SSA_NAMEs. */
617 if (COMPARISON_CLASS_P (cond
)
618 && TREE_CODE (TREE_OPERAND (cond
, 0)) == SSA_NAME
619 && TREE_CODE (TREE_OPERAND (cond
, 1)) == SSA_NAME
)
621 tree op0
= get_last_copy_of (TREE_OPERAND (cond
, 0));
622 tree op1
= get_last_copy_of (TREE_OPERAND (cond
, 1));
624 /* See if we can determine the predicate's value. */
625 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
627 fprintf (dump_file
, "Trying to determine truth value of ");
628 fprintf (dump_file
, "predicate ");
629 print_generic_stmt (dump_file
, cond
, 0);
632 /* We can fold COND and get a useful result only when we have
633 the same SSA_NAME on both sides of a comparison operator. */
636 tree folded_cond
= fold_binary (TREE_CODE (cond
), boolean_type_node
,
640 basic_block bb
= bb_for_stmt (stmt
);
641 *taken_edge_p
= find_taken_edge (bb
, folded_cond
);
643 retval
= SSA_PROP_INTERESTING
;
648 if (dump_file
&& (dump_flags
& TDF_DETAILS
) && *taken_edge_p
)
649 fprintf (dump_file
, "\nConditional will always take edge %d->%d\n",
650 (*taken_edge_p
)->src
->index
, (*taken_edge_p
)->dest
->index
);
656 /* Evaluate statement STMT. If the statement produces a new output
657 value, return SSA_PROP_INTERESTING and store the SSA_NAME holding
658 the new value in *RESULT_P.
660 If STMT is a conditional branch and we can determine its truth
661 value, set *TAKEN_EDGE_P accordingly.
663 If the new value produced by STMT is varying, return
666 static enum ssa_prop_result
667 copy_prop_visit_stmt (tree stmt
, edge
*taken_edge_p
, tree
*result_p
)
669 enum ssa_prop_result retval
;
671 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
673 fprintf (dump_file
, "\nVisiting statement:\n");
674 print_generic_stmt (dump_file
, stmt
, dump_flags
);
675 fprintf (dump_file
, "\n");
678 if (TREE_CODE (stmt
) == MODIFY_EXPR
679 && TREE_CODE (TREE_OPERAND (stmt
, 1)) == SSA_NAME
680 && (do_store_copy_prop
681 || TREE_CODE (TREE_OPERAND (stmt
, 0)) == SSA_NAME
))
683 /* If the statement is a copy assignment, evaluate its RHS to
684 see if the lattice value of its output has changed. */
685 retval
= copy_prop_visit_assignment (stmt
, result_p
);
687 else if (TREE_CODE (stmt
) == MODIFY_EXPR
688 && TREE_CODE (TREE_OPERAND (stmt
, 0)) == SSA_NAME
689 && do_store_copy_prop
690 && stmt_makes_single_load (stmt
))
692 /* If the statement is a copy assignment with a memory load
693 on the RHS, see if we know the value of this load and
694 update the lattice accordingly. */
695 prop_value_t
*val
= get_value_loaded_by (stmt
, copy_of
);
698 && is_gimple_reg (val
->value
)
699 && operand_equal_p (val
->mem_ref
, TREE_OPERAND (stmt
, 1), 0))
702 changed
= set_copy_of_val (TREE_OPERAND (stmt
, 0),
703 val
->value
, val
->mem_ref
);
706 *result_p
= TREE_OPERAND (stmt
, 0);
707 retval
= SSA_PROP_INTERESTING
;
710 retval
= SSA_PROP_NOT_INTERESTING
;
713 retval
= SSA_PROP_VARYING
;
715 else if (TREE_CODE (stmt
) == COND_EXPR
)
717 /* See if we can determine which edge goes out of a conditional
719 retval
= copy_prop_visit_cond_stmt (stmt
, taken_edge_p
);
722 retval
= SSA_PROP_VARYING
;
724 if (retval
== SSA_PROP_VARYING
)
729 /* Any other kind of statement is not interesting for constant
730 propagation and, therefore, not worth simulating. */
731 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
732 fprintf (dump_file
, "No interesting values produced.\n");
734 /* The assignment is not a copy operation. Don't visit this
735 statement again and mark all the definitions in the statement
736 to be copies of nothing. */
737 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, i
, SSA_OP_ALL_DEFS
)
738 set_copy_of_val (def
, def
, NULL_TREE
);
745 /* Visit PHI node PHI. If all the arguments produce the same value,
746 set it to be the value of the LHS of PHI. */
748 static enum ssa_prop_result
749 copy_prop_visit_phi_node (tree phi
)
751 enum ssa_prop_result retval
;
754 prop_value_t phi_val
= { 0, NULL_TREE
, NULL_TREE
};
756 lhs
= PHI_RESULT (phi
);
758 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
760 fprintf (dump_file
, "\nVisiting PHI node: ");
761 print_generic_expr (dump_file
, phi
, dump_flags
);
762 fprintf (dump_file
, "\n\n");
765 for (i
= 0; i
< PHI_NUM_ARGS (phi
); i
++)
767 prop_value_t
*arg_val
;
768 tree arg
= PHI_ARG_DEF (phi
, i
);
769 edge e
= PHI_ARG_EDGE (phi
, i
);
771 /* We don't care about values flowing through non-executable
773 if (!(e
->flags
& EDGE_EXECUTABLE
))
776 /* Constants in the argument list never generate a useful copy.
777 Similarly, names that flow through abnormal edges cannot be
778 used to derive copies. */
779 if (TREE_CODE (arg
) != SSA_NAME
|| SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg
))
785 /* Avoid copy propagation from an inner into an outer loop.
786 Otherwise, this may move loop variant variables outside of
787 their loops and prevent coalescing opportunities. If the
788 value was loop invariant, it will be hoisted by LICM and
789 exposed for copy propagation. */
790 if (loop_depth_of_name (arg
) > loop_depth_of_name (lhs
))
796 /* If the LHS appears in the argument list, ignore it. It is
797 irrelevant as a copy. */
798 if (arg
== lhs
|| get_last_copy_of (arg
) == lhs
)
801 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
803 fprintf (dump_file
, "\tArgument #%d: ", i
);
804 dump_copy_of (dump_file
, arg
);
805 fprintf (dump_file
, "\n");
808 arg_val
= get_copy_of_val (arg
);
810 /* If the LHS didn't have a value yet, make it a copy of the
811 first argument we find. Notice that while we make the LHS be
812 a copy of the argument itself, we take the memory reference
813 from the argument's value so that we can compare it to the
814 memory reference of all the other arguments. */
815 if (phi_val
.value
== NULL_TREE
)
818 phi_val
.mem_ref
= arg_val
->mem_ref
;
822 /* If PHI_VAL and ARG don't have a common copy-of chain, then
823 this PHI node cannot be a copy operation. Also, if we are
824 copy propagating stores and these two arguments came from
825 different memory references, they cannot be considered
827 if (get_last_copy_of (phi_val
.value
) != get_last_copy_of (arg
)
828 || (do_store_copy_prop
831 && simple_cst_equal (phi_val
.mem_ref
, arg_val
->mem_ref
) != 1))
838 if (phi_val
.value
&& set_copy_of_val (lhs
, phi_val
.value
, phi_val
.mem_ref
))
839 retval
= (phi_val
.value
!= lhs
) ? SSA_PROP_INTERESTING
: SSA_PROP_VARYING
;
841 retval
= SSA_PROP_NOT_INTERESTING
;
843 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
845 fprintf (dump_file
, "\nPHI node ");
846 dump_copy_of (dump_file
, lhs
);
847 fprintf (dump_file
, "\nTelling the propagator to ");
848 if (retval
== SSA_PROP_INTERESTING
)
849 fprintf (dump_file
, "add SSA edges out of this PHI and continue.");
850 else if (retval
== SSA_PROP_VARYING
)
851 fprintf (dump_file
, "add SSA edges out of this PHI and never visit again.");
853 fprintf (dump_file
, "do nothing with SSA edges and keep iterating.");
854 fprintf (dump_file
, "\n\n");
861 /* Initialize structures used for copy propagation. PHIS_ONLY is true
862 if we should only consider PHI nodes as generating copy propagation
866 init_copy_prop (void)
870 copy_of
= XNEWVEC (prop_value_t
, num_ssa_names
);
871 memset (copy_of
, 0, num_ssa_names
* sizeof (*copy_of
));
873 cached_last_copy_of
= XNEWVEC (tree
, num_ssa_names
);
874 memset (cached_last_copy_of
, 0, num_ssa_names
* sizeof (*cached_last_copy_of
));
878 block_stmt_iterator si
;
880 int depth
= bb
->loop_depth
;
882 for (si
= bsi_start (bb
); !bsi_end_p (si
); bsi_next (&si
))
884 tree stmt
= bsi_stmt (si
);
887 /* The only statements that we care about are those that may
888 generate useful copies. We also need to mark conditional
889 jumps so that their outgoing edges are added to the work
890 lists of the propagator.
892 Avoid copy propagation from an inner into an outer loop.
893 Otherwise, this may move loop variant variables outside of
894 their loops and prevent coalescing opportunities. If the
895 value was loop invariant, it will be hoisted by LICM and
896 exposed for copy propagation. */
897 if (stmt_ends_bb_p (stmt
))
898 DONT_SIMULATE_AGAIN (stmt
) = false;
899 else if (stmt_may_generate_copy (stmt
)
900 && loop_depth_of_name (TREE_OPERAND (stmt
, 1)) <= depth
)
901 DONT_SIMULATE_AGAIN (stmt
) = false;
903 DONT_SIMULATE_AGAIN (stmt
) = true;
905 /* Mark all the outputs of this statement as not being
906 the copy of anything. */
907 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter
, SSA_OP_ALL_DEFS
)
908 if (DONT_SIMULATE_AGAIN (stmt
))
909 set_copy_of_val (def
, def
, NULL_TREE
);
911 cached_last_copy_of
[SSA_NAME_VERSION (def
)] = def
;
914 for (phi
= phi_nodes (bb
); phi
; phi
= PHI_CHAIN (phi
))
916 def
= PHI_RESULT (phi
);
917 if (!do_store_copy_prop
&& !is_gimple_reg (def
))
918 DONT_SIMULATE_AGAIN (phi
) = true;
920 DONT_SIMULATE_AGAIN (phi
) = false;
922 if (DONT_SIMULATE_AGAIN (phi
))
923 set_copy_of_val (def
, def
, NULL_TREE
);
925 cached_last_copy_of
[SSA_NAME_VERSION (def
)] = def
;
931 /* Deallocate memory used in copy propagation and do final
935 fini_copy_prop (void)
940 /* Set the final copy-of value for each variable by traversing the
942 tmp
= XNEWVEC (prop_value_t
, num_ssa_names
);
943 memset (tmp
, 0, num_ssa_names
* sizeof (*tmp
));
944 for (i
= 1; i
< num_ssa_names
; i
++)
946 tree var
= ssa_name (i
);
947 if (var
&& copy_of
[i
].value
&& copy_of
[i
].value
!= var
)
948 tmp
[i
].value
= get_last_copy_of (var
);
951 substitute_and_fold (tmp
, false);
953 free (cached_last_copy_of
);
959 /* Main entry point to the copy propagator.
961 PHIS_ONLY is true if we should only consider PHI nodes as generating
962 copy propagation opportunities.
964 The algorithm propagates the value COPY-OF using ssa_propagate. For
965 every variable X_i, COPY-OF(X_i) indicates which variable is X_i created
966 from. The following example shows how the algorithm proceeds at a
970 2 a_2 = PHI <a_24, x_1>
972 4 x_1 = PHI <x_298, a_5, a_2>
974 The end result should be that a_2, a_5, a_24 and x_1 are a copy of
975 x_298. Propagation proceeds as follows.
977 Visit #1: a_24 is copy-of x_1. Value changed.
978 Visit #2: a_2 is copy-of x_1. Value changed.
979 Visit #3: a_5 is copy-of x_1. Value changed.
980 Visit #4: x_1 is copy-of x_298. Value changed.
981 Visit #1: a_24 is copy-of x_298. Value changed.
982 Visit #2: a_2 is copy-of x_298. Value changed.
983 Visit #3: a_5 is copy-of x_298. Value changed.
984 Visit #4: x_1 is copy-of x_298. Stable state reached.
986 When visiting PHI nodes, we only consider arguments that flow
987 through edges marked executable by the propagation engine. So,
988 when visiting statement #2 for the first time, we will only look at
989 the first argument (a_24) and optimistically assume that its value
990 is the copy of a_24 (x_1).
992 The problem with this approach is that it may fail to discover copy
993 relations in PHI cycles. Instead of propagating copy-of
994 values, we actually propagate copy-of chains. For instance:
1001 In this code fragment, COPY-OF (X_i) = { D_4, C_9, A_3, B_1 }.
1002 Obviously, we are only really interested in the last value of the
1003 chain, however the propagator needs to access the copy-of chain
1004 when visiting PHI nodes.
1006 To represent the copy-of chain, we use the array COPY_CHAINS, which
1007 holds the first link in the copy-of chain for every variable.
1008 If variable X_i is a copy of X_j, which in turn is a copy of X_k,
1009 the array will contain:
1011 COPY_CHAINS[i] = X_j
1012 COPY_CHAINS[j] = X_k
1013 COPY_CHAINS[k] = X_k
1015 Keeping copy-of chains instead of copy-of values directly becomes
1016 important when visiting PHI nodes. Suppose that we had the
1017 following PHI cycle, such that x_52 is already considered a copy of
1020 1 x_54 = PHI <x_53, x_52>
1021 2 x_53 = PHI <x_898, x_54>
1023 Visit #1: x_54 is copy-of x_53 (because x_52 is copy-of x_53)
1024 Visit #2: x_53 is copy-of x_898 (because x_54 is a copy of x_53,
1025 so it is considered irrelevant
1027 Visit #1: x_54 is copy-of nothing (x_53 is a copy-of x_898 and
1028 x_52 is a copy of x_53, so
1030 Visit #2: x_53 is copy-of nothing
1032 This problem is avoided by keeping a chain of copies, instead of
1033 the final copy-of value. Propagation will now only keep the first
1034 element of a variable's copy-of chain. When visiting PHI nodes,
1035 arguments are considered equal if their copy-of chains end in the
1036 same variable. So, as long as their copy-of chains overlap, we
1037 know that they will be a copy of the same variable, regardless of
1038 which variable that may be).
1040 Propagation would then proceed as follows (the notation a -> b
1041 means that a is a copy-of b):
1043 Visit #1: x_54 = PHI <x_53, x_52>
1046 Result: x_54 -> x_53. Value changed. Add SSA edges.
1048 Visit #1: x_53 = PHI <x_898, x_54>
1051 Result: x_53 -> x_898. Value changed. Add SSA edges.
1053 Visit #2: x_54 = PHI <x_53, x_52>
1055 x_52 -> x_53 -> x_898
1056 Result: x_54 -> x_898. Value changed. Add SSA edges.
1058 Visit #2: x_53 = PHI <x_898, x_54>
1061 Result: x_53 -> x_898. Value didn't change. Stable state
1063 Once the propagator stabilizes, we end up with the desired result
1064 x_53 and x_54 are both copies of x_898. */
1067 execute_copy_prop (bool store_copy_prop
)
1069 do_store_copy_prop
= store_copy_prop
;
1071 ssa_propagate (copy_prop_visit_stmt
, copy_prop_visit_phi_node
);
1077 gate_copy_prop (void)
1079 return flag_tree_copy_prop
!= 0;
1085 execute_copy_prop (false);
1089 struct tree_opt_pass pass_copy_prop
=
1091 "copyprop", /* name */
1092 gate_copy_prop
, /* gate */
1093 do_copy_prop
, /* execute */
1096 0, /* static_pass_number */
1097 TV_TREE_COPY_PROP
, /* tv_id */
1098 PROP_ssa
| PROP_alias
| PROP_cfg
, /* properties_required */
1099 0, /* properties_provided */
1100 0, /* properties_destroyed */
1101 0, /* todo_flags_start */
1106 | TODO_update_ssa
, /* todo_flags_finish */
1111 gate_store_copy_prop (void)
1113 /* STORE-COPY-PROP is enabled only with -ftree-store-copy-prop, but
1114 when -fno-tree-store-copy-prop is specified, we should run
1115 regular COPY-PROP. That's why the pass is enabled with either
1117 return flag_tree_store_copy_prop
!= 0 || flag_tree_copy_prop
!= 0;
1121 store_copy_prop (void)
1123 /* If STORE-COPY-PROP is not enabled, we just run regular COPY-PROP. */
1124 execute_copy_prop (flag_tree_store_copy_prop
!= 0);
1128 struct tree_opt_pass pass_store_copy_prop
=
1130 "store_copyprop", /* name */
1131 gate_store_copy_prop
, /* gate */
1132 store_copy_prop
, /* execute */
1135 0, /* static_pass_number */
1136 TV_TREE_STORE_COPY_PROP
, /* tv_id */
1137 PROP_ssa
| PROP_alias
| PROP_cfg
, /* properties_required */
1138 0, /* properties_provided */
1139 0, /* properties_destroyed */
1140 0, /* todo_flags_start */
1145 | TODO_update_ssa
, /* todo_flags_finish */