1 /* Routines for performing Temporary Expression Replacement (TER) in SSA trees.
2 Copyright (C) 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
3 Contributed by Andrew MacLeod <amacleod@redhat.com>
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 2, or (at your option)
12 GCC is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING. If not, write to
19 the Free Software Foundation, 51 Franklin Street, Fifth Floor,
20 Boston, MA 02110-1301, USA. */
25 #include "coretypes.h"
28 #include "diagnostic.h"
30 #include "tree-flow.h"
31 #include "tree-dump.h"
32 #include "tree-ssa-live.h"
35 /* Temporary Expression Replacement (TER)
37 Replace SSA version variables during out-of-ssa with their defining
38 expression if there is only one use of the variable.
40 This pass is required in order for the RTL expansion pass to see larger
41 chunks of code. This allows it to make better choices on RTL pattern
42 selection. When expand is rewritten and merged with out-of-ssa, and
43 understands SSA, this should be eliminated.
45 A pass is made through the function, one block at a time. No cross block
46 information is tracked.
48 Variables which only have one use, and whose defining stmt is considered
49 a replaceable expression (see is_replaceable_p) are tracked to see whether
50 they can be replaced at their use location.
56 if there are the only use of n_12 and a_2, TER will substitute in their
57 expressions in v_9, and end up with:
59 v_9 = (b_5 + 6) * (C * 10)
61 which will then have the ssa_name assigned to regular variables, and the
62 resulting code which will be passed ot the expander looks something like:
64 v = (b + 6) * (C * 10)
67 This requires ensuring that none of the variables used by the expression
68 change between the def point and where it is used. Furthermore, if any
69 of the ssa_names used in this expression are themselves replaceable, we
70 have to ensure none of that expressions' arguments change either.
71 Although SSA_NAMES themselves don't change, this pass is performed after
72 coalescing has coalesced different SSA_NAMES together, so there could be a
73 definition of an SSA_NAME which is coalesced with a use that causes a
76 PHI b_5 = <b_8(2), b_14(1)>
83 If b_5, b_8 and b_14 are all colaesced together...
84 The expression b_5 + 6 CANNOT replace the use in the statement defining v_9
85 because b_8 is in fact killing the value of b_5 since they share a partition
86 and will be assigned the same memory or regster location.
88 TER implements this but stepping through the instructions in a block and
89 tracking potential expressions for replacement, and the paritions they are
90 dependent on. Expressions are represented by the SSA_NAME_VERSION of the
91 DEF on the LHS of a GIMPLE_MODIFY_STMT and the expression is the RHS.
93 When a stmt is determined to be a possible replacement expression, the
94 following steps are taken:
96 EXPR_DECL_UID bitmap is allocated and set to the base variable UID of the
97 def and any uses in the expression. non-NULL means the expression is being
98 tracked. The UID's themselves are used to prevent TER substitution into
99 accumulating sequences.
105 this can result in very large expressions which don't accomplish anything
106 see PR tree-optimization/17549.
108 PARTITION_DEPENDENCIES is another bitmap array, and it has a bit set for any
109 partition which is used in the expression. This is primarily used to remove
110 an expression from the partition kill lists when a decision is made whether
111 to replace it or not. This is indexed by ssa version number as well, and
112 indicates a partition number. virtual operands are not tracked individually,
113 but they are summarized by an artifical partition called VIRTUAL_PARTITION.
114 This means a MAY or MUST def will kill *ALL* expressions that are dependant
115 on a virtual operand.
116 Note that the EXPR_DECL_UID and this bitmap represent very similar
117 information, but the info in one is not easy to obtain from the other.
119 KILL_LIST is yet another bitmap array, this time it is indexed by partition
120 number, and represents a list of active expressions which will will no
121 longer be valid if a definition into this partition takes place.
123 PARTITION_IN_USE is simply a bitmap which is used to track which partitions
124 currently have sokmething in their kill list. This is used at the end of
125 a block to clear out the KILL_LIST bitmaps at the end of each block.
127 NEW_REPLACEABLE_DEPENDENCIES is used as a temporary place to store
128 dependencies which will be reused by the current defintion. ALl the uses
129 on an expression are processed before anything else is done. If a use is
130 determined to be a replaceable expression AND the current stmt is also going
131 to be replaceable, all the dependencies of this replaceable use will be
132 picked up by the current stmt's expression. Rather than recreate them, they
133 are simply copied here and then copied into the new expression when it is
139 a_2's expression 'b_5 + 6' is determined to be replaceable at the use
140 location. It is dependent on the partition 'b_5' is in. This is cached into
141 the NEW_REPLACEABLE_DEPENDENCIES bitmap. and when v_8 is examined for
142 replaceablility, it is a candidate, and it is dependent on the partition
143 b_5 is in *NOT* a_2, as well as c_4's partition.
145 if v_8 is also replaceable:
149 x_9 is dependent on partitions b_5, and c_4
151 if a statement is found which has either of those partitions written to
152 before x_9 is used, then x_9 itself is NOT replaceable. */
155 /* Temporary Expression Replacement (TER) table information. */
157 typedef struct temp_expr_table_d
160 bitmap
*partition_dependencies
; /* Partitions expr is dependent on. */
161 tree
*replaceable_expressions
; /* Replacement expression table. */
162 bitmap
*expr_decl_uids
; /* Base uids of exprs. */
163 bitmap
*kill_list
; /* Expr's killed by a partition. */
164 int virtual_partition
; /* Psuedo partition for virtual ops. */
165 bitmap partition_in_use
; /* Partitions with kill entires. */
166 bitmap new_replaceable_dependencies
; /* Holding place for pending dep's. */
167 int *num_in_part
; /* # of ssa_names in a partition. */
168 } *temp_expr_table_p
;
170 /* Used to indicate a dependency on V_MAY_DEFs. */
171 #define VIRTUAL_PARTITION(table) (table->virtual_partition)
173 #ifdef ENABLE_CHECKING
174 extern void debug_ter (FILE *, temp_expr_table_p
);
178 /* Create a new TER table for MAP. */
180 static temp_expr_table_p
181 new_temp_expr_table (var_map map
)
186 t
= XNEW (struct temp_expr_table_d
);
189 t
->partition_dependencies
= XCNEWVEC (bitmap
, num_ssa_names
+ 1);
190 t
->expr_decl_uids
= XCNEWVEC (bitmap
, num_ssa_names
+ 1);
191 t
->kill_list
= XCNEWVEC (bitmap
, num_var_partitions (map
) + 1);
193 t
->partition_in_use
= BITMAP_ALLOC (NULL
);
195 t
->virtual_partition
= num_var_partitions (map
);
196 t
->new_replaceable_dependencies
= BITMAP_ALLOC (NULL
);
198 t
->replaceable_expressions
= NULL
;
199 t
->num_in_part
= XCNEWVEC (int, num_var_partitions (map
));
200 for (x
= 1; x
< num_ssa_names
; x
++)
203 tree name
= ssa_name (x
);
206 p
= var_to_partition (map
, name
);
207 if (p
!= NO_PARTITION
)
215 /* Free TER table T. If there are valid replacements, return the expression
219 free_temp_expr_table (temp_expr_table_p t
)
224 #ifdef ENABLE_CHECKING
226 for (x
= 0; x
<= num_var_partitions (t
->map
); x
++)
227 gcc_assert (!t
->kill_list
[x
]);
230 BITMAP_FREE (t
->partition_in_use
);
232 for (i
= 0; i
<= num_ssa_names
; i
++)
233 if (t
->expr_decl_uids
[i
])
234 BITMAP_FREE (t
->expr_decl_uids
[i
]);
235 free (t
->expr_decl_uids
);
238 free (t
->partition_dependencies
);
240 if (t
->replaceable_expressions
)
241 ret
= t
->replaceable_expressions
;
248 /* Return TRUE if VERSION is to be replaced by an expression in TAB. */
251 version_to_be_replaced_p (temp_expr_table_p tab
, int version
)
253 if (!tab
->replaceable_expressions
)
255 return tab
->replaceable_expressions
[version
] != NULL_TREE
;
259 /* Add partition P to the list if partititons VERSION is dependent on. TAB is
260 the expression table */
263 make_dependent_on_partition (temp_expr_table_p tab
, int version
, int p
)
265 if (!tab
->partition_dependencies
[version
])
266 tab
->partition_dependencies
[version
] = BITMAP_ALLOC (NULL
);
268 bitmap_set_bit (tab
->partition_dependencies
[version
], p
);
272 /* Add VER to the kill list for P. TAB is the expression table */
275 add_to_partition_kill_list (temp_expr_table_p tab
, int p
, int ver
)
277 if (!tab
->kill_list
[p
])
279 tab
->kill_list
[p
] = BITMAP_ALLOC (NULL
);
280 bitmap_set_bit (tab
->partition_in_use
, p
);
282 bitmap_set_bit (tab
->kill_list
[p
], ver
);
286 /* Remove VER from the partition kill list for P. TAB is the expression
290 remove_from_partition_kill_list (temp_expr_table_p tab
, int p
, int version
)
292 #ifdef ENABLE_CHECKING
293 gcc_assert (tab
->kill_list
[p
]);
295 bitmap_clear_bit (tab
->kill_list
[p
], version
);
296 if (bitmap_empty_p (tab
->kill_list
[p
]))
298 bitmap_clear_bit (tab
->partition_in_use
, p
);
299 BITMAP_FREE (tab
->kill_list
[p
]);
304 /* Add a dependency between the def of ssa VERSION and VAR. If VAR is
305 replaceable by an expression, add a dependence each of the elements of the
306 expression. These are contained in the new_replaceable list. TAB is the
310 add_dependence (temp_expr_table_p tab
, int version
, tree var
)
316 i
= SSA_NAME_VERSION (var
);
317 if (version_to_be_replaced_p (tab
, i
))
319 if (!bitmap_empty_p (tab
->new_replaceable_dependencies
))
321 /* Version will now be killed by a write to any partition the
322 substituted expression would have been killed by. */
323 EXECUTE_IF_SET_IN_BITMAP (tab
->new_replaceable_dependencies
, 0, x
, bi
)
324 add_to_partition_kill_list (tab
, x
, version
);
326 /* Rather than set partition_dependencies and in_use lists bit by
327 bit, simply OR in the new_replaceable_dependencies bits. */
328 if (!tab
->partition_dependencies
[version
])
329 tab
->partition_dependencies
[version
] = BITMAP_ALLOC (NULL
);
330 bitmap_ior_into (tab
->partition_dependencies
[version
],
331 tab
->new_replaceable_dependencies
);
332 bitmap_ior_into (tab
->partition_in_use
,
333 tab
->new_replaceable_dependencies
);
334 /* It is only necessary to add these once. */
335 bitmap_clear (tab
->new_replaceable_dependencies
);
340 i
= var_to_partition (tab
->map
, var
);
341 #ifdef ENABLE_CHECKING
342 gcc_assert (i
!= NO_PARTITION
);
343 gcc_assert (tab
->num_in_part
[i
] != 0);
345 /* Only dependencies on ssa_names which are coalesced with something need
346 to be tracked. Partitions with containing only a single SSA_NAME
347 *cannot* have their value changed. */
348 if (tab
->num_in_part
[i
] > 1)
350 add_to_partition_kill_list (tab
, i
, version
);
351 make_dependent_on_partition (tab
, version
, i
);
357 /* Return TRUE if expression STMT is suitable for replacement. */
360 is_replaceable_p (tree stmt
)
366 /* Only consider modify stmts. */
367 if (TREE_CODE (stmt
) != GIMPLE_MODIFY_STMT
)
370 /* Punt if there is more than 1 def. */
371 def
= SINGLE_SSA_TREE_OPERAND (stmt
, SSA_OP_DEF
);
375 /* Only consider definitions which have a single use. */
376 if (!single_imm_use (def
, &use_p
, &use_stmt
))
379 /* If the use isn't in this block, it wont be replaced either. */
380 if (bb_for_stmt (use_stmt
) != bb_for_stmt (stmt
))
383 /* Used in this block, but at the TOP of the block, not the end. */
384 if (TREE_CODE (use_stmt
) == PHI_NODE
)
387 /* There must be no V_MAY_DEFS or V_MUST_DEFS. */
388 if (!(ZERO_SSA_OPERANDS (stmt
, (SSA_OP_VMAYDEF
| SSA_OP_VMUSTDEF
))))
391 /* Float expressions must go through memory if float-store is on. */
393 && FLOAT_TYPE_P (TREE_TYPE (GENERIC_TREE_OPERAND (stmt
, 1))))
396 /* Calls to functions with side-effects cannot be replaced. */
397 if ((call_expr
= get_call_expr_in (stmt
)) != NULL_TREE
)
399 int call_flags
= call_expr_flags (call_expr
);
400 if (TREE_SIDE_EFFECTS (call_expr
)
401 && !(call_flags
& (ECF_PURE
| ECF_CONST
| ECF_NORETURN
)))
405 /* Leave any stmt with voltile operands alone as well. */
406 if (stmt_ann (stmt
)->has_volatile_ops
)
414 /* This function will remove the expression for VERSION from replacement
415 consideration in table TAB. If FREE_EXPR is true, then remove the
416 expression from consideration as well by freeing the decl uid bitmap. */
419 finished_with_expr (temp_expr_table_p tab
, int version
, bool free_expr
)
424 /* Remove this expression from its dependent lists. The partition dependence
425 list is retained and transfered later to whomever uses this version. */
426 if (tab
->partition_dependencies
[version
])
428 EXECUTE_IF_SET_IN_BITMAP (tab
->partition_dependencies
[version
], 0, i
, bi
)
429 remove_from_partition_kill_list (tab
, i
, version
);
430 BITMAP_FREE (tab
->partition_dependencies
[version
]);
433 BITMAP_FREE (tab
->expr_decl_uids
[version
]);
437 /* Create an expression entry fora replaceable expression. */
440 process_replaceable (temp_expr_table_p tab
, tree stmt
)
442 tree var
, def
, basevar
;
445 bitmap def_vars
, use_vars
;
447 #ifdef ENABLE_CHECKING
448 gcc_assert (is_replaceable_p (stmt
));
451 def
= SINGLE_SSA_TREE_OPERAND (stmt
, SSA_OP_DEF
);
452 version
= SSA_NAME_VERSION (def
);
453 basevar
= SSA_NAME_VAR (def
);
454 def_vars
= BITMAP_ALLOC (NULL
);
456 bitmap_set_bit (def_vars
, DECL_UID (basevar
));
458 /* Add this expression to the dependency list for each use partition. */
459 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, iter
, SSA_OP_USE
)
461 int var_version
= SSA_NAME_VERSION (var
);
463 use_vars
= tab
->expr_decl_uids
[var_version
];
464 add_dependence (tab
, version
, var
);
467 bitmap_ior_into (def_vars
, use_vars
);
468 BITMAP_FREE (tab
->expr_decl_uids
[var_version
]);
471 bitmap_set_bit (def_vars
, DECL_UID (SSA_NAME_VAR (var
)));
473 tab
->expr_decl_uids
[version
] = def_vars
;
475 /* If there are VUSES, add a dependence on virtual defs. */
476 if (!ZERO_SSA_OPERANDS (stmt
, SSA_OP_VUSE
))
478 make_dependent_on_partition (tab
, version
, VIRTUAL_PARTITION (tab
));
479 add_to_partition_kill_list (tab
, VIRTUAL_PARTITION (tab
), version
);
484 /* This function removes any expression in TAB which is dependent on PARTITION
485 from consideration, making it not replaceable. */
488 kill_expr (temp_expr_table_p tab
, int partition
)
492 /* Mark every active expr dependent on this var as not replaceable.
493 finished_with_expr can modify the bitmap, so we can't execute over it. */
494 while (tab
->kill_list
[partition
])
496 version
= bitmap_first_set_bit (tab
->kill_list
[partition
]);
497 finished_with_expr (tab
, version
, true);
500 #ifdef ENABLE_CHECKING
501 gcc_assert (!tab
->kill_list
[partition
]);
506 /* This function kills all expressions in TAB which are dependent on virtual
510 kill_virtual_exprs (temp_expr_table_p tab
)
512 kill_expr (tab
, VIRTUAL_PARTITION (tab
));
516 /* Mark the expression associated with VAR as replaceable, and enter
517 the defining stmt into the partition_dependencies table TAB. if
518 MORE_REPLACING is true, accumulate the pending partition dependencies. */
521 mark_replaceable (temp_expr_table_p tab
, tree var
, bool more_replacing
)
523 int version
= SSA_NAME_VERSION (var
);
525 /* Move the dependence list to the pending listpending. */
526 if (more_replacing
&& tab
->partition_dependencies
[version
])
527 bitmap_ior_into (tab
->new_replaceable_dependencies
,
528 tab
->partition_dependencies
[version
]);
530 finished_with_expr (tab
, version
, !more_replacing
);
532 /* Set the replaceable expression. */
533 if (!tab
->replaceable_expressions
)
534 tab
->replaceable_expressions
= XCNEWVEC (tree
, num_ssa_names
+ 1);
535 tab
->replaceable_expressions
[version
] = SSA_NAME_DEF_STMT (var
);
539 /* This function processes basic block BB, and looks for variables which can
540 be replaced by their expressions. Results are stored in the table TAB. */
543 find_replaceable_in_bb (temp_expr_table_p tab
, basic_block bb
)
545 block_stmt_iterator bsi
;
549 var_map map
= tab
->map
;
551 bool stmt_replaceable
;
553 for (bsi
= bsi_start (bb
); !bsi_end_p (bsi
); bsi_next (&bsi
))
555 stmt
= bsi_stmt (bsi
);
556 ann
= stmt_ann (stmt
);
558 stmt_replaceable
= is_replaceable_p (stmt
);
559 /* Determine if this stmt finishes an existing expression. */
560 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
562 unsigned ver
= SSA_NAME_VERSION (use
);
564 /* If this use is a potential replacement variable, process it. */
565 if (tab
->expr_decl_uids
[ver
])
567 bool same_root_var
= false;
569 bitmap vars
= tab
->expr_decl_uids
[ver
];
571 /* See if the root variables are the same. If they are, we
572 do not want to do the replacement to avoid problems with
573 code size, see PR tree-optimization/17549. */
574 if (!bitmap_empty_p (vars
))
575 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter2
, SSA_OP_DEF
)
577 if (bitmap_bit_p (vars
, DECL_UID (SSA_NAME_VAR (def
))))
579 same_root_var
= true;
584 /* Mark expression as replaceable unless stmt is volatile or the
585 def variable has the same root variable as something in the
586 substitution list. */
587 if (ann
->has_volatile_ops
|| same_root_var
)
588 finished_with_expr (tab
, ver
, true);
590 mark_replaceable (tab
, use
, stmt_replaceable
);
594 /* Next, see if this stmt kills off an active expression. */
595 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter
, SSA_OP_DEF
)
597 partition
= var_to_partition (map
, def
);
598 if (partition
!= NO_PARTITION
&& tab
->kill_list
[partition
])
599 kill_expr (tab
, partition
);
602 /* Now see if we are creating a new expression or not. */
603 if (stmt_replaceable
)
604 process_replaceable (tab
, stmt
);
606 /* Free any unused dependency lists. */
607 bitmap_clear (tab
->new_replaceable_dependencies
);
609 /* A V_{MAY,MUST}_DEF kills any expression using a virtual operand,
610 including the current stmt. */
611 if (!ZERO_SSA_OPERANDS (stmt
, SSA_OP_VIRTUAL_DEFS
))
612 kill_virtual_exprs (tab
);
617 /* This function is the driver routine for replacement of temporary expressions
618 in the SSA->normal phase, operating on MAP. If there are replaceable
619 expressions, a table is returned which maps SSA versions to the
620 expressions they should be replaced with. A NULL_TREE indicates no
621 replacement should take place. If there are no replacements at all,
622 NULL is returned by the function, otherwise an expression vector indexed
623 by SSA_NAME version numbers. */
626 find_replaceable_exprs (var_map map
)
629 temp_expr_table_p table
;
632 table
= new_temp_expr_table (map
);
635 find_replaceable_in_bb (table
, bb
);
636 gcc_assert (bitmap_empty_p (table
->partition_in_use
));
638 #ifdef ENABLE_CHECKING
641 /* Make sure all the tables have been cleared out. */
642 for (i
= 0; i
< num_ssa_names
+ 1; i
++)
644 gcc_assert (table
->partition_dependencies
[i
] == NULL
);
645 gcc_assert (table
->expr_decl_uids
[i
] == NULL
);
646 if (i
< num_var_partitions (map
))
647 gcc_assert (table
->kill_list
[i
] == NULL
);
653 ret
= free_temp_expr_table (table
);
658 /* Dump TER expression table EXPR to file F. */
661 dump_replaceable_exprs (FILE *f
, tree
*expr
)
666 fprintf (f
, "\nReplacing Expressions\n");
667 for (x
= 0; x
< (int)num_ssa_names
; x
++)
671 var
= SINGLE_SSA_TREE_OPERAND (stmt
, SSA_OP_DEF
);
672 gcc_assert (var
!= NULL_TREE
);
673 print_generic_expr (f
, var
, TDF_SLIM
);
674 fprintf (f
, " replace with --> ");
675 print_generic_expr (f
, TREE_OPERAND (stmt
, 1), TDF_SLIM
);
682 #ifdef ENABLE_CHECKING
683 /* Dump the status of the various tables in the expression table. This is used
684 exclusively to debug TER. F is the place to send debug info and T is the
685 table being debugged. */
688 debug_ter (FILE *f
, temp_expr_table_p t
)
693 fprintf (f
, "\nDumping current state of TER\n virtual partition = %d\n",
694 VIRTUAL_PARTITION (t
));
695 if (t
->replaceable_expressions
)
696 dump_replaceable_exprs (f
, t
->replaceable_expressions
);
697 fprintf (f
, "Currently tracking the following expressions:\n");
699 for (x
= 1; x
< num_ssa_names
; x
++)
700 if (t
->expr_decl_uids
[x
])
702 print_generic_expr (stderr
, ssa_name (x
), TDF_SLIM
);
703 fprintf (f
, " dep-parts : ");
704 if (t
->partition_dependencies
[x
]
705 && !bitmap_empty_p (t
->partition_dependencies
[x
]))
707 EXECUTE_IF_SET_IN_BITMAP (t
->partition_dependencies
[x
], 0, y
, bi
)
708 fprintf (f
, "P%d ",y
);
710 fprintf (stderr
, " basedecls: ");
711 EXECUTE_IF_SET_IN_BITMAP (t
->expr_decl_uids
[x
], 0, y
, bi
)
712 fprintf (f
, "%d ",y
);
713 fprintf (stderr
, "\n");
716 bitmap_print (f
, t
->partition_in_use
, "Partitions in use ",
717 "\npartition KILL lists:\n");
719 for (x
= 0; x
<= num_var_partitions (t
->map
); x
++)
722 fprintf (f
, "Partition %d : ", x
);
723 EXECUTE_IF_SET_IN_BITMAP (t
->kill_list
[x
], 0, y
, bi
)
724 fprintf (f
, "_%d ",y
);
727 fprintf (f
, "\n----------\n");