1 /* Routines for performing Temporary Expression Replacement (TER) in SSA trees.
2 Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
3 Free Software Foundation, Inc.
4 Contributed by Andrew MacLeod <amacleod@redhat.com>
6 This file is part of GCC.
8 GCC is free software; you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation; either version 3, or (at your option)
13 GCC is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
18 You should have received a copy of the GNU General Public License
19 along with GCC; see the file COPYING3. If not see
20 <http://www.gnu.org/licenses/>. */
25 #include "coretypes.h"
28 #include "tree-pretty-print.h"
29 #include "gimple-pretty-print.h"
31 #include "tree-flow.h"
32 #include "tree-dump.h"
33 #include "tree-ssa-live.h"
37 /* Temporary Expression Replacement (TER)
39 Replace SSA version variables during out-of-ssa with their defining
40 expression if there is only one use of the variable.
42 This pass is required in order for the RTL expansion pass to see larger
43 chunks of code. This allows it to make better choices on RTL pattern
44 selection. When expand is rewritten and merged with out-of-ssa, and
45 understands SSA, this should be eliminated.
47 A pass is made through the function, one block at a time. No cross block
48 information is tracked.
50 Variables which only have one use, and whose defining stmt is considered
51 a replaceable expression (see is_replaceable_p) are tracked to see whether
52 they can be replaced at their use location.
58 if there are the only use of n_12 and a_2, TER will substitute in their
59 expressions in v_9, and end up with:
61 v_9 = (b_5 + 6) * (C * 10)
63 which will then have the ssa_name assigned to regular variables, and the
64 resulting code which will be passed to the expander looks something like:
66 v = (b + 6) * (C * 10)
69 This requires ensuring that none of the variables used by the expression
70 change between the def point and where it is used. Furthermore, if any
71 of the ssa_names used in this expression are themselves replaceable, we
72 have to ensure none of that expressions' arguments change either.
73 Although SSA_NAMES themselves don't change, this pass is performed after
74 coalescing has coalesced different SSA_NAMES together, so there could be a
75 definition of an SSA_NAME which is coalesced with a use that causes a
78 PHI b_5 = <b_8(2), b_14(1)>
85 If b_5, b_8 and b_14 are all coalesced together...
86 The expression b_5 + 6 CANNOT replace the use in the statement defining v_9
87 because b_8 is in fact killing the value of b_5 since they share a partition
88 and will be assigned the same memory or register location.
90 TER implements this but stepping through the instructions in a block and
91 tracking potential expressions for replacement, and the partitions they are
92 dependent on. Expressions are represented by the SSA_NAME_VERSION of the
93 DEF on the LHS of a GIMPLE_ASSIGN and the expression is the RHS.
95 When a stmt is determined to be a possible replacement expression, the
96 following steps are taken:
98 EXPR_DECL_UID bitmap is allocated and set to the base variable UID of the
99 def and any uses in the expression. non-NULL means the expression is being
100 tracked. The UID's themselves are used to prevent TER substitution into
101 accumulating sequences, i.e.,
107 this can result in very large expressions which don't accomplish anything
108 see PR tree-optimization/17549.
110 PARTITION_DEPENDENCIES is another bitmap array, and it has a bit set for any
111 partition which is used in the expression. This is primarily used to remove
112 an expression from the partition kill lists when a decision is made whether
113 to replace it or not. This is indexed by ssa version number as well, and
114 indicates a partition number. virtual operands are not tracked individually,
115 but they are summarized by an artificial partition called VIRTUAL_PARTITION.
116 This means a MAY or MUST def will kill *ALL* expressions that are dependent
117 on a virtual operand.
118 Note that the EXPR_DECL_UID and this bitmap represent very similar
119 information, but the info in one is not easy to obtain from the other.
121 KILL_LIST is yet another bitmap array, this time it is indexed by partition
122 number, and represents a list of active expressions which will will no
123 longer be valid if a definition into this partition takes place.
125 PARTITION_IN_USE is simply a bitmap which is used to track which partitions
126 currently have something in their kill list. This is used at the end of
127 a block to clear out the KILL_LIST bitmaps at the end of each block.
129 NEW_REPLACEABLE_DEPENDENCIES is used as a temporary place to store
130 dependencies which will be reused by the current definition. All the uses
131 on an expression are processed before anything else is done. If a use is
132 determined to be a replaceable expression AND the current stmt is also going
133 to be replaceable, all the dependencies of this replaceable use will be
134 picked up by the current stmt's expression. Rather than recreate them, they
135 are simply copied here and then copied into the new expression when it is
141 a_2's expression 'b_5 + 6' is determined to be replaceable at the use
142 location. It is dependent on the partition 'b_5' is in. This is cached into
143 the NEW_REPLACEABLE_DEPENDENCIES bitmap, and when v_8 is examined for
144 replaceability, it is a candidate, and it is dependent on the partition
145 b_5 is in *NOT* a_2, as well as c_4's partition.
147 if v_8 is also replaceable:
151 x_9 is dependent on partitions b_5, and c_4
153 if a statement is found which has either of those partitions written to
154 before x_9 is used, then x_9 itself is NOT replaceable. */
157 /* Temporary Expression Replacement (TER) table information. */
159 typedef struct temp_expr_table_d
162 bitmap
*partition_dependencies
; /* Partitions expr is dependent on. */
163 bitmap replaceable_expressions
; /* Replacement expression table. */
164 bitmap
*expr_decl_uids
; /* Base uids of exprs. */
165 bitmap
*kill_list
; /* Expr's killed by a partition. */
166 int virtual_partition
; /* Pseudo partition for virtual ops. */
167 bitmap partition_in_use
; /* Partitions with kill entries. */
168 bitmap new_replaceable_dependencies
; /* Holding place for pending dep's. */
169 int *num_in_part
; /* # of ssa_names in a partition. */
170 } *temp_expr_table_p
;
172 /* Used to indicate a dependency on VDEFs. */
173 #define VIRTUAL_PARTITION(table) (table->virtual_partition)
175 #ifdef ENABLE_CHECKING
176 extern void debug_ter (FILE *, temp_expr_table_p
);
180 /* Create a new TER table for MAP. */
182 static temp_expr_table_p
183 new_temp_expr_table (var_map map
)
188 t
= XNEW (struct temp_expr_table_d
);
191 t
->partition_dependencies
= XCNEWVEC (bitmap
, num_ssa_names
+ 1);
192 t
->expr_decl_uids
= XCNEWVEC (bitmap
, num_ssa_names
+ 1);
193 t
->kill_list
= XCNEWVEC (bitmap
, num_var_partitions (map
) + 1);
195 t
->partition_in_use
= BITMAP_ALLOC (NULL
);
197 t
->virtual_partition
= num_var_partitions (map
);
198 t
->new_replaceable_dependencies
= BITMAP_ALLOC (NULL
);
200 t
->replaceable_expressions
= NULL
;
201 t
->num_in_part
= XCNEWVEC (int, num_var_partitions (map
));
202 for (x
= 1; x
< num_ssa_names
; x
++)
205 tree name
= ssa_name (x
);
208 p
= var_to_partition (map
, name
);
209 if (p
!= NO_PARTITION
)
217 /* Free TER table T. If there are valid replacements, return the expression
221 free_temp_expr_table (temp_expr_table_p t
)
225 #ifdef ENABLE_CHECKING
227 for (x
= 0; x
<= num_var_partitions (t
->map
); x
++)
228 gcc_assert (!t
->kill_list
[x
]);
229 for (x
= 0; x
< num_ssa_names
; x
++)
231 gcc_assert (t
->expr_decl_uids
[x
] == NULL
);
232 gcc_assert (t
->partition_dependencies
[x
] == NULL
);
236 BITMAP_FREE (t
->partition_in_use
);
237 BITMAP_FREE (t
->new_replaceable_dependencies
);
239 free (t
->expr_decl_uids
);
241 free (t
->partition_dependencies
);
242 free (t
->num_in_part
);
244 if (t
->replaceable_expressions
)
245 ret
= t
->replaceable_expressions
;
252 /* Return TRUE if VERSION is to be replaced by an expression in TAB. */
255 version_to_be_replaced_p (temp_expr_table_p tab
, int version
)
257 if (!tab
->replaceable_expressions
)
259 return bitmap_bit_p (tab
->replaceable_expressions
, version
);
263 /* Add partition P to the list if partitions VERSION is dependent on. TAB is
264 the expression table */
267 make_dependent_on_partition (temp_expr_table_p tab
, int version
, int p
)
269 if (!tab
->partition_dependencies
[version
])
270 tab
->partition_dependencies
[version
] = BITMAP_ALLOC (NULL
);
272 bitmap_set_bit (tab
->partition_dependencies
[version
], p
);
276 /* Add VER to the kill list for P. TAB is the expression table */
279 add_to_partition_kill_list (temp_expr_table_p tab
, int p
, int ver
)
281 if (!tab
->kill_list
[p
])
283 tab
->kill_list
[p
] = BITMAP_ALLOC (NULL
);
284 bitmap_set_bit (tab
->partition_in_use
, p
);
286 bitmap_set_bit (tab
->kill_list
[p
], ver
);
290 /* Remove VER from the partition kill list for P. TAB is the expression
294 remove_from_partition_kill_list (temp_expr_table_p tab
, int p
, int version
)
296 #ifdef ENABLE_CHECKING
297 gcc_assert (tab
->kill_list
[p
]);
299 bitmap_clear_bit (tab
->kill_list
[p
], version
);
300 if (bitmap_empty_p (tab
->kill_list
[p
]))
302 bitmap_clear_bit (tab
->partition_in_use
, p
);
303 BITMAP_FREE (tab
->kill_list
[p
]);
308 /* Add a dependency between the def of ssa VERSION and VAR. If VAR is
309 replaceable by an expression, add a dependence each of the elements of the
310 expression. These are contained in the new_replaceable list. TAB is the
314 add_dependence (temp_expr_table_p tab
, int version
, tree var
)
320 i
= SSA_NAME_VERSION (var
);
321 if (version_to_be_replaced_p (tab
, i
))
323 if (!bitmap_empty_p (tab
->new_replaceable_dependencies
))
325 /* Version will now be killed by a write to any partition the
326 substituted expression would have been killed by. */
327 EXECUTE_IF_SET_IN_BITMAP (tab
->new_replaceable_dependencies
, 0, x
, bi
)
328 add_to_partition_kill_list (tab
, x
, version
);
330 /* Rather than set partition_dependencies and in_use lists bit by
331 bit, simply OR in the new_replaceable_dependencies bits. */
332 if (!tab
->partition_dependencies
[version
])
333 tab
->partition_dependencies
[version
] = BITMAP_ALLOC (NULL
);
334 bitmap_ior_into (tab
->partition_dependencies
[version
],
335 tab
->new_replaceable_dependencies
);
336 bitmap_ior_into (tab
->partition_in_use
,
337 tab
->new_replaceable_dependencies
);
338 /* It is only necessary to add these once. */
339 bitmap_clear (tab
->new_replaceable_dependencies
);
344 i
= var_to_partition (tab
->map
, var
);
345 #ifdef ENABLE_CHECKING
346 gcc_assert (i
!= NO_PARTITION
);
347 gcc_assert (tab
->num_in_part
[i
] != 0);
349 /* Only dependencies on ssa_names which are coalesced with something need
350 to be tracked. Partitions with containing only a single SSA_NAME
351 *cannot* have their value changed. */
352 if (tab
->num_in_part
[i
] > 1)
354 add_to_partition_kill_list (tab
, i
, version
);
355 make_dependent_on_partition (tab
, version
, i
);
361 /* Return TRUE if expression STMT is suitable for replacement. */
364 is_replaceable_p (gimple stmt
)
369 location_t locus1
, locus2
;
372 /* Only consider modify stmts. */
373 if (!is_gimple_assign (stmt
))
376 /* If the statement may throw an exception, it cannot be replaced. */
377 if (stmt_could_throw_p (stmt
))
380 /* Punt if there is more than 1 def. */
381 def
= SINGLE_SSA_TREE_OPERAND (stmt
, SSA_OP_DEF
);
385 /* Only consider definitions which have a single use. */
386 if (!single_imm_use (def
, &use_p
, &use_stmt
))
389 /* If the use isn't in this block, it wont be replaced either. */
390 if (gimple_bb (use_stmt
) != gimple_bb (stmt
))
393 locus1
= gimple_location (stmt
);
394 block1
= gimple_block (stmt
);
396 if (gimple_code (use_stmt
) == GIMPLE_PHI
)
403 locus2
= gimple_location (use_stmt
);
404 block2
= gimple_block (use_stmt
);
408 && ((locus1
&& locus1
!= locus2
) || (block1
&& block1
!= block2
)))
411 /* Used in this block, but at the TOP of the block, not the end. */
412 if (gimple_code (use_stmt
) == GIMPLE_PHI
)
415 /* There must be no VDEFs. */
416 if (gimple_vdef (stmt
))
419 /* Without alias info we can't move around loads. */
420 if (gimple_references_memory_p (stmt
) && !optimize
)
423 /* Float expressions must go through memory if float-store is on. */
425 && FLOAT_TYPE_P (gimple_expr_type (stmt
)))
428 /* An assignment with a register variable on the RHS is not
430 if (gimple_assign_rhs_code (stmt
) == VAR_DECL
431 && DECL_HARD_REGISTER (gimple_assign_rhs1 (stmt
)))
434 /* No function calls can be replaced. */
435 if (is_gimple_call (stmt
))
438 /* Leave any stmt with volatile operands alone as well. */
439 if (gimple_has_volatile_ops (stmt
))
446 /* This function will remove the expression for VERSION from replacement
447 consideration in table TAB. If FREE_EXPR is true, then remove the
448 expression from consideration as well by freeing the decl uid bitmap. */
451 finished_with_expr (temp_expr_table_p tab
, int version
, bool free_expr
)
456 /* Remove this expression from its dependent lists. The partition dependence
457 list is retained and transfered later to whomever uses this version. */
458 if (tab
->partition_dependencies
[version
])
460 EXECUTE_IF_SET_IN_BITMAP (tab
->partition_dependencies
[version
], 0, i
, bi
)
461 remove_from_partition_kill_list (tab
, i
, version
);
462 BITMAP_FREE (tab
->partition_dependencies
[version
]);
465 BITMAP_FREE (tab
->expr_decl_uids
[version
]);
469 /* Create an expression entry for a replaceable expression. */
472 process_replaceable (temp_expr_table_p tab
, gimple stmt
)
474 tree var
, def
, basevar
;
477 bitmap def_vars
, use_vars
;
479 #ifdef ENABLE_CHECKING
480 gcc_assert (is_replaceable_p (stmt
));
483 def
= SINGLE_SSA_TREE_OPERAND (stmt
, SSA_OP_DEF
);
484 version
= SSA_NAME_VERSION (def
);
485 basevar
= SSA_NAME_VAR (def
);
486 def_vars
= BITMAP_ALLOC (NULL
);
488 bitmap_set_bit (def_vars
, DECL_UID (basevar
));
490 /* Add this expression to the dependency list for each use partition. */
491 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, iter
, SSA_OP_USE
)
493 int var_version
= SSA_NAME_VERSION (var
);
495 use_vars
= tab
->expr_decl_uids
[var_version
];
496 add_dependence (tab
, version
, var
);
499 bitmap_ior_into (def_vars
, use_vars
);
500 BITMAP_FREE (tab
->expr_decl_uids
[var_version
]);
503 bitmap_set_bit (def_vars
, DECL_UID (SSA_NAME_VAR (var
)));
505 tab
->expr_decl_uids
[version
] = def_vars
;
507 /* If there are VUSES, add a dependence on virtual defs. */
508 if (gimple_vuse (stmt
))
510 make_dependent_on_partition (tab
, version
, VIRTUAL_PARTITION (tab
));
511 add_to_partition_kill_list (tab
, VIRTUAL_PARTITION (tab
), version
);
516 /* This function removes any expression in TAB which is dependent on PARTITION
517 from consideration, making it not replaceable. */
520 kill_expr (temp_expr_table_p tab
, int partition
)
524 /* Mark every active expr dependent on this var as not replaceable.
525 finished_with_expr can modify the bitmap, so we can't execute over it. */
526 while (tab
->kill_list
[partition
])
528 version
= bitmap_first_set_bit (tab
->kill_list
[partition
]);
529 finished_with_expr (tab
, version
, true);
532 #ifdef ENABLE_CHECKING
533 gcc_assert (!tab
->kill_list
[partition
]);
538 /* This function kills all expressions in TAB which are dependent on virtual
542 kill_virtual_exprs (temp_expr_table_p tab
)
544 kill_expr (tab
, VIRTUAL_PARTITION (tab
));
548 /* Mark the expression associated with VAR as replaceable, and enter
549 the defining stmt into the partition_dependencies table TAB. If
550 MORE_REPLACING is true, accumulate the pending partition dependencies. */
553 mark_replaceable (temp_expr_table_p tab
, tree var
, bool more_replacing
)
555 int version
= SSA_NAME_VERSION (var
);
557 /* Move the dependence list to the pending listpending. */
558 if (more_replacing
&& tab
->partition_dependencies
[version
])
559 bitmap_ior_into (tab
->new_replaceable_dependencies
,
560 tab
->partition_dependencies
[version
]);
562 finished_with_expr (tab
, version
, !more_replacing
);
564 /* Set the replaceable expression. */
565 if (!tab
->replaceable_expressions
)
566 tab
->replaceable_expressions
= BITMAP_ALLOC (NULL
);
567 bitmap_set_bit (tab
->replaceable_expressions
, version
);
571 /* This function processes basic block BB, and looks for variables which can
572 be replaced by their expressions. Results are stored in the table TAB. */
575 find_replaceable_in_bb (temp_expr_table_p tab
, basic_block bb
)
577 gimple_stmt_iterator bsi
;
581 var_map map
= tab
->map
;
583 bool stmt_replaceable
;
585 for (bsi
= gsi_start_bb (bb
); !gsi_end_p (bsi
); gsi_next (&bsi
))
587 stmt
= gsi_stmt (bsi
);
589 if (is_gimple_debug (stmt
))
592 stmt_replaceable
= is_replaceable_p (stmt
);
594 /* Determine if this stmt finishes an existing expression. */
595 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
597 unsigned ver
= SSA_NAME_VERSION (use
);
599 /* If this use is a potential replacement variable, process it. */
600 if (tab
->expr_decl_uids
[ver
])
602 bool same_root_var
= false;
604 bitmap vars
= tab
->expr_decl_uids
[ver
];
606 /* See if the root variables are the same. If they are, we
607 do not want to do the replacement to avoid problems with
608 code size, see PR tree-optimization/17549. */
609 if (!bitmap_empty_p (vars
))
610 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter2
, SSA_OP_DEF
)
612 if (bitmap_bit_p (vars
, DECL_UID (SSA_NAME_VAR (def
))))
614 same_root_var
= true;
619 /* If the stmt does a memory store and the replacement
620 is a load aliasing it avoid creating overlapping
621 assignments which we cannot expand correctly. */
622 if (gimple_vdef (stmt
)
623 && gimple_assign_single_p (stmt
))
625 gimple def_stmt
= SSA_NAME_DEF_STMT (use
);
626 while (is_gimple_assign (def_stmt
)
627 && gimple_assign_rhs_code (def_stmt
) == SSA_NAME
)
629 = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (def_stmt
));
630 if (gimple_vuse (def_stmt
)
631 && gimple_assign_single_p (def_stmt
)
632 && refs_may_alias_p (gimple_assign_lhs (stmt
),
633 gimple_assign_rhs1 (def_stmt
)))
634 same_root_var
= true;
637 /* Mark expression as replaceable unless stmt is volatile or the
638 def variable has the same root variable as something in the
639 substitution list. */
640 if (gimple_has_volatile_ops (stmt
) || same_root_var
)
641 finished_with_expr (tab
, ver
, true);
643 mark_replaceable (tab
, use
, stmt_replaceable
);
647 /* Next, see if this stmt kills off an active expression. */
648 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter
, SSA_OP_DEF
)
650 partition
= var_to_partition (map
, def
);
651 if (partition
!= NO_PARTITION
&& tab
->kill_list
[partition
])
652 kill_expr (tab
, partition
);
655 /* Now see if we are creating a new expression or not. */
656 if (stmt_replaceable
)
657 process_replaceable (tab
, stmt
);
659 /* Free any unused dependency lists. */
660 bitmap_clear (tab
->new_replaceable_dependencies
);
662 /* A V_{MAY,MUST}_DEF kills any expression using a virtual operand,
663 including the current stmt. */
664 if (gimple_vdef (stmt
))
665 kill_virtual_exprs (tab
);
670 /* This function is the driver routine for replacement of temporary expressions
671 in the SSA->normal phase, operating on MAP. If there are replaceable
672 expressions, a table is returned which maps SSA versions to the
673 expressions they should be replaced with. A NULL_TREE indicates no
674 replacement should take place. If there are no replacements at all,
675 NULL is returned by the function, otherwise an expression vector indexed
676 by SSA_NAME version numbers. */
679 find_replaceable_exprs (var_map map
)
682 temp_expr_table_p table
;
685 table
= new_temp_expr_table (map
);
688 find_replaceable_in_bb (table
, bb
);
689 #ifdef ENABLE_CHECKING
690 gcc_assert (bitmap_empty_p (table
->partition_in_use
));
694 ret
= free_temp_expr_table (table
);
698 /* Dump TER expression table EXPR to file F. */
701 dump_replaceable_exprs (FILE *f
, bitmap expr
)
706 fprintf (f
, "\nReplacing Expressions\n");
707 for (x
= 0; x
< num_ssa_names
; x
++)
708 if (bitmap_bit_p (expr
, x
))
711 print_generic_expr (f
, var
, TDF_SLIM
);
712 fprintf (f
, " replace with --> ");
713 print_gimple_stmt (f
, SSA_NAME_DEF_STMT (var
), 0, TDF_SLIM
);
720 #ifdef ENABLE_CHECKING
721 /* Dump the status of the various tables in the expression table. This is used
722 exclusively to debug TER. F is the place to send debug info and T is the
723 table being debugged. */
726 debug_ter (FILE *f
, temp_expr_table_p t
)
731 fprintf (f
, "\nDumping current state of TER\n virtual partition = %d\n",
732 VIRTUAL_PARTITION (t
));
733 if (t
->replaceable_expressions
)
734 dump_replaceable_exprs (f
, t
->replaceable_expressions
);
735 fprintf (f
, "Currently tracking the following expressions:\n");
737 for (x
= 1; x
< num_ssa_names
; x
++)
738 if (t
->expr_decl_uids
[x
])
740 print_generic_expr (stderr
, ssa_name (x
), TDF_SLIM
);
741 fprintf (f
, " dep-parts : ");
742 if (t
->partition_dependencies
[x
]
743 && !bitmap_empty_p (t
->partition_dependencies
[x
]))
745 EXECUTE_IF_SET_IN_BITMAP (t
->partition_dependencies
[x
], 0, y
, bi
)
746 fprintf (f
, "P%d ",y
);
748 fprintf (stderr
, " basedecls: ");
749 EXECUTE_IF_SET_IN_BITMAP (t
->expr_decl_uids
[x
], 0, y
, bi
)
750 fprintf (f
, "%d ",y
);
751 fprintf (stderr
, "\n");
754 bitmap_print (f
, t
->partition_in_use
, "Partitions in use ",
755 "\npartition KILL lists:\n");
757 for (x
= 0; x
<= num_var_partitions (t
->map
); x
++)
760 fprintf (f
, "Partition %d : ", x
);
761 EXECUTE_IF_SET_IN_BITMAP (t
->kill_list
[x
], 0, y
, bi
)
762 fprintf (f
, "_%d ",y
);
765 fprintf (f
, "\n----------\n");