1 /* Routines for performing Temporary Expression Replacement (TER) in SSA trees.
2 Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation,
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 "diagnostic.h"
30 #include "tree-flow.h"
31 #include "tree-dump.h"
32 #include "tree-ssa-live.h"
36 /* Temporary Expression Replacement (TER)
38 Replace SSA version variables during out-of-ssa with their defining
39 expression if there is only one use of the variable.
41 This pass is required in order for the RTL expansion pass to see larger
42 chunks of code. This allows it to make better choices on RTL pattern
43 selection. When expand is rewritten and merged with out-of-ssa, and
44 understands SSA, this should be eliminated.
46 A pass is made through the function, one block at a time. No cross block
47 information is tracked.
49 Variables which only have one use, and whose defining stmt is considered
50 a replaceable expression (see is_replaceable_p) are tracked to see whether
51 they can be replaced at their use location.
57 if there are the only use of n_12 and a_2, TER will substitute in their
58 expressions in v_9, and end up with:
60 v_9 = (b_5 + 6) * (C * 10)
62 which will then have the ssa_name assigned to regular variables, and the
63 resulting code which will be passed to the expander looks something like:
65 v = (b + 6) * (C * 10)
68 This requires ensuring that none of the variables used by the expression
69 change between the def point and where it is used. Furthermore, if any
70 of the ssa_names used in this expression are themselves replaceable, we
71 have to ensure none of that expressions' arguments change either.
72 Although SSA_NAMES themselves don't change, this pass is performed after
73 coalescing has coalesced different SSA_NAMES together, so there could be a
74 definition of an SSA_NAME which is coalesced with a use that causes a
77 PHI b_5 = <b_8(2), b_14(1)>
84 If b_5, b_8 and b_14 are all coalesced together...
85 The expression b_5 + 6 CANNOT replace the use in the statement defining v_9
86 because b_8 is in fact killing the value of b_5 since they share a partition
87 and will be assigned the same memory or register location.
89 TER implements this but stepping through the instructions in a block and
90 tracking potential expressions for replacement, and the partitions they are
91 dependent on. Expressions are represented by the SSA_NAME_VERSION of the
92 DEF on the LHS of a GIMPLE_ASSIGN and the expression is the RHS.
94 When a stmt is determined to be a possible replacement expression, the
95 following steps are taken:
97 EXPR_DECL_UID bitmap is allocated and set to the base variable UID of the
98 def and any uses in the expression. non-NULL means the expression is being
99 tracked. The UID's themselves are used to prevent TER substitution into
100 accumulating sequences, i.e.,
106 this can result in very large expressions which don't accomplish anything
107 see PR tree-optimization/17549.
109 PARTITION_DEPENDENCIES is another bitmap array, and it has a bit set for any
110 partition which is used in the expression. This is primarily used to remove
111 an expression from the partition kill lists when a decision is made whether
112 to replace it or not. This is indexed by ssa version number as well, and
113 indicates a partition number. virtual operands are not tracked individually,
114 but they are summarized by an artificial partition called VIRTUAL_PARTITION.
115 This means a MAY or MUST def will kill *ALL* expressions that are dependent
116 on a virtual operand.
117 Note that the EXPR_DECL_UID and this bitmap represent very similar
118 information, but the info in one is not easy to obtain from the other.
120 KILL_LIST is yet another bitmap array, this time it is indexed by partition
121 number, and represents a list of active expressions which will will no
122 longer be valid if a definition into this partition takes place.
124 PARTITION_IN_USE is simply a bitmap which is used to track which partitions
125 currently have something in their kill list. This is used at the end of
126 a block to clear out the KILL_LIST bitmaps at the end of each block.
128 NEW_REPLACEABLE_DEPENDENCIES is used as a temporary place to store
129 dependencies which will be reused by the current definition. All the uses
130 on an expression are processed before anything else is done. If a use is
131 determined to be a replaceable expression AND the current stmt is also going
132 to be replaceable, all the dependencies of this replaceable use will be
133 picked up by the current stmt's expression. Rather than recreate them, they
134 are simply copied here and then copied into the new expression when it is
140 a_2's expression 'b_5 + 6' is determined to be replaceable at the use
141 location. It is dependent on the partition 'b_5' is in. This is cached into
142 the NEW_REPLACEABLE_DEPENDENCIES bitmap, and when v_8 is examined for
143 replaceability, it is a candidate, and it is dependent on the partition
144 b_5 is in *NOT* a_2, as well as c_4's partition.
146 if v_8 is also replaceable:
150 x_9 is dependent on partitions b_5, and c_4
152 if a statement is found which has either of those partitions written to
153 before x_9 is used, then x_9 itself is NOT replaceable. */
156 /* Temporary Expression Replacement (TER) table information. */
158 typedef struct temp_expr_table_d
161 bitmap
*partition_dependencies
; /* Partitions expr is dependent on. */
162 gimple
*replaceable_expressions
; /* Replacement expression table. */
163 bitmap
*expr_decl_uids
; /* Base uids of exprs. */
164 bitmap
*kill_list
; /* Expr's killed by a partition. */
165 int virtual_partition
; /* Pseudo partition for virtual ops. */
166 bitmap partition_in_use
; /* Partitions with kill entries. */
167 bitmap new_replaceable_dependencies
; /* Holding place for pending dep's. */
168 int *num_in_part
; /* # of ssa_names in a partition. */
169 } *temp_expr_table_p
;
171 /* Used to indicate a dependency on VDEFs. */
172 #define VIRTUAL_PARTITION(table) (table->virtual_partition)
174 #ifdef ENABLE_CHECKING
175 extern void debug_ter (FILE *, temp_expr_table_p
);
179 /* Create a new TER table for MAP. */
181 static temp_expr_table_p
182 new_temp_expr_table (var_map map
)
187 t
= XNEW (struct temp_expr_table_d
);
190 t
->partition_dependencies
= XCNEWVEC (bitmap
, num_ssa_names
+ 1);
191 t
->expr_decl_uids
= XCNEWVEC (bitmap
, num_ssa_names
+ 1);
192 t
->kill_list
= XCNEWVEC (bitmap
, num_var_partitions (map
) + 1);
194 t
->partition_in_use
= BITMAP_ALLOC (NULL
);
196 t
->virtual_partition
= num_var_partitions (map
);
197 t
->new_replaceable_dependencies
= BITMAP_ALLOC (NULL
);
199 t
->replaceable_expressions
= NULL
;
200 t
->num_in_part
= XCNEWVEC (int, num_var_partitions (map
));
201 for (x
= 1; x
< num_ssa_names
; x
++)
204 tree name
= ssa_name (x
);
207 p
= var_to_partition (map
, name
);
208 if (p
!= NO_PARTITION
)
216 /* Free TER table T. If there are valid replacements, return the expression
220 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
]);
228 for (x
= 0; x
< num_ssa_names
; x
++)
230 gcc_assert (t
->expr_decl_uids
[x
] == NULL
);
231 gcc_assert (t
->partition_dependencies
[x
] == NULL
);
235 BITMAP_FREE (t
->partition_in_use
);
236 BITMAP_FREE (t
->new_replaceable_dependencies
);
238 free (t
->expr_decl_uids
);
240 free (t
->partition_dependencies
);
241 free (t
->num_in_part
);
243 if (t
->replaceable_expressions
)
244 ret
= t
->replaceable_expressions
;
251 /* Return TRUE if VERSION is to be replaced by an expression in TAB. */
254 version_to_be_replaced_p (temp_expr_table_p tab
, int version
)
256 if (!tab
->replaceable_expressions
)
258 return tab
->replaceable_expressions
[version
] != NULL
;
262 /* Add partition P to the list if partitions VERSION is dependent on. TAB is
263 the expression table */
266 make_dependent_on_partition (temp_expr_table_p tab
, int version
, int p
)
268 if (!tab
->partition_dependencies
[version
])
269 tab
->partition_dependencies
[version
] = BITMAP_ALLOC (NULL
);
271 bitmap_set_bit (tab
->partition_dependencies
[version
], p
);
275 /* Add VER to the kill list for P. TAB is the expression table */
278 add_to_partition_kill_list (temp_expr_table_p tab
, int p
, int ver
)
280 if (!tab
->kill_list
[p
])
282 tab
->kill_list
[p
] = BITMAP_ALLOC (NULL
);
283 bitmap_set_bit (tab
->partition_in_use
, p
);
285 bitmap_set_bit (tab
->kill_list
[p
], ver
);
289 /* Remove VER from the partition kill list for P. TAB is the expression
293 remove_from_partition_kill_list (temp_expr_table_p tab
, int p
, int version
)
295 #ifdef ENABLE_CHECKING
296 gcc_assert (tab
->kill_list
[p
]);
298 bitmap_clear_bit (tab
->kill_list
[p
], version
);
299 if (bitmap_empty_p (tab
->kill_list
[p
]))
301 bitmap_clear_bit (tab
->partition_in_use
, p
);
302 BITMAP_FREE (tab
->kill_list
[p
]);
307 /* Add a dependency between the def of ssa VERSION and VAR. If VAR is
308 replaceable by an expression, add a dependence each of the elements of the
309 expression. These are contained in the new_replaceable list. TAB is the
313 add_dependence (temp_expr_table_p tab
, int version
, tree var
)
319 i
= SSA_NAME_VERSION (var
);
320 if (version_to_be_replaced_p (tab
, i
))
322 if (!bitmap_empty_p (tab
->new_replaceable_dependencies
))
324 /* Version will now be killed by a write to any partition the
325 substituted expression would have been killed by. */
326 EXECUTE_IF_SET_IN_BITMAP (tab
->new_replaceable_dependencies
, 0, x
, bi
)
327 add_to_partition_kill_list (tab
, x
, version
);
329 /* Rather than set partition_dependencies and in_use lists bit by
330 bit, simply OR in the new_replaceable_dependencies bits. */
331 if (!tab
->partition_dependencies
[version
])
332 tab
->partition_dependencies
[version
] = BITMAP_ALLOC (NULL
);
333 bitmap_ior_into (tab
->partition_dependencies
[version
],
334 tab
->new_replaceable_dependencies
);
335 bitmap_ior_into (tab
->partition_in_use
,
336 tab
->new_replaceable_dependencies
);
337 /* It is only necessary to add these once. */
338 bitmap_clear (tab
->new_replaceable_dependencies
);
343 i
= var_to_partition (tab
->map
, var
);
344 #ifdef ENABLE_CHECKING
345 gcc_assert (i
!= NO_PARTITION
);
346 gcc_assert (tab
->num_in_part
[i
] != 0);
348 /* Only dependencies on ssa_names which are coalesced with something need
349 to be tracked. Partitions with containing only a single SSA_NAME
350 *cannot* have their value changed. */
351 if (tab
->num_in_part
[i
] > 1)
353 add_to_partition_kill_list (tab
, i
, version
);
354 make_dependent_on_partition (tab
, version
, i
);
360 /* Return TRUE if expression STMT is suitable for replacement. */
363 is_replaceable_p (gimple stmt
)
368 location_t locus1
, locus2
;
371 /* Only consider modify stmts. */
372 if (!is_gimple_assign (stmt
))
375 /* If the statement may throw an exception, it cannot be replaced. */
376 if (stmt_could_throw_p (stmt
))
379 /* Punt if there is more than 1 def. */
380 def
= SINGLE_SSA_TREE_OPERAND (stmt
, SSA_OP_DEF
);
384 /* Only consider definitions which have a single use. */
385 if (!single_imm_use (def
, &use_p
, &use_stmt
))
388 /* If the use isn't in this block, it wont be replaced either. */
389 if (gimple_bb (use_stmt
) != gimple_bb (stmt
))
392 locus1
= gimple_location (stmt
);
393 block1
= gimple_block (stmt
);
395 if (gimple_code (use_stmt
) == GIMPLE_PHI
)
402 locus2
= gimple_location (use_stmt
);
403 block2
= gimple_block (use_stmt
);
407 && ((locus1
&& locus1
!= locus2
) || (block1
&& block1
!= block2
)))
410 /* Used in this block, but at the TOP of the block, not the end. */
411 if (gimple_code (use_stmt
) == GIMPLE_PHI
)
414 /* There must be no VDEFs. */
415 if (gimple_vdef (stmt
))
418 /* Without alias info we can't move around loads. */
419 if (gimple_references_memory_p (stmt
) && !optimize
)
422 /* Float expressions must go through memory if float-store is on. */
424 && FLOAT_TYPE_P (gimple_expr_type (stmt
)))
427 /* An assignment with a register variable on the RHS is not
429 if (gimple_assign_rhs_code (stmt
) == VAR_DECL
430 && DECL_HARD_REGISTER (gimple_assign_rhs1 (stmt
)))
433 /* No function calls can be replaced. */
434 if (is_gimple_call (stmt
))
437 /* Leave any stmt with volatile operands alone as well. */
438 if (gimple_has_volatile_ops (stmt
))
445 /* This function will remove the expression for VERSION from replacement
446 consideration in table TAB. If FREE_EXPR is true, then remove the
447 expression from consideration as well by freeing the decl uid bitmap. */
450 finished_with_expr (temp_expr_table_p tab
, int version
, bool free_expr
)
455 /* Remove this expression from its dependent lists. The partition dependence
456 list is retained and transfered later to whomever uses this version. */
457 if (tab
->partition_dependencies
[version
])
459 EXECUTE_IF_SET_IN_BITMAP (tab
->partition_dependencies
[version
], 0, i
, bi
)
460 remove_from_partition_kill_list (tab
, i
, version
);
461 BITMAP_FREE (tab
->partition_dependencies
[version
]);
464 BITMAP_FREE (tab
->expr_decl_uids
[version
]);
468 /* Create an expression entry for a replaceable expression. */
471 process_replaceable (temp_expr_table_p tab
, gimple stmt
)
473 tree var
, def
, basevar
;
476 bitmap def_vars
, use_vars
;
478 #ifdef ENABLE_CHECKING
479 gcc_assert (is_replaceable_p (stmt
));
482 def
= SINGLE_SSA_TREE_OPERAND (stmt
, SSA_OP_DEF
);
483 version
= SSA_NAME_VERSION (def
);
484 basevar
= SSA_NAME_VAR (def
);
485 def_vars
= BITMAP_ALLOC (NULL
);
487 bitmap_set_bit (def_vars
, DECL_UID (basevar
));
489 /* Add this expression to the dependency list for each use partition. */
490 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, iter
, SSA_OP_USE
)
492 int var_version
= SSA_NAME_VERSION (var
);
494 use_vars
= tab
->expr_decl_uids
[var_version
];
495 add_dependence (tab
, version
, var
);
498 bitmap_ior_into (def_vars
, use_vars
);
499 BITMAP_FREE (tab
->expr_decl_uids
[var_version
]);
502 bitmap_set_bit (def_vars
, DECL_UID (SSA_NAME_VAR (var
)));
504 tab
->expr_decl_uids
[version
] = def_vars
;
506 /* If there are VUSES, add a dependence on virtual defs. */
507 if (gimple_vuse (stmt
))
509 make_dependent_on_partition (tab
, version
, VIRTUAL_PARTITION (tab
));
510 add_to_partition_kill_list (tab
, VIRTUAL_PARTITION (tab
), version
);
515 /* This function removes any expression in TAB which is dependent on PARTITION
516 from consideration, making it not replaceable. */
519 kill_expr (temp_expr_table_p tab
, int partition
)
523 /* Mark every active expr dependent on this var as not replaceable.
524 finished_with_expr can modify the bitmap, so we can't execute over it. */
525 while (tab
->kill_list
[partition
])
527 version
= bitmap_first_set_bit (tab
->kill_list
[partition
]);
528 finished_with_expr (tab
, version
, true);
531 #ifdef ENABLE_CHECKING
532 gcc_assert (!tab
->kill_list
[partition
]);
537 /* This function kills all expressions in TAB which are dependent on virtual
541 kill_virtual_exprs (temp_expr_table_p tab
)
543 kill_expr (tab
, VIRTUAL_PARTITION (tab
));
547 /* Mark the expression associated with VAR as replaceable, and enter
548 the defining stmt into the partition_dependencies table TAB. If
549 MORE_REPLACING is true, accumulate the pending partition dependencies. */
552 mark_replaceable (temp_expr_table_p tab
, tree var
, bool more_replacing
)
554 int version
= SSA_NAME_VERSION (var
);
556 /* Move the dependence list to the pending listpending. */
557 if (more_replacing
&& tab
->partition_dependencies
[version
])
558 bitmap_ior_into (tab
->new_replaceable_dependencies
,
559 tab
->partition_dependencies
[version
]);
561 finished_with_expr (tab
, version
, !more_replacing
);
563 /* Set the replaceable expression. */
564 if (!tab
->replaceable_expressions
)
565 tab
->replaceable_expressions
= XCNEWVEC (gimple
, num_ssa_names
+ 1);
566 tab
->replaceable_expressions
[version
] = SSA_NAME_DEF_STMT (var
);
570 /* This function processes basic block BB, and looks for variables which can
571 be replaced by their expressions. Results are stored in the table TAB. */
574 find_replaceable_in_bb (temp_expr_table_p tab
, basic_block bb
)
576 gimple_stmt_iterator bsi
;
580 var_map map
= tab
->map
;
582 bool stmt_replaceable
;
584 for (bsi
= gsi_start_bb (bb
); !gsi_end_p (bsi
); gsi_next (&bsi
))
586 stmt
= gsi_stmt (bsi
);
588 stmt_replaceable
= is_replaceable_p (stmt
);
590 /* Determine if this stmt finishes an existing expression. */
591 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
593 unsigned ver
= SSA_NAME_VERSION (use
);
595 /* If this use is a potential replacement variable, process it. */
596 if (tab
->expr_decl_uids
[ver
])
598 bool same_root_var
= false;
600 bitmap vars
= tab
->expr_decl_uids
[ver
];
602 /* See if the root variables are the same. If they are, we
603 do not want to do the replacement to avoid problems with
604 code size, see PR tree-optimization/17549. */
605 if (!bitmap_empty_p (vars
))
606 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter2
, SSA_OP_DEF
)
608 if (bitmap_bit_p (vars
, DECL_UID (SSA_NAME_VAR (def
))))
610 same_root_var
= true;
615 /* Mark expression as replaceable unless stmt is volatile or the
616 def variable has the same root variable as something in the
617 substitution list. */
618 if (gimple_has_volatile_ops (stmt
) || same_root_var
)
619 finished_with_expr (tab
, ver
, true);
621 mark_replaceable (tab
, use
, stmt_replaceable
);
625 /* Next, see if this stmt kills off an active expression. */
626 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter
, SSA_OP_DEF
)
628 partition
= var_to_partition (map
, def
);
629 if (partition
!= NO_PARTITION
&& tab
->kill_list
[partition
])
630 kill_expr (tab
, partition
);
633 /* Now see if we are creating a new expression or not. */
634 if (stmt_replaceable
)
635 process_replaceable (tab
, stmt
);
637 /* Free any unused dependency lists. */
638 bitmap_clear (tab
->new_replaceable_dependencies
);
640 /* A V_{MAY,MUST}_DEF kills any expression using a virtual operand,
641 including the current stmt. */
642 if (gimple_vdef (stmt
))
643 kill_virtual_exprs (tab
);
648 /* This function is the driver routine for replacement of temporary expressions
649 in the SSA->normal phase, operating on MAP. If there are replaceable
650 expressions, a table is returned which maps SSA versions to the
651 expressions they should be replaced with. A NULL_TREE indicates no
652 replacement should take place. If there are no replacements at all,
653 NULL is returned by the function, otherwise an expression vector indexed
654 by SSA_NAME version numbers. */
657 find_replaceable_exprs (var_map map
)
660 temp_expr_table_p table
;
663 table
= new_temp_expr_table (map
);
666 find_replaceable_in_bb (table
, bb
);
667 #ifdef ENABLE_CHECKING
668 gcc_assert (bitmap_empty_p (table
->partition_in_use
));
672 ret
= free_temp_expr_table (table
);
676 /* Dump TER expression table EXPR to file F. */
679 dump_replaceable_exprs (FILE *f
, gimple
*expr
)
684 fprintf (f
, "\nReplacing Expressions\n");
685 for (x
= 0; x
< num_ssa_names
; x
++)
689 print_generic_expr (f
, var
, TDF_SLIM
);
690 fprintf (f
, " replace with --> ");
691 print_gimple_stmt (f
, expr
[x
], 0, TDF_SLIM
);
698 #ifdef ENABLE_CHECKING
699 /* Dump the status of the various tables in the expression table. This is used
700 exclusively to debug TER. F is the place to send debug info and T is the
701 table being debugged. */
704 debug_ter (FILE *f
, temp_expr_table_p t
)
709 fprintf (f
, "\nDumping current state of TER\n virtual partition = %d\n",
710 VIRTUAL_PARTITION (t
));
711 if (t
->replaceable_expressions
)
712 dump_replaceable_exprs (f
, t
->replaceable_expressions
);
713 fprintf (f
, "Currently tracking the following expressions:\n");
715 for (x
= 1; x
< num_ssa_names
; x
++)
716 if (t
->expr_decl_uids
[x
])
718 print_generic_expr (stderr
, ssa_name (x
), TDF_SLIM
);
719 fprintf (f
, " dep-parts : ");
720 if (t
->partition_dependencies
[x
]
721 && !bitmap_empty_p (t
->partition_dependencies
[x
]))
723 EXECUTE_IF_SET_IN_BITMAP (t
->partition_dependencies
[x
], 0, y
, bi
)
724 fprintf (f
, "P%d ",y
);
726 fprintf (stderr
, " basedecls: ");
727 EXECUTE_IF_SET_IN_BITMAP (t
->expr_decl_uids
[x
], 0, y
, bi
)
728 fprintf (f
, "%d ",y
);
729 fprintf (stderr
, "\n");
732 bitmap_print (f
, t
->partition_in_use
, "Partitions in use ",
733 "\npartition KILL lists:\n");
735 for (x
= 0; x
<= num_var_partitions (t
->map
); x
++)
738 fprintf (f
, "Partition %d : ", x
);
739 EXECUTE_IF_SET_IN_BITMAP (t
->kill_list
[x
], 0, y
, bi
)
740 fprintf (f
, "_%d ",y
);
743 fprintf (f
, "\n----------\n");