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"
32 #include "langhooks.h"
33 #include "hard-reg-set.h"
34 #include "basic-block.h"
38 #include "diagnostic.h"
40 #include "tree-flow.h"
41 #include "tree-gimple.h"
42 #include "tree-inline.h"
46 #include "tree-dump.h"
47 #include "tree-ssa-live.h"
48 #include "tree-pass.h"
53 /* Temporary Expression Replacement (TER)
55 Replace SSA version variables during out-of-ssa with their defining
56 expression if there is only one use of the variable.
58 This pass is required in order for the RTL expansion pass to see larger
59 chunks of code. This allows it to make better choices on RTL pattern
60 selection. When expand is rewritten and merged with out-of-ssa, and
61 understands SSA, this should be eliminated.
63 A pass is made through the function, one block at a time. No cross block
64 information is tracked.
66 Variables which only have one use, and whose defining stmt is considered
67 a replaceable expression (see is_replaceable_p) are tracked to see whether
68 they can be replaced at their use location.
74 if there are the only use of n_12 and a_2, TER will substitute in their
75 expressions in v_9, and end up with:
77 v_9 = (b_5 + 6) * (C * 10)
79 which will then have the ssa_name assigned to regular variables, and the
80 resulting code which will be passed ot the expander looks something like:
82 v = (b + 6) * (C * 10)
85 This requires ensuring that none of the variables used by the expression
86 change between the def point and where it is used. Furthermore, if any
87 of the ssa_names used in this expression are themselves replaceable, we
88 have to ensure none of that expressions' arguments change either.
89 Although SSA_NAMES themselves don't change, this pass is performed after
90 coalescing has coalesced different SSA_NAMES together, so there could be a
91 definition of an SSA_NAME which is coalesced with a use that causes a
94 PHI b_5 = <b_8(2), b_14(1)>
101 If b_5, b_8 and b_14 are all colaesced together...
102 The expression b_5 + 6 CANNOT replace the use in the statement defining v_9
103 because b_8 is in fact killing the value of b_5 since they share a partition
104 and will be assigned the same memory or regster location.
106 TER implements this but stepping through the instructions in a block and
107 tracking potential expressions for replacement, and the paritions they are
108 dependent on. Expressions are represented by the SSA_NAME_VERSION of the
109 DEF on the LHS of a GIMPLE_MODIFY_STMT and the expression is the RHS.
111 When a stmt is determined to be a possible replacement expression, the
112 following steps are taken:
114 EXPR_DECL_UID bitmap is allocated and set to the base variable UID of the
115 def and any uses in the expression. non-NULL means the expression is being
116 tracked. The UID's themselves are used to prevent TER substitution into
117 accumulating sequences.
123 this can result in very large expressions which don't accomplish anything
124 see PR tree-optimization/17549.
126 PARTITION_DEPENDENCIES is another bitmap array, and it has a bit set for any
127 partition which is used in the expression. This is primarily used to remove
128 an expression from the partition kill lists when a decision is made whether
129 to replace it or not. This is indexed by ssa version number as well, and
130 indicates a partition number. virtual operands are not tracked individually,
131 but they are summarized by an artifical partition called VIRTUAL_PARTITION.
132 This means a MAY or MUST def will kill *ALL* expressions that are dependant
133 on a virtual operand.
134 Note that the EXPR_DECL_UID and this bitmap represent very similar
135 information, but the info in one is not easy to obtain from the other.
137 KILL_LIST is yet another bitmap array, this time it is indexed by partition
138 number, and represents a list of active expressions which will will no
139 longer be valid if a definition into this partition takes place.
141 PARTITION_IN_USE is simply a bitmap which is used to track which partitions
142 currently have sokmething in their kill list. This is used at the end of
143 a block to clear out the KILL_LIST bitmaps at the end of each block.
145 NEW_REPLACEABLE_DEPENDENCIES is used as a temporary place to store
146 dependencies which will be reused by the current defintion. ALl the uses
147 on an expression are processed before anything else is done. If a use is
148 determined to be a replaceable expression AND the current stmt is also going
149 to be replaceable, all the dependencies of this replaceable use will be
150 picked up by the current stmt's expression. Rather than recreate them, they
151 are simply copied here and then copied into the new expression when it is
157 a_2's expression 'b_5 + 6' is determined to be replaceable at the use
158 location. It is dependent on the partition 'b_5' is in. This is cached into
159 the NEW_REPLACEABLE_DEPENDENCIES bitmap. and when v_8 is examined for
160 replaceablility, it is a candidate, and it is dependent on the partition
161 b_5 is in *NOT* a_2, as well as c_4's partition.
163 if v_8 is also replaceable:
167 x_9 is dependent on partitions b_5, and c_4
169 if a statement is found which has either of those partitions written to
170 before x_9 is used, then x_9 itself is NOT replaceable. */
173 /* Temporary Expression Replacement (TER) table information. */
175 typedef struct temp_expr_table_d
178 bitmap *partition_dependencies; /* Partitions expr is dependent on. */
179 tree *replaceable_expressions; /* Replacement expression table. */
180 bitmap *expr_decl_uids; /* Base uids of exprs. */
181 bitmap *kill_list; /* Expr's killed by a partition. */
182 int virtual_partition; /* Psuedo partition for virtual ops. */
183 bitmap partition_in_use; /* Partitions with kill entires. */
184 bitmap new_replaceable_dependencies; /* Holding place for pending dep's. */
185 int *num_in_part; /* # of ssa_names in a partition. */
186 } *temp_expr_table_p;
188 /* Used to indicate a dependency on V_MAY_DEFs. */
189 #define VIRTUAL_PARTITION(table) (table->virtual_partition)
191 #ifdef ENABLE_CHECKING
192 extern void debug_ter (FILE *, temp_expr_table_p);
196 /* Create a new TER table for MAP. */
198 static temp_expr_table_p
199 new_temp_expr_table (var_map map)
204 t = XNEW (struct temp_expr_table_d);
207 t->partition_dependencies = XCNEWVEC (bitmap, num_ssa_names + 1);
208 t->expr_decl_uids = XCNEWVEC (bitmap, num_ssa_names + 1);
209 t->kill_list = XCNEWVEC (bitmap, num_var_partitions (map) + 1);
211 t->partition_in_use = BITMAP_ALLOC (NULL);
213 t->virtual_partition = num_var_partitions (map);
214 t->new_replaceable_dependencies = BITMAP_ALLOC (NULL);
216 t->replaceable_expressions = NULL;
217 t->num_in_part = XCNEWVEC (int, num_var_partitions (map));
218 for (x = 1; x < num_ssa_names; x++)
221 tree name = ssa_name (x);
224 p = var_to_partition (map, name);
225 if (p != NO_PARTITION)
233 /* Free TER table T. If there are valid replacements, return the expression
237 free_temp_expr_table (temp_expr_table_p t)
242 #ifdef ENABLE_CHECKING
244 for (x = 0; x <= num_var_partitions (t->map); x++)
245 gcc_assert (!t->kill_list[x]);
248 BITMAP_FREE (t->partition_in_use);
250 for (i = 0; i <= num_ssa_names; i++)
251 if (t->expr_decl_uids[i])
252 BITMAP_FREE (t->expr_decl_uids[i]);
253 free (t->expr_decl_uids);
256 free (t->partition_dependencies);
258 if (t->replaceable_expressions)
259 ret = t->replaceable_expressions;
266 /* Return TRUE if VERSION is to be replaced by an expression in TAB. */
269 version_to_be_replaced_p (temp_expr_table_p tab, int version)
271 if (!tab->replaceable_expressions)
273 return tab->replaceable_expressions[version] != NULL_TREE;
277 /* Add partition P to the list if partititons VERSION is dependent on. TAB is
278 the expression table */
281 make_dependent_on_partition (temp_expr_table_p tab, int version, int p)
283 if (!tab->partition_dependencies[version])
284 tab->partition_dependencies[version] = BITMAP_ALLOC (NULL);
286 bitmap_set_bit (tab->partition_dependencies[version], p);
290 /* Add VER to the kill list for P. TAB is the expression table */
293 add_to_partition_kill_list (temp_expr_table_p tab, int p, int ver)
295 if (!tab->kill_list[p])
297 tab->kill_list[p] = BITMAP_ALLOC (NULL);
298 bitmap_set_bit (tab->partition_in_use, p);
300 bitmap_set_bit (tab->kill_list[p], ver);
304 /* Remove VER from the partition kill list for P. TAB is the expression
308 remove_from_partition_kill_list (temp_expr_table_p tab, int p, int version)
310 #ifdef ENABLE_CHECKING
311 gcc_assert (tab->kill_list[p]);
313 bitmap_clear_bit (tab->kill_list[p], version);
314 if (bitmap_empty_p (tab->kill_list[p]))
316 bitmap_clear_bit (tab->partition_in_use, p);
317 BITMAP_FREE (tab->kill_list[p]);
322 /* Add a dependency between the def of ssa VERSION and VAR. If VAR is
323 replaceable by an expression, add a dependence each of the elements of the
324 expression. These are contained in the new_replaceable list. TAB is the
328 add_dependence (temp_expr_table_p tab, int version, tree var)
334 i = SSA_NAME_VERSION (var);
335 if (version_to_be_replaced_p (tab, i))
337 if (!bitmap_empty_p (tab->new_replaceable_dependencies))
339 /* Version will now be killed by a write to any partition the
340 substituted expression would have been killed by. */
341 EXECUTE_IF_SET_IN_BITMAP (tab->new_replaceable_dependencies, 0, x, bi)
342 add_to_partition_kill_list (tab, x, version);
344 /* Rather than set partition_dependencies and in_use lists bit by
345 bit, simply OR in the new_replaceable_dependencies bits. */
346 if (!tab->partition_dependencies[version])
347 tab->partition_dependencies[version] = BITMAP_ALLOC (NULL);
348 bitmap_ior_into (tab->partition_dependencies[version],
349 tab->new_replaceable_dependencies);
350 bitmap_ior_into (tab->partition_in_use,
351 tab->new_replaceable_dependencies);
352 /* It is only necessary to add these once. */
353 bitmap_clear (tab->new_replaceable_dependencies);
358 i = var_to_partition (tab->map, var);
359 #ifdef ENABLE_CHECKING
360 gcc_assert (i != NO_PARTITION);
361 gcc_assert (tab->num_in_part[i] != 0);
363 /* Only dependencies on ssa_names which are coalesced with something need
364 to be tracked. Partitions with containing only a single SSA_NAME
365 *cannot* have their value changed. */
366 if (tab->num_in_part[i] > 1)
368 add_to_partition_kill_list (tab, i, version);
369 make_dependent_on_partition (tab, version, i);
375 /* Return TRUE if expression STMT is suitable for replacement. */
378 is_replaceable_p (tree stmt)
384 /* Only consider modify stmts. */
385 if (TREE_CODE (stmt) != GIMPLE_MODIFY_STMT)
388 /* Punt if there is more than 1 def. */
389 def = SINGLE_SSA_TREE_OPERAND (stmt, SSA_OP_DEF);
393 /* Only consider definitions which have a single use. */
394 if (!single_imm_use (def, &use_p, &use_stmt))
397 /* If the use isn't in this block, it wont be replaced either. */
398 if (bb_for_stmt (use_stmt) != bb_for_stmt (stmt))
401 /* Used in this block, but at the TOP of the block, not the end. */
402 if (TREE_CODE (use_stmt) == PHI_NODE)
405 /* There must be no V_MAY_DEFS or V_MUST_DEFS. */
406 if (!(ZERO_SSA_OPERANDS (stmt, (SSA_OP_VMAYDEF | SSA_OP_VMUSTDEF))))
409 /* Float expressions must go through memory if float-store is on. */
411 && FLOAT_TYPE_P (TREE_TYPE (GENERIC_TREE_OPERAND (stmt, 1))))
414 /* Calls to functions with side-effects cannot be replaced. */
415 if ((call_expr = get_call_expr_in (stmt)) != NULL_TREE)
417 int call_flags = call_expr_flags (call_expr);
418 if (TREE_SIDE_EFFECTS (call_expr)
419 && !(call_flags & (ECF_PURE | ECF_CONST | ECF_NORETURN)))
423 /* Leave any stmt with voltile operands alone as well. */
424 if (stmt_ann (stmt)->has_volatile_ops)
432 /* This function will remove the expression for VERSION from replacement
433 consideration in table TAB. If FREE_EXPR is true, then remove the
434 expression from consideration as well by freeing the decl uid bitmap. */
437 finished_with_expr (temp_expr_table_p tab, int version, bool free_expr)
442 /* Remove this expression from its dependent lists. The partition dependence
443 list is retained and transfered later to whomever uses this version. */
444 if (tab->partition_dependencies[version])
446 EXECUTE_IF_SET_IN_BITMAP (tab->partition_dependencies[version], 0, i, bi)
447 remove_from_partition_kill_list (tab, i, version);
448 BITMAP_FREE (tab->partition_dependencies[version]);
451 BITMAP_FREE (tab->expr_decl_uids[version]);
455 /* Create an expression entry fora replaceable expression. */
458 process_replaceable (temp_expr_table_p tab, tree stmt)
460 tree var, def, basevar;
463 bitmap def_vars, use_vars;
465 #ifdef ENABLE_CHECKING
466 gcc_assert (is_replaceable_p (stmt));
469 def = SINGLE_SSA_TREE_OPERAND (stmt, SSA_OP_DEF);
470 version = SSA_NAME_VERSION (def);
471 basevar = SSA_NAME_VAR (def);
472 def_vars = BITMAP_ALLOC (NULL);
474 bitmap_set_bit (def_vars, DECL_UID (basevar));
476 /* Add this expression to the dependency list for each use partition. */
477 FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_USE)
479 int var_version = SSA_NAME_VERSION (var);
481 use_vars = tab->expr_decl_uids[var_version];
482 add_dependence (tab, version, var);
485 bitmap_ior_into (def_vars, use_vars);
486 BITMAP_FREE (tab->expr_decl_uids[var_version]);
489 bitmap_set_bit (def_vars, DECL_UID (SSA_NAME_VAR (var)));
491 tab->expr_decl_uids[version] = def_vars;
493 /* If there are VUSES, add a dependence on virtual defs. */
494 if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_VUSE))
496 make_dependent_on_partition (tab, version, VIRTUAL_PARTITION (tab));
497 add_to_partition_kill_list (tab, VIRTUAL_PARTITION (tab), version);
502 /* This function removes any expression in TAB which is dependent on PARTITION
503 from consideration, making it not replaceable. */
506 kill_expr (temp_expr_table_p tab, int partition)
510 /* Mark every active expr dependent on this var as not replaceable.
511 finished_with_expr can modify the bitmap, so we can't execute over it. */
512 while (tab->kill_list[partition])
514 version = bitmap_first_set_bit (tab->kill_list[partition]);
515 finished_with_expr (tab, version, true);
518 #ifdef ENABLE_CHECKING
519 gcc_assert (!tab->kill_list[partition]);
524 /* This function kills all expressions in TAB which are dependent on virtual
528 kill_virtual_exprs (temp_expr_table_p tab)
530 kill_expr (tab, VIRTUAL_PARTITION (tab));
534 /* Mark the expression associated with VAR as replaceable, and enter
535 the defining stmt into the partition_dependencies table TAB. if
536 MORE_REPLACING is true, accumulate the pending partition dependencies. */
539 mark_replaceable (temp_expr_table_p tab, tree var, bool more_replacing)
541 int version = SSA_NAME_VERSION (var);
543 /* Move the dependence list to the pending listpending. */
544 if (more_replacing && tab->partition_dependencies[version])
545 bitmap_ior_into (tab->new_replaceable_dependencies,
546 tab->partition_dependencies[version]);
548 finished_with_expr (tab, version, !more_replacing);
550 /* Set the replaceable expression. */
551 if (!tab->replaceable_expressions)
552 tab->replaceable_expressions = XCNEWVEC (tree, num_ssa_names + 1);
553 tab->replaceable_expressions[version] = SSA_NAME_DEF_STMT (var);
557 /* This function processes basic block BB, and looks for variables which can
558 be replaced by their expressions. Results are stored in the table TAB. */
561 find_replaceable_in_bb (temp_expr_table_p tab, basic_block bb)
563 block_stmt_iterator bsi;
567 var_map map = tab->map;
569 bool stmt_replaceable;
571 for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
573 stmt = bsi_stmt (bsi);
574 ann = stmt_ann (stmt);
576 stmt_replaceable = is_replaceable_p (stmt);
577 /* Determine if this stmt finishes an existing expression. */
578 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
580 unsigned ver = SSA_NAME_VERSION (use);
582 /* If this use is a potential replacement variable, process it. */
583 if (tab->expr_decl_uids[ver])
585 bool same_root_var = false;
587 bitmap vars = tab->expr_decl_uids[ver];
589 /* See if the root variables are the same. If they are, we
590 do not want to do the replacement to avoid problems with
591 code size, see PR tree-optimization/17549. */
592 if (!bitmap_empty_p (vars))
593 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter2, SSA_OP_DEF)
595 if (bitmap_bit_p (vars, DECL_UID (SSA_NAME_VAR (def))))
597 same_root_var = true;
602 /* Mark expression as replaceable unless stmt is volatile or the
603 def variable has the same root variable as something in the
604 substitution list. */
605 if (ann->has_volatile_ops || same_root_var)
606 finished_with_expr (tab, ver, true);
608 mark_replaceable (tab, use, stmt_replaceable);
612 /* Next, see if this stmt kills off an active expression. */
613 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
615 partition = var_to_partition (map, def);
616 if (partition != NO_PARTITION && tab->kill_list[partition])
617 kill_expr (tab, partition);
620 /* Now see if we are creating a new expression or not. */
621 if (stmt_replaceable)
622 process_replaceable (tab, stmt);
624 /* Free any unused dependency lists. */
625 bitmap_clear (tab->new_replaceable_dependencies);
627 /* A V_{MAY,MUST}_DEF kills any expression using a virtual operand,
628 including the current stmt. */
629 if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_VIRTUAL_DEFS))
630 kill_virtual_exprs (tab);
635 /* This function is the driver routine for replacement of temporary expressions
636 in the SSA->normal phase, operating on MAP. If there are replaceable
637 expressions, a table is returned which maps SSA versions to the
638 expressions they should be replaced with. A NULL_TREE indicates no
639 replacement should take place. If there are no replacements at all,
640 NULL is returned by the function, otherwise an expression vector indexed
641 by SSA_NAME version numbers. */
644 find_replaceable_exprs (var_map map)
647 temp_expr_table_p table;
650 table = new_temp_expr_table (map);
653 find_replaceable_in_bb (table, bb);
654 gcc_assert (bitmap_empty_p (table->partition_in_use));
656 #ifdef ENABLE_CHECKING
659 /* Make sure all the tables have been cleared out. */
660 for (i = 0; i < num_ssa_names + 1; i++)
662 gcc_assert (table->partition_dependencies[i] == NULL);
663 gcc_assert (table->expr_decl_uids[i] == NULL);
664 if (i < num_var_partitions (map))
665 gcc_assert (table->kill_list[i] == NULL);
671 ret = free_temp_expr_table (table);
676 /* Dump TER expression table EXPR to file F. */
679 dump_replaceable_exprs (FILE *f, tree *expr)
684 fprintf (f, "\nReplacing Expressions\n");
685 for (x = 0; x < (int)num_ssa_names; x++)
689 var = SINGLE_SSA_TREE_OPERAND (stmt, SSA_OP_DEF);
690 gcc_assert (var != NULL_TREE);
691 print_generic_expr (f, var, TDF_SLIM);
692 fprintf (f, " replace with --> ");
693 print_generic_expr (f, TREE_OPERAND (stmt, 1), TDF_SLIM);
700 #ifdef ENABLE_CHECKING
701 /* Dump the status of the various tables in the expression table. This is used
702 exclusively to debug TER. F is the place to send debug info and T is the
703 table being debugged. */
706 debug_ter (FILE *f, temp_expr_table_p t)
711 fprintf (f, "\nDumping current state of TER\n virtual partition = %d\n",
712 VIRTUAL_PARTITION (t));
713 if (t->replaceable_expressions)
714 dump_replaceable_exprs (f, t->replaceable_expressions);
715 fprintf (f, "Currently tracking the following expressions:\n");
717 for (x = 1; x < num_ssa_names; x++)
718 if (t->expr_decl_uids[x])
720 print_generic_expr (stderr, ssa_name (x), TDF_SLIM);
721 fprintf (f, " dep-parts : ");
722 if (t->partition_dependencies[x]
723 && !bitmap_empty_p (t->partition_dependencies[x]))
725 EXECUTE_IF_SET_IN_BITMAP (t->partition_dependencies[x], 0, y, bi)
726 fprintf (f, "P%d ",y);
728 fprintf (stderr, " basedecls: ");
729 EXECUTE_IF_SET_IN_BITMAP (t->expr_decl_uids[x], 0, y, bi)
730 fprintf (f, "%d ",y);
731 fprintf (stderr, "\n");
734 bitmap_print (f, t->partition_in_use, "Partitions in use ",
735 "\npartition KILL lists:\n");
737 for (x = 0; x <= num_var_partitions (t->map); x++)
740 fprintf (f, "Partition %d : ", x);
741 EXECUTE_IF_SET_IN_BITMAP (t->kill_list[x], 0, y, bi)
742 fprintf (f, "_%d ",y);
745 fprintf (f, "\n----------\n");