1 /* Code sinking for trees
2 Copyright (C) 2001, 2002, 2003, 2004, 2007, 2008, 2009
3 Free Software Foundation, Inc.
4 Contributed by Daniel Berlin <dan@dberlin.org>
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/>. */
24 #include "coretypes.h"
28 #include "basic-block.h"
29 #include "diagnostic.h"
30 #include "tree-inline.h"
31 #include "tree-flow.h"
33 #include "tree-dump.h"
37 #include "tree-iterator.h"
39 #include "alloc-pool.h"
40 #include "tree-pass.h"
43 #include "langhooks.h"
47 1. Sinking store only using scalar promotion (IE without moving the RHS):
67 Store copy propagation will take care of the store elimination above.
70 2. Sinking using Partial Dead Code Elimination. */
75 /* The number of statements sunk down the flowgraph by code sinking. */
81 /* Given a PHI, and one of its arguments (DEF), find the edge for
82 that argument and return it. If the argument occurs twice in the PHI node,
86 find_bb_for_arg (gimple phi
, tree def
)
89 bool foundone
= false;
90 basic_block result
= NULL
;
91 for (i
= 0; i
< gimple_phi_num_args (phi
); i
++)
92 if (PHI_ARG_DEF (phi
, i
) == def
)
97 result
= gimple_phi_arg_edge (phi
, i
)->src
;
102 /* When the first immediate use is in a statement, then return true if all
103 immediate uses in IMM are in the same statement.
104 We could also do the case where the first immediate use is in a phi node,
105 and all the other uses are in phis in the same basic block, but this
106 requires some expensive checking later (you have to make sure no def/vdef
107 in the statement occurs for multiple edges in the various phi nodes it's
108 used in, so that you only have one place you can sink it to. */
111 all_immediate_uses_same_place (gimple stmt
)
113 gimple firstuse
= NULL
;
115 imm_use_iterator imm_iter
;
119 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, op_iter
, SSA_OP_ALL_DEFS
)
121 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, var
)
123 if (is_gimple_debug (USE_STMT (use_p
)))
125 if (firstuse
== NULL
)
126 firstuse
= USE_STMT (use_p
);
128 if (firstuse
!= USE_STMT (use_p
))
136 /* Some global stores don't necessarily have VDEF's of global variables,
137 but we still must avoid moving them around. */
140 is_hidden_global_store (gimple stmt
)
142 /* Check virtual definitions. If we get here, the only virtual
143 definitions we should see are those generated by assignment or call
145 if (gimple_vdef (stmt
))
149 gcc_assert (is_gimple_assign (stmt
) || is_gimple_call (stmt
));
151 /* Note that we must not check the individual virtual operands
152 here. In particular, if this is an aliased store, we could
153 end up with something like the following (SSA notation
154 redacted for brevity):
159 p_1 = (i_2 > 3) ? &x : p;
167 Notice that the store to '*p_1' should be preserved, if we
168 were to check the virtual definitions in that store, we would
169 not mark it needed. This is because 'x' is not a global
172 Therefore, we check the base address of the LHS. If the
173 address is a pointer, we check if its name tag or symbol tag is
174 a global variable. Otherwise, we check if the base variable
176 lhs
= gimple_get_lhs (stmt
);
178 if (REFERENCE_CLASS_P (lhs
))
179 lhs
= get_base_address (lhs
);
181 if (lhs
== NULL_TREE
)
183 /* If LHS is NULL, it means that we couldn't get the base
184 address of the reference. In which case, we should not
188 else if (DECL_P (lhs
))
190 /* If the store is to a global symbol, we need to keep it. */
191 if (is_global_var (lhs
))
195 else if (INDIRECT_REF_P (lhs
))
196 return ptr_deref_may_alias_global_p (TREE_OPERAND (lhs
, 0));
204 /* Find the nearest common dominator of all of the immediate uses in IMM. */
207 nearest_common_dominator_of_uses (gimple stmt
, bool *debug_stmts
)
209 bitmap blocks
= BITMAP_ALLOC (NULL
);
210 basic_block commondom
;
214 imm_use_iterator imm_iter
;
218 bitmap_clear (blocks
);
219 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, op_iter
, SSA_OP_ALL_DEFS
)
221 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, var
)
223 gimple usestmt
= USE_STMT (use_p
);
224 basic_block useblock
;
226 if (gimple_code (usestmt
) == GIMPLE_PHI
)
228 int idx
= PHI_ARG_INDEX_FROM_USE (use_p
);
230 useblock
= gimple_phi_arg_edge (usestmt
, idx
)->src
;
232 else if (is_gimple_debug (usestmt
))
239 useblock
= gimple_bb (usestmt
);
242 /* Short circuit. Nothing dominates the entry block. */
243 if (useblock
== ENTRY_BLOCK_PTR
)
245 BITMAP_FREE (blocks
);
248 bitmap_set_bit (blocks
, useblock
->index
);
251 commondom
= BASIC_BLOCK (bitmap_first_set_bit (blocks
));
252 EXECUTE_IF_SET_IN_BITMAP (blocks
, 0, j
, bi
)
253 commondom
= nearest_common_dominator (CDI_DOMINATORS
, commondom
,
255 BITMAP_FREE (blocks
);
259 /* Given a statement (STMT) and the basic block it is currently in (FROMBB),
260 determine the location to sink the statement to, if any.
261 Returns true if there is such location; in that case, TOGSI points to the
262 statement before that STMT should be moved. */
265 statement_sink_location (gimple stmt
, basic_block frombb
,
266 gimple_stmt_iterator
*togsi
)
270 use_operand_p one_use
= NULL_USE_OPERAND_P
;
275 imm_use_iterator imm_iter
;
278 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter
, SSA_OP_ALL_DEFS
)
280 FOR_EACH_IMM_USE_FAST (one_use
, imm_iter
, def
)
282 if (is_gimple_debug (USE_STMT (one_use
)))
287 if (one_use
!= NULL_USE_OPERAND_P
)
291 /* Return if there are no immediate uses of this stmt. */
292 if (one_use
== NULL_USE_OPERAND_P
)
295 if (gimple_code (stmt
) != GIMPLE_ASSIGN
)
298 /* There are a few classes of things we can't or don't move, some because we
299 don't have code to handle it, some because it's not profitable and some
300 because it's not legal.
302 We can't sink things that may be global stores, at least not without
303 calculating a lot more information, because we may cause it to no longer
304 be seen by an external routine that needs it depending on where it gets
307 We don't want to sink loads from memory.
309 We can't sink statements that end basic blocks without splitting the
310 incoming edge for the sink location to place it there.
312 We can't sink statements that have volatile operands.
314 We don't want to sink dead code, so anything with 0 immediate uses is not
317 Don't sink BLKmode assignments if current function has any local explicit
318 register variables, as BLKmode assignments may involve memcpy or memset
319 calls or, on some targets, inline expansion thereof that sometimes need
320 to use specific hard registers.
323 code
= gimple_assign_rhs_code (stmt
);
324 if (stmt_ends_bb_p (stmt
)
325 || gimple_has_side_effects (stmt
)
326 || is_hidden_global_store (stmt
)
327 || gimple_has_volatile_ops (stmt
)
328 || gimple_vuse (stmt
)
329 || (cfun
->has_local_explicit_reg_vars
330 && TYPE_MODE (TREE_TYPE (gimple_assign_lhs (stmt
))) == BLKmode
))
333 FOR_EACH_SSA_DEF_OPERAND (def_p
, stmt
, iter
, SSA_OP_ALL_DEFS
)
335 tree def
= DEF_FROM_PTR (def_p
);
336 if (is_global_var (SSA_NAME_VAR (def
))
337 || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def
))
341 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_ALL_USES
)
343 tree use
= USE_FROM_PTR (use_p
);
344 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (use
))
348 /* If all the immediate uses are not in the same place, find the nearest
349 common dominator of all the immediate uses. For PHI nodes, we have to
350 find the nearest common dominator of all of the predecessor blocks, since
351 that is where insertion would have to take place. */
352 if (!all_immediate_uses_same_place (stmt
))
354 bool debug_stmts
= false;
355 basic_block commondom
= nearest_common_dominator_of_uses (stmt
,
358 if (commondom
== frombb
)
361 /* Our common dominator has to be dominated by frombb in order to be a
362 trivially safe place to put this statement, since it has multiple
364 if (!dominated_by_p (CDI_DOMINATORS
, commondom
, frombb
))
367 /* It doesn't make sense to move to a dominator that post-dominates
368 frombb, because it means we've just moved it into a path that always
369 executes if frombb executes, instead of reducing the number of
371 if (dominated_by_p (CDI_POST_DOMINATORS
, frombb
, commondom
))
373 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
374 fprintf (dump_file
, "Not moving store, common dominator post-dominates from block.\n");
378 if (commondom
== frombb
|| commondom
->loop_depth
> frombb
->loop_depth
)
380 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
382 fprintf (dump_file
, "Common dominator of all uses is %d\n",
386 *togsi
= gsi_after_labels (commondom
);
391 use
= USE_STMT (one_use
);
392 if (gimple_code (use
) != GIMPLE_PHI
)
394 sinkbb
= gimple_bb (use
);
395 if (sinkbb
== frombb
|| sinkbb
->loop_depth
> frombb
->loop_depth
396 || sinkbb
->loop_father
!= frombb
->loop_father
)
399 /* Move the expression to a post dominator can't reduce the number of
401 if (dominated_by_p (CDI_POST_DOMINATORS
, frombb
, sinkbb
))
404 *togsi
= gsi_for_stmt (use
);
409 /* Note that at this point, all uses must be in the same statement, so it
410 doesn't matter which def op we choose, pick the first one. */
411 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter
, SSA_OP_ALL_DEFS
)
414 sinkbb
= find_bb_for_arg (use
, def
);
418 /* This will happen when you have
419 a_3 = PHI <a_13, a_26>
423 If the use is a phi, and is in the same bb as the def,
426 if (gimple_bb (use
) == frombb
)
428 if (sinkbb
== frombb
|| sinkbb
->loop_depth
> frombb
->loop_depth
429 || sinkbb
->loop_father
!= frombb
->loop_father
)
432 /* Move the expression to a post dominator can't reduce the number of
434 if (dominated_by_p (CDI_POST_DOMINATORS
, frombb
, sinkbb
))
437 *togsi
= gsi_after_labels (sinkbb
);
442 /* Perform code sinking on BB */
445 sink_code_in_bb (basic_block bb
)
448 gimple_stmt_iterator gsi
;
453 /* If this block doesn't dominate anything, there can't be any place to sink
454 the statements to. */
455 if (first_dom_son (CDI_DOMINATORS
, bb
) == NULL
)
458 /* We can't move things across abnormal edges, so don't try. */
459 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
460 if (e
->flags
& EDGE_ABNORMAL
)
463 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
);)
465 gimple stmt
= gsi_stmt (gsi
);
466 gimple_stmt_iterator togsi
;
468 if (!statement_sink_location (stmt
, bb
, &togsi
))
470 if (!gsi_end_p (gsi
))
477 fprintf (dump_file
, "Sinking ");
478 print_gimple_stmt (dump_file
, stmt
, 0, TDF_VOPS
);
479 fprintf (dump_file
, " from bb %d to bb %d\n",
480 bb
->index
, (gsi_bb (togsi
))->index
);
483 /* If this is the end of the basic block, we need to insert at the end
484 of the basic block. */
485 if (gsi_end_p (togsi
))
486 gsi_move_to_bb_end (&gsi
, gsi_bb (togsi
));
488 gsi_move_before (&gsi
, &togsi
);
492 /* If we've just removed the last statement of the BB, the
493 gsi_end_p() test below would fail, but gsi_prev() would have
494 succeeded, and we want it to succeed. So we keep track of
495 whether we're at the last statement and pick up the new last
499 gsi
= gsi_last_bb (bb
);
504 if (!gsi_end_p (gsi
))
509 for (son
= first_dom_son (CDI_POST_DOMINATORS
, bb
);
511 son
= next_dom_son (CDI_POST_DOMINATORS
, son
))
513 sink_code_in_bb (son
);
517 /* Perform code sinking.
518 This moves code down the flowgraph when we know it would be
519 profitable to do so, or it wouldn't increase the number of
520 executions of the statement.
533 a_6 = PHI (a_5, a_1);
536 we'll transform this into:
547 a_6 = PHI (a_5, a_1);
550 Note that this reduces the number of computations of a = b + c to 1
551 when we take the else edge, instead of 2.
554 execute_sink_code (void)
556 loop_optimizer_init (LOOPS_NORMAL
);
558 connect_infinite_loops_to_exit ();
559 memset (&sink_stats
, 0, sizeof (sink_stats
));
560 calculate_dominance_info (CDI_DOMINATORS
);
561 calculate_dominance_info (CDI_POST_DOMINATORS
);
562 sink_code_in_bb (EXIT_BLOCK_PTR
);
563 statistics_counter_event (cfun
, "Sunk statements", sink_stats
.sunk
);
564 free_dominance_info (CDI_POST_DOMINATORS
);
565 remove_fake_exit_edges ();
566 loop_optimizer_finalize ();
569 /* Gate and execute functions for PRE. */
574 execute_sink_code ();
581 return flag_tree_sink
!= 0;
584 struct gimple_opt_pass pass_sink_code
=
589 gate_sink
, /* gate */
590 do_sink
, /* execute */
593 0, /* static_pass_number */
594 TV_TREE_SINK
, /* tv_id */
595 PROP_no_crit_edges
| PROP_cfg
596 | PROP_ssa
, /* properties_required */
597 0, /* properties_provided */
598 0, /* properties_destroyed */
599 0, /* todo_flags_start */
603 | TODO_verify_ssa
/* todo_flags_finish */