1 /* Code sinking for trees
2 Copyright (C) 2001, 2002, 2003, 2004, 2007, 2008, 2009, 2010
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"
27 #include "basic-block.h"
28 #include "gimple-pretty-print.h"
29 #include "tree-inline.h"
30 #include "tree-flow.h"
32 #include "tree-dump.h"
36 #include "tree-iterator.h"
37 #include "alloc-pool.h"
38 #include "tree-pass.h"
41 #include "langhooks.h"
45 1. Sinking store only using scalar promotion (IE without moving the RHS):
65 Store copy propagation will take care of the store elimination above.
68 2. Sinking using Partial Dead Code Elimination. */
73 /* The number of statements sunk down the flowgraph by code sinking. */
79 /* Given a PHI, and one of its arguments (DEF), find the edge for
80 that argument and return it. If the argument occurs twice in the PHI node,
84 find_bb_for_arg (gimple phi
, tree def
)
87 bool foundone
= false;
88 basic_block result
= NULL
;
89 for (i
= 0; i
< gimple_phi_num_args (phi
); i
++)
90 if (PHI_ARG_DEF (phi
, i
) == def
)
95 result
= gimple_phi_arg_edge (phi
, i
)->src
;
100 /* When the first immediate use is in a statement, then return true if all
101 immediate uses in IMM are in the same statement.
102 We could also do the case where the first immediate use is in a phi node,
103 and all the other uses are in phis in the same basic block, but this
104 requires some expensive checking later (you have to make sure no def/vdef
105 in the statement occurs for multiple edges in the various phi nodes it's
106 used in, so that you only have one place you can sink it to. */
109 all_immediate_uses_same_place (gimple stmt
)
111 gimple firstuse
= NULL
;
113 imm_use_iterator imm_iter
;
117 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, op_iter
, SSA_OP_ALL_DEFS
)
119 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, var
)
121 if (is_gimple_debug (USE_STMT (use_p
)))
123 if (firstuse
== NULL
)
124 firstuse
= USE_STMT (use_p
);
126 if (firstuse
!= USE_STMT (use_p
))
134 /* Some global stores don't necessarily have VDEF's of global variables,
135 but we still must avoid moving them around. */
138 is_hidden_global_store (gimple stmt
)
140 /* Check virtual definitions. If we get here, the only virtual
141 definitions we should see are those generated by assignment or call
143 if (gimple_vdef (stmt
))
147 gcc_assert (is_gimple_assign (stmt
) || is_gimple_call (stmt
));
149 /* Note that we must not check the individual virtual operands
150 here. In particular, if this is an aliased store, we could
151 end up with something like the following (SSA notation
152 redacted for brevity):
157 p_1 = (i_2 > 3) ? &x : p;
165 Notice that the store to '*p_1' should be preserved, if we
166 were to check the virtual definitions in that store, we would
167 not mark it needed. This is because 'x' is not a global
170 Therefore, we check the base address of the LHS. If the
171 address is a pointer, we check if its name tag or symbol tag is
172 a global variable. Otherwise, we check if the base variable
174 lhs
= gimple_get_lhs (stmt
);
176 if (REFERENCE_CLASS_P (lhs
))
177 lhs
= get_base_address (lhs
);
179 if (lhs
== NULL_TREE
)
181 /* If LHS is NULL, it means that we couldn't get the base
182 address of the reference. In which case, we should not
186 else if (DECL_P (lhs
))
188 /* If the store is to a global symbol, we need to keep it. */
189 if (is_global_var (lhs
))
193 else if (INDIRECT_REF_P (lhs
)
194 || TREE_CODE (lhs
) == MEM_REF
)
195 return ptr_deref_may_alias_global_p (TREE_OPERAND (lhs
, 0));
196 else if (CONSTANT_CLASS_P (lhs
))
205 /* Find the nearest common dominator of all of the immediate uses in IMM. */
208 nearest_common_dominator_of_uses (gimple stmt
, bool *debug_stmts
)
210 bitmap blocks
= BITMAP_ALLOC (NULL
);
211 basic_block commondom
;
215 imm_use_iterator imm_iter
;
219 bitmap_clear (blocks
);
220 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, op_iter
, SSA_OP_ALL_DEFS
)
222 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, var
)
224 gimple usestmt
= USE_STMT (use_p
);
225 basic_block useblock
;
227 if (gimple_code (usestmt
) == GIMPLE_PHI
)
229 int idx
= PHI_ARG_INDEX_FROM_USE (use_p
);
231 useblock
= gimple_phi_arg_edge (usestmt
, idx
)->src
;
233 else if (is_gimple_debug (usestmt
))
240 useblock
= gimple_bb (usestmt
);
243 /* Short circuit. Nothing dominates the entry block. */
244 if (useblock
== ENTRY_BLOCK_PTR
)
246 BITMAP_FREE (blocks
);
249 bitmap_set_bit (blocks
, useblock
->index
);
252 commondom
= BASIC_BLOCK (bitmap_first_set_bit (blocks
));
253 EXECUTE_IF_SET_IN_BITMAP (blocks
, 0, j
, bi
)
254 commondom
= nearest_common_dominator (CDI_DOMINATORS
, commondom
,
256 BITMAP_FREE (blocks
);
260 /* Given a statement (STMT) and the basic block it is currently in (FROMBB),
261 determine the location to sink the statement to, if any.
262 Returns true if there is such location; in that case, TOGSI points to the
263 statement before that STMT should be moved. */
266 statement_sink_location (gimple stmt
, basic_block frombb
,
267 gimple_stmt_iterator
*togsi
)
271 use_operand_p one_use
= NULL_USE_OPERAND_P
;
276 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 if (stmt_ends_bb_p (stmt
)
324 || gimple_has_side_effects (stmt
)
325 || is_hidden_global_store (stmt
)
326 || gimple_has_volatile_ops (stmt
)
327 || gimple_vuse (stmt
)
328 || (cfun
->has_local_explicit_reg_vars
329 && TYPE_MODE (TREE_TYPE (gimple_assign_lhs (stmt
))) == BLKmode
))
332 FOR_EACH_SSA_DEF_OPERAND (def_p
, stmt
, iter
, SSA_OP_ALL_DEFS
)
334 tree def
= DEF_FROM_PTR (def_p
);
335 if (is_global_var (SSA_NAME_VAR (def
))
336 || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def
))
340 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_ALL_USES
)
342 tree use
= USE_FROM_PTR (use_p
);
343 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (use
))
347 /* If all the immediate uses are not in the same place, find the nearest
348 common dominator of all the immediate uses. For PHI nodes, we have to
349 find the nearest common dominator of all of the predecessor blocks, since
350 that is where insertion would have to take place. */
351 if (!all_immediate_uses_same_place (stmt
))
353 bool debug_stmts
= false;
354 basic_block commondom
= nearest_common_dominator_of_uses (stmt
,
357 if (commondom
== frombb
)
360 /* Our common dominator has to be dominated by frombb in order to be a
361 trivially safe place to put this statement, since it has multiple
363 if (!dominated_by_p (CDI_DOMINATORS
, commondom
, frombb
))
366 /* It doesn't make sense to move to a dominator that post-dominates
367 frombb, because it means we've just moved it into a path that always
368 executes if frombb executes, instead of reducing the number of
370 if (dominated_by_p (CDI_POST_DOMINATORS
, frombb
, commondom
))
372 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
373 fprintf (dump_file
, "Not moving store, common dominator post-dominates from block.\n");
377 if (commondom
== frombb
|| commondom
->loop_depth
> frombb
->loop_depth
)
379 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
381 fprintf (dump_file
, "Common dominator of all uses is %d\n",
385 *togsi
= gsi_after_labels (commondom
);
390 use
= USE_STMT (one_use
);
391 if (gimple_code (use
) != GIMPLE_PHI
)
393 sinkbb
= gimple_bb (use
);
394 if (sinkbb
== frombb
|| sinkbb
->loop_depth
> frombb
->loop_depth
395 || sinkbb
->loop_father
!= frombb
->loop_father
)
398 /* Move the expression to a post dominator can't reduce the number of
400 if (dominated_by_p (CDI_POST_DOMINATORS
, frombb
, sinkbb
))
403 *togsi
= gsi_for_stmt (use
);
408 /* Note that at this point, all uses must be in the same statement, so it
409 doesn't matter which def op we choose, pick the first one. */
410 FOR_EACH_SSA_TREE_OPERAND (def
, stmt
, iter
, SSA_OP_ALL_DEFS
)
413 sinkbb
= find_bb_for_arg (use
, def
);
417 /* This will happen when you have
418 a_3 = PHI <a_13, a_26>
422 If the use is a phi, and is in the same bb as the def,
425 if (gimple_bb (use
) == frombb
)
427 if (sinkbb
== frombb
|| sinkbb
->loop_depth
> frombb
->loop_depth
428 || sinkbb
->loop_father
!= frombb
->loop_father
)
431 /* Move the expression to a post dominator can't reduce the number of
433 if (dominated_by_p (CDI_POST_DOMINATORS
, frombb
, sinkbb
))
436 *togsi
= gsi_after_labels (sinkbb
);
441 /* Perform code sinking on BB */
444 sink_code_in_bb (basic_block bb
)
447 gimple_stmt_iterator gsi
;
452 /* If this block doesn't dominate anything, there can't be any place to sink
453 the statements to. */
454 if (first_dom_son (CDI_DOMINATORS
, bb
) == NULL
)
457 /* We can't move things across abnormal edges, so don't try. */
458 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
459 if (e
->flags
& EDGE_ABNORMAL
)
462 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
);)
464 gimple stmt
= gsi_stmt (gsi
);
465 gimple_stmt_iterator togsi
;
467 if (!statement_sink_location (stmt
, bb
, &togsi
))
469 if (!gsi_end_p (gsi
))
476 fprintf (dump_file
, "Sinking ");
477 print_gimple_stmt (dump_file
, stmt
, 0, TDF_VOPS
);
478 fprintf (dump_file
, " from bb %d to bb %d\n",
479 bb
->index
, (gsi_bb (togsi
))->index
);
482 /* If this is the end of the basic block, we need to insert at the end
483 of the basic block. */
484 if (gsi_end_p (togsi
))
485 gsi_move_to_bb_end (&gsi
, gsi_bb (togsi
));
487 gsi_move_before (&gsi
, &togsi
);
491 /* If we've just removed the last statement of the BB, the
492 gsi_end_p() test below would fail, but gsi_prev() would have
493 succeeded, and we want it to succeed. So we keep track of
494 whether we're at the last statement and pick up the new last
498 gsi
= gsi_last_bb (bb
);
503 if (!gsi_end_p (gsi
))
508 for (son
= first_dom_son (CDI_POST_DOMINATORS
, bb
);
510 son
= next_dom_son (CDI_POST_DOMINATORS
, son
))
512 sink_code_in_bb (son
);
516 /* Perform code sinking.
517 This moves code down the flowgraph when we know it would be
518 profitable to do so, or it wouldn't increase the number of
519 executions of the statement.
532 a_6 = PHI (a_5, a_1);
535 we'll transform this into:
546 a_6 = PHI (a_5, a_1);
549 Note that this reduces the number of computations of a = b + c to 1
550 when we take the else edge, instead of 2.
553 execute_sink_code (void)
555 loop_optimizer_init (LOOPS_NORMAL
);
557 connect_infinite_loops_to_exit ();
558 memset (&sink_stats
, 0, sizeof (sink_stats
));
559 calculate_dominance_info (CDI_DOMINATORS
);
560 calculate_dominance_info (CDI_POST_DOMINATORS
);
561 sink_code_in_bb (EXIT_BLOCK_PTR
);
562 statistics_counter_event (cfun
, "Sunk statements", sink_stats
.sunk
);
563 free_dominance_info (CDI_POST_DOMINATORS
);
564 remove_fake_exit_edges ();
565 loop_optimizer_finalize ();
568 /* Gate and execute functions for PRE. */
573 execute_sink_code ();
580 return flag_tree_sink
!= 0;
583 struct gimple_opt_pass pass_sink_code
=
588 gate_sink
, /* gate */
589 do_sink
, /* execute */
592 0, /* static_pass_number */
593 TV_TREE_SINK
, /* tv_id */
594 PROP_no_crit_edges
| PROP_cfg
595 | PROP_ssa
, /* properties_required */
596 0, /* properties_provided */
597 0, /* properties_destroyed */
598 0, /* todo_flags_start */
602 | TODO_verify_ssa
/* todo_flags_finish */