1 /* Code sinking for trees
2 Copyright (C) 2001-2013 Free Software Foundation, Inc.
3 Contributed by Daniel Berlin <dan@dberlin.org>
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 3, 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 COPYING3. If not see
19 <http://www.gnu.org/licenses/>. */
23 #include "coretypes.h"
26 #include "basic-block.h"
27 #include "gimple-pretty-print.h"
28 #include "tree-inline.h"
32 #include "tree-iterator.h"
33 #include "alloc-pool.h"
34 #include "tree-pass.h"
41 1. Sinking store only using scalar promotion (IE without moving the RHS):
61 Store copy propagation will take care of the store elimination above.
64 2. Sinking using Partial Dead Code Elimination. */
69 /* The number of statements sunk down the flowgraph by code sinking. */
75 /* Given a PHI, and one of its arguments (DEF), find the edge for
76 that argument and return it. If the argument occurs twice in the PHI node,
80 find_bb_for_arg (gimple phi
, tree def
)
83 bool foundone
= false;
84 basic_block result
= NULL
;
85 for (i
= 0; i
< gimple_phi_num_args (phi
); i
++)
86 if (PHI_ARG_DEF (phi
, i
) == def
)
91 result
= gimple_phi_arg_edge (phi
, i
)->src
;
96 /* When the first immediate use is in a statement, then return true if all
97 immediate uses in IMM are in the same statement.
98 We could also do the case where the first immediate use is in a phi node,
99 and all the other uses are in phis in the same basic block, but this
100 requires some expensive checking later (you have to make sure no def/vdef
101 in the statement occurs for multiple edges in the various phi nodes it's
102 used in, so that you only have one place you can sink it to. */
105 all_immediate_uses_same_place (gimple stmt
)
107 gimple firstuse
= NULL
;
109 imm_use_iterator imm_iter
;
113 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, op_iter
, SSA_OP_ALL_DEFS
)
115 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, var
)
117 if (is_gimple_debug (USE_STMT (use_p
)))
119 if (firstuse
== NULL
)
120 firstuse
= USE_STMT (use_p
);
122 if (firstuse
!= USE_STMT (use_p
))
130 /* Find the nearest common dominator of all of the immediate uses in IMM. */
133 nearest_common_dominator_of_uses (gimple stmt
, bool *debug_stmts
)
135 bitmap blocks
= BITMAP_ALLOC (NULL
);
136 basic_block commondom
;
140 imm_use_iterator imm_iter
;
144 bitmap_clear (blocks
);
145 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, op_iter
, SSA_OP_ALL_DEFS
)
147 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, var
)
149 gimple usestmt
= USE_STMT (use_p
);
150 basic_block useblock
;
152 if (gimple_code (usestmt
) == GIMPLE_PHI
)
154 int idx
= PHI_ARG_INDEX_FROM_USE (use_p
);
156 useblock
= gimple_phi_arg_edge (usestmt
, idx
)->src
;
158 else if (is_gimple_debug (usestmt
))
165 useblock
= gimple_bb (usestmt
);
168 /* Short circuit. Nothing dominates the entry block. */
169 if (useblock
== ENTRY_BLOCK_PTR
)
171 BITMAP_FREE (blocks
);
174 bitmap_set_bit (blocks
, useblock
->index
);
177 commondom
= BASIC_BLOCK (bitmap_first_set_bit (blocks
));
178 EXECUTE_IF_SET_IN_BITMAP (blocks
, 0, j
, bi
)
179 commondom
= nearest_common_dominator (CDI_DOMINATORS
, commondom
,
181 BITMAP_FREE (blocks
);
185 /* Given EARLY_BB and LATE_BB, two blocks in a path through the dominator
186 tree, return the best basic block between them (inclusive) to place
189 We want the most control dependent block in the shallowest loop nest.
191 If the resulting block is in a shallower loop nest, then use it. Else
192 only use the resulting block if it has significantly lower execution
193 frequency than EARLY_BB to avoid gratutious statement movement. We
194 consider statements with VOPS more desirable to move.
196 This pass would obviously benefit from PDO as it utilizes block
197 frequencies. It would also benefit from recomputing frequencies
198 if profile data is not available since frequencies often get out
199 of sync with reality. */
202 select_best_block (basic_block early_bb
,
206 basic_block best_bb
= late_bb
;
207 basic_block temp_bb
= late_bb
;
210 while (temp_bb
!= early_bb
)
212 /* If we've moved into a lower loop nest, then that becomes
214 if (bb_loop_depth (temp_bb
) < bb_loop_depth (best_bb
))
217 /* Walk up the dominator tree, hopefully we'll find a shallower
219 temp_bb
= get_immediate_dominator (CDI_DOMINATORS
, temp_bb
);
222 /* If we found a shallower loop nest, then we always consider that
223 a win. This will always give us the most control dependent block
224 within that loop nest. */
225 if (bb_loop_depth (best_bb
) < bb_loop_depth (early_bb
))
228 /* Get the sinking threshold. If the statement to be moved has memory
229 operands, then increase the threshold by 7% as those are even more
230 profitable to avoid, clamping at 100%. */
231 threshold
= PARAM_VALUE (PARAM_SINK_FREQUENCY_THRESHOLD
);
232 if (gimple_vuse (stmt
) || gimple_vdef (stmt
))
239 /* If BEST_BB is at the same nesting level, then require it to have
240 significantly lower execution frequency to avoid gratutious movement. */
241 if (bb_loop_depth (best_bb
) == bb_loop_depth (early_bb
)
242 && best_bb
->frequency
< (early_bb
->frequency
* threshold
/ 100.0))
245 /* No better block found, so return EARLY_BB, which happens to be the
246 statement's original block. */
250 /* Given a statement (STMT) and the basic block it is currently in (FROMBB),
251 determine the location to sink the statement to, if any.
252 Returns true if there is such location; in that case, TOGSI points to the
253 statement before that STMT should be moved. */
256 statement_sink_location (gimple stmt
, basic_block frombb
,
257 gimple_stmt_iterator
*togsi
)
260 use_operand_p one_use
= NULL_USE_OPERAND_P
;
265 imm_use_iterator imm_iter
;
267 /* We only can sink assignments. */
268 if (!is_gimple_assign (stmt
))
271 /* We only can sink stmts with a single definition. */
272 def_p
= single_ssa_def_operand (stmt
, SSA_OP_ALL_DEFS
);
273 if (def_p
== NULL_DEF_OPERAND_P
)
276 /* Return if there are no immediate uses of this stmt. */
277 if (has_zero_uses (DEF_FROM_PTR (def_p
)))
280 /* There are a few classes of things we can't or don't move, some because we
281 don't have code to handle it, some because it's not profitable and some
282 because it's not legal.
284 We can't sink things that may be global stores, at least not without
285 calculating a lot more information, because we may cause it to no longer
286 be seen by an external routine that needs it depending on where it gets
289 We don't want to sink loads from memory.
291 We can't sink statements that end basic blocks without splitting the
292 incoming edge for the sink location to place it there.
294 We can't sink statements that have volatile operands.
296 We don't want to sink dead code, so anything with 0 immediate uses is not
299 Don't sink BLKmode assignments if current function has any local explicit
300 register variables, as BLKmode assignments may involve memcpy or memset
301 calls or, on some targets, inline expansion thereof that sometimes need
302 to use specific hard registers.
305 if (stmt_ends_bb_p (stmt
)
306 || gimple_has_side_effects (stmt
)
307 || gimple_has_volatile_ops (stmt
)
308 || (gimple_vuse (stmt
) && !gimple_vdef (stmt
))
309 || (cfun
->has_local_explicit_reg_vars
310 && TYPE_MODE (TREE_TYPE (gimple_assign_lhs (stmt
))) == BLKmode
))
313 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (DEF_FROM_PTR (def_p
)))
316 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_ALL_USES
)
318 tree use
= USE_FROM_PTR (use_p
);
319 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (use
))
325 /* If stmt is a store the one and only use needs to be the VOP
327 if (gimple_vdef (stmt
))
329 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, DEF_FROM_PTR (def_p
))
331 gimple use_stmt
= USE_STMT (use_p
);
333 /* A killing definition is not a use. */
334 if ((gimple_has_lhs (use_stmt
)
335 && operand_equal_p (gimple_assign_lhs (stmt
),
336 gimple_get_lhs (use_stmt
), 0))
337 || stmt_kills_ref_p (use_stmt
, gimple_assign_lhs (stmt
)))
339 /* If use_stmt is or might be a nop assignment then USE_STMT
340 acts as a use as well as definition. */
342 && ref_maybe_used_by_stmt_p (use_stmt
,
343 gimple_assign_lhs (stmt
)))
348 if (gimple_code (use_stmt
) != GIMPLE_PHI
)
360 /* If all the immediate uses are not in the same place, find the nearest
361 common dominator of all the immediate uses. For PHI nodes, we have to
362 find the nearest common dominator of all of the predecessor blocks, since
363 that is where insertion would have to take place. */
364 else if (!all_immediate_uses_same_place (stmt
))
366 bool debug_stmts
= false;
367 basic_block commondom
= nearest_common_dominator_of_uses (stmt
,
370 if (commondom
== frombb
)
373 /* Our common dominator has to be dominated by frombb in order to be a
374 trivially safe place to put this statement, since it has multiple
376 if (!dominated_by_p (CDI_DOMINATORS
, commondom
, frombb
))
379 commondom
= select_best_block (frombb
, commondom
, stmt
);
381 if (commondom
== frombb
)
384 *togsi
= gsi_after_labels (commondom
);
390 FOR_EACH_IMM_USE_FAST (one_use
, imm_iter
, DEF_FROM_PTR (def_p
))
392 if (is_gimple_debug (USE_STMT (one_use
)))
396 use
= USE_STMT (one_use
);
398 if (gimple_code (use
) != GIMPLE_PHI
)
400 sinkbb
= gimple_bb (use
);
401 sinkbb
= select_best_block (frombb
, gimple_bb (use
), stmt
);
403 if (sinkbb
== frombb
)
406 *togsi
= gsi_for_stmt (use
);
412 sinkbb
= find_bb_for_arg (use
, DEF_FROM_PTR (def_p
));
414 /* This can happen if there are multiple uses in a PHI. */
418 sinkbb
= select_best_block (frombb
, sinkbb
, stmt
);
419 if (!sinkbb
|| sinkbb
== frombb
)
422 /* If the latch block is empty, don't make it non-empty by sinking
423 something into it. */
424 if (sinkbb
== frombb
->loop_father
->latch
425 && empty_block_p (sinkbb
))
428 *togsi
= gsi_after_labels (sinkbb
);
433 /* Perform code sinking on BB */
436 sink_code_in_bb (basic_block bb
)
439 gimple_stmt_iterator gsi
;
444 /* If this block doesn't dominate anything, there can't be any place to sink
445 the statements to. */
446 if (first_dom_son (CDI_DOMINATORS
, bb
) == NULL
)
449 /* We can't move things across abnormal edges, so don't try. */
450 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
451 if (e
->flags
& EDGE_ABNORMAL
)
454 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
);)
456 gimple stmt
= gsi_stmt (gsi
);
457 gimple_stmt_iterator togsi
;
459 if (!statement_sink_location (stmt
, bb
, &togsi
))
461 if (!gsi_end_p (gsi
))
468 fprintf (dump_file
, "Sinking ");
469 print_gimple_stmt (dump_file
, stmt
, 0, TDF_VOPS
);
470 fprintf (dump_file
, " from bb %d to bb %d\n",
471 bb
->index
, (gsi_bb (togsi
))->index
);
474 /* Update virtual operands of statements in the path we
476 if (gimple_vdef (stmt
))
478 imm_use_iterator iter
;
482 FOR_EACH_IMM_USE_STMT (vuse_stmt
, iter
, gimple_vdef (stmt
))
483 if (gimple_code (vuse_stmt
) != GIMPLE_PHI
)
484 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
485 SET_USE (use_p
, gimple_vuse (stmt
));
488 /* If this is the end of the basic block, we need to insert at the end
489 of the basic block. */
490 if (gsi_end_p (togsi
))
491 gsi_move_to_bb_end (&gsi
, gsi_bb (togsi
));
493 gsi_move_before (&gsi
, &togsi
);
497 /* If we've just removed the last statement of the BB, the
498 gsi_end_p() test below would fail, but gsi_prev() would have
499 succeeded, and we want it to succeed. So we keep track of
500 whether we're at the last statement and pick up the new last
504 gsi
= gsi_last_bb (bb
);
509 if (!gsi_end_p (gsi
))
514 for (son
= first_dom_son (CDI_POST_DOMINATORS
, bb
);
516 son
= next_dom_son (CDI_POST_DOMINATORS
, son
))
518 sink_code_in_bb (son
);
522 /* Perform code sinking.
523 This moves code down the flowgraph when we know it would be
524 profitable to do so, or it wouldn't increase the number of
525 executions of the statement.
538 a_6 = PHI (a_5, a_1);
541 we'll transform this into:
552 a_6 = PHI (a_5, a_1);
555 Note that this reduces the number of computations of a = b + c to 1
556 when we take the else edge, instead of 2.
559 execute_sink_code (void)
561 loop_optimizer_init (LOOPS_NORMAL
);
563 connect_infinite_loops_to_exit ();
564 memset (&sink_stats
, 0, sizeof (sink_stats
));
565 calculate_dominance_info (CDI_DOMINATORS
);
566 calculate_dominance_info (CDI_POST_DOMINATORS
);
567 sink_code_in_bb (EXIT_BLOCK_PTR
);
568 statistics_counter_event (cfun
, "Sunk statements", sink_stats
.sunk
);
569 free_dominance_info (CDI_POST_DOMINATORS
);
570 remove_fake_exit_edges ();
571 loop_optimizer_finalize ();
574 /* Gate and execute functions for PRE. */
579 execute_sink_code ();
586 return flag_tree_sink
!= 0;
591 const pass_data pass_data_sink_code
=
593 GIMPLE_PASS
, /* type */
595 OPTGROUP_NONE
, /* optinfo_flags */
597 true, /* has_execute */
598 TV_TREE_SINK
, /* tv_id */
599 ( PROP_no_crit_edges
| PROP_cfg
| PROP_ssa
), /* properties_required */
600 0, /* properties_provided */
601 0, /* properties_destroyed */
602 0, /* todo_flags_start */
603 ( TODO_update_ssa
| TODO_verify_ssa
604 | TODO_verify_flow
), /* todo_flags_finish */
607 class pass_sink_code
: public gimple_opt_pass
610 pass_sink_code(gcc::context
*ctxt
)
611 : gimple_opt_pass(pass_data_sink_code
, ctxt
)
614 /* opt_pass methods: */
615 bool gate () { return gate_sink (); }
616 unsigned int execute () { return do_sink (); }
618 }; // class pass_sink_code
623 make_pass_sink_code (gcc::context
*ctxt
)
625 return new pass_sink_code (ctxt
);