1 /* Code sinking for trees
2 Copyright (C) 2001, 2002, 2003, 2004 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 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, 59 Temple Place - Suite 330,
20 Boston, MA 02111-1307, USA. */
24 #include "coretypes.h"
29 #include "basic-block.h"
30 #include "diagnostic.h"
31 #include "tree-inline.h"
32 #include "tree-flow.h"
33 #include "tree-gimple.h"
34 #include "tree-dump.h"
38 #include "tree-iterator.h"
40 #include "alloc-pool.h"
41 #include "tree-pass.h"
44 #include "langhooks.h"
48 1. Sinking store only using scalar promotion (IE without moving the RHS):
68 Store copy propagation will take care of the store elimination above.
71 2. Sinking using Partial Dead Code Elimination. */
76 /* The number of statements sunk down the flowgraph by code sinking. */
82 /* Given a PHI, and one of its arguments (DEF), find the edge for
83 that argument and return it. If the argument occurs twice in the PHI node,
87 find_bb_for_arg (tree phi, tree def)
90 bool foundone = false;
91 basic_block result = NULL;
92 for (i = 0; i < PHI_NUM_ARGS (phi); i++)
93 if (PHI_ARG_DEF (phi, i) == def)
98 result = PHI_ARG_EDGE (phi, i)->src;
103 /* When the first immediate use is in a statement, then return true if all
104 immediate uses in IMM are in the same statement.
105 We could also do the case where the first immediate use is in a phi node,
106 and all the other uses are in phis in the same basic block, but this
107 requires some expensive checking later (you have to make sure no def/vdef
108 in the statement occurs for multiple edges in the various phi nodes it's
109 used in, so that you only have one place you can sink it to. */
112 all_immediate_uses_same_place (tree stmt)
114 tree firstuse = NULL_TREE;
116 imm_use_iterator imm_iter;
120 FOR_EACH_SSA_TREE_OPERAND (var, stmt, op_iter, SSA_OP_ALL_DEFS)
122 FOR_EACH_IMM_USE_FAST (use_p, imm_iter, var)
124 if (firstuse == NULL_TREE)
125 firstuse = USE_STMT (use_p);
127 if (firstuse != USE_STMT (use_p))
135 /* Some global stores don't necessarily have V_MAY_DEF's of global variables,
136 but we still must avoid moving them around. */
139 is_hidden_global_store (tree stmt)
141 stmt_ann_t ann = stmt_ann (stmt);
142 v_may_def_optype v_may_defs;
143 v_must_def_optype v_must_defs;
145 /* Check virtual definitions. If we get here, the only virtual
146 definitions we should see are those generated by assignment
148 v_may_defs = V_MAY_DEF_OPS (ann);
149 v_must_defs = V_MUST_DEF_OPS (ann);
150 if (NUM_V_MAY_DEFS (v_may_defs) > 0 || NUM_V_MUST_DEFS (v_must_defs) > 0)
154 gcc_assert (TREE_CODE (stmt) == MODIFY_EXPR);
156 /* Note that we must not check the individual virtual operands
157 here. In particular, if this is an aliased store, we could
158 end up with something like the following (SSA notation
159 redacted for brevity):
164 p_1 = (i_2 > 3) ? &x : p;
166 # x_4 = V_MAY_DEF <x_3>
172 Notice that the store to '*p_1' should be preserved, if we
173 were to check the virtual definitions in that store, we would
174 not mark it needed. This is because 'x' is not a global
177 Therefore, we check the base address of the LHS. If the
178 address is a pointer, we check if its name tag or type tag is
179 a global variable. Otherwise, we check if the base variable
181 lhs = TREE_OPERAND (stmt, 0);
182 if (REFERENCE_CLASS_P (lhs))
183 lhs = get_base_address (lhs);
185 if (lhs == NULL_TREE)
187 /* If LHS is NULL, it means that we couldn't get the base
188 address of the reference. In which case, we should not
192 else if (DECL_P (lhs))
194 /* If the store is to a global symbol, we need to keep it. */
195 if (is_global_var (lhs))
199 else if (INDIRECT_REF_P (lhs))
201 tree ptr = TREE_OPERAND (lhs, 0);
202 struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr);
203 tree nmt = (pi) ? pi->name_mem_tag : NULL_TREE;
204 tree tmt = var_ann (SSA_NAME_VAR (ptr))->type_mem_tag;
206 /* If either the name tag or the type tag for PTR is a
207 global variable, then the store is necessary. */
208 if ((nmt && is_global_var (nmt))
209 || (tmt && is_global_var (tmt)))
220 /* Find the nearest common dominator of all of the immediate uses in IMM. */
223 nearest_common_dominator_of_uses (tree stmt)
225 bitmap blocks = BITMAP_ALLOC (NULL);
226 basic_block commondom;
230 imm_use_iterator imm_iter;
234 bitmap_clear (blocks);
235 FOR_EACH_SSA_TREE_OPERAND (var, stmt, op_iter, SSA_OP_ALL_DEFS)
237 FOR_EACH_IMM_USE_FAST (use_p, imm_iter, var)
239 tree usestmt = USE_STMT (use_p);
240 basic_block useblock;
241 if (TREE_CODE (usestmt) == PHI_NODE)
243 int idx = PHI_ARG_INDEX_FROM_USE (use_p);
245 useblock = PHI_ARG_EDGE (usestmt, idx)->src;
246 /* Short circuit. Nothing dominates the entry block. */
247 if (useblock == ENTRY_BLOCK_PTR)
249 BITMAP_FREE (blocks);
252 bitmap_set_bit (blocks, useblock->index);
256 useblock = bb_for_stmt (usestmt);
258 /* Short circuit. Nothing dominates the entry block. */
259 if (useblock == ENTRY_BLOCK_PTR)
261 BITMAP_FREE (blocks);
264 bitmap_set_bit (blocks, useblock->index);
268 commondom = BASIC_BLOCK (bitmap_first_set_bit (blocks));
269 EXECUTE_IF_SET_IN_BITMAP (blocks, 0, j, bi)
270 commondom = nearest_common_dominator (CDI_DOMINATORS, commondom,
272 BITMAP_FREE (blocks);
276 /* Given a statement (STMT) and the basic block it is currently in (FROMBB),
277 determine the location to sink the statement to, if any.
278 Return the basic block to sink it to, or NULL if we should not sink
282 statement_sink_location (tree stmt, basic_block frombb)
285 use_operand_p one_use = NULL_USE_OPERAND_P;
292 imm_use_iterator imm_iter;
294 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
296 FOR_EACH_IMM_USE_FAST (one_use, imm_iter, def)
300 if (one_use != NULL_USE_OPERAND_P)
304 /* Return if there are no immediate uses of this stmt. */
305 if (one_use == NULL_USE_OPERAND_P)
308 if (TREE_CODE (stmt) != MODIFY_EXPR)
310 rhs = TREE_OPERAND (stmt, 1);
312 /* There are a few classes of things we can't or don't move, some because we
313 don't have code to handle it, some because it's not profitable and some
314 because it's not legal.
316 We can't sink things that may be global stores, at least not without
317 calculating a lot more information, because we may cause it to no longer
318 be seen by an external routine that needs it depending on where it gets
321 We don't want to sink loads from memory.
323 We can't sink statements that end basic blocks without splitting the
324 incoming edge for the sink location to place it there.
326 We can't sink statements that have volatile operands.
328 We don't want to sink dead code, so anything with 0 immediate uses is not
332 ann = stmt_ann (stmt);
333 if (NUM_VUSES (STMT_VUSE_OPS (stmt)) != 0
334 || stmt_ends_bb_p (stmt)
335 || TREE_SIDE_EFFECTS (rhs)
336 || TREE_CODE (rhs) == EXC_PTR_EXPR
337 || TREE_CODE (rhs) == FILTER_EXPR
338 || is_hidden_global_store (stmt)
339 || ann->has_volatile_ops)
342 FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, iter, SSA_OP_ALL_DEFS)
344 tree def = DEF_FROM_PTR (def_p);
345 if (is_global_var (SSA_NAME_VAR (def))
346 || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def))
350 FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_ALL_USES)
352 tree use = USE_FROM_PTR (use_p);
353 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (use))
357 /* If all the immediate uses are not in the same place, find the nearest
358 common dominator of all the immediate uses. For PHI nodes, we have to
359 find the nearest common dominator of all of the predecessor blocks, since
360 that is where insertion would have to take place. */
361 if (!all_immediate_uses_same_place (stmt))
363 basic_block commondom = nearest_common_dominator_of_uses (stmt);
365 if (commondom == frombb)
368 /* Our common dominator has to be dominated by frombb in order to be a
369 trivially safe place to put this statement, since it has multiple
371 if (!dominated_by_p (CDI_DOMINATORS, commondom, frombb))
374 /* It doesn't make sense to move to a dominator that post-dominates
375 frombb, because it means we've just moved it into a path that always
376 executes if frombb executes, instead of reducing the number of
378 if (dominated_by_p (CDI_POST_DOMINATORS, frombb, commondom))
380 if (dump_file && (dump_flags & TDF_DETAILS))
381 fprintf (dump_file, "Not moving store, common dominator post-dominates from block.\n");
385 if (commondom == frombb || commondom->loop_depth > frombb->loop_depth)
387 if (dump_file && (dump_flags & TDF_DETAILS))
389 fprintf (dump_file, "Common dominator of all uses is %d\n",
392 return first_stmt (commondom);
395 use = USE_STMT (one_use);
396 if (TREE_CODE (use) != PHI_NODE)
398 sinkbb = bb_for_stmt (use);
399 if (sinkbb == frombb || sinkbb->loop_depth > frombb->loop_depth
400 || sinkbb->loop_father != frombb->loop_father)
405 /* Note that at this point, all uses must be in the same statement, so it
406 doesn't matter which def op we choose. */
407 if (STMT_DEF_OPS (stmt) == NULL)
409 if (STMT_V_MAY_DEF_OPS (stmt) != NULL)
410 def = V_MAY_DEF_RESULT (STMT_V_MAY_DEF_OPS (stmt), 0);
411 else if (STMT_V_MUST_DEF_OPS (stmt) != NULL)
412 def = V_MUST_DEF_RESULT (STMT_V_MUST_DEF_OPS (stmt), 0);
417 def = DEF_OP (STMT_DEF_OPS (stmt), 0);
419 sinkbb = find_bb_for_arg (use, def);
423 /* This will happen when you have
424 a_3 = PHI <a_13, a_26>
426 a_26 = V_MAY_DEF <a_3>
428 If the use is a phi, and is in the same bb as the def,
431 if (bb_for_stmt (use) == frombb)
433 if (sinkbb == frombb || sinkbb->loop_depth > frombb->loop_depth
434 || sinkbb->loop_father != frombb->loop_father)
437 return first_stmt (sinkbb);
440 /* Perform code sinking on BB */
443 sink_code_in_bb (basic_block bb)
446 block_stmt_iterator bsi;
450 /* If this block doesn't dominate anything, there can't be any place to sink
451 the statements to. */
452 if (first_dom_son (CDI_DOMINATORS, bb) == NULL)
455 /* We can't move things across abnormal edges, so don't try. */
456 FOR_EACH_EDGE (e, ei, bb->succs)
457 if (e->flags & EDGE_ABNORMAL)
460 for (bsi = bsi_last (bb); !bsi_end_p (bsi);)
462 tree stmt = bsi_stmt (bsi);
463 block_stmt_iterator tobsi;
465 get_stmt_operands (stmt);
467 sinkstmt = statement_sink_location (stmt, bb);
470 if (!bsi_end_p (bsi))
476 fprintf (dump_file, "Sinking ");
477 print_generic_expr (dump_file, stmt, TDF_VOPS);
478 fprintf (dump_file, " from bb %d to bb %d\n",
479 bb->index, bb_for_stmt (sinkstmt)->index);
481 tobsi = bsi_for_stmt (sinkstmt);
482 /* Find the first non-label. */
483 while (!bsi_end_p (tobsi)
484 && TREE_CODE (bsi_stmt (tobsi)) == LABEL_EXPR)
487 /* If this is the end of the basic block, we need to insert at the end
488 of the basic block. */
489 if (bsi_end_p (tobsi))
490 bsi_move_to_bb_end (&bsi, bb_for_stmt (sinkstmt));
492 bsi_move_before (&bsi, &tobsi);
495 if (!bsi_end_p (bsi))
500 for (son = first_dom_son (CDI_POST_DOMINATORS, bb);
502 son = next_dom_son (CDI_POST_DOMINATORS, son))
504 sink_code_in_bb (son);
508 /* Perform code sinking.
509 This moves code down the flowgraph when we know it would be
510 profitable to do so, or it wouldn't increase the number of
511 executions of the statement.
524 a_6 = PHI (a_5, a_1);
527 we'll transform this into:
538 a_6 = PHI (a_5, a_1);
541 Note that this reduces the number of computations of a = b + c to 1
542 when we take the else edge, instead of 2.
545 execute_sink_code (void)
547 struct loops *loops = loop_optimizer_init (dump_file);
548 connect_infinite_loops_to_exit ();
549 memset (&sink_stats, 0, sizeof (sink_stats));
550 calculate_dominance_info (CDI_DOMINATORS | CDI_POST_DOMINATORS);
551 sink_code_in_bb (EXIT_BLOCK_PTR);
552 if (dump_file && (dump_flags & TDF_STATS))
553 fprintf (dump_file, "Sunk statements:%d\n", sink_stats.sunk);
554 free_dominance_info (CDI_POST_DOMINATORS);
555 remove_fake_exit_edges ();
556 loop_optimizer_finalize (loops, dump_file);
559 /* Gate and execute functions for PRE. */
564 execute_sink_code ();
570 return flag_tree_sink != 0;
573 struct tree_opt_pass pass_sink_code =
576 gate_sink, /* gate */
577 do_sink, /* execute */
580 0, /* static_pass_number */
581 TV_TREE_SINK, /* tv_id */
582 PROP_no_crit_edges | PROP_cfg
583 | PROP_ssa | PROP_alias, /* properties_required */
584 0, /* properties_provided */
585 0, /* properties_destroyed */
586 0, /* todo_flags_start */
587 TODO_rename_vars | TODO_dump_func | TODO_ggc_collect | TODO_verify_ssa, /* todo_flags_finish */