1 /* CFG cleanup for trees.
2 Copyright (C) 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING. If not, write to
18 the Free Software Foundation, 51 Franklin Street, Fifth Floor,
19 Boston, MA 02110-1301, USA. */
23 #include "coretypes.h"
28 #include "hard-reg-set.h"
29 #include "basic-block.h"
36 #include "langhooks.h"
37 #include "diagnostic.h"
38 #include "tree-flow.h"
40 #include "tree-dump.h"
41 #include "tree-pass.h"
45 #include "cfglayout.h"
47 #include "tree-ssa-propagate.h"
48 #include "tree-scalar-evolution.h"
50 /* Remove any fallthru edge from EV. Return true if an edge was removed. */
53 remove_fallthru_edge (VEC(edge,gc) *ev)
58 FOR_EACH_EDGE (e, ei, ev)
59 if ((e->flags & EDGE_FALLTHRU) != 0)
67 /* Disconnect an unreachable block in the control expression starting
71 cleanup_control_expr_graph (basic_block bb, block_stmt_iterator bsi)
75 tree expr = bsi_stmt (bsi), val;
77 if (!single_succ_p (bb))
82 switch (TREE_CODE (expr))
85 val = fold (COND_EXPR_COND (expr));
89 val = fold (SWITCH_COND (expr));
90 if (TREE_CODE (val) != INTEGER_CST)
98 taken_edge = find_taken_edge (bb, val);
102 /* Remove all the edges except the one that is always executed. */
103 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
107 taken_edge->probability += e->probability;
108 taken_edge->count += e->count;
115 if (taken_edge->probability > REG_BR_PROB_BASE)
116 taken_edge->probability = REG_BR_PROB_BASE;
119 taken_edge = single_succ_edge (bb);
121 bsi_remove (&bsi, true);
122 taken_edge->flags = EDGE_FALLTHRU;
124 /* We removed some paths from the cfg. */
125 free_dominance_info (CDI_DOMINATORS);
130 /* A list of all the noreturn calls passed to modify_stmt.
131 cleanup_control_flow uses it to detect cases where a mid-block
132 indirect call has been turned into a noreturn call. When this
133 happens, all the instructions after the call are no longer
134 reachable and must be deleted as dead. */
136 VEC(tree,gc) *modified_noreturn_calls;
138 /* Try to remove superfluous control structures. */
141 cleanup_control_flow (void)
144 block_stmt_iterator bsi;
148 /* Detect cases where a mid-block call is now known not to return. */
149 while (VEC_length (tree, modified_noreturn_calls))
151 stmt = VEC_pop (tree, modified_noreturn_calls);
152 bb = bb_for_stmt (stmt);
153 if (bb != NULL && last_stmt (bb) != stmt && noreturn_call_p (stmt))
154 split_block (bb, stmt);
164 stmt = bsi_stmt (bsi);
165 if (TREE_CODE (stmt) == COND_EXPR
166 || TREE_CODE (stmt) == SWITCH_EXPR)
167 retval |= cleanup_control_expr_graph (bb, bsi);
169 /* If we had a computed goto which has a compile-time determinable
170 destination, then we can eliminate the goto. */
171 if (TREE_CODE (stmt) == GOTO_EXPR
172 && TREE_CODE (GOTO_DESTINATION (stmt)) == ADDR_EXPR
173 && TREE_CODE (TREE_OPERAND (GOTO_DESTINATION (stmt), 0)) == LABEL_DECL)
178 basic_block target_block;
179 bool removed_edge = false;
181 /* First look at all the outgoing edges. Delete any outgoing
182 edges which do not go to the right block. For the one
183 edge which goes to the right block, fix up its flags. */
184 label = TREE_OPERAND (GOTO_DESTINATION (stmt), 0);
185 target_block = label_to_block (label);
186 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
188 if (e->dest != target_block)
195 /* Turn off the EDGE_ABNORMAL flag. */
196 e->flags &= ~EDGE_ABNORMAL;
198 /* And set EDGE_FALLTHRU. */
199 e->flags |= EDGE_FALLTHRU;
204 /* If we removed one or more edges, then we will need to fix the
205 dominators. It may be possible to incrementally update them. */
207 free_dominance_info (CDI_DOMINATORS);
209 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the
210 relevant information we need. */
211 bsi_remove (&bsi, true);
215 /* Check for indirect calls that have been turned into
217 if (noreturn_call_p (stmt) && remove_fallthru_edge (bb->succs))
219 free_dominance_info (CDI_DOMINATORS);
226 /* Return true if basic block BB does nothing except pass control
227 flow to another block and that we can safely insert a label at
228 the start of the successor block.
230 As a precondition, we require that BB be not equal to
234 tree_forwarder_block_p (basic_block bb, bool phi_wanted)
236 block_stmt_iterator bsi;
238 /* BB must have a single outgoing edge. */
239 if (single_succ_p (bb) != 1
240 /* If PHI_WANTED is false, BB must not have any PHI nodes.
241 Otherwise, BB must have PHI nodes. */
242 || (phi_nodes (bb) != NULL_TREE) != phi_wanted
243 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */
244 || single_succ (bb) == EXIT_BLOCK_PTR
245 /* Nor should this be an infinite loop. */
246 || single_succ (bb) == bb
247 /* BB may not have an abnormal outgoing edge. */
248 || (single_succ_edge (bb)->flags & EDGE_ABNORMAL))
252 gcc_assert (bb != ENTRY_BLOCK_PTR);
255 /* Now walk through the statements backward. We can ignore labels,
256 anything else means this is not a forwarder block. */
257 for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi))
259 tree stmt = bsi_stmt (bsi);
261 switch (TREE_CODE (stmt))
264 if (DECL_NONLOCAL (LABEL_EXPR_LABEL (stmt)))
273 if (find_edge (ENTRY_BLOCK_PTR, bb))
279 /* Protect loop latches, headers and preheaders. */
280 if (bb->loop_father->header == bb)
282 dest = EDGE_SUCC (bb, 0)->dest;
284 if (dest->loop_father->header == dest)
291 /* Return true if BB has at least one abnormal incoming edge. */
294 has_abnormal_incoming_edge_p (basic_block bb)
299 FOR_EACH_EDGE (e, ei, bb->preds)
300 if (e->flags & EDGE_ABNORMAL)
306 /* If all the PHI nodes in DEST have alternatives for E1 and E2 and
307 those alternatives are equal in each of the PHI nodes, then return
308 true, else return false. */
311 phi_alternatives_equal (basic_block dest, edge e1, edge e2)
313 int n1 = e1->dest_idx;
314 int n2 = e2->dest_idx;
317 for (phi = phi_nodes (dest); phi; phi = PHI_CHAIN (phi))
319 tree val1 = PHI_ARG_DEF (phi, n1);
320 tree val2 = PHI_ARG_DEF (phi, n2);
322 gcc_assert (val1 != NULL_TREE);
323 gcc_assert (val2 != NULL_TREE);
325 if (!operand_equal_for_phi_arg_p (val1, val2))
332 /* Removes forwarder block BB. Returns false if this failed. If a new
333 forwarder block is created due to redirection of edges, it is
334 stored to worklist. */
337 remove_forwarder_block (basic_block bb, basic_block **worklist)
339 edge succ = single_succ_edge (bb), e, s;
340 basic_block dest = succ->dest;
344 block_stmt_iterator bsi, bsi_to;
345 bool seen_abnormal_edge = false;
347 /* We check for infinite loops already in tree_forwarder_block_p.
348 However it may happen that the infinite loop is created
349 afterwards due to removal of forwarders. */
353 /* If the destination block consists of a nonlocal label, do not merge
355 label = first_stmt (dest);
357 && TREE_CODE (label) == LABEL_EXPR
358 && DECL_NONLOCAL (LABEL_EXPR_LABEL (label)))
361 /* If there is an abnormal edge to basic block BB, but not into
362 dest, problems might occur during removal of the phi node at out
363 of ssa due to overlapping live ranges of registers.
365 If there is an abnormal edge in DEST, the problems would occur
366 anyway since cleanup_dead_labels would then merge the labels for
367 two different eh regions, and rest of exception handling code
370 So if there is an abnormal edge to BB, proceed only if there is
371 no abnormal edge to DEST and there are no phi nodes in DEST. */
372 if (has_abnormal_incoming_edge_p (bb))
374 seen_abnormal_edge = true;
376 if (has_abnormal_incoming_edge_p (dest)
377 || phi_nodes (dest) != NULL_TREE)
381 /* If there are phi nodes in DEST, and some of the blocks that are
382 predecessors of BB are also predecessors of DEST, check that the
383 phi node arguments match. */
384 if (phi_nodes (dest))
386 FOR_EACH_EDGE (e, ei, bb->preds)
388 s = find_edge (e->src, dest);
392 if (!phi_alternatives_equal (dest, succ, s))
397 /* Redirect the edges. */
398 for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
400 if (e->flags & EDGE_ABNORMAL)
402 /* If there is an abnormal edge, redirect it anyway, and
403 move the labels to the new block to make it legal. */
404 s = redirect_edge_succ_nodup (e, dest);
407 s = redirect_edge_and_branch (e, dest);
411 /* Create arguments for the phi nodes, since the edge was not
413 for (phi = phi_nodes (dest); phi; phi = PHI_CHAIN (phi))
414 add_phi_arg (phi, PHI_ARG_DEF (phi, succ->dest_idx), s);
418 /* The source basic block might become a forwarder. We know
419 that it was not a forwarder before, since it used to have
420 at least two outgoing edges, so we may just add it to
422 if (tree_forwarder_block_p (s->src, false))
423 *(*worklist)++ = s->src;
427 if (seen_abnormal_edge)
429 /* Move the labels to the new block, so that the redirection of
430 the abnormal edges works. */
432 bsi_to = bsi_start (dest);
433 for (bsi = bsi_start (bb); !bsi_end_p (bsi); )
435 label = bsi_stmt (bsi);
436 gcc_assert (TREE_CODE (label) == LABEL_EXPR);
437 bsi_remove (&bsi, false);
438 bsi_insert_before (&bsi_to, label, BSI_CONTINUE_LINKING);
442 /* Update the dominators. */
443 if (dom_info_available_p (CDI_DOMINATORS))
445 basic_block dom, dombb, domdest;
447 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
448 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
451 /* Shortcut to avoid calling (relatively expensive)
452 nearest_common_dominator unless necessary. */
456 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
458 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
461 /* And kill the forwarder block. */
462 delete_basic_block (bb);
467 /* Removes forwarder blocks. */
470 cleanup_forwarder_blocks (void)
473 bool changed = false;
474 basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks);
475 basic_block *current = worklist;
479 if (tree_forwarder_block_p (bb, false))
483 while (current != worklist)
486 changed |= remove_forwarder_block (bb, ¤t);
493 /* Do one round of CFG cleanup. */
496 cleanup_tree_cfg_1 (void)
500 retval = cleanup_control_flow ();
501 retval |= delete_unreachable_blocks ();
503 /* Forwarder blocks can carry line number information which is
504 useful when debugging, so we only clean them up when
509 /* cleanup_forwarder_blocks can redirect edges out of
510 SWITCH_EXPRs, which can get expensive. So we want to enable
511 recording of edge to CASE_LABEL_EXPR mappings around the call
512 to cleanup_forwarder_blocks. */
513 start_recording_case_labels ();
514 retval |= cleanup_forwarder_blocks ();
515 end_recording_case_labels ();
518 /* Merging the blocks may create new opportunities for folding
519 conditional branches (due to the elimination of single-valued PHI
521 retval |= merge_seq_blocks ();
527 /* Remove unreachable blocks and other miscellaneous clean up work.
528 Return true if the flowgraph was modified, false otherwise. */
531 cleanup_tree_cfg (void)
533 bool retval, changed;
535 timevar_push (TV_TREE_CLEANUP_CFG);
537 /* Iterate until there are no more cleanups left to do. If any
538 iteration changed the flowgraph, set CHANGED to true. */
542 retval = cleanup_tree_cfg_1 ();
549 #ifdef ENABLE_CHECKING
553 timevar_pop (TV_TREE_CLEANUP_CFG);
558 /* Cleanup cfg and repair loop structures. */
561 cleanup_tree_cfg_loop (void)
563 bool changed = cleanup_tree_cfg ();
567 bitmap changed_bbs = BITMAP_ALLOC (NULL);
568 fix_loop_structure (current_loops, changed_bbs);
569 calculate_dominance_info (CDI_DOMINATORS);
571 /* This usually does nothing. But sometimes parts of cfg that originally
572 were inside a loop get out of it due to edge removal (since they
573 become unreachable by back edges from latch). */
574 rewrite_into_loop_closed_ssa (changed_bbs, TODO_update_ssa);
576 BITMAP_FREE (changed_bbs);
578 #ifdef ENABLE_CHECKING
579 verify_loop_structure (current_loops);
585 /* Merge the PHI nodes at BB into those at BB's sole successor. */
588 remove_forwarder_block_with_phi (basic_block bb)
590 edge succ = single_succ_edge (bb);
591 basic_block dest = succ->dest;
593 basic_block dombb, domdest, dom;
595 /* We check for infinite loops already in tree_forwarder_block_p.
596 However it may happen that the infinite loop is created
597 afterwards due to removal of forwarders. */
601 /* If the destination block consists of a nonlocal label, do not
603 label = first_stmt (dest);
605 && TREE_CODE (label) == LABEL_EXPR
606 && DECL_NONLOCAL (LABEL_EXPR_LABEL (label)))
609 /* Redirect each incoming edge to BB to DEST. */
610 while (EDGE_COUNT (bb->preds) > 0)
612 edge e = EDGE_PRED (bb, 0), s;
615 s = find_edge (e->src, dest);
618 /* We already have an edge S from E->src to DEST. If S and
619 E->dest's sole successor edge have the same PHI arguments
620 at DEST, redirect S to DEST. */
621 if (phi_alternatives_equal (dest, s, succ))
623 e = redirect_edge_and_branch (e, dest);
624 PENDING_STMT (e) = NULL_TREE;
628 /* PHI arguments are different. Create a forwarder block by
629 splitting E so that we can merge PHI arguments on E to
631 e = single_succ_edge (split_edge (e));
634 s = redirect_edge_and_branch (e, dest);
636 /* redirect_edge_and_branch must not create a new edge. */
639 /* Add to the PHI nodes at DEST each PHI argument removed at the
641 for (phi = phi_nodes (dest); phi; phi = PHI_CHAIN (phi))
643 tree def = PHI_ARG_DEF (phi, succ->dest_idx);
645 if (TREE_CODE (def) == SSA_NAME)
649 /* If DEF is one of the results of PHI nodes removed during
650 redirection, replace it with the PHI argument that used
652 for (var = PENDING_STMT (e); var; var = TREE_CHAIN (var))
654 tree old_arg = TREE_PURPOSE (var);
655 tree new_arg = TREE_VALUE (var);
665 add_phi_arg (phi, def, s);
668 PENDING_STMT (e) = NULL;
671 /* Update the dominators. */
672 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
673 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
676 /* Shortcut to avoid calling (relatively expensive)
677 nearest_common_dominator unless necessary. */
681 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
683 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
685 /* Remove BB since all of BB's incoming edges have been redirected
687 delete_basic_block (bb);
690 /* This pass merges PHI nodes if one feeds into another. For example,
691 suppose we have the following:
698 # tem_6 = PHI <tem_17(8), tem_23(7)>;
701 # tem_3 = PHI <tem_6(9), tem_2(5)>;
704 Then we merge the first PHI node into the second one like so:
711 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
716 merge_phi_nodes (void)
718 basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks);
719 basic_block *current = worklist;
722 calculate_dominance_info (CDI_DOMINATORS);
724 /* Find all PHI nodes that we may be able to merge. */
729 /* Look for a forwarder block with PHI nodes. */
730 if (!tree_forwarder_block_p (bb, true))
733 dest = single_succ (bb);
735 /* We have to feed into another basic block with PHI
737 if (!phi_nodes (dest)
738 /* We don't want to deal with a basic block with
740 || has_abnormal_incoming_edge_p (bb))
743 if (!dominated_by_p (CDI_DOMINATORS, dest, bb))
745 /* If BB does not dominate DEST, then the PHI nodes at
746 DEST must be the only users of the results of the PHI
753 unsigned int dest_idx = single_succ_edge (bb)->dest_idx;
755 /* BB dominates DEST. There may be many users of the PHI
756 nodes in BB. However, there is still a trivial case we
757 can handle. If the result of every PHI in BB is used
758 only by a PHI in DEST, then we can trivially merge the
759 PHI nodes from BB into DEST. */
760 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
762 tree result = PHI_RESULT (phi);
763 int num_uses = num_imm_uses (result);
764 use_operand_p imm_use;
767 /* If the PHI's result is never used, then we can just
772 /* Get the single use of the result of this PHI node. */
773 if (!single_imm_use (result, &imm_use, &use_stmt)
774 || TREE_CODE (use_stmt) != PHI_NODE
775 || bb_for_stmt (use_stmt) != dest
776 || PHI_ARG_DEF (use_stmt, dest_idx) != result)
780 /* If the loop above iterated thorugh all the PHI nodes
781 in BB, then we can merge the PHIs from BB into DEST. */
787 /* Now let's drain WORKLIST. */
788 while (current != worklist)
791 remove_forwarder_block_with_phi (bb);
798 gate_merge_phi (void)
803 struct tree_opt_pass pass_merge_phi = {
804 "mergephi", /* name */
805 gate_merge_phi, /* gate */
806 merge_phi_nodes, /* execute */
809 0, /* static_pass_number */
810 TV_TREE_MERGE_PHI, /* tv_id */
811 PROP_cfg | PROP_ssa, /* properties_required */
812 0, /* properties_provided */
813 0, /* properties_destroyed */
814 0, /* todo_flags_start */
815 TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */