| /* Generic dominator tree walker |
| Copyright (C) 2003, 2004, 2005, 2007, 2008 Free Software Foundation, |
| Inc. |
| Contributed by Diego Novillo <dnovillo@redhat.com> |
| |
| This file is part of GCC. |
| |
| GCC is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 3, or (at your option) |
| any later version. |
| |
| GCC is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| GNU General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GCC; see the file COPYING3. If not see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include "config.h" |
| #include "system.h" |
| #include "coretypes.h" |
| #include "tm.h" |
| #include "tree.h" |
| #include "basic-block.h" |
| #include "tree-flow.h" |
| #include "domwalk.h" |
| #include "ggc.h" |
| |
| /* This file implements a generic walker for dominator trees. |
| |
| To understand the dominator walker one must first have a grasp of dominators, |
| immediate dominators and the dominator tree. |
| |
| Dominators |
| A block B1 is said to dominate B2 if every path from the entry to B2 must |
| pass through B1. Given the dominance relationship, we can proceed to |
| compute immediate dominators. Note it is not important whether or not |
| our definition allows a block to dominate itself. |
| |
| Immediate Dominators: |
| Every block in the CFG has no more than one immediate dominator. The |
| immediate dominator of block BB must dominate BB and must not dominate |
| any other dominator of BB and must not be BB itself. |
| |
| Dominator tree: |
| If we then construct a tree where each node is a basic block and there |
| is an edge from each block's immediate dominator to the block itself, then |
| we have a dominator tree. |
| |
| |
| [ Note this walker can also walk the post-dominator tree, which is |
| defined in a similar manner. i.e., block B1 is said to post-dominate |
| block B2 if all paths from B2 to the exit block must pass through |
| B1. ] |
| |
| For example, given the CFG |
| |
| 1 |
| | |
| 2 |
| / \ |
| 3 4 |
| / \ |
| +---------->5 6 |
| | / \ / |
| | +--->8 7 |
| | | / | |
| | +--9 11 |
| | / | |
| +--- 10 ---> 12 |
| |
| |
| We have a dominator tree which looks like |
| |
| 1 |
| | |
| 2 |
| / \ |
| / \ |
| 3 4 |
| / / \ \ |
| | | | | |
| 5 6 7 12 |
| | | |
| 8 11 |
| | |
| 9 |
| | |
| 10 |
| |
| |
| |
| The dominator tree is the basis for a number of analysis, transformation |
| and optimization algorithms that operate on a semi-global basis. |
| |
| The dominator walker is a generic routine which visits blocks in the CFG |
| via a depth first search of the dominator tree. In the example above |
| the dominator walker might visit blocks in the following order |
| 1, 2, 3, 4, 5, 8, 9, 10, 6, 7, 11, 12. |
| |
| The dominator walker has a number of callbacks to perform actions |
| during the walk of the dominator tree. There are two callbacks |
| which walk statements, one before visiting the dominator children, |
| one after visiting the dominator children. There is a callback |
| before and after each statement walk callback. In addition, the |
| dominator walker manages allocation/deallocation of data structures |
| which are local to each block visited. |
| |
| The dominator walker is meant to provide a generic means to build a pass |
| which can analyze or transform/optimize a function based on walking |
| the dominator tree. One simply fills in the dominator walker data |
| structure with the appropriate callbacks and calls the walker. |
| |
| We currently use the dominator walker to prune the set of variables |
| which might need PHI nodes (which can greatly improve compile-time |
| performance in some cases). |
| |
| We also use the dominator walker to rewrite the function into SSA form |
| which reduces code duplication since the rewriting phase is inherently |
| a walk of the dominator tree. |
| |
| And (of course), we use the dominator walker to drive our dominator |
| optimizer, which is a semi-global optimizer. |
| |
| TODO: |
| |
| Walking statements is based on the block statement iterator abstraction, |
| which is currently an abstraction over walking tree statements. Thus |
| the dominator walker is currently only useful for trees. */ |
| |
| /* Recursively walk the dominator tree. |
| |
| WALK_DATA contains a set of callbacks to perform pass-specific |
| actions during the dominator walk as well as a stack of block local |
| data maintained during the dominator walk. |
| |
| BB is the basic block we are currently visiting. */ |
| |
| void |
| walk_dominator_tree (struct dom_walk_data *walk_data, basic_block bb) |
| { |
| void *bd = NULL; |
| basic_block dest; |
| gimple_stmt_iterator gsi; |
| bool is_interesting; |
| basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks * 2); |
| int sp = 0; |
| |
| while (true) |
| { |
| /* Don't worry about unreachable blocks. */ |
| if (EDGE_COUNT (bb->preds) > 0 |
| || bb == ENTRY_BLOCK_PTR |
| || bb == EXIT_BLOCK_PTR) |
| { |
| /* If block BB is not interesting to the caller, then none of the |
| callbacks that walk the statements in BB are going to be |
| executed. */ |
| is_interesting = walk_data->interesting_blocks == NULL |
| || TEST_BIT (walk_data->interesting_blocks, |
| bb->index); |
| |
| /* Callback to initialize the local data structure. */ |
| if (walk_data->initialize_block_local_data) |
| { |
| bool recycled; |
| |
| /* First get some local data, reusing any local data |
| pointer we may have saved. */ |
| if (VEC_length (void_p, walk_data->free_block_data) > 0) |
| { |
| bd = VEC_pop (void_p, walk_data->free_block_data); |
| recycled = 1; |
| } |
| else |
| { |
| bd = xcalloc (1, walk_data->block_local_data_size); |
| recycled = 0; |
| } |
| |
| /* Push the local data into the local data stack. */ |
| VEC_safe_push (void_p, heap, walk_data->block_data_stack, bd); |
| |
| /* Call the initializer. */ |
| walk_data->initialize_block_local_data (walk_data, bb, |
| recycled); |
| |
| } |
| |
| /* Callback for operations to execute before we have walked the |
| dominator children, but before we walk statements. */ |
| if (walk_data->before_dom_children_before_stmts) |
| (*walk_data->before_dom_children_before_stmts) (walk_data, bb); |
| |
| /* Statement walk before walking dominator children. */ |
| if (is_interesting && walk_data->before_dom_children_walk_stmts) |
| { |
| if (walk_data->walk_stmts_backward) |
| for (gsi = gsi_last (bb_seq (bb)); !gsi_end_p (gsi); |
| gsi_prev (&gsi)) |
| (*walk_data->before_dom_children_walk_stmts) (walk_data, bb, |
| gsi); |
| else |
| for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) |
| (*walk_data->before_dom_children_walk_stmts) (walk_data, bb, |
| gsi); |
| } |
| |
| /* Callback for operations to execute before we have walked the |
| dominator children, and after we walk statements. */ |
| if (walk_data->before_dom_children_after_stmts) |
| (*walk_data->before_dom_children_after_stmts) (walk_data, bb); |
| |
| /* Mark the current BB to be popped out of the recursion stack |
| once children are processed. */ |
| worklist[sp++] = bb; |
| worklist[sp++] = NULL; |
| |
| for (dest = first_dom_son (walk_data->dom_direction, bb); |
| dest; dest = next_dom_son (walk_data->dom_direction, dest)) |
| worklist[sp++] = dest; |
| } |
| /* NULL is used to signalize pop operation in recursion stack. */ |
| while (sp > 0 && !worklist[sp - 1]) |
| { |
| --sp; |
| bb = worklist[--sp]; |
| is_interesting = walk_data->interesting_blocks == NULL |
| || TEST_BIT (walk_data->interesting_blocks, |
| bb->index); |
| /* Callback for operations to execute after we have walked the |
| dominator children, but before we walk statements. */ |
| if (walk_data->after_dom_children_before_stmts) |
| (*walk_data->after_dom_children_before_stmts) (walk_data, bb); |
| |
| /* Statement walk after walking dominator children. */ |
| if (is_interesting && walk_data->after_dom_children_walk_stmts) |
| { |
| if (walk_data->walk_stmts_backward) |
| for (gsi = gsi_last (bb_seq (bb)); !gsi_end_p (gsi); |
| gsi_prev (&gsi)) |
| (*walk_data->after_dom_children_walk_stmts) (walk_data, bb, |
| gsi); |
| else |
| for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) |
| (*walk_data->after_dom_children_walk_stmts) (walk_data, bb, |
| gsi); |
| } |
| |
| /* Callback for operations to execute after we have walked the |
| dominator children and after we have walked statements. */ |
| if (walk_data->after_dom_children_after_stmts) |
| (*walk_data->after_dom_children_after_stmts) (walk_data, bb); |
| |
| if (walk_data->initialize_block_local_data) |
| { |
| /* And finally pop the record off the block local data stack. */ |
| bd = VEC_pop (void_p, walk_data->block_data_stack); |
| /* And save the block data so that we can re-use it. */ |
| VEC_safe_push (void_p, heap, walk_data->free_block_data, bd); |
| } |
| } |
| if (sp) |
| bb = worklist[--sp]; |
| else |
| break; |
| } |
| free (worklist); |
| } |
| |
| void |
| init_walk_dominator_tree (struct dom_walk_data *walk_data) |
| { |
| walk_data->free_block_data = NULL; |
| walk_data->block_data_stack = NULL; |
| } |
| |
| void |
| fini_walk_dominator_tree (struct dom_walk_data *walk_data) |
| { |
| if (walk_data->initialize_block_local_data) |
| { |
| while (VEC_length (void_p, walk_data->free_block_data) > 0) |
| free (VEC_pop (void_p, walk_data->free_block_data)); |
| } |
| |
| VEC_free (void_p, heap, walk_data->free_block_data); |
| VEC_free (void_p, heap, walk_data->block_data_stack); |
| } |
