1169689Skan/* Generic dominator tree walker 2169689Skan Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc. 3169689Skan Contributed by Diego Novillo <dnovillo@redhat.com> 4169689Skan 5169689SkanThis file is part of GCC. 6169689Skan 7169689SkanGCC is free software; you can redistribute it and/or modify 8169689Skanit under the terms of the GNU General Public License as published by 9169689Skanthe Free Software Foundation; either version 2, or (at your option) 10169689Skanany later version. 11169689Skan 12169689SkanGCC is distributed in the hope that it will be useful, 13169689Skanbut WITHOUT ANY WARRANTY; without even the implied warranty of 14169689SkanMERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15169689SkanGNU General Public License for more details. 16169689Skan 17169689SkanYou should have received a copy of the GNU General Public License 18169689Skanalong with GCC; see the file COPYING. If not, write to 19169689Skanthe Free Software Foundation, 51 Franklin Street, Fifth Floor, 20169689SkanBoston, MA 02110-1301, USA. */ 21169689Skan 22169689Skan#include "config.h" 23169689Skan#include "system.h" 24169689Skan#include "coretypes.h" 25169689Skan#include "tm.h" 26169689Skan#include "tree.h" 27169689Skan#include "basic-block.h" 28169689Skan#include "tree-flow.h" 29169689Skan#include "domwalk.h" 30169689Skan#include "ggc.h" 31169689Skan 32169689Skan/* This file implements a generic walker for dominator trees. 33169689Skan 34169689Skan To understand the dominator walker one must first have a grasp of dominators, 35169689Skan immediate dominators and the dominator tree. 36169689Skan 37169689Skan Dominators 38169689Skan A block B1 is said to dominate B2 if every path from the entry to B2 must 39169689Skan pass through B1. Given the dominance relationship, we can proceed to 40169689Skan compute immediate dominators. Note it is not important whether or not 41169689Skan our definition allows a block to dominate itself. 42169689Skan 43169689Skan Immediate Dominators: 44169689Skan Every block in the CFG has no more than one immediate dominator. The 45169689Skan immediate dominator of block BB must dominate BB and must not dominate 46169689Skan any other dominator of BB and must not be BB itself. 47169689Skan 48169689Skan Dominator tree: 49169689Skan If we then construct a tree where each node is a basic block and there 50169689Skan is an edge from each block's immediate dominator to the block itself, then 51169689Skan we have a dominator tree. 52169689Skan 53169689Skan 54169689Skan [ Note this walker can also walk the post-dominator tree, which is 55169689Skan defined in a similar manner. i.e., block B1 is said to post-dominate 56169689Skan block B2 if all paths from B2 to the exit block must pass through 57169689Skan B1. ] 58169689Skan 59169689Skan For example, given the CFG 60169689Skan 61169689Skan 1 62169689Skan | 63169689Skan 2 64169689Skan / \ 65169689Skan 3 4 66169689Skan / \ 67169689Skan +---------->5 6 68169689Skan | / \ / 69169689Skan | +--->8 7 70169689Skan | | / | 71169689Skan | +--9 11 72169689Skan | / | 73169689Skan +--- 10 ---> 12 74169689Skan 75169689Skan 76169689Skan We have a dominator tree which looks like 77169689Skan 78169689Skan 1 79169689Skan | 80169689Skan 2 81169689Skan / \ 82169689Skan / \ 83169689Skan 3 4 84169689Skan / / \ \ 85169689Skan | | | | 86169689Skan 5 6 7 12 87169689Skan | | 88169689Skan 8 11 89169689Skan | 90169689Skan 9 91169689Skan | 92169689Skan 10 93169689Skan 94169689Skan 95169689Skan 96169689Skan The dominator tree is the basis for a number of analysis, transformation 97169689Skan and optimization algorithms that operate on a semi-global basis. 98169689Skan 99169689Skan The dominator walker is a generic routine which visits blocks in the CFG 100169689Skan via a depth first search of the dominator tree. In the example above 101169689Skan the dominator walker might visit blocks in the following order 102169689Skan 1, 2, 3, 4, 5, 8, 9, 10, 6, 7, 11, 12. 103169689Skan 104169689Skan The dominator walker has a number of callbacks to perform actions 105169689Skan during the walk of the dominator tree. There are two callbacks 106169689Skan which walk statements, one before visiting the dominator children, 107169689Skan one after visiting the dominator children. There is a callback 108169689Skan before and after each statement walk callback. In addition, the 109169689Skan dominator walker manages allocation/deallocation of data structures 110169689Skan which are local to each block visited. 111169689Skan 112169689Skan The dominator walker is meant to provide a generic means to build a pass 113169689Skan which can analyze or transform/optimize a function based on walking 114169689Skan the dominator tree. One simply fills in the dominator walker data 115169689Skan structure with the appropriate callbacks and calls the walker. 116169689Skan 117169689Skan We currently use the dominator walker to prune the set of variables 118169689Skan which might need PHI nodes (which can greatly improve compile-time 119169689Skan performance in some cases). 120169689Skan 121169689Skan We also use the dominator walker to rewrite the function into SSA form 122169689Skan which reduces code duplication since the rewriting phase is inherently 123169689Skan a walk of the dominator tree. 124169689Skan 125169689Skan And (of course), we use the dominator walker to drive a our dominator 126169689Skan optimizer, which is a semi-global optimizer. 127169689Skan 128169689Skan TODO: 129169689Skan 130169689Skan Walking statements is based on the block statement iterator abstraction, 131169689Skan which is currently an abstraction over walking tree statements. Thus 132169689Skan the dominator walker is currently only useful for trees. */ 133169689Skan 134169689Skan/* Recursively walk the dominator tree. 135169689Skan 136169689Skan WALK_DATA contains a set of callbacks to perform pass-specific 137169689Skan actions during the dominator walk as well as a stack of block local 138169689Skan data maintained during the dominator walk. 139169689Skan 140169689Skan BB is the basic block we are currently visiting. */ 141169689Skan 142169689Skanvoid 143169689Skanwalk_dominator_tree (struct dom_walk_data *walk_data, basic_block bb) 144169689Skan{ 145169689Skan void *bd = NULL; 146169689Skan basic_block dest; 147169689Skan block_stmt_iterator bsi; 148169689Skan bool is_interesting; 149169689Skan basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks * 2); 150169689Skan int sp = 0; 151169689Skan 152169689Skan while (true) 153169689Skan { 154169689Skan /* Don't worry about unreachable blocks. */ 155169689Skan if (EDGE_COUNT (bb->preds) > 0 || bb == ENTRY_BLOCK_PTR) 156169689Skan { 157169689Skan /* If block BB is not interesting to the caller, then none of the 158169689Skan callbacks that walk the statements in BB are going to be 159169689Skan executed. */ 160169689Skan is_interesting = walk_data->interesting_blocks == NULL 161169689Skan || TEST_BIT (walk_data->interesting_blocks, 162169689Skan bb->index); 163169689Skan 164169689Skan /* Callback to initialize the local data structure. */ 165169689Skan if (walk_data->initialize_block_local_data) 166169689Skan { 167169689Skan bool recycled; 168169689Skan 169169689Skan /* First get some local data, reusing any local data pointer we may 170169689Skan have saved. */ 171169689Skan if (VEC_length (void_p, walk_data->free_block_data) > 0) 172169689Skan { 173169689Skan bd = VEC_pop (void_p, walk_data->free_block_data); 174169689Skan recycled = 1; 175169689Skan } 176169689Skan else 177169689Skan { 178169689Skan bd = xcalloc (1, walk_data->block_local_data_size); 179169689Skan recycled = 0; 180169689Skan } 181169689Skan 182169689Skan /* Push the local data into the local data stack. */ 183169689Skan VEC_safe_push (void_p, heap, walk_data->block_data_stack, bd); 184169689Skan 185169689Skan /* Call the initializer. */ 186169689Skan walk_data->initialize_block_local_data (walk_data, bb, 187169689Skan recycled); 188169689Skan 189169689Skan } 190169689Skan 191169689Skan /* Callback for operations to execute before we have walked the 192169689Skan dominator children, but before we walk statements. */ 193169689Skan if (walk_data->before_dom_children_before_stmts) 194169689Skan (*walk_data->before_dom_children_before_stmts) (walk_data, bb); 195169689Skan 196169689Skan /* Statement walk before walking dominator children. */ 197169689Skan if (is_interesting && walk_data->before_dom_children_walk_stmts) 198169689Skan { 199169689Skan if (walk_data->walk_stmts_backward) 200169689Skan for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi)) 201169689Skan (*walk_data->before_dom_children_walk_stmts) (walk_data, bb, 202169689Skan bsi); 203169689Skan else 204169689Skan for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi)) 205169689Skan (*walk_data->before_dom_children_walk_stmts) (walk_data, bb, 206169689Skan bsi); 207169689Skan } 208169689Skan 209169689Skan /* Callback for operations to execute before we have walked the 210169689Skan dominator children, and after we walk statements. */ 211169689Skan if (walk_data->before_dom_children_after_stmts) 212169689Skan (*walk_data->before_dom_children_after_stmts) (walk_data, bb); 213169689Skan 214169689Skan /* Mark the current BB to be popped out of the recursion stack 215169689Skan once childs are processed. */ 216169689Skan worklist[sp++] = bb; 217169689Skan worklist[sp++] = NULL; 218169689Skan 219169689Skan for (dest = first_dom_son (walk_data->dom_direction, bb); 220169689Skan dest; dest = next_dom_son (walk_data->dom_direction, dest)) 221169689Skan worklist[sp++] = dest; 222169689Skan } 223169689Skan /* NULL is used to signalize pop operation in recursion stack. */ 224169689Skan while (sp > 0 && !worklist[sp - 1]) 225169689Skan { 226169689Skan --sp; 227169689Skan bb = worklist[--sp]; 228169689Skan is_interesting = walk_data->interesting_blocks == NULL 229169689Skan || TEST_BIT (walk_data->interesting_blocks, 230169689Skan bb->index); 231169689Skan /* Callback for operations to execute after we have walked the 232169689Skan dominator children, but before we walk statements. */ 233169689Skan if (walk_data->after_dom_children_before_stmts) 234169689Skan (*walk_data->after_dom_children_before_stmts) (walk_data, bb); 235169689Skan 236169689Skan /* Statement walk after walking dominator children. */ 237169689Skan if (is_interesting && walk_data->after_dom_children_walk_stmts) 238169689Skan { 239169689Skan if (walk_data->walk_stmts_backward) 240169689Skan for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi)) 241169689Skan (*walk_data->after_dom_children_walk_stmts) (walk_data, bb, 242169689Skan bsi); 243169689Skan else 244169689Skan for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi)) 245169689Skan (*walk_data->after_dom_children_walk_stmts) (walk_data, bb, 246169689Skan bsi); 247169689Skan } 248169689Skan 249169689Skan /* Callback for operations to execute after we have walked the 250169689Skan dominator children and after we have walked statements. */ 251169689Skan if (walk_data->after_dom_children_after_stmts) 252169689Skan (*walk_data->after_dom_children_after_stmts) (walk_data, bb); 253169689Skan 254169689Skan if (walk_data->initialize_block_local_data) 255169689Skan { 256169689Skan /* And finally pop the record off the block local data stack. */ 257169689Skan bd = VEC_pop (void_p, walk_data->block_data_stack); 258169689Skan /* And save the block data so that we can re-use it. */ 259169689Skan VEC_safe_push (void_p, heap, walk_data->free_block_data, bd); 260169689Skan } 261169689Skan } 262169689Skan if (sp) 263169689Skan bb = worklist[--sp]; 264169689Skan else 265169689Skan break; 266169689Skan } 267169689Skan free (worklist); 268169689Skan} 269169689Skan 270169689Skanvoid 271169689Skaninit_walk_dominator_tree (struct dom_walk_data *walk_data) 272169689Skan{ 273169689Skan walk_data->free_block_data = NULL; 274169689Skan walk_data->block_data_stack = NULL; 275169689Skan} 276169689Skan 277169689Skanvoid 278169689Skanfini_walk_dominator_tree (struct dom_walk_data *walk_data) 279169689Skan{ 280169689Skan if (walk_data->initialize_block_local_data) 281169689Skan { 282169689Skan while (VEC_length (void_p, walk_data->free_block_data) > 0) 283169689Skan free (VEC_pop (void_p, walk_data->free_block_data)); 284169689Skan } 285169689Skan 286169689Skan VEC_free (void_p, heap, walk_data->free_block_data); 287169689Skan VEC_free (void_p, heap, walk_data->block_data_stack); 288169689Skan} 289