1/* Loop unswitching. 2 Copyright (C) 2004, 2005 Free Software Foundation, Inc. 3 4This file is part of GCC. 5 6GCC is free software; you can redistribute it and/or modify it 7under the terms of the GNU General Public License as published by the 8Free Software Foundation; either version 2, or (at your option) any 9later version. 10 11GCC is distributed in the hope that it will be useful, but WITHOUT 12ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14for more details. 15 16You should have received a copy of the GNU General Public License 17along with GCC; see the file COPYING. If not, write to the Free 18Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 1902110-1301, USA. */ 20 21#include "config.h" 22#include "system.h" 23#include "coretypes.h" 24#include "tm.h" 25#include "tree.h" 26#include "rtl.h" 27#include "tm_p.h" 28#include "hard-reg-set.h" 29#include "basic-block.h" 30#include "output.h" 31#include "diagnostic.h" 32#include "tree-flow.h" 33#include "tree-dump.h" 34#include "timevar.h" 35#include "cfgloop.h" 36#include "domwalk.h" 37#include "params.h" 38#include "tree-pass.h" 39 40/* This file implements the loop unswitching, i.e. transformation of loops like 41 42 while (A) 43 { 44 if (inv) 45 B; 46 47 X; 48 49 if (!inv) 50 C; 51 } 52 53 where inv is the loop invariant, into 54 55 if (inv) 56 { 57 while (A) 58 { 59 B; 60 X; 61 } 62 } 63 else 64 { 65 while (A) 66 { 67 X; 68 C; 69 } 70 } 71 72 Inv is considered invariant iff the values it compares are both invariant; 73 tree-ssa-loop-im.c ensures that all the suitable conditions are in this 74 shape. */ 75 76static struct loop *tree_unswitch_loop (struct loops *, struct loop *, basic_block, 77 tree); 78static bool tree_unswitch_single_loop (struct loops *, struct loop *, int); 79static tree tree_may_unswitch_on (basic_block, struct loop *); 80 81/* Main entry point. Perform loop unswitching on all suitable LOOPS. */ 82 83unsigned int 84tree_ssa_unswitch_loops (struct loops *loops) 85{ 86 int i, num; 87 struct loop *loop; 88 bool changed = false; 89 90 /* Go through inner loops (only original ones). */ 91 num = loops->num; 92 93 for (i = 1; i < num; i++) 94 { 95 /* Removed loop? */ 96 loop = loops->parray[i]; 97 if (!loop) 98 continue; 99 100 if (loop->inner) 101 continue; 102 103 changed |= tree_unswitch_single_loop (loops, loop, 0); 104 } 105 106 if (changed) 107 return TODO_cleanup_cfg; 108 return 0; 109} 110 111/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its 112 basic blocks (for what it means see comments below). */ 113 114static tree 115tree_may_unswitch_on (basic_block bb, struct loop *loop) 116{ 117 tree stmt, def, cond, use; 118 basic_block def_bb; 119 ssa_op_iter iter; 120 121 /* BB must end in a simple conditional jump. */ 122 stmt = last_stmt (bb); 123 if (!stmt || TREE_CODE (stmt) != COND_EXPR) 124 return NULL_TREE; 125 126 /* Condition must be invariant. */ 127 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE) 128 { 129 def = SSA_NAME_DEF_STMT (use); 130 def_bb = bb_for_stmt (def); 131 if (def_bb 132 && flow_bb_inside_loop_p (loop, def_bb)) 133 return NULL_TREE; 134 } 135 136 cond = COND_EXPR_COND (stmt); 137 /* To keep the things simple, we do not directly remove the conditions, 138 but just replace tests with 0/1. Prevent the infinite loop where we 139 would unswitch again on such a condition. */ 140 if (integer_zerop (cond) || integer_nonzerop (cond)) 141 return NULL_TREE; 142 143 return cond; 144} 145 146/* Simplifies COND using checks in front of the entry of the LOOP. Just very 147 simplish (sufficient to prevent us from duplicating loop in unswitching 148 unnecessarily). */ 149 150static tree 151simplify_using_entry_checks (struct loop *loop, tree cond) 152{ 153 edge e = loop_preheader_edge (loop); 154 tree stmt; 155 156 while (1) 157 { 158 stmt = last_stmt (e->src); 159 if (stmt 160 && TREE_CODE (stmt) == COND_EXPR 161 && operand_equal_p (COND_EXPR_COND (stmt), cond, 0)) 162 return (e->flags & EDGE_TRUE_VALUE 163 ? boolean_true_node 164 : boolean_false_node); 165 166 if (!single_pred_p (e->src)) 167 return cond; 168 169 e = single_pred_edge (e->src); 170 if (e->src == ENTRY_BLOCK_PTR) 171 return cond; 172 } 173} 174 175/* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow 176 it to grow too much, it is too easy to create example on that the code would 177 grow exponentially. */ 178 179static bool 180tree_unswitch_single_loop (struct loops *loops, struct loop *loop, int num) 181{ 182 basic_block *bbs; 183 struct loop *nloop; 184 unsigned i; 185 tree cond = NULL_TREE, stmt; 186 bool changed = false; 187 188 /* Do not unswitch too much. */ 189 if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL)) 190 { 191 if (dump_file && (dump_flags & TDF_DETAILS)) 192 fprintf (dump_file, ";; Not unswitching anymore, hit max level\n"); 193 return false; 194 } 195 196 /* Only unswitch innermost loops. */ 197 if (loop->inner) 198 { 199 if (dump_file && (dump_flags & TDF_DETAILS)) 200 fprintf (dump_file, ";; Not unswitching, not innermost loop\n"); 201 return false; 202 } 203 204 /* The loop should not be too large, to limit code growth. */ 205 if (tree_num_loop_insns (loop) 206 > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS)) 207 { 208 if (dump_file && (dump_flags & TDF_DETAILS)) 209 fprintf (dump_file, ";; Not unswitching, loop too big\n"); 210 return false; 211 } 212 213 i = 0; 214 bbs = get_loop_body (loop); 215 216 while (1) 217 { 218 /* Find a bb to unswitch on. */ 219 for (; i < loop->num_nodes; i++) 220 if ((cond = tree_may_unswitch_on (bbs[i], loop))) 221 break; 222 223 if (i == loop->num_nodes) 224 { 225 free (bbs); 226 return changed; 227 } 228 229 cond = simplify_using_entry_checks (loop, cond); 230 stmt = last_stmt (bbs[i]); 231 if (integer_nonzerop (cond)) 232 { 233 /* Remove false path. */ 234 COND_EXPR_COND (stmt) = boolean_true_node; 235 changed = true; 236 } 237 else if (integer_zerop (cond)) 238 { 239 /* Remove true path. */ 240 COND_EXPR_COND (stmt) = boolean_false_node; 241 changed = true; 242 } 243 else 244 break; 245 246 update_stmt (stmt); 247 i++; 248 } 249 250 if (dump_file && (dump_flags & TDF_DETAILS)) 251 fprintf (dump_file, ";; Unswitching loop\n"); 252 253 initialize_original_copy_tables (); 254 /* Unswitch the loop on this condition. */ 255 nloop = tree_unswitch_loop (loops, loop, bbs[i], cond); 256 if (!nloop) 257 { 258 free_original_copy_tables (); 259 free (bbs); 260 return changed; 261 } 262 263 /* Update the SSA form after unswitching. */ 264 update_ssa (TODO_update_ssa); 265 free_original_copy_tables (); 266 267 /* Invoke itself on modified loops. */ 268 tree_unswitch_single_loop (loops, nloop, num + 1); 269 tree_unswitch_single_loop (loops, loop, num + 1); 270 free (bbs); 271 return true; 272} 273 274/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support 275 unswitching of innermost loops. COND is the condition determining which 276 loop is entered -- the new loop is entered if COND is true. Returns NULL 277 if impossible, new loop otherwise. */ 278 279static struct loop * 280tree_unswitch_loop (struct loops *loops, struct loop *loop, 281 basic_block unswitch_on, tree cond) 282{ 283 basic_block condition_bb; 284 285 /* Some sanity checking. */ 286 gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on)); 287 gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2); 288 gcc_assert (loop->inner == NULL); 289 290 return loop_version (loops, loop, unshare_expr (cond), 291 &condition_bb, false); 292} 293