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 83void 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 cleanup_tree_cfg_loop (); 108} 109 110/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its 111 basic blocks (for what it means see comments below). */ 112 113static tree 114tree_may_unswitch_on (basic_block bb, struct loop *loop) 115{ 116 tree stmt, def, cond, use; 117 basic_block def_bb; 118 ssa_op_iter iter; 119 120 /* BB must end in a simple conditional jump. */ 121 stmt = last_stmt (bb); 122 if (!stmt || TREE_CODE (stmt) != COND_EXPR) 123 return NULL_TREE; 124 125 /* Condition must be invariant. */ 126 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE) 127 { 128 def = SSA_NAME_DEF_STMT (use); 129 def_bb = bb_for_stmt (def); 130 if (def_bb 131 && flow_bb_inside_loop_p (loop, def_bb)) 132 return NULL_TREE; 133 } 134 135 cond = COND_EXPR_COND (stmt); 136 /* To keep the things simple, we do not directly remove the conditions, 137 but just replace tests with 0/1. Prevent the infinite loop where we 138 would unswitch again on such a condition. */ 139 if (integer_zerop (cond) || integer_nonzerop (cond)) 140 return NULL_TREE; 141 142 return cond; 143} 144 145/* Simplifies COND using checks in front of the entry of the LOOP. Just very 146 simplish (sufficient to prevent us from duplicating loop in unswitching 147 unnecessarily). */ 148 149static tree 150simplify_using_entry_checks (struct loop *loop, tree cond) 151{ 152 edge e = loop_preheader_edge (loop); 153 tree stmt; 154 155 while (1) 156 { 157 stmt = last_stmt (e->src); 158 if (stmt 159 && TREE_CODE (stmt) == COND_EXPR 160 && operand_equal_p (COND_EXPR_COND (stmt), cond, 0)) 161 return (e->flags & EDGE_TRUE_VALUE 162 ? boolean_true_node 163 : boolean_false_node); 164 165 if (!single_pred_p (e->src)) 166 return cond; 167 168 e = single_pred_edge (e->src); 169 if (e->src == ENTRY_BLOCK_PTR) 170 return cond; 171 } 172} 173 174/* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow 175 it to grow too much, it is too easy to create example on that the code would 176 grow exponentially. */ 177 178static bool 179tree_unswitch_single_loop (struct loops *loops, struct loop *loop, int num) 180{ 181 basic_block *bbs; 182 struct loop *nloop; 183 unsigned i; 184 tree cond = NULL_TREE, stmt; 185 bool changed = false; 186 187 /* Do not unswitch too much. */ 188 if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL)) 189 { 190 if (dump_file && (dump_flags & TDF_DETAILS)) 191 fprintf (dump_file, ";; Not unswitching anymore, hit max level\n"); 192 return false; 193 } 194 195 /* Only unswitch innermost loops. */ 196 if (loop->inner) 197 { 198 if (dump_file && (dump_flags & TDF_DETAILS)) 199 fprintf (dump_file, ";; Not unswitching, not innermost loop\n"); 200 return false; 201 } 202 203 /* The loop should not be too large, to limit code growth. */ 204 if (tree_num_loop_insns (loop) 205 > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS)) 206 { 207 if (dump_file && (dump_flags & TDF_DETAILS)) 208 fprintf (dump_file, ";; Not unswitching, loop too big\n"); 209 return false; 210 } 211 212 i = 0; 213 bbs = get_loop_body (loop); 214 215 while (1) 216 { 217 /* Find a bb to unswitch on. */ 218 for (; i < loop->num_nodes; i++) 219 if ((cond = tree_may_unswitch_on (bbs[i], loop))) 220 break; 221 222 if (i == loop->num_nodes) 223 { 224 free (bbs); 225 return changed; 226 } 227 228 cond = simplify_using_entry_checks (loop, cond); 229 stmt = last_stmt (bbs[i]); 230 if (integer_nonzerop (cond)) 231 { 232 /* Remove false path. */ 233 COND_EXPR_COND (stmt) = boolean_true_node; 234 changed = true; 235 } 236 else if (integer_zerop (cond)) 237 { 238 /* Remove true path. */ 239 COND_EXPR_COND (stmt) = boolean_false_node; 240 changed = true; 241 } 242 else 243 break; 244 245 update_stmt (stmt); 246 i++; 247 } 248 249 if (dump_file && (dump_flags & TDF_DETAILS)) 250 fprintf (dump_file, ";; Unswitching loop\n"); 251 252 initialize_original_copy_tables (); 253 /* Unswitch the loop on this condition. */ 254 nloop = tree_unswitch_loop (loops, loop, bbs[i], cond); 255 if (!nloop) 256 { 257 free_original_copy_tables (); 258 return changed; 259 } 260 261 /* Update the SSA form after unswitching. */ 262 update_ssa (TODO_update_ssa); 263 free_original_copy_tables (); 264 265 /* Invoke itself on modified loops. */ 266 tree_unswitch_single_loop (loops, nloop, num + 1); 267 tree_unswitch_single_loop (loops, loop, num + 1); 268 return true; 269} 270 271/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support 272 unswitching of innermost loops. COND is the condition determining which 273 loop is entered -- the new loop is entered if COND is true. Returns NULL 274 if impossible, new loop otherwise. */ 275 276static struct loop * 277tree_unswitch_loop (struct loops *loops, struct loop *loop, 278 basic_block unswitch_on, tree cond) 279{ 280 basic_block condition_bb; 281 282 /* Some sanity checking. */ 283 gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on)); 284 gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2); 285 gcc_assert (loop->inner == NULL); 286 287 return loop_version (loops, loop, unshare_expr (cond), 288 &condition_bb, false); 289} 290