gcc/cfgloop.h

   1 /* Natural loop functions
   2    Copyright (C) 1987, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
   3    Free Software Foundation, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 2, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING.  If not, write to the Free
  19 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
  20 02111-1307, USA.  */
  21
  22 /* Structure to hold decision about unrolling/peeling.  */
  23 enum lpt_dec
  24 {
  25   LPT_NONE,
  26   LPT_PEEL_COMPLETELY,
  27   LPT_PEEL_SIMPLE,
  28   LPT_UNROLL_CONSTANT,
  29   LPT_UNROLL_RUNTIME,
  30   LPT_UNROLL_STUPID
  31 };
  32
  33 struct lpt_decision
  34 {
  35   enum lpt_dec decision;
  36   unsigned times;
  37 };
  38
  39 /* Description of loop for simple loop unrolling.  */
  40 struct loop_desc
  41 {
  42   int postincr;         /* 1 if increment/decrement is done after loop exit condition.  */
  43   rtx stride;           /* Value added to VAR in each iteration.  */
  44   rtx var;              /* Loop control variable.  */
  45   enum machine_mode inner_mode;
  46                         /* The mode from that it is extended.  */
  47   enum rtx_code extend; /* With this extend.  */
  48   rtx var_alts;         /* List of definitions of its initial value.  */
  49   rtx lim;              /* Expression var is compared with.  */
  50   rtx lim_alts;         /* List of definitions of its initial value.  */
  51   bool const_iter;      /* True if it iterates constant number of times.  */
  52   unsigned HOST_WIDE_INT niter;
  53                         /* Number of iterations if it is constant.  */
  54   bool may_be_zero;     /* If we cannot determine that the first iteration will pass.  */
  55   enum rtx_code cond;   /* Exit condition.  */
  56   int neg;              /* Set to 1 if loop ends when condition is satisfied.  */
  57   edge out_edge;        /* The exit edge.  */
  58   edge in_edge;         /* And the other one.  */
  59   int n_branches;       /* Number of branches inside the loop.  */
  60 };
  61
  62 /* Structure to hold information for each natural loop.  */
  63 struct loop
  64 {
  65   /* Index into loops array.  */
  66   int num;
  67
  68   /* Basic block of loop header.  */
  69   basic_block header;
  70
  71   /* Basic block of loop latch.  */
  72   basic_block latch;
  73
  74   /* Basic block of loop preheader or NULL if it does not exist.  */
  75   basic_block pre_header;
  76
  77   /* For loop unrolling/peeling decision.  */
  78   struct lpt_decision lpt_decision;
  79
  80   /* Simple loop description.  */
  81   int simple;
  82   struct loop_desc desc;
  83   int has_desc;
  84
  85   /* Number of loop insns.  */
  86   unsigned ninsns;
  87
  88   /* Average number of executed insns per iteration.  */
  89   unsigned av_ninsns;
  90
  91   /* Array of edges along the preheader extended basic block trace.
  92      The source of the first edge is the root node of preheader
  93      extended basic block, if it exists.  */
  94   edge *pre_header_edges;
  95
  96   /* Number of edges along the pre_header extended basic block trace.  */
  97   int num_pre_header_edges;
  98
  99   /* The first block in the loop.  This is not necessarily the same as
 100      the loop header.  */
 101   basic_block first;
 102
 103   /* The last block in the loop.  This is not necessarily the same as
 104      the loop latch.  */
 105   basic_block last;
 106
 107   /* Bitmap of blocks contained within the loop.  */
 108   sbitmap nodes;
 109
 110   /* Number of blocks contained within the loop.  */
 111   unsigned num_nodes;
 112
 113   /* Array of edges that enter the loop.  */
 114   edge *entry_edges;
 115
 116   /* Number of edges that enter the loop.  */
 117   int num_entries;
 118
 119   /* Array of edges that exit the loop.  */
 120   edge *exit_edges;
 121
 122   /* Number of edges that exit the loop.  */
 123   int num_exits;
 124
 125   /* Bitmap of blocks that dominate all exits of the loop.  */
 126   sbitmap exits_doms;
 127
 128   /* The loop nesting depth.  */
 129   int depth;
 130
 131   /* Superloops of the loop.  */
 132   struct loop **pred;
 133
 134   /* The height of the loop (enclosed loop levels) within the loop
 135      hierarchy tree.  */
 136   int level;
 137
 138   /* The outer (parent) loop or NULL if outermost loop.  */
 139   struct loop *outer;
 140
 141   /* The first inner (child) loop or NULL if innermost loop.  */
 142   struct loop *inner;
 143
 144   /* Link to the next (sibling) loop.  */
 145   struct loop *next;
 146
 147   /* Loop that is copy of this loop.  */
 148   struct loop *copy;
 149
 150   /* Nonzero if the loop is invalid (e.g., contains setjmp.).  */
 151   int invalid;
 152
 153   /* Auxiliary info specific to a pass.  */
 154   void *aux;
 155
 156   /* The following are currently used by loop.c but they are likely to
 157      disappear as loop.c is converted to use the CFG.  */
 158
 159   /* Nonzero if the loop has a NOTE_INSN_LOOP_VTOP.  */
 160   rtx vtop;
 161
 162   /* Nonzero if the loop has a NOTE_INSN_LOOP_CONT.
 163      A continue statement will generate a branch to NEXT_INSN (cont).  */
 164   rtx cont;
 165
 166   /* The dominator of cont.  */
 167   rtx cont_dominator;
 168
 169   /* The NOTE_INSN_LOOP_BEG.  */
 170   rtx start;
 171
 172   /* The NOTE_INSN_LOOP_END.  */
 173   rtx end;
 174
 175   /* For a rotated loop that is entered near the bottom,
 176      this is the label at the top.  Otherwise it is zero.  */
 177   rtx top;
 178
 179   /* Place in the loop where control enters.  */
 180   rtx scan_start;
 181
 182   /* The position where to sink insns out of the loop.  */
 183   rtx sink;
 184
 185   /* List of all LABEL_REFs which refer to code labels outside the
 186      loop.  Used by routines that need to know all loop exits, such as
 187      final_biv_value and final_giv_value.
 188
 189      This does not include loop exits due to return instructions.
 190      This is because all bivs and givs are pseudos, and hence must be
 191      dead after a return, so the presence of a return does not affect
 192      any of the optimizations that use this info.  It is simpler to
 193      just not include return instructions on this list.  */
 194   rtx exit_labels;
 195
 196   /* The number of LABEL_REFs on exit_labels for this loop and all
 197      loops nested inside it.  */
 198   int exit_count;
 199 };
 200
 201 /* Flags for state of loop structure.  */
 202 enum
 203 {
 204   LOOPS_HAVE_PREHEADERS = 1,
 205   LOOPS_HAVE_SIMPLE_LATCHES = 2,
 206   LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS = 4
 207 };
 208
 209 /* Structure to hold CFG information about natural loops within a function.  */
 210 struct loops
 211 {
 212   /* Number of natural loops in the function.  */
 213   unsigned num;
 214
 215   /* Maximum nested loop level in the function.  */
 216   unsigned levels;
 217
 218   /* Array of natural loop descriptors (scanning this array in reverse order
 219      will find the inner loops before their enclosing outer loops).  */
 220   struct loop *array;
 221
 222   /* The above array is unused in new loop infrastructure and is kept only for
 223      purposes of the old loop optimizer.  Instead we store just pointers to
 224      loops here.  */
 225   struct loop **parray;
 226
 227   /* Pointer to root of loop hierarchy tree.  */
 228   struct loop *tree_root;
 229
 230   /* Information derived from the CFG.  */
 231   struct cfg
 232   {
 233     /* The ordering of the basic blocks in a depth first search.  */
 234     int *dfs_order;
 235
 236     /* The reverse completion ordering of the basic blocks found in a
 237        depth first search.  */
 238     int *rc_order;
 239   } cfg;
 240
 241   /* Headers shared by multiple loops that should be merged.  */
 242   sbitmap shared_headers;
 243
 244   /* State of loops.  */
 245   int state;
 246 };
 247
 248 /* Flags for loop discovery.  */
 249
 250 #define LOOP_TREE               1       /* Build loop hierarchy tree.  */
 251 #define LOOP_PRE_HEADER         2       /* Analyze loop preheader.  */
 252 #define LOOP_ENTRY_EDGES        4       /* Find entry edges.  */
 253 #define LOOP_EXIT_EDGES         8       /* Find exit edges.  */
 254 #define LOOP_EDGES              (LOOP_ENTRY_EDGES | LOOP_EXIT_EDGES)
 255 #define LOOP_ALL               15       /* All of the above  */
 256
 257 /* Loop recognition.  */
 258 extern int flow_loops_find (struct loops *, int flags);
 259 extern int flow_loops_update (struct loops *, int flags);
 260 extern void flow_loops_free (struct loops *);
 261 extern void flow_loops_dump (const struct loops *, FILE *,
 262                              void (*)(const struct loop *, FILE *, int), int);
 263 extern void flow_loop_dump (const struct loop *, FILE *,
 264                             void (*)(const struct loop *, FILE *, int), int);
 265 extern int flow_loop_scan (struct loop *, int);
 266 extern void flow_loop_free (struct loop *);
 267 void mark_irreducible_loops (struct loops *);
 268
 269 /* Loop data structure manipulation/querying.  */
 270 extern void flow_loop_tree_node_add (struct loop *, struct loop *);
 271 extern void flow_loop_tree_node_remove (struct loop *);
 272 extern bool flow_loop_outside_edge_p (const struct loop *, edge);
 273 extern bool flow_loop_nested_p  (const struct loop *, const struct loop *);
 274 extern bool flow_bb_inside_loop_p (const struct loop *, const basic_block);
 275 extern struct loop * find_common_loop (struct loop *, struct loop *);
 276 extern int num_loop_insns (struct loop *);
 277 extern int average_num_loop_insns (struct loop *);
 278
 279 /* Loops & cfg manipulation.  */
 280 extern basic_block *get_loop_body (const struct loop *);
 281 extern basic_block *get_loop_body_in_dom_order (const struct loop *);
 282 extern edge *get_loop_exit_edges (const struct loop *, unsigned *);
 283 extern unsigned num_loop_branches (const struct loop *);
 284
 285 extern edge loop_preheader_edge (const struct loop *);
 286 extern edge loop_latch_edge (const struct loop *);
 287
 288 extern void add_bb_to_loop (basic_block, struct loop *);
 289 extern void remove_bb_from_loops (basic_block);
 290
 291 extern void cancel_loop (struct loops *, struct loop *);
 292 extern void cancel_loop_tree (struct loops *, struct loop *);
 293
 294 extern basic_block loop_split_edge_with (edge, rtx);
 295 extern int fix_loop_placement (struct loop *);
 296
 297 enum
 298 {
 299   CP_SIMPLE_PREHEADERS = 1
 300 };
 301
 302 extern void create_preheaders (struct loops *, int);
 303 extern void force_single_succ_latches (struct loops *);
 304
 305 extern void verify_loop_structure (struct loops *);
 306
 307 /* Loop analysis.  */
 308 extern bool simple_loop_p (struct loop *, struct loop_desc *);
 309 extern rtx count_loop_iterations (struct loop_desc *, rtx, rtx);
 310 extern bool just_once_each_iteration_p (struct loop *, basic_block);
 311 extern unsigned expected_loop_iterations (const struct loop *);
 312
 313 /* Loop manipulation.  */
 314 extern bool can_duplicate_loop_p (struct loop *loop);
 315
 316 #define DLTHE_FLAG_UPDATE_FREQ  1       /* Update frequencies in
 317                                            duplicate_loop_to_header_edge.  */
 318
 319 extern int duplicate_loop_to_header_edge (struct loop *, edge, struct loops *,
 320                                           unsigned, sbitmap, edge, edge *,
 321                                           unsigned *, int);
 322 extern struct loop *loopify (struct loops *, edge, edge, basic_block);
 323 extern void unloop (struct loops *, struct loop *);
 324 extern bool remove_path (struct loops *, edge);
 325 extern edge split_loop_bb (basic_block, rtx);
 326
 327 /* Induction variable analysis.  */
 328
 329 /* The description of induction variable.  The things are a bit complicated
 330    due to need to handle subregs and extends.  The value of the object described
 331    by it can be obtained as follows (all computations are done in extend_mode):
 332
 333    Value in i-th iteration is
 334      delta + mult * extend_{extend_mode} (subreg_{mode} (base + i * step)).
 335
 336    If first_special is true, the value in the first iteration is
 337      delta + mult * base
 338
 339    If extend = NIL, first_special must be false, delta 0, mult 1 and value is
 340      subreg_{mode} (base + i * step)
 341
 342    The get_iv_value function can be used to obtain these expressions.
 343
 344    ??? Add a third mode field that would specify the mode in that inner
 345    computation is done, which would enable it to be different from the
 346    outer one?  */
 347
 348 struct rtx_iv
 349 {
 350   /* Its base and step (mode of base and step is supposed to be extend_mode,
 351      see the description above).  */
 352   rtx base, step;
 353
 354   /* The type of extend applied to it (SIGN_EXTEND, ZERO_EXTEND or NIL).  */
 355   enum rtx_code extend;
 356
 357   /* Operations applied in the extended mode.  */
 358   rtx delta, mult;
 359
 360   /* The mode it is extended to.  */
 361   enum machine_mode extend_mode;
 362
 363   /* The mode the variable iterates in.  */
 364   enum machine_mode mode;
 365
 366   /* Whether we have already filled the remaining fields.  */
 367   unsigned analysed : 1;
 368
 369   /* Whether the first iteration needs to be handled specially.  */
 370   unsigned first_special : 1;
 371 };
 372
 373 /* This should replace struct loop_desc.  We keep this just so that we are
 374    able to compare the results.  */
 375
 376 struct niter_desc
 377 {
 378   /* The edge out of the loop.  */
 379   edge out_edge;
 380
 381   /* The other edge leading from the condition.  */
 382   edge in_edge;
 383
 384   /* True if we are able to say anything about number of iterations of the
 385      loop.  */
 386   bool simple_p;
 387
 388   /* True if the loop iterates the constant number of times.  */
 389   bool const_iter;
 390
 391   /* Number of iterations if constant.  */
 392   unsigned HOST_WIDEST_INT niter;
 393
 394   /* Upper bound on the number of iterations.  */
 395   unsigned HOST_WIDEST_INT niter_max;
 396
 397   /* Assumptions under that the rest of the information is valid.  */
 398   rtx assumptions;
 399
 400   /* Assumptions under that the loop ends before reaching the latch,
 401      even if value of niter_expr says otherwise.  */
 402   rtx noloop_assumptions;
 403
 404   /* Condition under that the loop is infinite.  */
 405   rtx infinite;
 406
 407   /* Whether the comparison is signed.  */
 408   bool signed_p;
 409
 410   /* The mode in that niter_expr should be computed.  */
 411   enum machine_mode mode;
 412
 413   /* The number of iterations of the loop.  */
 414   rtx niter_expr;
 415 };
 416
 417 extern void iv_analysis_loop_init (struct loop *);
 418 extern rtx iv_get_reaching_def (rtx, rtx);
 419 extern bool iv_analyze (rtx, rtx, struct rtx_iv *);
 420 extern rtx get_iv_value (struct rtx_iv *, rtx);
 421 extern void find_simple_exit (struct loop *, struct niter_desc *);
 422 extern void iv_number_of_iterations (struct loop *, rtx, rtx,
 423                                      struct niter_desc *);
 424 extern void iv_analysis_done (void);
 425
 426 extern struct niter_desc *get_simple_loop_desc (struct loop *loop);
 427 extern void free_simple_loop_desc (struct loop *loop);
 428
 429 static inline struct niter_desc *
 430 simple_loop_desc (struct loop *loop)
 431 {
 432   return loop->aux;
 433 }
 434
 435 /* Loop optimizer initialization.  */
 436 extern struct loops *loop_optimizer_init (FILE *);
 437 extern void loop_optimizer_finalize (struct loops *, FILE *);
 438
 439 /* Optimization passes.  */
 440 extern void unswitch_loops (struct loops *);
 441
 442 enum
 443 {
 444   UAP_PEEL = 1,         /* Enables loop peeling.  */
 445   UAP_UNROLL = 2,       /* Enables peeling of loops if it seems profitable.  */
 446   UAP_UNROLL_ALL = 4    /* Enables peeling of all loops.  */
 447 };
 448
 449 extern void unroll_and_peel_loops (struct loops *, int);