gcc/loop.h

   1 /* Loop optimization definitions for GNU C-Compiler
   2    Copyright (C) 1991, 1995, 1998, 1999, 2000, 2001, 2002
   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 #include "bitmap.h"
  23 #include "sbitmap.h"
  24 #include "hard-reg-set.h"
  25 #include "basic-block.h"
  26
  27 /* Flags passed to loop_optimize.  */
  28 #define LOOP_UNROLL 1
  29 #define LOOP_BCT 2
  30 #define LOOP_PREFETCH 4
  31 #define LOOP_AUTO_UNROLL 8
  32
  33 /* Get the loop info pointer of a loop.  */
  34 #define LOOP_INFO(LOOP) ((struct loop_info *) (LOOP)->aux)
  35
  36 /* Get a pointer to the loop movables structure.  */
  37 #define LOOP_MOVABLES(LOOP) (&LOOP_INFO (LOOP)->movables)
  38
  39 /* Get a pointer to the loop registers structure.  */
  40 #define LOOP_REGS(LOOP) (&LOOP_INFO (LOOP)->regs)
  41
  42 /* Get a pointer to the loop induction variables structure.  */
  43 #define LOOP_IVS(LOOP) (&LOOP_INFO (LOOP)->ivs)
  44
  45 /* Get the luid of an insn.  Catch the error of trying to reference the LUID
  46    of an insn added during loop, since these don't have LUIDs.  */
  47
  48 #define INSN_LUID(INSN)                 \
  49   (INSN_UID (INSN) < max_uid_for_loop ? uid_luid[INSN_UID (INSN)] \
  50    : (abort (), -1))
  51
  52 #define REGNO_FIRST_LUID(REGNO) uid_luid[REGNO_FIRST_UID (REGNO)]
  53 #define REGNO_LAST_LUID(REGNO) uid_luid[REGNO_LAST_UID (REGNO)]
  54
  55
  56 /* A "basic induction variable" or biv is a pseudo reg that is set
  57    (within this loop) only by incrementing or decrementing it.  */
  58 /* A "general induction variable" or giv is a pseudo reg whose
  59    value is a linear function of a biv.  */
  60
  61 /* Bivs are recognized by `basic_induction_var';
  62    Givs by `general_induction_var'.  */
  63
  64 /* An enum for the two different types of givs, those that are used
  65    as memory addresses and those that are calculated into registers.  */
  66 enum g_types
  67 {
  68   DEST_ADDR,
  69   DEST_REG
  70 };
  71
  72
  73 /* A `struct induction' is created for every instruction that sets
  74    an induction variable (either a biv or a giv).  */
  75
  76 struct induction
  77 {
  78   rtx insn;                     /* The insn that sets a biv or giv */
  79   rtx new_reg;                  /* New register, containing strength reduced
  80                                    version of this giv.  */
  81   rtx src_reg;                  /* Biv from which this giv is computed.
  82                                    (If this is a biv, then this is the biv.) */
  83   enum g_types giv_type;        /* Indicate whether DEST_ADDR or DEST_REG */
  84   rtx dest_reg;                 /* Destination register for insn: this is the
  85                                    register which was the biv or giv.
  86                                    For a biv, this equals src_reg.
  87                                    For a DEST_ADDR type giv, this is 0.  */
  88   rtx *location;                /* Place in the insn where this giv occurs.
  89                                    If GIV_TYPE is DEST_REG, this is 0.  */
  90                                 /* For a biv, this is the place where add_val
  91                                    was found.  */
  92   enum machine_mode mode;       /* The mode of this biv or giv */
  93   rtx mem;                      /* For DEST_ADDR, the memory object.  */
  94   rtx mult_val;                 /* Multiplicative factor for src_reg.  */
  95   rtx add_val;                  /* Additive constant for that product.  */
  96   int benefit;                  /* Gain from eliminating this insn.  */
  97   rtx final_value;              /* If the giv is used outside the loop, and its
  98                                    final value could be calculated, it is put
  99                                    here, and the giv is made replaceable.  Set
 100                                    the giv to this value before the loop.  */
 101   unsigned combined_with;       /* The number of givs this giv has been
 102                                    combined with.  If nonzero, this giv
 103                                    cannot combine with any other giv.  */
 104   unsigned replaceable : 1;     /* 1 if we can substitute the strength-reduced
 105                                    variable for the original variable.
 106                                    0 means they must be kept separate and the
 107                                    new one must be copied into the old pseudo
 108                                    reg each time the old one is set.  */
 109   unsigned not_replaceable : 1; /* Used to prevent duplicating work.  This is
 110                                    1 if we know that the giv definitely can
 111                                    not be made replaceable, in which case we
 112                                    don't bother checking the variable again
 113                                    even if further info is available.
 114                                    Both this and the above can be zero.  */
 115   unsigned ignore : 1;          /* 1 prohibits further processing of giv */
 116   unsigned always_computable : 1;/* 1 if this value is computable every
 117                                     iteration.  */
 118   unsigned always_executed : 1; /* 1 if this set occurs each iteration.  */
 119   unsigned maybe_multiple : 1;  /* Only used for a biv and  1 if this biv
 120                                    update may be done multiple times per
 121                                    iteration.  */
 122   unsigned cant_derive : 1;     /* For giv's, 1 if this giv cannot derive
 123                                    another giv.  This occurs in many cases
 124                                    where a giv's lifetime spans an update to
 125                                    a biv.  */
 126   unsigned maybe_dead : 1;      /* 1 if this giv might be dead.  In that case,
 127                                    we won't use it to eliminate a biv, it
 128                                    would probably lose.  */
 129   unsigned auto_inc_opt : 1;    /* 1 if this giv had its increment output next
 130                                    to it to try to form an auto-inc address.  */
 131   unsigned unrolled : 1;        /* 1 if new register has been allocated and
 132                                    initialized in unrolled loop.  */
 133   unsigned shared : 1;
 134   unsigned no_const_addval : 1; /* 1 if add_val does not contain a const.  */
 135   int lifetime;                 /* Length of life of this giv */
 136   rtx derive_adjustment;        /* If nonzero, is an adjustment to be
 137                                    subtracted from add_val when this giv
 138                                    derives another.  This occurs when the
 139                                    giv spans a biv update by incrementation.  */
 140   rtx ext_dependent;            /* If nonzero, is a sign or zero extension
 141                                    if a biv on which this giv is dependent.  */
 142   struct induction *next_iv;    /* For givs, links together all givs that are
 143                                    based on the same biv.  For bivs, links
 144                                    together all biv entries that refer to the
 145                                    same biv register.  */
 146   struct induction *same;       /* If this giv has been combined with another
 147                                    giv, this points to the base giv.  The base
 148                                    giv will have COMBINED_WITH nonzero.  */
 149   HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
 150                                    is split, and a constant is eliminated from
 151                                    the address, the -constant is stored here
 152                                    for later use.  */
 153   struct induction *same_insn;  /* If there are multiple identical givs in
 154                                    the same insn, then all but one have this
 155                                    field set, and they all point to the giv
 156                                    that doesn't have this field set.  */
 157   rtx last_use;                 /* For a giv made from a biv increment, this is
 158                                    a substitute for the lifetime information.  */
 159 };
 160
 161
 162 /* A `struct iv_class' is created for each biv.  */
 163
 164 struct iv_class
 165 {
 166   unsigned int regno;           /* Pseudo reg which is the biv.  */
 167   int biv_count;                /* Number of insns setting this reg.  */
 168   struct induction *biv;        /* List of all insns that set this reg.  */
 169   int giv_count;                /* Number of DEST_REG givs computed from this
 170                                    biv.  The resulting count is only used in
 171                                    check_dbra_loop.  */
 172   struct induction *giv;        /* List of all insns that compute a giv
 173                                    from this reg.  */
 174   int total_benefit;            /* Sum of BENEFITs of all those givs.  */
 175   rtx initial_value;            /* Value of reg at loop start.  */
 176   rtx initial_test;             /* Test performed on BIV before loop.  */
 177   rtx final_value;              /* Value of reg at loop end, if known.  */
 178   struct iv_class *next;        /* Links all class structures together.  */
 179   rtx init_insn;                /* insn which initializes biv, 0 if none.  */
 180   rtx init_set;                 /* SET of INIT_INSN, if any.  */
 181   unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
 182   unsigned eliminable : 1;      /* 1 if plausible candidate for
 183                                    elimination.  */
 184   unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for
 185                                    this.  */
 186   unsigned reversed : 1;        /* 1 if we reversed the loop that this
 187                                    biv controls.  */
 188   unsigned all_reduced : 1;     /* 1 if all givs using this biv have
 189                                    been reduced.  */
 190 };
 191
 192
 193 /* Definitions used by the basic induction variable discovery code.  */
 194 enum iv_mode
 195 {
 196   UNKNOWN_INDUCT,
 197   BASIC_INDUCT,
 198   NOT_BASIC_INDUCT,
 199   GENERAL_INDUCT
 200 };
 201
 202
 203 /* A `struct iv' is created for every register.  */
 204
 205 struct iv
 206 {
 207   enum iv_mode type;
 208   union
 209   {
 210     struct iv_class *class;
 211     struct induction *info;
 212   } iv;
 213 };
 214
 215
 216 #define REG_IV_TYPE(ivs, n) ivs->regs[n].type
 217 #define REG_IV_INFO(ivs, n) ivs->regs[n].iv.info
 218 #define REG_IV_CLASS(ivs, n) ivs->regs[n].iv.class
 219
 220
 221 struct loop_ivs
 222 {
 223   /* Indexed by register number, contains pointer to `struct
 224      iv' if register is an induction variable.  */
 225   struct iv *regs;
 226
 227   /* Size of regs array.  */
 228   unsigned int n_regs;
 229
 230   /* The head of a list which links together (via the next field)
 231      every iv class for the current loop.  */
 232   struct iv_class *list;
 233 };
 234
 235
 236 typedef struct loop_mem_info
 237 {
 238   rtx mem;      /* The MEM itself.  */
 239   rtx reg;      /* Corresponding pseudo, if any.  */
 240   int optimize; /* Nonzero if we can optimize access to this MEM.  */
 241 } loop_mem_info;
 242
 243
 244
 245 struct loop_reg
 246 {
 247   /* Number of times the reg is set during the loop being scanned.
 248      During code motion, a negative value indicates a reg that has
 249      been made a candidate; in particular -2 means that it is an
 250      candidate that we know is equal to a constant and -1 means that
 251      it is a candidate not known equal to a constant.  After code
 252      motion, regs moved have 0 (which is accurate now) while the
 253      failed candidates have the original number of times set.
 254
 255      Therefore, at all times, == 0 indicates an invariant register;
 256      < 0 a conditionally invariant one.  */
 257   int set_in_loop;
 258
 259   /* Original value of set_in_loop; same except that this value
 260      is not set negative for a reg whose sets have been made candidates
 261      and not set to 0 for a reg that is moved.  */
 262   int n_times_set;
 263
 264   /* Contains the insn in which a register was used if it was used
 265      exactly once; contains const0_rtx if it was used more than once.  */
 266   rtx single_usage;
 267
 268   /* Nonzero indicates that the register cannot be moved or strength
 269      reduced.  */
 270   char may_not_optimize;
 271
 272   /* Nonzero means reg N has already been moved out of one loop.
 273      This reduces the desire to move it out of another.  */
 274   char moved_once;
 275 };
 276
 277
 278 struct loop_regs
 279 {
 280   int num;                      /* Number of regs used in table.  */
 281   int size;                     /* Size of table.  */
 282   struct loop_reg *array;       /* Register usage info. array.  */
 283   int multiple_uses;            /* Nonzero if a reg has multiple uses.  */
 284 };
 285
 286
 287
 288 struct loop_movables
 289 {
 290   /* Head of movable chain.  */
 291   struct movable *head;
 292   /* Last movable in chain.  */
 293   struct movable *last;
 294 };
 295
 296
 297 /* Information pertaining to a loop.  */
 298
 299 struct loop_info
 300 {
 301   /* Nonzero if there is a subroutine call in the current loop.  */
 302   int has_call;
 303   /* Nonzero if there is a libcall in the current loop.  */
 304   int has_libcall;
 305   /* Nonzero if there is a non constant call in the current loop.  */
 306   int has_nonconst_call;
 307   /* Nonzero if there is a prefetch instruction in the current loop.  */
 308   int has_prefetch;
 309   /* Nonzero if there is a volatile memory reference in the current
 310      loop.  */
 311   int has_volatile;
 312   /* Nonzero if there is a tablejump in the current loop.  */
 313   int has_tablejump;
 314   /* Nonzero if there are ways to leave the loop other than falling
 315      off the end.  */
 316   int has_multiple_exit_targets;
 317   /* Nonzero if there is an indirect jump in the current function.  */
 318   int has_indirect_jump;
 319   /* Whether loop unrolling has emitted copies of the loop body so
 320      that the main loop needs no exit tests.  */
 321   int preconditioned;
 322   /* Register or constant initial loop value.  */
 323   rtx initial_value;
 324   /* Register or constant value used for comparison test.  */
 325   rtx comparison_value;
 326   /* Register or constant approximate final value.  */
 327   rtx final_value;
 328   /* Register or constant initial loop value with term common to
 329      final_value removed.  */
 330   rtx initial_equiv_value;
 331   /* Register or constant final loop value with term common to
 332      initial_value removed.  */
 333   rtx final_equiv_value;
 334   /* Register corresponding to iteration variable.  */
 335   rtx iteration_var;
 336   /* Constant loop increment.  */
 337   rtx increment;
 338   enum rtx_code comparison_code;
 339   /* Holds the number of loop iterations.  It is zero if the number
 340      could not be calculated.  Must be unsigned since the number of
 341      iterations can be as high as 2^wordsize - 1.  For loops with a
 342      wider iterator, this number will be zero if the number of loop
 343      iterations is too large for an unsigned integer to hold.  */
 344   unsigned HOST_WIDE_INT n_iterations;
 345   /* The number of times the loop body was unrolled.  */
 346   unsigned int unroll_number;
 347   int used_count_register;
 348   /* The loop iterator induction variable.  */
 349   struct iv_class *iv;
 350   /* List of MEMs that are stored in this loop.  */
 351   rtx store_mems;
 352   /* Array of MEMs that are used (read or written) in this loop, but
 353      cannot be aliased by anything in this loop, except perhaps
 354      themselves.  In other words, if mems[i] is altered during
 355      the loop, it is altered by an expression that is rtx_equal_p to
 356      it.  */
 357   loop_mem_info *mems;
 358   /* The index of the next available slot in MEMS.  */
 359   int mems_idx;
 360   /* The number of elements allocated in MEMS.  */
 361   int mems_allocated;
 362   /* Nonzero if we don't know what MEMs were changed in the current
 363      loop.  This happens if the loop contains a call (in which case
 364      `has_call' will also be set) or if we store into more than
 365      NUM_STORES MEMs.  */
 366   int unknown_address_altered;
 367   /* The above doesn't count any readonly memory locations that are
 368      stored.  This does.  */
 369   int unknown_constant_address_altered;
 370   /* Count of memory write instructions discovered in the loop.  */
 371   int num_mem_sets;
 372   /* The insn where the first of these was found.  */
 373   rtx first_loop_store_insn;
 374   /* The chain of movable insns in loop.  */
 375   struct loop_movables movables;
 376   /* The registers used the in loop.  */
 377   struct loop_regs regs;
 378   /* The induction variable information in loop.  */
 379   struct loop_ivs ivs;
 380   /* Nonzero if call is in pre_header extended basic block.  */
 381   int pre_header_has_call;
 382 };
 383
 384
 385 /* Variables declared in loop.c, but also needed in unroll.c.  */
 386
 387 extern int *uid_luid;
 388 extern int max_uid_for_loop;
 389 extern unsigned int max_reg_before_loop;
 390 extern struct loop **uid_loop;
 391 extern FILE *loop_dump_stream;
 392
 393
 394 /* Forward declarations for non-static functions declared in loop.c and
 395    unroll.c.  */
 396 int loop_invariant_p PARAMS ((const struct loop *, rtx));
 397 rtx get_condition_for_loop PARAMS ((const struct loop *, rtx));
 398 void loop_iv_add_mult_hoist PARAMS ((const struct loop *, rtx, rtx, rtx, rtx));
 399 void loop_iv_add_mult_sink PARAMS ((const struct loop *, rtx, rtx, rtx, rtx));
 400 void loop_iv_add_mult_emit_before PARAMS ((const struct loop *, rtx,
 401                                            rtx, rtx, rtx,
 402                                            basic_block, rtx));
 403 rtx express_from PARAMS ((struct induction *, struct induction *));
 404 rtx extend_value_for_giv PARAMS ((struct induction *, rtx));
 405
 406 void unroll_loop PARAMS ((struct loop *, int, int));
 407 rtx biv_total_increment PARAMS ((const struct iv_class *));
 408 unsigned HOST_WIDE_INT loop_iterations PARAMS ((struct loop *));
 409 int precondition_loop_p PARAMS ((const struct loop *,
 410                                  rtx *, rtx *, rtx *,
 411                                  enum machine_mode *mode));
 412 rtx final_biv_value PARAMS ((const struct loop *, struct iv_class *));
 413 rtx final_giv_value PARAMS ((const struct loop *, struct induction *));
 414 void emit_unrolled_add PARAMS ((rtx, rtx, rtx));
 415 int back_branch_in_range_p PARAMS ((const struct loop *, rtx));
 416
 417 int loop_insn_first_p PARAMS ((rtx, rtx));
 418 typedef rtx (*loop_insn_callback) PARAMS ((struct loop *, rtx, int, int));
 419 void for_each_insn_in_loop PARAMS ((struct loop *, loop_insn_callback));
 420 rtx loop_insn_emit_before PARAMS((const struct loop *, basic_block,
 421                                   rtx, rtx));
 422 rtx loop_insn_sink PARAMS((const struct loop *, rtx));
 423 rtx loop_insn_hoist PARAMS((const struct loop *, rtx));
 424
 425 /* Forward declarations for non-static functions declared in doloop.c.  */
 426 int doloop_optimize PARAMS ((const struct loop *));