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)                 \
  53   (REGNO_FIRST_UID (REGNO) < max_uid_for_loop   \
  54         ? uid_luid[REGNO_FIRST_UID (REGNO)]     \
  55         : 0)
  56 #define REGNO_LAST_LUID(REGNO)                  \
  57   (REGNO_LAST_UID (REGNO) < max_uid_for_loop    \
  58         ? uid_luid[REGNO_LAST_UID (REGNO)]      \
  59         : INT_MAX)
  60
  61 /* A "basic induction variable" or biv is a pseudo reg that is set
  62    (within this loop) only by incrementing or decrementing it.  */
  63 /* A "general induction variable" or giv is a pseudo reg whose
  64    value is a linear function of a biv.  */
  65
  66 /* Bivs are recognized by `basic_induction_var';
  67    Givs by `general_induction_var'.  */
  68
  69 /* An enum for the two different types of givs, those that are used
  70    as memory addresses and those that are calculated into registers.  */
  71 enum g_types
  72 {
  73   DEST_ADDR,
  74   DEST_REG
  75 };
  76
  77
  78 /* A `struct induction' is created for every instruction that sets
  79    an induction variable (either a biv or a giv).  */
  80
  81 struct induction
  82 {
  83   rtx insn;                     /* The insn that sets a biv or giv */
  84   rtx new_reg;                  /* New register, containing strength reduced
  85                                    version of this giv.  */
  86   rtx src_reg;                  /* Biv from which this giv is computed.
  87                                    (If this is a biv, then this is the biv.) */
  88   enum g_types giv_type;        /* Indicate whether DEST_ADDR or DEST_REG */
  89   rtx dest_reg;                 /* Destination register for insn: this is the
  90                                    register which was the biv or giv.
  91                                    For a biv, this equals src_reg.
  92                                    For a DEST_ADDR type giv, this is 0.  */
  93   rtx *location;                /* Place in the insn where this giv occurs.
  94                                    If GIV_TYPE is DEST_REG, this is 0.  */
  95                                 /* For a biv, this is the place where add_val
  96                                    was found.  */
  97   enum machine_mode mode;       /* The mode of this biv or giv */
  98   rtx mem;                      /* For DEST_ADDR, the memory object.  */
  99   rtx mult_val;                 /* Multiplicative factor for src_reg.  */
 100   rtx add_val;                  /* Additive constant for that product.  */
 101   int benefit;                  /* Gain from eliminating this insn.  */
 102   rtx final_value;              /* If the giv is used outside the loop, and its
 103                                    final value could be calculated, it is put
 104                                    here, and the giv is made replaceable.  Set
 105                                    the giv to this value before the loop.  */
 106   unsigned combined_with;       /* The number of givs this giv has been
 107                                    combined with.  If nonzero, this giv
 108                                    cannot combine with any other giv.  */
 109   unsigned replaceable : 1;     /* 1 if we can substitute the strength-reduced
 110                                    variable for the original variable.
 111                                    0 means they must be kept separate and the
 112                                    new one must be copied into the old pseudo
 113                                    reg each time the old one is set.  */
 114   unsigned not_replaceable : 1; /* Used to prevent duplicating work.  This is
 115                                    1 if we know that the giv definitely can
 116                                    not be made replaceable, in which case we
 117                                    don't bother checking the variable again
 118                                    even if further info is available.
 119                                    Both this and the above can be zero.  */
 120   unsigned ignore : 1;          /* 1 prohibits further processing of giv */
 121   unsigned always_computable : 1;/* 1 if this value is computable every
 122                                     iteration.  */
 123   unsigned always_executed : 1; /* 1 if this set occurs each iteration.  */
 124   unsigned maybe_multiple : 1;  /* Only used for a biv and  1 if this biv
 125                                    update may be done multiple times per
 126                                    iteration.  */
 127   unsigned cant_derive : 1;     /* For giv's, 1 if this giv cannot derive
 128                                    another giv.  This occurs in many cases
 129                                    where a giv's lifetime spans an update to
 130                                    a biv.  */
 131   unsigned maybe_dead : 1;      /* 1 if this giv might be dead.  In that case,
 132                                    we won't use it to eliminate a biv, it
 133                                    would probably lose.  */
 134   unsigned auto_inc_opt : 1;    /* 1 if this giv had its increment output next
 135                                    to it to try to form an auto-inc address.  */
 136   unsigned unrolled : 1;        /* 1 if new register has been allocated and
 137                                    initialized in unrolled loop.  */
 138   unsigned shared : 1;
 139   unsigned no_const_addval : 1; /* 1 if add_val does not contain a const.  */
 140   int lifetime;                 /* Length of life of this giv */
 141   rtx derive_adjustment;        /* If nonzero, is an adjustment to be
 142                                    subtracted from add_val when this giv
 143                                    derives another.  This occurs when the
 144                                    giv spans a biv update by incrementation.  */
 145   rtx ext_dependent;            /* If nonzero, is a sign or zero extension
 146                                    if a biv on which this giv is dependent.  */
 147   struct induction *next_iv;    /* For givs, links together all givs that are
 148                                    based on the same biv.  For bivs, links
 149                                    together all biv entries that refer to the
 150                                    same biv register.  */
 151   struct induction *same;       /* If this giv has been combined with another
 152                                    giv, this points to the base giv.  The base
 153                                    giv will have COMBINED_WITH nonzero.  */
 154   HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
 155                                    is split, and a constant is eliminated from
 156                                    the address, the -constant is stored here
 157                                    for later use.  */
 158   struct induction *same_insn;  /* If there are multiple identical givs in
 159                                    the same insn, then all but one have this
 160                                    field set, and they all point to the giv
 161                                    that doesn't have this field set.  */
 162   rtx last_use;                 /* For a giv made from a biv increment, this is
 163                                    a substitute for the lifetime information.  */
 164 };
 165
 166
 167 /* A `struct iv_class' is created for each biv.  */
 168
 169 struct iv_class
 170 {
 171   unsigned int regno;           /* Pseudo reg which is the biv.  */
 172   int biv_count;                /* Number of insns setting this reg.  */
 173   struct induction *biv;        /* List of all insns that set this reg.  */
 174   int giv_count;                /* Number of DEST_REG givs computed from this
 175                                    biv.  The resulting count is only used in
 176                                    check_dbra_loop.  */
 177   struct induction *giv;        /* List of all insns that compute a giv
 178                                    from this reg.  */
 179   int total_benefit;            /* Sum of BENEFITs of all those givs.  */
 180   rtx initial_value;            /* Value of reg at loop start.  */
 181   rtx initial_test;             /* Test performed on BIV before loop.  */
 182   rtx final_value;              /* Value of reg at loop end, if known.  */
 183   struct iv_class *next;        /* Links all class structures together.  */
 184   rtx init_insn;                /* insn which initializes biv, 0 if none.  */
 185   rtx init_set;                 /* SET of INIT_INSN, if any.  */
 186   unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
 187   unsigned eliminable : 1;      /* 1 if plausible candidate for
 188                                    elimination.  */
 189   unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for
 190                                    this.  */
 191   unsigned reversed : 1;        /* 1 if we reversed the loop that this
 192                                    biv controls.  */
 193   unsigned all_reduced : 1;     /* 1 if all givs using this biv have
 194                                    been reduced.  */
 195 };
 196
 197
 198 /* Definitions used by the basic induction variable discovery code.  */
 199 enum iv_mode
 200 {
 201   UNKNOWN_INDUCT,
 202   BASIC_INDUCT,
 203   NOT_BASIC_INDUCT,
 204   GENERAL_INDUCT
 205 };
 206
 207
 208 /* A `struct iv' is created for every register.  */
 209
 210 struct iv
 211 {
 212   enum iv_mode type;
 213   union
 214   {
 215     struct iv_class *class;
 216     struct induction *info;
 217   } iv;
 218 };
 219
 220
 221 #define REG_IV_TYPE(ivs, n) ivs->regs[n].type
 222 #define REG_IV_INFO(ivs, n) ivs->regs[n].iv.info
 223 #define REG_IV_CLASS(ivs, n) ivs->regs[n].iv.class
 224
 225
 226 struct loop_ivs
 227 {
 228   /* Indexed by register number, contains pointer to `struct
 229      iv' if register is an induction variable.  */
 230   struct iv *regs;
 231
 232   /* Size of regs array.  */
 233   unsigned int n_regs;
 234
 235   /* The head of a list which links together (via the next field)
 236      every iv class for the current loop.  */
 237   struct iv_class *list;
 238 };
 239
 240
 241 typedef struct loop_mem_info
 242 {
 243   rtx mem;      /* The MEM itself.  */
 244   rtx reg;      /* Corresponding pseudo, if any.  */
 245   int optimize; /* Nonzero if we can optimize access to this MEM.  */
 246 } loop_mem_info;
 247
 248
 249
 250 struct loop_reg
 251 {
 252   /* Number of times the reg is set during the loop being scanned.
 253      During code motion, a negative value indicates a reg that has
 254      been made a candidate; in particular -2 means that it is an
 255      candidate that we know is equal to a constant and -1 means that
 256      it is a candidate not known equal to a constant.  After code
 257      motion, regs moved have 0 (which is accurate now) while the
 258      failed candidates have the original number of times set.
 259
 260      Therefore, at all times, == 0 indicates an invariant register;
 261      < 0 a conditionally invariant one.  */
 262   int set_in_loop;
 263
 264   /* Original value of set_in_loop; same except that this value
 265      is not set negative for a reg whose sets have been made candidates
 266      and not set to 0 for a reg that is moved.  */
 267   int n_times_set;
 268
 269   /* Contains the insn in which a register was used if it was used
 270      exactly once; contains const0_rtx if it was used more than once.  */
 271   rtx single_usage;
 272
 273   /* Nonzero indicates that the register cannot be moved or strength
 274      reduced.  */
 275   char may_not_optimize;
 276
 277   /* Nonzero means reg N has already been moved out of one loop.
 278      This reduces the desire to move it out of another.  */
 279   char moved_once;
 280 };
 281
 282
 283 struct loop_regs
 284 {
 285   int num;                      /* Number of regs used in table.  */
 286   int size;                     /* Size of table.  */
 287   struct loop_reg *array;       /* Register usage info. array.  */
 288   int multiple_uses;            /* Nonzero if a reg has multiple uses.  */
 289 };
 290
 291
 292
 293 struct loop_movables
 294 {
 295   /* Head of movable chain.  */
 296   struct movable *head;
 297   /* Last movable in chain.  */
 298   struct movable *last;
 299 };
 300
 301
 302 /* Information pertaining to a loop.  */
 303
 304 struct loop_info
 305 {
 306   /* Nonzero if there is a subroutine call in the current loop.  */
 307   int has_call;
 308   /* Nonzero if there is a libcall in the current loop.  */
 309   int has_libcall;
 310   /* Nonzero if there is a non constant call in the current loop.  */
 311   int has_nonconst_call;
 312   /* Nonzero if there is a prefetch instruction in the current loop.  */
 313   int has_prefetch;
 314   /* Nonzero if there is a volatile memory reference in the current
 315      loop.  */
 316   int has_volatile;
 317   /* Nonzero if there is a tablejump in the current loop.  */
 318   int has_tablejump;
 319   /* Nonzero if there are ways to leave the loop other than falling
 320      off the end.  */
 321   int has_multiple_exit_targets;
 322   /* Nonzero if there is an indirect jump in the current function.  */
 323   int has_indirect_jump;
 324   /* Whether loop unrolling has emitted copies of the loop body so
 325      that the main loop needs no exit tests.  */
 326   int preconditioned;
 327   /* Register or constant initial loop value.  */
 328   rtx initial_value;
 329   /* Register or constant value used for comparison test.  */
 330   rtx comparison_value;
 331   /* Register or constant approximate final value.  */
 332   rtx final_value;
 333   /* Register or constant initial loop value with term common to
 334      final_value removed.  */
 335   rtx initial_equiv_value;
 336   /* Register or constant final loop value with term common to
 337      initial_value removed.  */
 338   rtx final_equiv_value;
 339   /* Register corresponding to iteration variable.  */
 340   rtx iteration_var;
 341   /* Constant loop increment.  */
 342   rtx increment;
 343   enum rtx_code comparison_code;
 344   /* Holds the number of loop iterations.  It is zero if the number
 345      could not be calculated.  Must be unsigned since the number of
 346      iterations can be as high as 2^wordsize - 1.  For loops with a
 347      wider iterator, this number will be zero if the number of loop
 348      iterations is too large for an unsigned integer to hold.  */
 349   unsigned HOST_WIDE_INT n_iterations;
 350   /* The number of times the loop body was unrolled.  */
 351   unsigned int unroll_number;
 352   int used_count_register;
 353   /* The loop iterator induction variable.  */
 354   struct iv_class *iv;
 355   /* List of MEMs that are stored in this loop.  */
 356   rtx store_mems;
 357   /* Array of MEMs that are used (read or written) in this loop, but
 358      cannot be aliased by anything in this loop, except perhaps
 359      themselves.  In other words, if mems[i] is altered during
 360      the loop, it is altered by an expression that is rtx_equal_p to
 361      it.  */
 362   loop_mem_info *mems;
 363   /* The index of the next available slot in MEMS.  */
 364   int mems_idx;
 365   /* The number of elements allocated in MEMS.  */
 366   int mems_allocated;
 367   /* Nonzero if we don't know what MEMs were changed in the current
 368      loop.  This happens if the loop contains a call (in which case
 369      `has_call' will also be set) or if we store into more than
 370      NUM_STORES MEMs.  */
 371   int unknown_address_altered;
 372   /* The above doesn't count any readonly memory locations that are
 373      stored.  This does.  */
 374   int unknown_constant_address_altered;
 375   /* Count of memory write instructions discovered in the loop.  */
 376   int num_mem_sets;
 377   /* The insn where the first of these was found.  */
 378   rtx first_loop_store_insn;
 379   /* The chain of movable insns in loop.  */
 380   struct loop_movables movables;
 381   /* The registers used the in loop.  */
 382   struct loop_regs regs;
 383   /* The induction variable information in loop.  */
 384   struct loop_ivs ivs;
 385   /* Nonzero if call is in pre_header extended basic block.  */
 386   int pre_header_has_call;
 387 };
 388
 389
 390 /* Variables declared in loop.c, but also needed in unroll.c.  */
 391
 392 extern int *uid_luid;
 393 extern int max_uid_for_loop;
 394 extern unsigned int max_reg_before_loop;
 395 extern struct loop **uid_loop;
 396 extern FILE *loop_dump_stream;
 397
 398
 399 /* Forward declarations for non-static functions declared in loop.c and
 400    unroll.c.  */
 401 int loop_invariant_p PARAMS ((const struct loop *, rtx));
 402 rtx get_condition_for_loop PARAMS ((const struct loop *, rtx));
 403 void loop_iv_add_mult_hoist PARAMS ((const struct loop *, rtx, rtx, rtx, rtx));
 404 void loop_iv_add_mult_sink PARAMS ((const struct loop *, rtx, rtx, rtx, rtx));
 405 void loop_iv_add_mult_emit_before PARAMS ((const struct loop *, rtx,
 406                                            rtx, rtx, rtx,
 407                                            basic_block, rtx));
 408 rtx express_from PARAMS ((struct induction *, struct induction *));
 409 rtx extend_value_for_giv PARAMS ((struct induction *, rtx));
 410
 411 void unroll_loop PARAMS ((struct loop *, int, int));
 412 rtx biv_total_increment PARAMS ((const struct iv_class *));
 413 unsigned HOST_WIDE_INT loop_iterations PARAMS ((struct loop *));
 414 int precondition_loop_p PARAMS ((const struct loop *,
 415                                  rtx *, rtx *, rtx *,
 416                                  enum machine_mode *mode));
 417 rtx final_biv_value PARAMS ((const struct loop *, struct iv_class *));
 418 rtx final_giv_value PARAMS ((const struct loop *, struct induction *));
 419 void emit_unrolled_add PARAMS ((rtx, rtx, rtx));
 420 int back_branch_in_range_p PARAMS ((const struct loop *, rtx));
 421
 422 int loop_insn_first_p PARAMS ((rtx, rtx));
 423 typedef rtx (*loop_insn_callback) PARAMS ((struct loop *, rtx, int, int));
 424 void for_each_insn_in_loop PARAMS ((struct loop *, loop_insn_callback));
 425 rtx loop_insn_emit_before PARAMS((const struct loop *, basic_block,
 426                                   rtx, rtx));
 427 rtx loop_insn_sink PARAMS((const struct loop *, rtx));
 428 rtx loop_insn_hoist PARAMS((const struct loop *, rtx));
 429
 430 /* Forward declarations for non-static functions declared in doloop.c.  */
 431 int doloop_optimize PARAMS ((const struct loop *));