gcc/loop.h

   1 /* Loop optimization definitions for GCC
   2    Copyright (C) 1991, 1995, 1998, 1999, 2000, 2001, 2002, 2003
   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;       /* For givs, if the giv has been combined with
 152                                    another giv, this points to the base giv.
 153                                    The base giv will have COMBINED_WITH nonzero.
 154                                    For bivs, if the biv has the same LOCATION
 155                                    than another biv, this points to the base
 156                                    biv.  */
 157   HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
 158                                    is split, and a constant is eliminated from
 159                                    the address, the -constant is stored here
 160                                    for later use.  */
 161   struct induction *same_insn;  /* If there are multiple identical givs in
 162                                    the same insn, then all but one have this
 163                                    field set, and they all point to the giv
 164                                    that doesn't have this field set.  */
 165   rtx last_use;                 /* For a giv made from a biv increment, this is
 166                                    a substitute for the lifetime information.  */
 167 };
 168
 169
 170 /* A `struct iv_class' is created for each biv.  */
 171
 172 struct iv_class
 173 {
 174   unsigned int regno;           /* Pseudo reg which is the biv.  */
 175   int biv_count;                /* Number of insns setting this reg.  */
 176   struct induction *biv;        /* List of all insns that set this reg.  */
 177   int giv_count;                /* Number of DEST_REG givs computed from this
 178                                    biv.  The resulting count is only used in
 179                                    check_dbra_loop.  */
 180   struct induction *giv;        /* List of all insns that compute a giv
 181                                    from this reg.  */
 182   int total_benefit;            /* Sum of BENEFITs of all those givs.  */
 183   rtx initial_value;            /* Value of reg at loop start.  */
 184   rtx initial_test;             /* Test performed on BIV before loop.  */
 185   rtx final_value;              /* Value of reg at loop end, if known.  */
 186   struct iv_class *next;        /* Links all class structures together.  */
 187   rtx init_insn;                /* insn which initializes biv, 0 if none.  */
 188   rtx init_set;                 /* SET of INIT_INSN, if any.  */
 189   unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
 190   unsigned eliminable : 1;      /* 1 if plausible candidate for
 191                                    elimination.  */
 192   unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for
 193                                    this.  */
 194   unsigned reversed : 1;        /* 1 if we reversed the loop that this
 195                                    biv controls.  */
 196   unsigned all_reduced : 1;     /* 1 if all givs using this biv have
 197                                    been reduced.  */
 198 };
 199
 200
 201 /* Definitions used by the basic induction variable discovery code.  */
 202 enum iv_mode
 203 {
 204   UNKNOWN_INDUCT,
 205   BASIC_INDUCT,
 206   NOT_BASIC_INDUCT,
 207   GENERAL_INDUCT
 208 };
 209
 210
 211 /* A `struct iv' is created for every register.  */
 212
 213 struct iv
 214 {
 215   enum iv_mode type;
 216   union
 217   {
 218     struct iv_class *class;
 219     struct induction *info;
 220   } iv;
 221 };
 222
 223
 224 #define REG_IV_TYPE(ivs, n) ivs->regs[n].type
 225 #define REG_IV_INFO(ivs, n) ivs->regs[n].iv.info
 226 #define REG_IV_CLASS(ivs, n) ivs->regs[n].iv.class
 227
 228
 229 struct loop_ivs
 230 {
 231   /* Indexed by register number, contains pointer to `struct
 232      iv' if register is an induction variable.  */
 233   struct iv *regs;
 234
 235   /* Size of regs array.  */
 236   unsigned int n_regs;
 237
 238   /* The head of a list which links together (via the next field)
 239      every iv class for the current loop.  */
 240   struct iv_class *list;
 241 };
 242
 243
 244 typedef struct loop_mem_info
 245 {
 246   rtx mem;      /* The MEM itself.  */
 247   rtx reg;      /* Corresponding pseudo, if any.  */
 248   int optimize; /* Nonzero if we can optimize access to this MEM.  */
 249 } loop_mem_info;
 250
 251
 252
 253 struct loop_reg
 254 {
 255   /* Number of times the reg is set during the loop being scanned.
 256      During code motion, a negative value indicates a reg that has
 257      been made a candidate; in particular -2 means that it is an
 258      candidate that we know is equal to a constant and -1 means that
 259      it is a candidate not known equal to a constant.  After code
 260      motion, regs moved have 0 (which is accurate now) while the
 261      failed candidates have the original number of times set.
 262
 263      Therefore, at all times, == 0 indicates an invariant register;
 264      < 0 a conditionally invariant one.  */
 265   int set_in_loop;
 266
 267   /* Original value of set_in_loop; same except that this value
 268      is not set negative for a reg whose sets have been made candidates
 269      and not set to 0 for a reg that is moved.  */
 270   int n_times_set;
 271
 272   /* Contains the insn in which a register was used if it was used
 273      exactly once; contains const0_rtx if it was used more than once.  */
 274   rtx single_usage;
 275
 276   /* Nonzero indicates that the register cannot be moved or strength
 277      reduced.  */
 278   char may_not_optimize;
 279
 280   /* Nonzero means reg N has already been moved out of one loop.
 281      This reduces the desire to move it out of another.  */
 282   char moved_once;
 283 };
 284
 285
 286 struct loop_regs
 287 {
 288   int num;                      /* Number of regs used in table.  */
 289   int size;                     /* Size of table.  */
 290   struct loop_reg *array;       /* Register usage info. array.  */
 291   int multiple_uses;            /* Nonzero if a reg has multiple uses.  */
 292 };
 293
 294
 295
 296 struct loop_movables
 297 {
 298   /* Head of movable chain.  */
 299   struct movable *head;
 300   /* Last movable in chain.  */
 301   struct movable *last;
 302 };
 303
 304
 305 /* Information pertaining to a loop.  */
 306
 307 struct loop_info
 308 {
 309   /* Nonzero if there is a subroutine call in the current loop.  */
 310   int has_call;
 311   /* Nonzero if there is a libcall in the current loop.  */
 312   int has_libcall;
 313   /* Nonzero if there is a non constant call in the current loop.  */
 314   int has_nonconst_call;
 315   /* Nonzero if there is a prefetch instruction in the current loop.  */
 316   int has_prefetch;
 317   /* Nonzero if there is a volatile memory reference in the current
 318      loop.  */
 319   int has_volatile;
 320   /* Nonzero if there is a tablejump in the current loop.  */
 321   int has_tablejump;
 322   /* Nonzero if there are ways to leave the loop other than falling
 323      off the end.  */
 324   int has_multiple_exit_targets;
 325   /* Nonzero if there is an indirect jump in the current function.  */
 326   int has_indirect_jump;
 327   /* Whether loop unrolling has emitted copies of the loop body so
 328      that the main loop needs no exit tests.  */
 329   int preconditioned;
 330   /* Register or constant initial loop value.  */
 331   rtx initial_value;
 332   /* Register or constant value used for comparison test.  */
 333   rtx comparison_value;
 334   /* Register or constant approximate final value.  */
 335   rtx final_value;
 336   /* Register or constant initial loop value with term common to
 337      final_value removed.  */
 338   rtx initial_equiv_value;
 339   /* Register or constant final loop value with term common to
 340      initial_value removed.  */
 341   rtx final_equiv_value;
 342   /* Register corresponding to iteration variable.  */
 343   rtx iteration_var;
 344   /* Constant loop increment.  */
 345   rtx increment;
 346   enum rtx_code comparison_code;
 347   /* Holds the number of loop iterations.  It is zero if the number
 348      could not be calculated.  Must be unsigned since the number of
 349      iterations can be as high as 2^wordsize - 1.  For loops with a
 350      wider iterator, this number will be zero if the number of loop
 351      iterations is too large for an unsigned integer to hold.  */
 352   unsigned HOST_WIDE_INT n_iterations;
 353   /* The number of times the loop body was unrolled.  */
 354   unsigned int unroll_number;
 355   int used_count_register;
 356   /* The loop iterator induction variable.  */
 357   struct iv_class *iv;
 358   /* List of MEMs that are stored in this loop.  */
 359   rtx store_mems;
 360   /* Array of MEMs that are used (read or written) in this loop, but
 361      cannot be aliased by anything in this loop, except perhaps
 362      themselves.  In other words, if mems[i] is altered during
 363      the loop, it is altered by an expression that is rtx_equal_p to
 364      it.  */
 365   loop_mem_info *mems;
 366   /* The index of the next available slot in MEMS.  */
 367   int mems_idx;
 368   /* The number of elements allocated in MEMS.  */
 369   int mems_allocated;
 370   /* Nonzero if we don't know what MEMs were changed in the current
 371      loop.  This happens if the loop contains a call (in which case
 372      `has_call' will also be set) or if we store into more than
 373      NUM_STORES MEMs.  */
 374   int unknown_address_altered;
 375   /* The above doesn't count any readonly memory locations that are
 376      stored.  This does.  */
 377   int unknown_constant_address_altered;
 378   /* Count of memory write instructions discovered in the loop.  */
 379   int num_mem_sets;
 380   /* The insn where the first of these was found.  */
 381   rtx first_loop_store_insn;
 382   /* The chain of movable insns in loop.  */
 383   struct loop_movables movables;
 384   /* The registers used the in loop.  */
 385   struct loop_regs regs;
 386   /* The induction variable information in loop.  */
 387   struct loop_ivs ivs;
 388   /* Nonzero if call is in pre_header extended basic block.  */
 389   int pre_header_has_call;
 390 };
 391
 392
 393 /* Variables declared in loop.c, but also needed in unroll.c.  */
 394
 395 extern int *uid_luid;
 396 extern int max_uid_for_loop;
 397 extern unsigned int max_reg_before_loop;
 398 extern struct loop **uid_loop;
 399 extern FILE *loop_dump_stream;
 400
 401
 402 /* Forward declarations for non-static functions declared in loop.c and
 403    unroll.c.  */
 404 extern int loop_invariant_p (const struct loop *, rtx);
 405 extern rtx get_condition_for_loop (const struct loop *, rtx);
 406 extern void loop_iv_add_mult_hoist (const struct loop *, rtx, rtx, rtx, rtx);
 407 extern void loop_iv_add_mult_sink (const struct loop *, rtx, rtx, rtx, rtx);
 408 extern void loop_iv_add_mult_emit_before (const struct loop *, rtx, rtx,
 409                                           rtx, rtx, basic_block, rtx);
 410 extern rtx express_from (struct induction *, struct induction *);
 411 extern rtx extend_value_for_giv (struct induction *, rtx);
 412
 413 extern void unroll_loop (struct loop *, int, int);
 414 extern rtx biv_total_increment (const struct iv_class *);
 415 extern unsigned HOST_WIDE_INT loop_iterations (struct loop *);
 416 extern int precondition_loop_p (const struct loop *, rtx *, rtx *, rtx *,
 417                                 enum machine_mode *mode);
 418 extern rtx final_biv_value (const struct loop *, struct iv_class *);
 419 extern rtx final_giv_value (const struct loop *, struct induction *);
 420 extern void emit_unrolled_add (rtx, rtx, rtx);
 421 extern int back_branch_in_range_p (const struct loop *, rtx);
 422
 423 extern int loop_insn_first_p (rtx, rtx);
 424 typedef rtx (*loop_insn_callback) (struct loop *, rtx, int, int);
 425 extern void for_each_insn_in_loop (struct loop *, loop_insn_callback);
 426 extern rtx loop_insn_emit_before (const struct loop *, basic_block, rtx, rtx);
 427 extern rtx loop_insn_sink (const struct loop *, rtx);
 428 extern rtx loop_insn_hoist (const struct loop *, rtx);
 429
 430 /* Forward declarations for non-static functions declared in doloop.c.  */
 431 extern int doloop_optimize (const struct loop *);