gcc/loop.h

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