gcc/loop.h

   1 /* Loop optimization definitions for GNU C-Compiler
   2    Copyright (C) 1991, 1995, 1998, 1999, 2000 Free Software Foundation, Inc.
   3
   4 This file is part of GNU CC.
   5
   6 GNU CC is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU CC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU CC; see the file COPYING.  If not, write to
  18 the Free Software Foundation, 59 Temple Place - Suite 330,
  19 Boston, MA 02111-1307, USA.  */
  20
  21 #include "varray.h"
  22 #include "bitmap.h"
  23
  24 /* Flags passed to loop_optimize.  */
  25 #define LOOP_UNROLL 1
  26 #define LOOP_BCT 2
  27
  28 /* Get the loop info pointer of a loop.  */
  29 #define LOOP_INFO(LOOP) ((struct loop_info *) (LOOP)->aux)
  30
  31 /* Get a pointer to the loop registers structure.  */
  32 #define LOOP_REGS(LOOP) (&LOOP_INFO (loop)->regs)
  33
  34 /* Get a pointer to the loop induction variables structure.  */
  35 #define LOOP_IVS(LOOP) (&LOOP_INFO (loop)->ivs)
  36
  37 /* Get the luid of an insn.  Catch the error of trying to reference the LUID
  38    of an insn added during loop, since these don't have LUIDs.  */
  39
  40 #define INSN_LUID(INSN)                 \
  41   (INSN_UID (INSN) < max_uid_for_loop ? uid_luid[INSN_UID (INSN)] \
  42    : (abort (), -1))
  43
  44 /* A "basic induction variable" or biv is a pseudo reg that is set
  45    (within this loop) only by incrementing or decrementing it.  */
  46 /* A "general induction variable" or giv is a pseudo reg whose
  47    value is a linear function of a biv.  */
  48
  49 /* Bivs are recognized by `basic_induction_var';
  50    Givs by `general_induct_var'.  */
  51
  52 /* An enum for the two different types of givs, those that are used
  53    as memory addresses and those that are calculated into registers.  */
  54 enum g_types
  55 {
  56   DEST_ADDR,
  57   DEST_REG
  58 };
  59
  60 /* A `struct induction' is created for every instruction that sets
  61    an induction variable (either a biv or a giv).  */
  62
  63 struct induction
  64 {
  65   rtx insn;                     /* The insn that sets a biv or giv */
  66   rtx new_reg;                  /* New register, containing strength reduced
  67                                    version of this giv.  */
  68   rtx src_reg;                  /* Biv from which this giv is computed.
  69                                    (If this is a biv, then this is the biv.) */
  70   enum g_types giv_type;        /* Indicate whether DEST_ADDR or DEST_REG */
  71   rtx dest_reg;                 /* Destination register for insn: this is the
  72                                    register which was the biv or giv.
  73                                    For a biv, this equals src_reg.
  74                                    For a DEST_ADDR type giv, this is 0.  */
  75   rtx *location;                /* Place in the insn where this giv occurs.
  76                                    If GIV_TYPE is DEST_REG, this is 0.  */
  77                                 /* For a biv, this is the place where add_val
  78                                    was found.  */
  79   enum machine_mode mode;       /* The mode of this biv or giv */
  80   enum machine_mode mem_mode;   /* For DEST_ADDR, mode of the memory object.  */
  81   rtx mult_val;                 /* Multiplicative factor for src_reg.  */
  82   rtx add_val;                  /* Additive constant for that product.  */
  83   int benefit;                  /* Gain from eliminating this insn.  */
  84   rtx final_value;              /* If the giv is used outside the loop, and its
  85                                    final value could be calculated, it is put
  86                                    here, and the giv is made replaceable.  Set
  87                                    the giv to this value before the loop.  */
  88   unsigned combined_with;       /* The number of givs this giv has been
  89                                    combined with.  If nonzero, this giv
  90                                    cannot combine with any other giv.  */
  91   unsigned replaceable : 1;     /* 1 if we can substitute the strength-reduced
  92                                    variable for the original variable.
  93                                    0 means they must be kept separate and the
  94                                    new one must be copied into the old pseudo
  95                                    reg each time the old one is set.  */
  96   unsigned not_replaceable : 1; /* Used to prevent duplicating work.  This is
  97                                    1 if we know that the giv definitely can
  98                                    not be made replaceable, in which case we
  99                                    don't bother checking the variable again
 100                                    even if further info is available.
 101                                    Both this and the above can be zero.  */
 102   unsigned ignore : 1;          /* 1 prohibits further processing of giv */
 103   unsigned always_computable : 1;/* 1 if this value is computable every
 104                                     iteration.  */
 105   unsigned always_executed : 1; /* 1 if this set occurs each iteration.  */
 106   unsigned maybe_multiple : 1;  /* Only used for a biv and  1 if this biv
 107                                    update may be done multiple times per
 108                                    iteration.  */
 109   unsigned cant_derive : 1;     /* For giv's, 1 if this giv cannot derive
 110                                    another giv.  This occurs in many cases
 111                                    where a giv's lifetime spans an update to
 112                                    a biv.  */
 113   unsigned maybe_dead : 1;      /* 1 if this giv might be dead.  In that case,
 114                                    we won't use it to eliminate a biv, it
 115                                    would probably lose.  */
 116   unsigned auto_inc_opt : 1;    /* 1 if this giv had its increment output next
 117                                    to it to try to form an auto-inc address.  */
 118   unsigned unrolled : 1;        /* 1 if new register has been allocated and
 119                                    initialized in unrolled loop.  */
 120   unsigned shared : 1;
 121   unsigned no_const_addval : 1; /* 1 if add_val does not contain a const.  */
 122   int lifetime;                 /* Length of life of this giv */
 123   rtx derive_adjustment;        /* If nonzero, is an adjustment to be
 124                                    subtracted from add_val when this giv
 125                                    derives another.  This occurs when the
 126                                    giv spans a biv update by incrementation.  */
 127   rtx ext_dependant;            /* If nonzero, is a sign or zero extension
 128                                    if a biv on which this giv is dependant.  */
 129   struct induction *next_iv;    /* For givs, links together all givs that are
 130                                    based on the same biv.  For bivs, links
 131                                    together all biv entries that refer to the
 132                                    same biv register.  */
 133   struct induction *same;       /* If this giv has been combined with another
 134                                    giv, this points to the base giv.  The base
 135                                    giv will have COMBINED_WITH non-zero.  */
 136   struct induction *derived_from;/* For a giv, if we decided to derive this
 137                                    giv from another one.  */
 138   HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
 139                                    is split, and a constant is eliminated from
 140                                    the address, the -constant is stored here
 141                                    for later use.  */
 142   int ix;                       /* Used by recombine_givs, as n index into
 143                                    the stats array.  */
 144   struct induction *same_insn;  /* If there are multiple identical givs in
 145                                    the same insn, then all but one have this
 146                                    field set, and they all point to the giv
 147                                    that doesn't have this field set.  */
 148   rtx last_use;                 /* For a giv made from a biv increment, this is
 149                                    a substitute for the lifetime information.  */
 150 };
 151
 152 /* A `struct iv_class' is created for each biv.  */
 153
 154 struct iv_class
 155 {
 156   unsigned int regno;           /* Pseudo reg which is the biv.  */
 157   int biv_count;                /* Number of insns setting this reg.  */
 158   struct induction *biv;        /* List of all insns that set this reg.  */
 159   int giv_count;                /* Number of DEST_REG givs computed from this
 160                                    biv.  The resulting count is only used in
 161                                    check_dbra_loop.  */
 162   struct induction *giv;        /* List of all insns that compute a giv
 163                                    from this reg.  */
 164   int total_benefit;            /* Sum of BENEFITs of all those givs */
 165   rtx initial_value;            /* Value of reg at loop start */
 166   rtx initial_test;             /* Test performed on BIV before loop */
 167   struct iv_class *next;        /* Links all class structures together */
 168   rtx init_insn;                /* insn which initializes biv, 0 if none.  */
 169   rtx init_set;                 /* SET of INIT_INSN, if any.  */
 170   unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
 171   unsigned eliminable : 1;      /* 1 if plausible candidate for elimination.  */
 172   unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for this.  */
 173   unsigned reversed : 1;        /* 1 if we reversed the loop that this
 174                                    biv controls.  */
 175 };
 176
 177 typedef struct loop_mem_info
 178 {
 179   rtx mem;      /* The MEM itself.  */
 180   rtx reg;      /* Corresponding pseudo, if any.  */
 181   int optimize; /* Nonzero if we can optimize access to this MEM.  */
 182 } loop_mem_info;
 183
 184 struct loop_ivs
 185 {
 186   /* Indexed by register number, indicates whether or not register is
 187      an induction variable, and if so what type.  */
 188   varray_type reg_iv_type;
 189
 190   /* Indexed by register number, contains pointer to `struct
 191      induction' if register is an induction variable.  This holds
 192      general info for all induction variables.  */
 193   varray_type reg_iv_info;
 194
 195   /* Indexed by register number, contains pointer to `struct iv_class'
 196      if register is a basic induction variable.  This holds info
 197      describing the class (a related group) of induction variables
 198      that the biv belongs to.  */
 199   struct iv_class **reg_biv_class;
 200
 201   /* The head of a list which links together (via the next field)
 202      every iv class for the current loop.  */
 203   struct iv_class *loop_iv_list;
 204
 205   /* Givs made from biv increments are always splittable for loop
 206      unrolling.  Since there is no regscan info for them, we have to
 207      keep track of them separately.  */
 208   unsigned int first_increment_giv;
 209   unsigned int last_increment_giv;
 210 };
 211
 212 struct loop_regs
 213 {
 214   int num;
 215
 216   /* Indexed by register number, contains the number of times the reg
 217      is set during the loop being scanned.
 218      During code motion, a negative value indicates a reg that has been
 219      made a candidate; in particular -2 means that it is an candidate that
 220      we know is equal to a constant and -1 means that it is an candidate
 221      not known equal to a constant.
 222      After code motion, regs moved have 0 (which is accurate now)
 223      while the failed candidates have the original number of times set.
 224
 225      Therefore, at all times, == 0 indicates an invariant register;
 226      < 0 a conditionally invariant one.  */
 227   varray_type set_in_loop;
 228
 229   /* Original value of set_in_loop; same except that this value
 230      is not set negative for a reg whose sets have been made candidates
 231      and not set to 0 for a reg that is moved.  */
 232   varray_type n_times_set;
 233
 234   /* Index by register number, 1 indicates that the register
 235      cannot be moved or strength reduced.  */
 236   varray_type may_not_optimize;
 237
 238   /* Contains the insn in which a register was used if it was used
 239      exactly once; contains const0_rtx if it was used more than once.  */
 240   varray_type single_usage;
 241
 242   /* Nonzero means reg N has already been moved out of one loop.
 243      This reduces the desire to move it out of another.  */
 244   char *moved_once;
 245
 246   int multiple_uses;
 247 };
 248
 249 /* Information pertaining to a loop.  */
 250
 251 struct loop_info
 252 {
 253   /* Nonzero if there is a subroutine call in the current loop.  */
 254   int has_call;
 255   /* Nonzero if there is a volatile memory reference in the current
 256      loop.  */
 257   int has_volatile;
 258   /* Nonzero if there is a tablejump in the current loop.  */
 259   int has_tablejump;
 260   /* Nonzero if there are ways to leave the loop other than falling
 261      off the end.  */
 262   int has_multiple_exit_targets;
 263   /* Nonzero if there is an indirect jump in the current function.  */
 264   int has_indirect_jump;
 265   /* Register or constant initial loop value.  */
 266   rtx initial_value;
 267   /* Register or constant value used for comparison test.  */
 268   rtx comparison_value;
 269   /* Register or constant approximate final value.  */
 270   rtx final_value;
 271   /* Register or constant initial loop value with term common to
 272      final_value removed.  */
 273   rtx initial_equiv_value;
 274   /* Register or constant final loop value with term common to
 275      initial_value removed.  */
 276   rtx final_equiv_value;
 277   /* Register corresponding to iteration variable.  */
 278   rtx iteration_var;
 279   /* Constant loop increment.  */
 280   rtx increment;
 281   enum rtx_code comparison_code;
 282   /* Holds the number of loop iterations.  It is zero if the number
 283      could not be calculated.  Must be unsigned since the number of
 284      iterations can be as high as 2^wordsize - 1.  For loops with a
 285      wider iterator, this number will be zero if the number of loop
 286      iterations is too large for an unsigned integer to hold.  */
 287   unsigned HOST_WIDE_INT n_iterations;
 288   /* The number of times the loop body was unrolled.  */
 289   unsigned int unroll_number;
 290   int used_count_register;
 291   /* The loop iterator induction variable.  */
 292   struct iv_class *iv;
 293   /* List of MEMs that are stored in this loop.  */
 294   rtx store_mems;
 295   /* Array of MEMs that are used (read or written) in this loop, but
 296      cannot be aliased by anything in this loop, except perhaps
 297      themselves.  In other words, if mems[i] is altered during
 298      the loop, it is altered by an expression that is rtx_equal_p to
 299      it.  */
 300   loop_mem_info *mems;
 301   /* The index of the next available slot in MEMS.  */
 302   int mems_idx;
 303   /* The number of elements allocated in MEMS.  */
 304   int mems_allocated;
 305   /* Nonzero if we don't know what MEMs were changed in the current
 306      loop.  This happens if the loop contains a call (in which case
 307      `has_call' will also be set) or if we store into more than
 308      NUM_STORES MEMs.  */
 309   int unknown_address_altered;
 310   /* The above doesn't count any readonly memory locations that are
 311      stored.  This does.  */
 312   int unknown_constant_address_altered;
 313   /* Count of memory write instructions discovered in the loop.  */
 314   int num_mem_sets;
 315   /* The insn where the first of these was found.  */
 316   rtx first_loop_store_insn;
 317   /* The registers used the in loop.  */
 318   struct loop_regs regs;
 319   /* The induction variable information in loop.  */
 320   struct loop_ivs ivs;
 321 };
 322
 323 /* Definitions used by the basic induction variable discovery code.  */
 324 enum iv_mode
 325 {
 326   UNKNOWN_INDUCT,
 327   BASIC_INDUCT,
 328   NOT_BASIC_INDUCT,
 329   GENERAL_INDUCT
 330 };
 331
 332 /* Variables declared in loop.c, but also needed in unroll.c.  */
 333
 334 extern int *uid_luid;
 335 extern int max_uid_for_loop;
 336 extern unsigned int max_reg_before_loop;
 337 extern struct loop **uid_loop;
 338 extern FILE *loop_dump_stream;
 339
 340 #define REG_IV_TYPE(ivs, n) \
 341   (*(enum iv_mode *) &VARRAY_INT(ivs->reg_iv_type, (n)))
 342 #define REG_IV_INFO(ivs, n) \
 343   (*(struct induction **) &VARRAY_GENERIC_PTR(ivs->reg_iv_info, (n)))
 344
 345 /* Forward declarations for non-static functions declared in loop.c and
 346    unroll.c.  */
 347 int loop_invariant_p PARAMS ((const struct loop *, rtx));
 348 rtx get_condition_for_loop PARAMS ((const struct loop *, rtx));
 349 void emit_iv_add_mult PARAMS ((rtx, rtx, rtx, rtx, rtx));
 350 rtx express_from PARAMS ((struct induction *, struct induction *));
 351 rtx extend_value_for_giv PARAMS ((struct induction *, rtx));
 352
 353 void unroll_loop PARAMS ((struct loop *, int, rtx, int));
 354 rtx biv_total_increment PARAMS ((struct iv_class *));
 355 unsigned HOST_WIDE_INT loop_iterations PARAMS ((struct loop *));
 356 int precondition_loop_p PARAMS ((const struct loop *,
 357                                  rtx *, rtx *, rtx *,
 358                                  enum machine_mode *mode));
 359 rtx final_biv_value PARAMS ((const struct loop *, struct iv_class *));
 360 rtx final_giv_value PARAMS ((const struct loop *, struct induction *));
 361 void emit_unrolled_add PARAMS ((rtx, rtx, rtx));
 362 int back_branch_in_range_p PARAMS ((const struct loop *, rtx));
 363
 364 int loop_insn_first_p PARAMS ((rtx, rtx));
 365 typedef rtx (*loop_insn_callback) PARAMS ((struct loop *, rtx, int, int));
 366 void for_each_insn_in_loop PARAMS ((struct loop *, loop_insn_callback));
 367
 368 /* Forward declarations for non-static functions declared in doloop.c.  */
 369 int doloop_optimize PARAMS ((const struct loop *));