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