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 "bitmap.h"
  22 #include "sbitmap.h"
  23 #include "hard-reg-set.h"
  24 #include "basic-block.h"
  25
  26 /* Flags passed to loop_optimize.  */
  27 #define LOOP_UNROLL 1
  28 #define LOOP_BCT 2
  29
  30 /* Get the loop info pointer of a loop.  */
  31 #define LOOP_INFO(LOOP) ((struct loop_info *) (LOOP)->aux)
  32
  33 /* Get a pointer to the loop movables structure.  */
  34 #define LOOP_MOVABLES(LOOP) (&LOOP_INFO (loop)->movables)
  35
  36 /* Get a pointer to the loop registers structure.  */
  37 #define LOOP_REGS(LOOP) (&LOOP_INFO (loop)->regs)
  38
  39 /* Get a pointer to the loop induction variables structure.  */
  40 #define LOOP_IVS(LOOP) (&LOOP_INFO (loop)->ivs)
  41
  42 /* Get the luid of an insn.  Catch the error of trying to reference the LUID
  43    of an insn added during loop, since these don't have LUIDs.  */
  44
  45 #define INSN_LUID(INSN)                 \
  46   (INSN_UID (INSN) < max_uid_for_loop ? uid_luid[INSN_UID (INSN)] \
  47    : (abort (), -1))
  48
  49 #define REGNO_FIRST_LUID(REGNO) uid_luid[REGNO_FIRST_UID (REGNO)]
  50 #define REGNO_LAST_LUID(REGNO) uid_luid[REGNO_LAST_UID (REGNO)]
  51
  52
  53 /* A "basic induction variable" or biv is a pseudo reg that is set
  54    (within this loop) only by incrementing or decrementing it.  */
  55 /* A "general induction variable" or giv is a pseudo reg whose
  56    value is a linear function of a biv.  */
  57
  58 /* Bivs are recognized by `basic_induction_var';
  59    Givs by `general_induction_var'.  */
  60
  61 /* An enum for the two different types of givs, those that are used
  62    as memory addresses and those that are calculated into registers.  */
  63 enum g_types
  64 {
  65   DEST_ADDR,
  66   DEST_REG
  67 };
  68
  69
  70 /* A `struct induction' is created for every instruction that sets
  71    an induction variable (either a biv or a giv).  */
  72
  73 struct induction
  74 {
  75   rtx insn;                     /* The insn that sets a biv or giv */
  76   rtx new_reg;                  /* New register, containing strength reduced
  77                                    version of this giv.  */
  78   rtx src_reg;                  /* Biv from which this giv is computed.
  79                                    (If this is a biv, then this is the biv.) */
  80   enum g_types giv_type;        /* Indicate whether DEST_ADDR or DEST_REG */
  81   rtx dest_reg;                 /* Destination register for insn: this is the
  82                                    register which was the biv or giv.
  83                                    For a biv, this equals src_reg.
  84                                    For a DEST_ADDR type giv, this is 0.  */
  85   rtx *location;                /* Place in the insn where this giv occurs.
  86                                    If GIV_TYPE is DEST_REG, this is 0.  */
  87                                 /* For a biv, this is the place where add_val
  88                                    was found.  */
  89   enum machine_mode mode;       /* The mode of this biv or giv */
  90   enum machine_mode mem_mode;   /* For DEST_ADDR, mode of the memory object.  */
  91   rtx mult_val;                 /* Multiplicative factor for src_reg.  */
  92   rtx add_val;                  /* Additive constant for that product.  */
  93   int benefit;                  /* Gain from eliminating this insn.  */
  94   rtx final_value;              /* If the giv is used outside the loop, and its
  95                                    final value could be calculated, it is put
  96                                    here, and the giv is made replaceable.  Set
  97                                    the giv to this value before the loop.  */
  98   unsigned combined_with;       /* The number of givs this giv has been
  99                                    combined with.  If nonzero, this giv
 100                                    cannot combine with any other giv.  */
 101   unsigned replaceable : 1;     /* 1 if we can substitute the strength-reduced
 102                                    variable for the original variable.
 103                                    0 means they must be kept separate and the
 104                                    new one must be copied into the old pseudo
 105                                    reg each time the old one is set.  */
 106   unsigned not_replaceable : 1; /* Used to prevent duplicating work.  This is
 107                                    1 if we know that the giv definitely can
 108                                    not be made replaceable, in which case we
 109                                    don't bother checking the variable again
 110                                    even if further info is available.
 111                                    Both this and the above can be zero.  */
 112   unsigned ignore : 1;          /* 1 prohibits further processing of giv */
 113   unsigned always_computable : 1;/* 1 if this value is computable every
 114                                     iteration.  */
 115   unsigned always_executed : 1; /* 1 if this set occurs each iteration.  */
 116   unsigned maybe_multiple : 1;  /* Only used for a biv and  1 if this biv
 117                                    update may be done multiple times per
 118                                    iteration.  */
 119   unsigned cant_derive : 1;     /* For giv's, 1 if this giv cannot derive
 120                                    another giv.  This occurs in many cases
 121                                    where a giv's lifetime spans an update to
 122                                    a biv.  */
 123   unsigned maybe_dead : 1;      /* 1 if this giv might be dead.  In that case,
 124                                    we won't use it to eliminate a biv, it
 125                                    would probably lose.  */
 126   unsigned auto_inc_opt : 1;    /* 1 if this giv had its increment output next
 127                                    to it to try to form an auto-inc address.  */
 128   unsigned unrolled : 1;        /* 1 if new register has been allocated and
 129                                    initialized in unrolled loop.  */
 130   unsigned shared : 1;
 131   unsigned no_const_addval : 1; /* 1 if add_val does not contain a const.  */
 132   int lifetime;                 /* Length of life of this giv */
 133   rtx derive_adjustment;        /* If nonzero, is an adjustment to be
 134                                    subtracted from add_val when this giv
 135                                    derives another.  This occurs when the
 136                                    giv spans a biv update by incrementation.  */
 137   rtx ext_dependant;            /* If nonzero, is a sign or zero extension
 138                                    if a biv on which this giv is dependant.  */
 139   struct induction *next_iv;    /* For givs, links together all givs that are
 140                                    based on the same biv.  For bivs, links
 141                                    together all biv entries that refer to the
 142                                    same biv register.  */
 143   struct induction *same;       /* If this giv has been combined with another
 144                                    giv, this points to the base giv.  The base
 145                                    giv will have COMBINED_WITH non-zero.  */
 146   HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
 147                                    is split, and a constant is eliminated from
 148                                    the address, the -constant is stored here
 149                                    for later use.  */
 150   struct induction *same_insn;  /* If there are multiple identical givs in
 151                                    the same insn, then all but one have this
 152                                    field set, and they all point to the giv
 153                                    that doesn't have this field set.  */
 154   rtx last_use;                 /* For a giv made from a biv increment, this is
 155                                    a substitute for the lifetime information.  */
 156 };
 157
 158
 159 /* A `struct iv_class' is created for each biv.  */
 160
 161 struct iv_class
 162 {
 163   unsigned int regno;           /* Pseudo reg which is the biv.  */
 164   int biv_count;                /* Number of insns setting this reg.  */
 165   struct induction *biv;        /* List of all insns that set this reg.  */
 166   int giv_count;                /* Number of DEST_REG givs computed from this
 167                                    biv.  The resulting count is only used in
 168                                    check_dbra_loop.  */
 169   struct induction *giv;        /* List of all insns that compute a giv
 170                                    from this reg.  */
 171   int total_benefit;            /* Sum of BENEFITs of all those givs.  */
 172   rtx initial_value;            /* Value of reg at loop start.  */
 173   rtx initial_test;             /* Test performed on BIV before loop.  */
 174   rtx final_value;              /* Value of reg at loop end, if known.  */
 175   struct iv_class *next;        /* Links all class structures together.  */
 176   rtx init_insn;                /* insn which initializes biv, 0 if none.  */
 177   rtx init_set;                 /* SET of INIT_INSN, if any.  */
 178   unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
 179   unsigned eliminable : 1;      /* 1 if plausible candidate for
 180                                    elimination.  */
 181   unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for
 182                                    this.  */
 183   unsigned reversed : 1;        /* 1 if we reversed the loop that this
 184                                    biv controls.  */
 185   unsigned all_reduced : 1;     /* 1 if all givs using this biv have
 186                                    been reduced. */
 187 };
 188
 189
 190 /* Definitions used by the basic induction variable discovery code.  */
 191 enum iv_mode
 192 {
 193   UNKNOWN_INDUCT,
 194   BASIC_INDUCT,
 195   NOT_BASIC_INDUCT,
 196   GENERAL_INDUCT
 197 };
 198
 199
 200 /* A `struct iv' is created for every register.  */
 201
 202 struct iv
 203 {
 204   enum iv_mode type;
 205   union
 206   {
 207     struct iv_class *class;
 208     struct induction *info;
 209   } iv;
 210 };
 211
 212
 213 #define REG_IV_TYPE(ivs, n) ivs->regs[n].type
 214 #define REG_IV_INFO(ivs, n) ivs->regs[n].iv.info
 215 #define REG_IV_CLASS(ivs, n) ivs->regs[n].iv.class
 216
 217
 218 struct loop_ivs
 219 {
 220   /* Indexed by register number, contains pointer to `struct
 221      iv' if register is an induction variable.  */
 222   struct iv *regs;
 223
 224   /* Size of regs array.  */
 225   unsigned int n_regs;
 226
 227   /* The head of a list which links together (via the next field)
 228      every iv class for the current loop.  */
 229   struct iv_class *list;
 230 };
 231
 232
 233 typedef struct loop_mem_info
 234 {
 235   rtx mem;      /* The MEM itself.  */
 236   rtx reg;      /* Corresponding pseudo, if any.  */
 237   int optimize; /* Nonzero if we can optimize access to this MEM.  */
 238 } loop_mem_info;
 239
 240
 241
 242 struct loop_reg
 243 {
 244   /* Number of times the reg is set during the loop being scanned.
 245      During code motion, a negative value indicates a reg that has
 246      been made a candidate; in particular -2 means that it is an
 247      candidate that we know is equal to a constant and -1 means that
 248      it is an candidate not known equal to a constant.  After code
 249      motion, regs moved have 0 (which is accurate now) while the
 250      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   int 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   int n_times_set;
 260
 261   /* Contains the insn in which a register was used if it was used
 262      exactly once; contains const0_rtx if it was used more than once.  */
 263   rtx single_usage;
 264
 265   /* Nonzero indicates that the register cannot be moved or strength
 266      reduced.  */
 267   char may_not_optimize;
 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
 274
 275 struct loop_regs
 276 {
 277   int num;                      /* Number of regs used in table.  */
 278   int size;                     /* Size of table.  */
 279   struct loop_reg *array;       /* Register usage info. array.  */
 280   int multiple_uses;            /* Nonzero if a reg has multiple uses.  */
 281 };
 282
 283
 284
 285 struct loop_movables
 286 {
 287   /* Head of movable chain.  */
 288   struct movable *head;
 289   /* Last movable in chain.  */
 290   struct movable *last;
 291   /* Number of movables in the loop.  */
 292   int num;
 293 };
 294
 295
 296 /* Information pertaining to a loop.  */
 297
 298 struct loop_info
 299 {
 300   /* Nonzero if there is a subroutine call in the current loop.  */
 301   int has_call;
 302   /* Nonzero if there is a libcall in the current loop.  */
 303   int has_libcall;
 304   /* Nonzero if there is a non constant call in the current loop.  */
 305   int has_nonconst_call;
 306   /* Nonzero if there is a volatile memory reference in the current
 307      loop.  */
 308   int has_volatile;
 309   /* Nonzero if there is a tablejump in the current loop.  */
 310   int has_tablejump;
 311   /* Nonzero if there are ways to leave the loop other than falling
 312      off the end.  */
 313   int has_multiple_exit_targets;
 314   /* Nonzero if there is an indirect jump in the current function.  */
 315   int has_indirect_jump;
 316   /* Register or constant initial loop value.  */
 317   rtx initial_value;
 318   /* Register or constant value used for comparison test.  */
 319   rtx comparison_value;
 320   /* Register or constant approximate final value.  */
 321   rtx final_value;
 322   /* Register or constant initial loop value with term common to
 323      final_value removed.  */
 324   rtx initial_equiv_value;
 325   /* Register or constant final loop value with term common to
 326      initial_value removed.  */
 327   rtx final_equiv_value;
 328   /* Register corresponding to iteration variable.  */
 329   rtx iteration_var;
 330   /* Constant loop increment.  */
 331   rtx increment;
 332   enum rtx_code comparison_code;
 333   /* Holds the number of loop iterations.  It is zero if the number
 334      could not be calculated.  Must be unsigned since the number of
 335      iterations can be as high as 2^wordsize - 1.  For loops with a
 336      wider iterator, this number will be zero if the number of loop
 337      iterations is too large for an unsigned integer to hold.  */
 338   unsigned HOST_WIDE_INT n_iterations;
 339   /* The number of times the loop body was unrolled.  */
 340   unsigned int unroll_number;
 341   int used_count_register;
 342   /* The loop iterator induction variable.  */
 343   struct iv_class *iv;
 344   /* List of MEMs that are stored in this loop.  */
 345   rtx store_mems;
 346   /* Array of MEMs that are used (read or written) in this loop, but
 347      cannot be aliased by anything in this loop, except perhaps
 348      themselves.  In other words, if mems[i] is altered during
 349      the loop, it is altered by an expression that is rtx_equal_p to
 350      it.  */
 351   loop_mem_info *mems;
 352   /* The index of the next available slot in MEMS.  */
 353   int mems_idx;
 354   /* The number of elements allocated in MEMS.  */
 355   int mems_allocated;
 356   /* Nonzero if we don't know what MEMs were changed in the current
 357      loop.  This happens if the loop contains a call (in which case
 358      `has_call' will also be set) or if we store into more than
 359      NUM_STORES MEMs.  */
 360   int unknown_address_altered;
 361   /* The above doesn't count any readonly memory locations that are
 362      stored.  This does.  */
 363   int unknown_constant_address_altered;
 364   /* Count of memory write instructions discovered in the loop.  */
 365   int num_mem_sets;
 366   /* The insn where the first of these was found.  */
 367   rtx first_loop_store_insn;
 368   /* The chain of movable insns in loop.  */
 369   struct loop_movables movables;
 370   /* The registers used the in loop.  */
 371   struct loop_regs regs;
 372   /* The induction variable information in loop.  */
 373   struct loop_ivs ivs;
 374   /* Non-zero if call is in pre_header extended basic block.  */
 375   int pre_header_has_call;
 376 };
 377
 378
 379 /* Variables declared in loop.c, but also needed in unroll.c.  */
 380
 381 extern int *uid_luid;
 382 extern int max_uid_for_loop;
 383 extern unsigned int max_reg_before_loop;
 384 extern struct loop **uid_loop;
 385 extern FILE *loop_dump_stream;
 386
 387
 388 /* Forward declarations for non-static functions declared in loop.c and
 389    unroll.c.  */
 390 int loop_invariant_p PARAMS ((const struct loop *, rtx));
 391 rtx get_condition_for_loop PARAMS ((const struct loop *, rtx));
 392 void loop_iv_add_mult_hoist PARAMS ((const struct loop *, rtx, rtx, rtx, rtx));
 393 void loop_iv_add_mult_sink PARAMS ((const struct loop *, rtx, rtx, rtx, rtx));
 394 void loop_iv_add_mult_emit_before PARAMS ((const struct loop *, rtx,
 395                                            rtx, rtx, rtx,
 396                                            basic_block, rtx));
 397 rtx express_from PARAMS ((struct induction *, struct induction *));
 398 rtx extend_value_for_giv PARAMS ((struct induction *, rtx));
 399
 400 void unroll_loop PARAMS ((struct loop *, int, int));
 401 rtx biv_total_increment PARAMS ((struct iv_class *));
 402 unsigned HOST_WIDE_INT loop_iterations PARAMS ((struct loop *));
 403 int precondition_loop_p PARAMS ((const struct loop *,
 404                                  rtx *, rtx *, rtx *,
 405                                  enum machine_mode *mode));
 406 rtx final_biv_value PARAMS ((const struct loop *, struct iv_class *));
 407 rtx final_giv_value PARAMS ((const struct loop *, struct induction *));
 408 void emit_unrolled_add PARAMS ((rtx, rtx, rtx));
 409 int back_branch_in_range_p PARAMS ((const struct loop *, rtx));
 410
 411 int loop_insn_first_p PARAMS ((rtx, rtx));
 412 typedef rtx (*loop_insn_callback) PARAMS ((struct loop *, rtx, int, int));
 413 void for_each_insn_in_loop PARAMS ((struct loop *, loop_insn_callback));
 414 rtx loop_insn_sink PARAMS((const struct loop *, rtx));
 415 rtx loop_insn_hoist PARAMS((const struct loop *, rtx));
 416
 417 /* Forward declarations for non-static functions declared in doloop.c.  */
 418 int doloop_optimize PARAMS ((const struct loop *));