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
  29 /* Get the loop info pointer of a loop.  */
  30 #define LOOP_INFO(LOOP) ((struct loop_info *) (LOOP)->aux)
  31
  32 /* Get the luid of an insn.  Catch the error of trying to reference the LUID
  33    of an insn added during loop, since these don't have LUIDs.  */
  34
  35 #define INSN_LUID(INSN)                 \
  36   (INSN_UID (INSN) < max_uid_for_loop ? uid_luid[INSN_UID (INSN)] \
  37    : (abort (), -1))
  38
  39 /* A "basic induction variable" or biv is a pseudo reg that is set
  40    (within this loop) only by incrementing or decrementing it.  */
  41 /* A "general induction variable" or giv is a pseudo reg whose
  42    value is a linear function of a biv.  */
  43
  44 /* Bivs are recognized by `basic_induction_var';
  45    Givs by `general_induct_var'.  */
  46
  47 /* An enum for the two different types of givs, those that are used
  48    as memory addresses and those that are calculated into registers.  */
  49 enum g_types { DEST_ADDR, DEST_REG };
  50
  51 /* A `struct induction' is created for every instruction that sets
  52    an induction variable (either a biv or a giv).  */
  53
  54 struct induction
  55 {
  56   rtx insn;                     /* The insn that sets a biv or giv */
  57   rtx new_reg;                  /* New register, containing strength reduced
  58                                    version of this giv.  */
  59   rtx src_reg;                  /* Biv from which this giv is computed.
  60                                    (If this is a biv, then this is the biv.) */
  61   enum g_types giv_type;        /* Indicate whether DEST_ADDR or DEST_REG */
  62   rtx dest_reg;                 /* Destination register for insn: this is the
  63                                    register which was the biv or giv.
  64                                    For a biv, this equals src_reg.
  65                                    For a DEST_ADDR type giv, this is 0.  */
  66   rtx *location;                /* Place in the insn where this giv occurs.
  67                                    If GIV_TYPE is DEST_REG, this is 0.  */
  68                                 /* For a biv, this is the place where add_val
  69                                    was found.  */
  70   enum machine_mode mode;       /* The mode of this biv or giv */
  71   enum machine_mode mem_mode;   /* For DEST_ADDR, mode of the memory object. */
  72   rtx mult_val;                 /* Multiplicative factor for src_reg.  */
  73   rtx add_val;                  /* Additive constant for that product.  */
  74   int benefit;                  /* Gain from eliminating this insn.  */
  75   rtx final_value;              /* If the giv is used outside the loop, and its
  76                                    final value could be calculated, it is put
  77                                    here, and the giv is made replaceable.  Set
  78                                    the giv to this value before the loop.  */
  79   unsigned combined_with;       /* The number of givs this giv has been
  80                                    combined with.  If nonzero, this giv
  81                                    cannot combine with any other giv.  */
  82   unsigned replaceable : 1;     /* 1 if we can substitute the strength-reduced
  83                                    variable for the original variable.
  84                                    0 means they must be kept separate and the
  85                                    new one must be copied into the old pseudo
  86                                    reg each time the old one is set.  */
  87   unsigned not_replaceable : 1; /* Used to prevent duplicating work.  This is
  88                                    1 if we know that the giv definitely can
  89                                    not be made replaceable, in which case we
  90                                    don't bother checking the variable again
  91                                    even if further info is available.
  92                                    Both this and the above can be zero.  */
  93   unsigned ignore : 1;          /* 1 prohibits further processing of giv */
  94   unsigned always_computable : 1;/* 1 if this value is computable every
  95                                     iteration.  */
  96   unsigned always_executed : 1; /* 1 if this set occurs each iteration.  */
  97   unsigned maybe_multiple : 1;  /* Only used for a biv and  1 if this biv
  98                                    update may be done multiple times per
  99                                    iteration. */
 100   unsigned cant_derive : 1;     /* For giv's, 1 if this giv cannot derive
 101                                    another giv.  This occurs in many cases
 102                                    where a giv's lifetime spans an update to
 103                                    a biv. */
 104   unsigned maybe_dead : 1;      /* 1 if this giv might be dead.  In that case,
 105                                    we won't use it to eliminate a biv, it
 106                                    would probably lose. */
 107   unsigned auto_inc_opt : 1;    /* 1 if this giv had its increment output next
 108                                    to it to try to form an auto-inc address. */
 109   unsigned unrolled : 1;        /* 1 if new register has been allocated and
 110                                    initialized in unrolled loop.  */
 111   unsigned shared : 1;
 112   unsigned no_const_addval : 1; /* 1 if add_val does not contain a const. */
 113   int lifetime;                 /* Length of life of this giv */
 114   rtx derive_adjustment;        /* If nonzero, is an adjustment to be
 115                                    subtracted from add_val when this giv
 116                                    derives another.  This occurs when the
 117                                    giv spans a biv update by incrementation. */
 118   struct induction *next_iv;    /* For givs, links together all givs that are
 119                                    based on the same biv.  For bivs, links
 120                                    together all biv entries that refer to the
 121                                    same biv register.  */
 122   struct induction *same;       /* If this giv has been combined with another
 123                                    giv, this points to the base giv.  The base
 124                                    giv will have COMBINED_WITH non-zero.  */
 125   struct induction *derived_from;/* For a giv, if we decided to derive this
 126                                    giv from another one.  */
 127   HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
 128                                    is split, and a constant is eliminated from
 129                                    the address, the -constant is stored here
 130                                    for later use. */
 131   int ix;                       /* Used by recombine_givs, as n index into
 132                                    the stats array.  */
 133   struct induction *same_insn;  /* If there are multiple identical givs in
 134                                    the same insn, then all but one have this
 135                                    field set, and they all point to the giv
 136                                    that doesn't have this field set.  */
 137   rtx last_use;                 /* For a giv made from a biv increment, this is
 138                                    a substitute for the lifetime information. */
 139 };
 140
 141 /* A `struct iv_class' is created for each biv.  */
 142
 143 struct iv_class {
 144   unsigned int regno;           /* Pseudo reg which is the biv.  */
 145   int biv_count;                /* Number of insns setting this reg.  */
 146   struct induction *biv;        /* List of all insns that set this reg.  */
 147   int giv_count;                /* Number of DEST_REG givs computed from this
 148                                    biv.  The resulting count is only used in
 149                                    check_dbra_loop.  */
 150   struct induction *giv;        /* List of all insns that compute a giv
 151                                    from this reg.  */
 152   int total_benefit;            /* Sum of BENEFITs of all those givs */
 153   rtx initial_value;            /* Value of reg at loop start */
 154   rtx initial_test;             /* Test performed on BIV before loop */
 155   struct iv_class *next;        /* Links all class structures together */
 156   rtx init_insn;                /* insn which initializes biv, 0 if none. */
 157   rtx init_set;                 /* SET of INIT_INSN, if any. */
 158   unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
 159   unsigned eliminable : 1;      /* 1 if plausible candidate for elimination. */
 160   unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for this. */
 161   unsigned reversed : 1;        /* 1 if we reversed the loop that this
 162                                    biv controls. */
 163 };
 164
 165 /* Information required to calculate the number of loop iterations.
 166    This is set by loop_iterations.  */
 167
 168 struct loop_info
 169 {
 170   /* Nonzero if there is a subroutine call in the current loop.  */
 171   int has_call;
 172   /* Nonzero if there is a volatile memory reference in the current
 173      loop.  */
 174   int has_volatile;
 175   /* Nonzero if there is a tablejump in the current loop.  */
 176   int has_tablejump;
 177   /* Nonzero if there are ways to leave the loop other than falling
 178      off the end.  */
 179   int has_multiple_exit_targets;
 180   /* Nonzero if there is an indirect jump in the current function.  */
 181   int has_indirect_jump;
 182   /* Register or constant initial loop value.  */
 183   rtx initial_value;
 184   /* Register or constant value used for comparison test.  */
 185   rtx comparison_value;
 186   /* Register or constant approximate final value.  */
 187   rtx final_value;
 188   /* Register or constant initial loop value with term common to
 189      final_value removed.  */
 190   rtx initial_equiv_value;
 191   /* Register or constant final loop value with term common to
 192      initial_value removed.  */
 193   rtx final_equiv_value;
 194   /* Register corresponding to iteration variable.  */
 195   rtx iteration_var;
 196   /* Constant loop increment.  */
 197   rtx increment;
 198   enum rtx_code comparison_code;
 199   /* Holds the number of loop iterations.  It is zero if the number
 200      could not be calculated.  Must be unsigned since the number of
 201      iterations can be as high as 2^wordsize - 1.  For loops with a
 202      wider iterator, this number will be zero if the number of loop
 203      iterations is too large for an unsigned integer to hold.  */
 204   unsigned HOST_WIDE_INT n_iterations;
 205   /* The number of times the loop body was unrolled.  */
 206   unsigned int unroll_number;
 207   int used_count_register;
 208 };
 209
 210 /* Definitions used by the basic induction variable discovery code.  */
 211 enum iv_mode { UNKNOWN_INDUCT, BASIC_INDUCT, NOT_BASIC_INDUCT,
 212                  GENERAL_INDUCT };
 213
 214 /* Variables declared in loop.c, but also needed in unroll.c.  */
 215
 216 extern int *uid_luid;
 217 extern int max_uid_for_loop;
 218 extern unsigned int max_reg_before_loop;
 219 extern struct loop **uid_loop;
 220 extern FILE *loop_dump_stream;
 221
 222 extern varray_type reg_iv_type;
 223 extern varray_type reg_iv_info;
 224
 225 #define REG_IV_TYPE(n) \
 226   (*(enum iv_mode *) &VARRAY_INT(reg_iv_type, (n)))
 227 #define REG_IV_INFO(n) \
 228   (*(struct induction **) &VARRAY_GENERIC_PTR(reg_iv_info, (n)))
 229
 230 extern struct iv_class **reg_biv_class;
 231 extern struct iv_class *loop_iv_list;
 232
 233 extern unsigned int first_increment_giv, last_increment_giv;
 234
 235 /* Forward declarations for non-static functions declared in loop.c and
 236    unroll.c.  */
 237 int loop_invariant_p PARAMS ((const struct loop *, rtx));
 238 rtx get_condition_for_loop PARAMS ((const struct loop *, rtx));
 239 void emit_iv_add_mult PARAMS ((rtx, rtx, rtx, rtx, rtx));
 240 rtx express_from PARAMS ((struct induction *, struct induction *));
 241
 242 void unroll_loop PARAMS ((struct loop *, int, rtx, int));
 243 rtx biv_total_increment PARAMS ((struct iv_class *));
 244 unsigned HOST_WIDE_INT loop_iterations PARAMS ((struct loop *));
 245 int precondition_loop_p PARAMS ((const struct loop *,
 246                                rtx *, rtx *, rtx *,
 247                                enum machine_mode *mode));
 248 rtx final_biv_value PARAMS ((const struct loop *, struct iv_class *));
 249 rtx final_giv_value PARAMS ((const struct loop *, struct induction *));
 250 void emit_unrolled_add PARAMS ((rtx, rtx, rtx));
 251 int back_branch_in_range_p PARAMS ((const struct loop *, rtx));
 252
 253 int loop_insn_first_p PARAMS ((rtx, rtx));
 254 typedef rtx (*loop_insn_callback ) PARAMS ((struct loop *, rtx, int, int));
 255 void for_each_insn_in_loop PARAMS ((struct loop *, loop_insn_callback));
 256