gcc/loop.h

   1 /* Loop optimization definitions for GNU C-Compiler
   2    Copyright (C) 1991, 1995, 1998, 1999 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
  23 /* Get the luid of an insn.  Catch the error of trying to reference the LUID
  24    of an insn added during loop, since these don't have LUIDs.  */
  25
  26 #define INSN_LUID(INSN)                 \
  27   (INSN_UID (INSN) < max_uid_for_loop ? uid_luid[INSN_UID (INSN)] \
  28    : (abort (), -1))
  29
  30 /* A "basic induction variable" or biv is a pseudo reg that is set
  31    (within this loop) only by incrementing or decrementing it.  */
  32 /* A "general induction variable" or giv is a pseudo reg whose
  33    value is a linear function of a biv.  */
  34
  35 /* Bivs are recognized by `basic_induction_var';
  36    Givs by `general_induct_var'.  */
  37
  38 /* An enum for the two different types of givs, those that are used
  39    as memory addresses and those that are calculated into registers.  */
  40 enum g_types { DEST_ADDR, DEST_REG };
  41
  42 /* A `struct induction' is created for every instruction that sets
  43    an induction variable (either a biv or a giv).  */
  44
  45 struct induction
  46 {
  47   rtx insn;                     /* The insn that sets a biv or giv */
  48   rtx new_reg;                  /* New register, containing strength reduced
  49                                    version of this giv.  */
  50   rtx src_reg;                  /* Biv from which this giv is computed.
  51                                    (If this is a biv, then this is the biv.) */
  52   enum g_types giv_type;        /* Indicate whether DEST_ADDR or DEST_REG */
  53   rtx dest_reg;                 /* Destination register for insn: this is the
  54                                    register which was the biv or giv.
  55                                    For a biv, this equals src_reg.
  56                                    For a DEST_ADDR type giv, this is 0.  */
  57   rtx *location;                /* Place in the insn where this giv occurs.
  58                                    If GIV_TYPE is DEST_REG, this is 0.  */
  59                                 /* For a biv, this is the place where add_val
  60                                    was found.  */
  61   enum machine_mode mode;       /* The mode of this biv or giv */
  62   enum machine_mode mem_mode;   /* For DEST_ADDR, mode of the memory object. */
  63   rtx mult_val;                 /* Multiplicative factor for src_reg.  */
  64   rtx add_val;                  /* Additive constant for that product.  */
  65   int benefit;                  /* Gain from eliminating this insn.  */
  66   rtx final_value;              /* If the giv is used outside the loop, and its
  67                                    final value could be calculated, it is put
  68                                    here, and the giv is made replaceable.  Set
  69                                    the giv to this value before the loop.  */
  70   unsigned combined_with;       /* The number of givs this giv has been
  71                                    combined with.  If nonzero, this giv
  72                                    cannot combine with any other giv.  */
  73   unsigned replaceable : 1;     /* 1 if we can substitute the strength-reduced
  74                                    variable for the original variable.
  75                                    0 means they must be kept separate and the
  76                                    new one must be copied into the old pseudo
  77                                    reg each time the old one is set.  */
  78   unsigned not_replaceable : 1; /* Used to prevent duplicating work.  This is
  79                                    1 if we know that the giv definitely can
  80                                    not be made replaceable, in which case we
  81                                    don't bother checking the variable again
  82                                    even if further info is available.
  83                                    Both this and the above can be zero.  */
  84   unsigned ignore : 1;          /* 1 prohibits further processing of giv */
  85   unsigned always_computable : 1;/* 1 if this value is computable every
  86                                     iteration.  */
  87   unsigned always_executed : 1; /* 1 if this set occurs each iteration.  */
  88   unsigned maybe_multiple : 1;  /* Only used for a biv and  1 if this biv
  89                                    update may be done multiple times per
  90                                    iteration. */
  91   unsigned cant_derive : 1;     /* For giv's, 1 if this giv cannot derive
  92                                    another giv.  This occurs in many cases
  93                                    where a giv's lifetime spans an update to
  94                                    a biv. */
  95   unsigned maybe_dead : 1;      /* 1 if this giv might be dead.  In that case,
  96                                    we won't use it to eliminate a biv, it
  97                                    would probably lose. */
  98   unsigned auto_inc_opt : 1;    /* 1 if this giv had its increment output next
  99                                    to it to try to form an auto-inc address. */
 100   unsigned unrolled : 1;        /* 1 if new register has been allocated and
 101                                    initialized in unrolled loop.  */
 102   unsigned shared : 1;
 103   unsigned no_const_addval : 1; /* 1 if add_val does not contain a const. */
 104   int lifetime;                 /* Length of life of this giv */
 105   rtx derive_adjustment;        /* If nonzero, is an adjustment to be
 106                                    subtracted from add_val when this giv
 107                                    derives another.  This occurs when the
 108                                    giv spans a biv update by incrementation. */
 109   struct induction *next_iv;    /* For givs, links together all givs that are
 110                                    based on the same biv.  For bivs, links
 111                                    together all biv entries that refer to the
 112                                    same biv register.  */
 113   struct induction *same;       /* If this giv has been combined with another
 114                                    giv, this points to the base giv.  The base
 115                                    giv will have COMBINED_WITH non-zero.  */
 116   struct induction *derived_from;/* For a giv, if we decided to derive this
 117                                    giv from another one.  */
 118   HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
 119                                    is split, and a constant is eliminated from
 120                                    the address, the -constant is stored here
 121                                    for later use. */
 122   int ix;                       /* Used by recombine_givs, as n index into
 123                                    the stats array.  */
 124   struct induction *same_insn;  /* If there are multiple identical givs in
 125                                    the same insn, then all but one have this
 126                                    field set, and they all point to the giv
 127                                    that doesn't have this field set.  */
 128   rtx last_use;                 /* For a giv made from a biv increment, this is
 129                                    a substitute for the lifetime information. */
 130 };
 131
 132 /* A `struct iv_class' is created for each biv.  */
 133
 134 struct iv_class {
 135   int regno;                    /* Pseudo reg which is the biv.  */
 136   int biv_count;                /* Number of insns setting this reg.  */
 137   struct induction *biv;        /* List of all insns that set this reg.  */
 138   int giv_count;                /* Number of DEST_REG givs computed from this
 139                                    biv.  The resulting count is only used in
 140                                    check_dbra_loop.  */
 141   struct induction *giv;        /* List of all insns that compute a giv
 142                                    from this reg.  */
 143   int total_benefit;            /* Sum of BENEFITs of all those givs */
 144   rtx initial_value;            /* Value of reg at loop start */
 145   rtx initial_test;             /* Test performed on BIV before loop */
 146   struct iv_class *next;        /* Links all class structures together */
 147   rtx init_insn;                /* insn which initializes biv, 0 if none. */
 148   rtx init_set;                 /* SET of INIT_INSN, if any. */
 149   unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
 150   unsigned eliminable : 1;      /* 1 if plausible candidate for elimination. */
 151   unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for this. */
 152   unsigned reversed : 1;        /* 1 if we reversed the loop that this
 153                                    biv controls. */
 154 };
 155
 156 /* Information required to calculate the number of loop iterations.
 157    This is set by loop_iterations.  */
 158
 159 struct loop_info
 160 {
 161   /* Register or constant initial loop value.  */
 162   rtx initial_value;
 163   /* Register or constant value used for comparison test.  */
 164   rtx comparison_value;
 165   /* Register or constant approximate final value.  */
 166   rtx final_value;
 167   /* Register or constant initial loop value with term common to
 168      final_value removed.  */
 169   rtx initial_equiv_value;
 170   /* Register or constant final loop value with term common to
 171      initial_value removed.  */
 172   rtx final_equiv_value;
 173   /* Register corresponding to iteration variable.  */
 174   rtx iteration_var;
 175   /* Constant loop increment.  */
 176   rtx increment;
 177   enum rtx_code comparison_code;
 178   /* Holds the number of loop iterations.  It is zero if the number
 179      could not be calculated.  Must be unsigned since the number of
 180      iterations can be as high as 2^wordsize - 1.  For loops with a
 181      wider iterator, this number will be zero if the number of loop
 182      iterations is too large for an unsigned integer to hold.  */
 183   unsigned HOST_WIDE_INT n_iterations;
 184   /* The loop unrolling factor.
 185      Potential values:
 186      0: unrolled
 187      1: not unrolled.
 188      -1: completely unrolled
 189      >0: holds the unroll exact factor.  */
 190   unsigned int unroll_number;
 191   /* Non-zero if the loop has a NOTE_INSN_LOOP_VTOP.  */
 192   rtx vtop;
 193 };
 194
 195 /* Definitions used by the basic induction variable discovery code.  */
 196 enum iv_mode { UNKNOWN_INDUCT, BASIC_INDUCT, NOT_BASIC_INDUCT,
 197                  GENERAL_INDUCT };
 198
 199 /* Variables declared in loop.c, but also needed in unroll.c.  */
 200
 201 extern int *uid_luid;
 202 extern int max_uid_for_loop;
 203 extern int *uid_loop_num;
 204 extern int *loop_outer_loop;
 205 extern rtx *loop_number_exit_labels;
 206 extern int *loop_number_exit_count;
 207 extern int max_reg_before_loop;
 208
 209 extern FILE *loop_dump_stream;
 210
 211 extern varray_type reg_iv_type;
 212 extern varray_type reg_iv_info;
 213
 214 #define REG_IV_TYPE(n) \
 215   (*(enum iv_mode *) &VARRAY_INT(reg_iv_type, (n)))
 216 #define REG_IV_INFO(n) \
 217   (*(struct induction **) &VARRAY_GENERIC_PTR(reg_iv_info, (n)))
 218
 219 extern struct iv_class **reg_biv_class;
 220 extern struct iv_class *loop_iv_list;
 221
 222 extern int first_increment_giv, last_increment_giv;
 223
 224 /* Forward declarations for non-static functions declared in loop.c and
 225    unroll.c.  */
 226 int invariant_p PROTO((rtx));
 227 rtx get_condition_for_loop PROTO((rtx));
 228 void emit_iv_add_mult PROTO((rtx, rtx, rtx, rtx, rtx));
 229 rtx express_from PROTO((struct induction *, struct induction *));
 230
 231 void unroll_loop PROTO((rtx, int, rtx, rtx, struct loop_info *, int));
 232 rtx biv_total_increment PROTO((struct iv_class *, rtx, rtx));
 233 unsigned HOST_WIDE_INT loop_iterations PROTO((rtx, rtx, struct loop_info *));
 234 int precondition_loop_p PROTO((rtx, struct loop_info *,
 235                                rtx *, rtx *, rtx *,
 236                                enum machine_mode *mode));
 237 rtx final_biv_value PROTO((struct iv_class *, rtx, rtx,
 238                            unsigned HOST_WIDE_INT));
 239 rtx final_giv_value PROTO((struct induction *, rtx, rtx,
 240                            unsigned HOST_WIDE_INT));
 241 void emit_unrolled_add PROTO((rtx, rtx, rtx));
 242 int back_branch_in_range_p PROTO((rtx, rtx, rtx));
 243 int loop_insn_first_p PROTO((rtx, rtx));
 244
 245 extern int *loop_unroll_number;
 246
 247 /* Forward declarations for non-static functions declared in stmt.c.  */
 248 void find_loop_tree_blocks PROTO((void));
 249 void unroll_block_trees PROTO((void));