gcc/loop.h

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