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 "basic-block.h"
  23
  24 /* Get the loop info pointer of a loop.  */
  25 #define LOOP_INFO(LOOP) ((struct loop_info *) (LOOP)->aux)
  26
  27 /* Get the luid of an insn.  Catch the error of trying to reference the LUID
  28    of an insn added during loop, since these don't have LUIDs.  */
  29
  30 #define INSN_LUID(INSN)                 \
  31   (INSN_UID (INSN) < max_uid_for_loop ? uid_luid[INSN_UID (INSN)] \
  32    : (abort (), -1))
  33
  34 /* A "basic induction variable" or biv is a pseudo reg that is set
  35    (within this loop) only by incrementing or decrementing it.  */
  36 /* A "general induction variable" or giv is a pseudo reg whose
  37    value is a linear function of a biv.  */
  38
  39 /* Bivs are recognized by `basic_induction_var';
  40    Givs by `general_induct_var'.  */
  41
  42 /* An enum for the two different types of givs, those that are used
  43    as memory addresses and those that are calculated into registers.  */
  44 enum g_types { DEST_ADDR, DEST_REG };
  45
  46 /* A `struct induction' is created for every instruction that sets
  47    an induction variable (either a biv or a giv).  */
  48
  49 struct induction
  50 {
  51   rtx insn;                     /* The insn that sets a biv or giv */
  52   rtx new_reg;                  /* New register, containing strength reduced
  53                                    version of this giv.  */
  54   rtx src_reg;                  /* Biv from which this giv is computed.
  55                                    (If this is a biv, then this is the biv.) */
  56   enum g_types giv_type;        /* Indicate whether DEST_ADDR or DEST_REG */
  57   rtx dest_reg;                 /* Destination register for insn: this is the
  58                                    register which was the biv or giv.
  59                                    For a biv, this equals src_reg.
  60                                    For a DEST_ADDR type giv, this is 0.  */
  61   rtx *location;                /* Place in the insn where this giv occurs.
  62                                    If GIV_TYPE is DEST_REG, this is 0.  */
  63                                 /* For a biv, this is the place where add_val
  64                                    was found.  */
  65   enum machine_mode mode;       /* The mode of this biv or giv */
  66   enum machine_mode mem_mode;   /* For DEST_ADDR, mode of the memory object. */
  67   rtx mult_val;                 /* Multiplicative factor for src_reg.  */
  68   rtx add_val;                  /* Additive constant for that product.  */
  69   int benefit;                  /* Gain from eliminating this insn.  */
  70   rtx final_value;              /* If the giv is used outside the loop, and its
  71                                    final value could be calculated, it is put
  72                                    here, and the giv is made replaceable.  Set
  73                                    the giv to this value before the loop.  */
  74   unsigned combined_with;       /* The number of givs this giv has been
  75                                    combined with.  If nonzero, this giv
  76                                    cannot combine with any other giv.  */
  77   unsigned replaceable : 1;     /* 1 if we can substitute the strength-reduced
  78                                    variable for the original variable.
  79                                    0 means they must be kept separate and the
  80                                    new one must be copied into the old pseudo
  81                                    reg each time the old one is set.  */
  82   unsigned not_replaceable : 1; /* Used to prevent duplicating work.  This is
  83                                    1 if we know that the giv definitely can
  84                                    not be made replaceable, in which case we
  85                                    don't bother checking the variable again
  86                                    even if further info is available.
  87                                    Both this and the above can be zero.  */
  88   unsigned ignore : 1;          /* 1 prohibits further processing of giv */
  89   unsigned always_computable : 1;/* 1 if this value is computable every
  90                                     iteration.  */
  91   unsigned always_executed : 1; /* 1 if this set occurs each iteration.  */
  92   unsigned maybe_multiple : 1;  /* Only used for a biv and  1 if this biv
  93                                    update may be done multiple times per
  94                                    iteration. */
  95   unsigned cant_derive : 1;     /* For giv's, 1 if this giv cannot derive
  96                                    another giv.  This occurs in many cases
  97                                    where a giv's lifetime spans an update to
  98                                    a biv. */
  99   unsigned maybe_dead : 1;      /* 1 if this giv might be dead.  In that case,
 100                                    we won't use it to eliminate a biv, it
 101                                    would probably lose. */
 102   unsigned auto_inc_opt : 1;    /* 1 if this giv had its increment output next
 103                                    to it to try to form an auto-inc address. */
 104   unsigned unrolled : 1;        /* 1 if new register has been allocated and
 105                                    initialized in unrolled loop.  */
 106   unsigned shared : 1;
 107   unsigned no_const_addval : 1; /* 1 if add_val does not contain a const. */
 108   unsigned multi_insn_incr : 1; /* 1 if multiple insns updated the biv.  */
 109   int lifetime;                 /* Length of life of this giv */
 110   rtx derive_adjustment;        /* If nonzero, is an adjustment to be
 111                                    subtracted from add_val when this giv
 112                                    derives another.  This occurs when the
 113                                    giv spans a biv update by incrementation. */
 114   struct induction *next_iv;    /* For givs, links together all givs that are
 115                                    based on the same biv.  For bivs, links
 116                                    together all biv entries that refer to the
 117                                    same biv register.  */
 118   struct induction *same;       /* If this giv has been combined with another
 119                                    giv, this points to the base giv.  The base
 120                                    giv will have COMBINED_WITH non-zero.  */
 121   struct induction *derived_from;/* For a giv, if we decided to derive this
 122                                    giv from another one.  */
 123   HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
 124                                    is split, and a constant is eliminated from
 125                                    the address, the -constant is stored here
 126                                    for later use. */
 127   int ix;                       /* Used by recombine_givs, as n index into
 128                                    the stats array.  */
 129   struct induction *same_insn;  /* If there are multiple identical givs in
 130                                    the same insn, then all but one have this
 131                                    field set, and they all point to the giv
 132                                    that doesn't have this field set.  */
 133   rtx last_use;                 /* For a giv made from a biv increment, this is
 134                                    a substitute for the lifetime information. */
 135 };
 136
 137 /* A `struct iv_class' is created for each biv.  */
 138
 139 struct iv_class {
 140   int regno;                    /* Pseudo reg which is the biv.  */
 141   int biv_count;                /* Number of insns setting this reg.  */
 142   struct induction *biv;        /* List of all insns that set this reg.  */
 143   int giv_count;                /* Number of DEST_REG givs computed from this
 144                                    biv.  The resulting count is only used in
 145                                    check_dbra_loop.  */
 146   struct induction *giv;        /* List of all insns that compute a giv
 147                                    from this reg.  */
 148   int total_benefit;            /* Sum of BENEFITs of all those givs */
 149   rtx initial_value;            /* Value of reg at loop start */
 150   rtx initial_test;             /* Test performed on BIV before loop */
 151   struct iv_class *next;        /* Links all class structures together */
 152   rtx init_insn;                /* insn which initializes biv, 0 if none. */
 153   rtx init_set;                 /* SET of INIT_INSN, if any. */
 154   unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
 155   unsigned eliminable : 1;      /* 1 if plausible candidate for elimination. */
 156   unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for this. */
 157   unsigned reversed : 1;        /* 1 if we reversed the loop that this
 158                                    biv controls. */
 159 };
 160
 161 /* Information required to calculate the number of loop iterations.
 162    This is set by loop_iterations.  */
 163
 164 struct loop_info
 165 {
 166   /* Nonzero if there is a subroutine call in the current loop.  */
 167   int has_call;
 168   /* Nonzero if there is a volatile memory reference in the current
 169      loop.  */
 170   int has_volatile;
 171   /* Nonzero if there is a tablejump in the current loop.  */
 172   int has_tablejump;
 173   /* Nonzero if there are ways to leave the loop other than falling
 174      off the end.  */
 175   int has_multiple_exit_targets;
 176   /* Nonzero if there is an indirect jump in the current function.  */
 177   int has_indirect_jump;
 178   /* Register or constant initial loop value.  */
 179   rtx initial_value;
 180   /* Register or constant value used for comparison test.  */
 181   rtx comparison_value;
 182   /* Register or constant approximate final value.  */
 183   rtx final_value;
 184   /* Register or constant initial loop value with term common to
 185      final_value removed.  */
 186   rtx initial_equiv_value;
 187   /* Register or constant final loop value with term common to
 188      initial_value removed.  */
 189   rtx final_equiv_value;
 190   /* Register corresponding to iteration variable.  */
 191   rtx iteration_var;
 192   /* Constant loop increment.  */
 193   rtx increment;
 194   enum rtx_code comparison_code;
 195   /* Holds the number of loop iterations.  It is zero if the number
 196      could not be calculated.  Must be unsigned since the number of
 197      iterations can be as high as 2^wordsize - 1.  For loops with a
 198      wider iterator, this number will be zero if the number of loop
 199      iterations is too large for an unsigned integer to hold.  */
 200   unsigned HOST_WIDE_INT n_iterations;
 201   /* The number of times the loop body was unrolled.  */
 202   unsigned int unroll_number;
 203   int used_count_register;
 204 };
 205
 206 /* Definitions used by the basic induction variable discovery code.  */
 207 enum iv_mode { UNKNOWN_INDUCT, BASIC_INDUCT, NOT_BASIC_INDUCT,
 208                  GENERAL_INDUCT };
 209
 210 /* Variables declared in loop.c, but also needed in unroll.c.  */
 211
 212 extern int *uid_luid;
 213 extern int max_uid_for_loop;
 214 extern int max_reg_before_loop;
 215 extern struct loop **uid_loop;
 216 extern FILE *loop_dump_stream;
 217
 218 extern varray_type reg_iv_type;
 219 extern varray_type reg_iv_info;
 220
 221 #define REG_IV_TYPE(n) \
 222   (*(enum iv_mode *) &VARRAY_INT(reg_iv_type, (n)))
 223 #define REG_IV_INFO(n) \
 224   (*(struct induction **) &VARRAY_GENERIC_PTR(reg_iv_info, (n)))
 225
 226 extern struct iv_class **reg_biv_class;
 227 extern struct iv_class *loop_iv_list;
 228
 229 extern int first_increment_giv, last_increment_giv;
 230
 231 /* Forward declarations for non-static functions declared in loop.c and
 232    unroll.c.  */
 233 int loop_invariant_p PARAMS ((const struct loop *, rtx));
 234 rtx get_condition_for_loop PARAMS ((const struct loop *, rtx));
 235 void emit_iv_add_mult PARAMS ((rtx, rtx, rtx, rtx, rtx));
 236 rtx express_from PARAMS ((struct induction *, struct induction *));
 237
 238 void unroll_loop PARAMS ((struct loop *, int, rtx, int));
 239 rtx biv_total_increment PARAMS ((struct iv_class *));
 240 unsigned HOST_WIDE_INT loop_iterations PARAMS ((struct loop *));
 241 int precondition_loop_p PARAMS ((const struct loop *,
 242                                rtx *, rtx *, rtx *,
 243                                enum machine_mode *mode));
 244 rtx final_biv_value PARAMS ((const struct loop *, struct iv_class *));
 245 rtx final_giv_value PARAMS ((const struct loop *, struct induction *));
 246 void emit_unrolled_add PARAMS ((rtx, rtx, rtx));
 247 int back_branch_in_range_p PARAMS ((const struct loop *, rtx));
 248
 249 int loop_insn_first_p PARAMS ((rtx, rtx));
 250
 251 /* Forward declarations for non-static functions declared in stmt.c.  */
 252 void find_loop_tree_blocks PARAMS ((void));
 253 void unroll_block_trees PARAMS ((void));