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