gcc/loop.h

   1 /* Loop optimization definitions for GNU C-Compiler
   2    Copyright (C) 1991 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, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  19
  20 /* Get the luid of an insn.  Catch the error of trying to reference the LUID
  21    of an insn added during loop, since these don't have LUIDs.  */
  22
  23 #define INSN_LUID(INSN)                 \
  24   (INSN_UID (INSN) < max_uid_for_loop ? uid_luid[INSN_UID (INSN)] \
  25    : (abort (), -1))
  26
  27 /* A "basic induction variable" or biv is a pseudo reg that is set
  28    (within this loop) only by incrementing or decrementing it.  */
  29 /* A "general induction variable" or giv is a pseudo reg whose
  30    value is a linear function of a biv.  */
  31
  32 /* Bivs are recognized by `basic_induction_var';
  33    Givs by `general_induct_var'.  */
  34
  35 /* An enum for the two different types of givs, those that are used
  36    as memory addresses and those that are calculated into registers.  */
  37 enum g_types { DEST_ADDR, DEST_REG };
  38
  39 /* A `struct induction' is created for every instruction that sets
  40    an induction variable (either a biv or a giv).  */
  41
  42 struct induction
  43 {
  44   rtx insn;                     /* The insn that sets a biv or giv */
  45   rtx new_reg;                  /* New register, containing strength reduced
  46                                    version of this giv.  */
  47   rtx src_reg;                  /* Biv from which this giv is computed.
  48                                    (If this is a biv, then this is the biv.) */
  49   enum g_types giv_type;        /* Indicate whether DEST_ADDR or DEST_REG */
  50   rtx dest_reg;                 /* Destination register for insn: this is the
  51                                    register which was the biv or giv.
  52                                    For a biv, this equals src_reg.
  53                                    For a DEST_ADDR type giv, this is 0.  */
  54   rtx *location;                /* Place in the insn where this giv occurs.
  55                                    If GIV_TYPE is DEST_REG, this is 0.  */
  56   enum machine_mode mode;       /* The mode of this biv or giv */
  57   enum machine_mode mem_mode;   /* For DEST_ADDR, mode of the memory object. */
  58   rtx mult_val;                 /* Multiplicative factor for src_reg.  */
  59   rtx add_val;                  /* Additive constant for that product.  */
  60   int benefit;                  /* Gain from eliminating this insn.  */
  61   rtx final_value;              /* If the giv is used outside the loop, and its
  62                                    final value could be calculated, it is put
  63                                    here, and the giv is made replaceable.  Set
  64                                    the giv to this value before the loop.  */
  65   unsigned replaceable : 1;     /* 1 if we can substitute the strength-reduced
  66                                    variable for the original variable.
  67                                    0 means they must be kept separate and the
  68                                    new one must be copied into the old pseudo
  69                                    reg each time the old one is set.  */
  70   unsigned not_replaceable : 1; /* Used to prevent duplicating work.  This is
  71                                    1 if we know that the giv definitely can
  72                                    not be made replaceable, in which case we
  73                                    don't bother checking the variable again
  74                                    even if further info is available.
  75                                    Both this and the above can be zero.  */
  76   unsigned ignore : 1;          /* 1 prohibits further processing of giv */
  77   unsigned always_computable : 1;/* 1 if this set occurs each iteration */
  78   unsigned maybe_multiple : 1;  /* Only used for a biv and  1 if this biv
  79                                    update may be done multiple times per
  80                                    iteration. */
  81   unsigned cant_derive : 1;     /* For giv's, 1 if this giv cannot derive
  82                                    another giv.  This occurs in many cases
  83                                    where a giv's lifetime spans an update to
  84                                    a biv. */
  85   unsigned combined_with : 1;   /* 1 if this giv has been combined with.  It
  86                                    then cannot combine with any other giv.  */
  87   unsigned maybe_dead : 1;      /* 1 if this giv might be dead.  In that case,
  88                                    we won't use it to eliminate a biv, it
  89                                    would probably lose. */
  90   int lifetime;                 /* Length of life of this giv */
  91   int times_used;               /* # times this giv is used. */
  92   rtx derive_adjustment;        /* If nonzero, is an adjustment to be
  93                                    subtracted from add_val when this giv
  94                                    derives another.  This occurs when the
  95                                    giv spans a biv update by incrementation. */
  96   struct induction *next_iv;    /* For givs, links together all givs that are
  97                                    based on the same biv.  For bivs, links
  98                                    together all biv entries that refer to the
  99                                    same biv register.  */
 100   struct induction *same;       /* If this giv has been combined with another
 101                                    giv, this points to the base giv.  The base
 102                                    giv will have COMBINED_WITH non-zero.  */
 103   HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
 104                                    is split, and a constant is eliminated from
 105                                    the address, the -constant is stored here
 106                                    for later use. */
 107   struct induction *same_insn;  /* If there are multiple identical givs in
 108                                    the same insn, then all but one have this
 109                                    field set, and they all point to the giv
 110                                    that doesn't have this field set.  */
 111 };
 112
 113 /* A `struct iv_class' is created for each biv.  */
 114
 115 struct iv_class {
 116   int regno;                    /* Pseudo reg which is the biv.  */
 117   int biv_count;                /* Number of insns setting this reg.  */
 118   struct induction *biv;        /* List of all insns that set this reg.  */
 119   int giv_count;                /* Number of DEST_REG givs computed from this
 120                                    biv.  The resulting count is only used in
 121                                    check_dbra_loop.  */
 122   struct induction *giv;        /* List of all insns that compute a giv
 123                                    from this reg.  */
 124   int total_benefit;            /* Sum of BENEFITs of all those givs */
 125   rtx initial_value;            /* Value of reg at loop start */
 126   rtx initial_test;             /* Test performed on BIV before loop */
 127   struct iv_class *next;        /* Links all class structures together */
 128   rtx init_insn;                /* insn which initializes biv, 0 if none. */
 129   rtx init_set;                 /* SET of INIT_INSN, if any. */
 130   unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
 131   unsigned eliminable : 1;      /* 1 if plausible candidate for elimination. */
 132   unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for this. */
 133   unsigned reversed : 1;        /* 1 if we reversed the loop that this
 134                                    biv controls. */
 135 };
 136
 137 /* Definitions used by the basic induction variable discovery code.  */
 138 enum iv_mode { UNKNOWN_INDUCT, BASIC_INDUCT, NOT_BASIC_INDUCT,
 139                  GENERAL_INDUCT };
 140
 141 /* Variables declared in loop.c, but also needed in unroll.c.  */
 142
 143 extern int *uid_luid;
 144 extern int max_uid_for_loop;
 145 extern int *uid_loop_num;
 146 extern int *loop_outer_loop;
 147 extern rtx *loop_number_exit_labels;
 148 extern unsigned HOST_WIDE_INT loop_n_iterations;
 149 extern int max_reg_before_loop;
 150
 151 extern FILE *loop_dump_stream;
 152
 153 extern enum iv_mode *reg_iv_type;
 154 extern struct induction **reg_iv_info;
 155 extern struct iv_class **reg_biv_class;
 156 extern struct iv_class *loop_iv_list;
 157
 158 /* Forward declarations for non-static functions declared in loop.c and
 159    unroll.c.  */
 160 int invariant_p PROTO((rtx));
 161 rtx get_condition_for_loop PROTO((rtx));
 162 void emit_iv_add_mult PROTO((rtx, rtx, rtx, rtx, rtx));
 163
 164 /* Forward declarations for non-static functions declared in stmt.c.  */
 165 void find_loop_tree_blocks PROTO((void));
 166 void unroll_block_trees PROTO((void));
 167
 168 void unroll_loop PROTO((rtx, int, rtx, rtx, int));
 169 rtx biv_total_increment PROTO((struct iv_class *, rtx, rtx));
 170 unsigned HOST_WIDE_INT loop_iterations PROTO((rtx, rtx));
 171 rtx final_biv_value PROTO((struct iv_class *, rtx, rtx));
 172 rtx final_giv_value PROTO((struct induction *, rtx, rtx));
 173 void emit_unrolled_add PROTO((rtx, rtx, rtx));