source: trunk/third/gcc/loop.h @ 11288

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1/* Loop optimization definitions for GNU C-Compiler
2   Copyright (C) 1991, 1995 Free Software Foundation, Inc.
3
4This file is part of GNU CC.
5
6GNU CC is free software; you can redistribute it and/or modify
7it under the terms of the GNU General Public License as published by
8the Free Software Foundation; either version 2, or (at your option)
9any later version.
10
11GNU CC is distributed in the hope that it will be useful,
12but WITHOUT ANY WARRANTY; without even the implied warranty of
13MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14GNU General Public License for more details.
15
16You should have received a copy of the GNU General Public License
17along with GNU CC; see the file COPYING.  If not, write to
18the Free Software Foundation, 59 Temple Place - Suite 330,
19Boston, 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.  */
38enum 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
43struct 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  int lifetime;                 /* Length of life of this giv */
96  int times_used;               /* # times this giv is used. */
97  rtx derive_adjustment;        /* If nonzero, is an adjustment to be
98                                   subtracted from add_val when this giv
99                                   derives another.  This occurs when the
100                                   giv spans a biv update by incrementation. */
101  struct induction *next_iv;    /* For givs, links together all givs that are
102                                   based on the same biv.  For bivs, links
103                                   together all biv entries that refer to the
104                                   same biv register.  */
105  struct induction *same;       /* If this giv has been combined with another
106                                   giv, this points to the base giv.  The base
107                                   giv will have COMBINED_WITH non-zero.  */
108  HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
109                                   is split, and a constant is eliminated from
110                                   the address, the -constant is stored here
111                                   for later use. */
112  struct induction *same_insn;  /* If there are multiple identical givs in
113                                   the same insn, then all but one have this
114                                   field set, and they all point to the giv
115                                   that doesn't have this field set.  */
116};
117
118/* A `struct iv_class' is created for each biv.  */
119
120struct iv_class {
121  int regno;                    /* Pseudo reg which is the biv.  */
122  int biv_count;                /* Number of insns setting this reg.  */
123  struct induction *biv;        /* List of all insns that set this reg.  */
124  int giv_count;                /* Number of DEST_REG givs computed from this
125                                   biv.  The resulting count is only used in
126                                   check_dbra_loop.  */
127  struct induction *giv;        /* List of all insns that compute a giv
128                                   from this reg.  */
129  int total_benefit;            /* Sum of BENEFITs of all those givs */
130  rtx initial_value;            /* Value of reg at loop start */
131  rtx initial_test;             /* Test performed on BIV before loop */
132  struct iv_class *next;        /* Links all class structures together */
133  rtx init_insn;                /* insn which initializes biv, 0 if none. */
134  rtx init_set;                 /* SET of INIT_INSN, if any. */
135  unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
136  unsigned eliminable : 1;      /* 1 if plausible candidate for elimination. */
137  unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for this. */
138  unsigned reversed : 1;        /* 1 if we reversed the loop that this
139                                   biv controls. */
140};
141
142/* Definitions used by the basic induction variable discovery code.  */
143enum iv_mode { UNKNOWN_INDUCT, BASIC_INDUCT, NOT_BASIC_INDUCT,
144                 GENERAL_INDUCT };
145
146/* Variables declared in loop.c, but also needed in unroll.c.  */
147
148extern int *uid_luid;
149extern int max_uid_for_loop;
150extern int *uid_loop_num;
151extern int *loop_outer_loop;
152extern rtx *loop_number_exit_labels;
153extern int *loop_number_exit_count;
154extern unsigned HOST_WIDE_INT loop_n_iterations;
155extern int max_reg_before_loop;
156
157extern FILE *loop_dump_stream;
158
159extern enum iv_mode *reg_iv_type;
160extern struct induction **reg_iv_info;
161extern struct iv_class **reg_biv_class;
162extern struct iv_class *loop_iv_list;
163
164/* Forward declarations for non-static functions declared in loop.c and
165   unroll.c.  */
166int invariant_p PROTO((rtx));
167rtx get_condition_for_loop PROTO((rtx));
168void emit_iv_add_mult PROTO((rtx, rtx, rtx, rtx, rtx));
169
170/* Forward declarations for non-static functions declared in stmt.c.  */
171void find_loop_tree_blocks PROTO((void));
172void unroll_block_trees PROTO((void));
173
174void unroll_loop PROTO((rtx, int, rtx, rtx, int));
175rtx biv_total_increment PROTO((struct iv_class *, rtx, rtx));
176unsigned HOST_WIDE_INT loop_iterations PROTO((rtx, rtx));
177rtx final_biv_value PROTO((struct iv_class *, rtx, rtx));
178rtx final_giv_value PROTO((struct induction *, rtx, rtx));
179void emit_unrolled_add PROTO((rtx, rtx, rtx));
180int back_branch_in_range_p PROTO((rtx, rtx, rtx));
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