source: trunk/third/gcc/loop.h @ 8834

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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 set occurs each iteration */
79  unsigned maybe_multiple : 1;  /* Only used for a biv and  1 if this biv
80                                   update may be done multiple times per
81                                   iteration. */
82  unsigned cant_derive : 1;     /* For giv's, 1 if this giv cannot derive
83                                   another giv.  This occurs in many cases
84                                   where a giv's lifetime spans an update to
85                                   a biv. */
86  unsigned combined_with : 1;   /* 1 if this giv has been combined with.  It
87                                   then cannot combine with any other giv.  */
88  unsigned maybe_dead : 1;      /* 1 if this giv might be dead.  In that case,
89                                   we won't use it to eliminate a biv, it
90                                   would probably lose. */
91  int lifetime;                 /* Length of life of this giv */
92  int times_used;               /* # times this giv is used. */
93  rtx derive_adjustment;        /* If nonzero, is an adjustment to be
94                                   subtracted from add_val when this giv
95                                   derives another.  This occurs when the
96                                   giv spans a biv update by incrementation. */
97  struct induction *next_iv;    /* For givs, links together all givs that are
98                                   based on the same biv.  For bivs, links
99                                   together all biv entries that refer to the
100                                   same biv register.  */
101  struct induction *same;       /* If this giv has been combined with another
102                                   giv, this points to the base giv.  The base
103                                   giv will have COMBINED_WITH non-zero.  */
104  HOST_WIDE_INT const_adjust;   /* Used by loop unrolling, when an address giv
105                                   is split, and a constant is eliminated from
106                                   the address, the -constant is stored here
107                                   for later use. */
108  struct induction *same_insn;  /* If there are multiple identical givs in
109                                   the same insn, then all but one have this
110                                   field set, and they all point to the giv
111                                   that doesn't have this field set.  */
112};
113
114/* A `struct iv_class' is created for each biv.  */
115
116struct iv_class {
117  int regno;                    /* Pseudo reg which is the biv.  */
118  int biv_count;                /* Number of insns setting this reg.  */
119  struct induction *biv;        /* List of all insns that set this reg.  */
120  int giv_count;                /* Number of DEST_REG givs computed from this
121                                   biv.  The resulting count is only used in
122                                   check_dbra_loop.  */
123  struct induction *giv;        /* List of all insns that compute a giv
124                                   from this reg.  */
125  int total_benefit;            /* Sum of BENEFITs of all those givs */
126  rtx initial_value;            /* Value of reg at loop start */
127  rtx initial_test;             /* Test performed on BIV before loop */
128  struct iv_class *next;        /* Links all class structures together */
129  rtx init_insn;                /* insn which initializes biv, 0 if none. */
130  rtx init_set;                 /* SET of INIT_INSN, if any. */
131  unsigned incremented : 1;     /* 1 if somewhere incremented/decremented */
132  unsigned eliminable : 1;      /* 1 if plausible candidate for elimination. */
133  unsigned nonneg : 1;          /* 1 if we added a REG_NONNEG note for this. */
134  unsigned reversed : 1;        /* 1 if we reversed the loop that this
135                                   biv controls. */
136};
137
138/* Definitions used by the basic induction variable discovery code.  */
139enum iv_mode { UNKNOWN_INDUCT, BASIC_INDUCT, NOT_BASIC_INDUCT,
140                 GENERAL_INDUCT };
141
142/* Variables declared in loop.c, but also needed in unroll.c.  */
143
144extern int *uid_luid;
145extern int max_uid_for_loop;
146extern int *uid_loop_num;
147extern int *loop_outer_loop;
148extern rtx *loop_number_exit_labels;
149extern int *loop_number_exit_count;
150extern unsigned HOST_WIDE_INT loop_n_iterations;
151extern int max_reg_before_loop;
152
153extern FILE *loop_dump_stream;
154
155extern enum iv_mode *reg_iv_type;
156extern struct induction **reg_iv_info;
157extern struct iv_class **reg_biv_class;
158extern struct iv_class *loop_iv_list;
159
160/* Forward declarations for non-static functions declared in loop.c and
161   unroll.c.  */
162int invariant_p PROTO((rtx));
163rtx get_condition_for_loop PROTO((rtx));
164void emit_iv_add_mult PROTO((rtx, rtx, rtx, rtx, rtx));
165
166/* Forward declarations for non-static functions declared in stmt.c.  */
167void find_loop_tree_blocks PROTO((void));
168void unroll_block_trees PROTO((void));
169
170void unroll_loop PROTO((rtx, int, rtx, rtx, int));
171rtx biv_total_increment PROTO((struct iv_class *, rtx, rtx));
172unsigned HOST_WIDE_INT loop_iterations PROTO((rtx, rtx));
173rtx final_biv_value PROTO((struct iv_class *, rtx, rtx));
174rtx final_giv_value PROTO((struct induction *, rtx, rtx));
175void emit_unrolled_add PROTO((rtx, rtx, rtx));
176int back_branch_in_range_p PROTO((rtx, rtx, rtx));
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