src/compiler/glsl/loop_analysis.h

   1 /* -*- c++ -*- */
   2 /*
   3  * Copyright © 2010 Intel Corporation
   4  *
   5  * Permission is hereby granted, free of charge, to any person obtaining a
   6  * copy of this software and associated documentation files (the "Software"),
   7  * to deal in the Software without restriction, including without limitation
   8  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   9  * and/or sell copies of the Software, and to permit persons to whom the
  10  * Software is furnished to do so, subject to the following conditions:
  11  *
  12  * The above copyright notice and this permission notice (including the next
  13  * paragraph) shall be included in all copies or substantial portions of the
  14  * Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  22  * DEALINGS IN THE SOFTWARE.
  23  */
  24
  25 #pragma once
  26 #ifndef LOOP_ANALYSIS_H
  27 #define LOOP_ANALYSIS_H
  28
  29 #include "ir.h"
  30 #include "program/hash_table.h"
  31
  32 /**
  33  * Analyze and classify all variables used in all loops in the instruction list
  34  */
  35 extern class loop_state *
  36 analyze_loop_variables(exec_list *instructions);
  37
  38
  39 /**
  40  * Fill in loop control fields
  41  *
  42  * Based on analysis of loop variables, this function tries to remove
  43  * redundant sequences in the loop of the form
  44  *
  45  *  (if (expression bool ...) (break))
  46  *
  47  * For example, if it is provable that one loop exit condition will
  48  * always be satisfied before another, the unnecessary exit condition will be
  49  * removed.
  50  */
  51 extern bool
  52 set_loop_controls(exec_list *instructions, loop_state *ls);
  53
  54
  55 extern bool
  56 unroll_loops(exec_list *instructions, loop_state *ls,
  57              const struct gl_shader_compiler_options *options);
  58
  59 ir_rvalue *
  60 find_initial_value(ir_loop *loop, ir_variable *var);
  61
  62 int
  63 calculate_iterations(ir_rvalue *from, ir_rvalue *to, ir_rvalue *increment,
  64                      enum ir_expression_operation op);
  65
  66
  67 /**
  68  * Tracking for all variables used in a loop
  69  */
  70 class loop_variable_state : public exec_node {
  71 public:
  72    class loop_variable *get(const ir_variable *);
  73    class loop_variable *insert(ir_variable *);
  74    class loop_variable *get_or_insert(ir_variable *, bool in_assignee);
  75    class loop_terminator *insert(ir_if *);
  76
  77
  78    /**
  79     * Variables that have not yet been classified
  80     */
  81    exec_list variables;
  82
  83    /**
  84     * Variables whose values are constant within the body of the loop
  85     *
  86     * This list contains \c loop_variable objects.
  87     */
  88    exec_list constants;
  89
  90    /**
  91     * Induction variables for this loop
  92     *
  93     * This list contains \c loop_variable objects.
  94     */
  95    exec_list induction_variables;
  96
  97    /**
  98     * Simple if-statements that lead to the termination of the loop
  99     *
 100     * This list contains \c loop_terminator objects.
 101     *
 102     * \sa is_loop_terminator
 103     */
 104    exec_list terminators;
 105
 106    /**
 107     * If any of the terminators in \c terminators leads to termination of the
 108     * loop after a constant number of iterations, this is the terminator that
 109     * leads to termination after the smallest number of iterations.  Otherwise
 110     * NULL.
 111     */
 112    loop_terminator *limiting_terminator;
 113
 114    /**
 115     * Hash table containing all variables accessed in this loop
 116     */
 117    hash_table *var_hash;
 118
 119    /**
 120     * Number of ir_loop_jump instructions that operate on this loop
 121     */
 122    unsigned num_loop_jumps;
 123
 124    /**
 125     * Whether this loop contains any function calls.
 126     */
 127    bool contains_calls;
 128
 129    loop_variable_state()
 130    {
 131       this->num_loop_jumps = 0;
 132       this->contains_calls = false;
 133       this->var_hash = hash_table_ctor(0, hash_table_pointer_hash,
 134                                        hash_table_pointer_compare);
 135       this->limiting_terminator = NULL;
 136    }
 137
 138    ~loop_variable_state()
 139    {
 140       hash_table_dtor(this->var_hash);
 141    }
 142
 143    DECLARE_RALLOC_CXX_OPERATORS(loop_variable_state)
 144 };
 145
 146
 147 class loop_variable : public exec_node {
 148 public:
 149    /** The variable in question. */
 150    ir_variable *var;
 151
 152    /** Is the variable read in the loop before it is written? */
 153    bool read_before_write;
 154
 155    /** Are all variables in the RHS of the assignment loop constants? */
 156    bool rhs_clean;
 157
 158    /**
 159     * Is there an assignment to the variable that is conditional, or inside a
 160     * nested loop?
 161     */
 162    bool conditional_or_nested_assignment;
 163
 164    /** Reference to the first assignment to the variable in the loop body. */
 165    ir_assignment *first_assignment;
 166
 167    /** Number of assignments to the variable in the loop body. */
 168    unsigned num_assignments;
 169
 170    /**
 171     * Increment value for a loop induction variable
 172     *
 173     * If this is a loop induction variable, the amount by which the variable
 174     * is incremented on each iteration through the loop.
 175     *
 176     * If this is not a loop induction variable, NULL.
 177     */
 178    ir_rvalue *increment;
 179
 180
 181    inline bool is_induction_var() const
 182    {
 183       /* Induction variables always have a non-null increment, and vice
 184        * versa.
 185        */
 186       return this->increment != NULL;
 187    }
 188
 189
 190    inline bool is_loop_constant() const
 191    {
 192       const bool is_const = (this->num_assignments == 0)
 193          || (((this->num_assignments == 1)
 194              && !this->conditional_or_nested_assignment
 195              && !this->read_before_write
 196              && this->rhs_clean) || this->var->data.read_only);
 197
 198       /* If the RHS of *the* assignment is clean, then there must be exactly
 199        * one assignment of the variable.
 200        */
 201       assert((this->rhs_clean && (this->num_assignments == 1))
 202              || !this->rhs_clean);
 203
 204       return is_const;
 205    }
 206
 207    void record_reference(bool in_assignee,
 208                          bool in_conditional_code_or_nested_loop,
 209                          ir_assignment *current_assignment);
 210 };
 211
 212
 213 class loop_terminator : public exec_node {
 214 public:
 215    loop_terminator()
 216       : ir(NULL), iterations(-1)
 217    {
 218    }
 219
 220    /**
 221     * Statement which terminates the loop.
 222     */
 223    ir_if *ir;
 224
 225    /**
 226     * The number of iterations after which the terminator is known to
 227     * terminate the loop (if that is a fixed value).  Otherwise -1.
 228     */
 229    int iterations;
 230 };
 231
 232
 233 class loop_state {
 234 public:
 235    ~loop_state();
 236
 237    /**
 238     * Get the loop variable state data for a particular loop
 239     */
 240    loop_variable_state *get(const ir_loop *);
 241
 242    loop_variable_state *insert(ir_loop *ir);
 243
 244    bool loop_found;
 245
 246 private:
 247    loop_state();
 248
 249    /**
 250     * Hash table containing all loops that have been analyzed.
 251     */
 252    hash_table *ht;
 253
 254    void *mem_ctx;
 255
 256    friend loop_state *analyze_loop_variables(exec_list *instructions);
 257 };
 258
 259 #endif /* LOOP_ANALYSIS_H */