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 #ifndef LOOP_ANALYSIS_H
  26 #define LOOP_ANALYSIS_H
  27
  28 #include "ir.h"
  29 #include "util/hash_table.h"
  30
  31 /**
  32  * Analyze and classify all variables used in all loops in the instruction list
  33  */
  34 extern class loop_state *
  35 analyze_loop_variables(exec_list *instructions);
  36
  37
  38 /**
  39  * Fill in loop control fields
  40  *
  41  * Based on analysis of loop variables, this function tries to remove
  42  * redundant sequences in the loop of the form
  43  *
  44  *  (if (expression bool ...) (break))
  45  *
  46  * For example, if it is provable that one loop exit condition will
  47  * always be satisfied before another, the unnecessary exit condition will be
  48  * removed.
  49  */
  50 extern bool
  51 set_loop_controls(exec_list *instructions, loop_state *ls);
  52
  53
  54 extern bool
  55 unroll_loops(exec_list *instructions, loop_state *ls,
  56              const struct gl_shader_compiler_options *options);
  57
  58 ir_rvalue *
  59 find_initial_value(ir_loop *loop, ir_variable *var);
  60
  61 int
  62 calculate_iterations(ir_rvalue *from, ir_rvalue *to, ir_rvalue *increment,
  63                      enum ir_expression_operation op);
  64
  65
  66 /**
  67  * Tracking for all variables used in a loop
  68  */
  69 class loop_variable_state : public exec_node {
  70 public:
  71    class loop_variable *get(const ir_variable *);
  72    class loop_variable *insert(ir_variable *);
  73    class loop_variable *get_or_insert(ir_variable *, bool in_assignee);
  74    class loop_terminator *insert(ir_if *);
  75
  76
  77    /**
  78     * Variables that have not yet been classified
  79     */
  80    exec_list variables;
  81
  82    /**
  83     * Variables whose values are constant within the body of the loop
  84     *
  85     * This list contains \c loop_variable objects.
  86     */
  87    exec_list constants;
  88
  89    /**
  90     * Induction variables for this loop
  91     *
  92     * This list contains \c loop_variable objects.
  93     */
  94    exec_list induction_variables;
  95
  96    /**
  97     * Simple if-statements that lead to the termination of the loop
  98     *
  99     * This list contains \c loop_terminator objects.
 100     *
 101     * \sa is_loop_terminator
 102     */
 103    exec_list terminators;
 104
 105    /**
 106     * If any of the terminators in \c terminators leads to termination of the
 107     * loop after a constant number of iterations, this is the terminator that
 108     * leads to termination after the smallest number of iterations.  Otherwise
 109     * NULL.
 110     */
 111    loop_terminator *limiting_terminator;
 112
 113    /**
 114     * Hash table containing all variables accessed in this loop
 115     */
 116    hash_table *var_hash;
 117
 118    /**
 119     * Number of ir_loop_jump instructions that operate on this loop
 120     */
 121    unsigned num_loop_jumps;
 122
 123    /**
 124     * Whether this loop contains any function calls.
 125     */
 126    bool contains_calls;
 127
 128    loop_variable_state()
 129    {
 130       this->num_loop_jumps = 0;
 131       this->contains_calls = false;
 132       this->var_hash = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
 133                                                _mesa_key_pointer_equal);
 134       this->limiting_terminator = NULL;
 135    }
 136
 137    ~loop_variable_state()
 138    {
 139       _mesa_hash_table_destroy(this->var_hash, NULL);
 140    }
 141
 142    DECLARE_RALLOC_CXX_OPERATORS(loop_variable_state)
 143 };
 144
 145
 146 class loop_variable : public exec_node {
 147 public:
 148    /** The variable in question. */
 149    ir_variable *var;
 150
 151    /** Is the variable read in the loop before it is written? */
 152    bool read_before_write;
 153
 154    /** Are all variables in the RHS of the assignment loop constants? */
 155    bool rhs_clean;
 156
 157    /**
 158     * Is there an assignment to the variable that is conditional, or inside a
 159     * nested loop?
 160     */
 161    bool conditional_or_nested_assignment;
 162
 163    /** Reference to the first assignment to the variable in the loop body. */
 164    ir_assignment *first_assignment;
 165
 166    /** Number of assignments to the variable in the loop body. */
 167    unsigned num_assignments;
 168
 169    /**
 170     * Increment value for a loop induction variable
 171     *
 172     * If this is a loop induction variable, the amount by which the variable
 173     * is incremented on each iteration through the loop.
 174     *
 175     * If this is not a loop induction variable, NULL.
 176     */
 177    ir_rvalue *increment;
 178
 179
 180    inline bool is_induction_var() const
 181    {
 182       /* Induction variables always have a non-null increment, and vice
 183        * versa.
 184        */
 185       return this->increment != NULL;
 186    }
 187
 188
 189    inline bool is_loop_constant() const
 190    {
 191       const bool is_const = (this->num_assignments == 0)
 192          || (((this->num_assignments == 1)
 193              && !this->conditional_or_nested_assignment
 194              && !this->read_before_write
 195              && this->rhs_clean) || this->var->data.read_only);
 196
 197       /* If the RHS of *the* assignment is clean, then there must be exactly
 198        * one assignment of the variable.
 199        */
 200       assert((this->rhs_clean && (this->num_assignments == 1))
 201              || !this->rhs_clean);
 202
 203       return is_const;
 204    }
 205
 206    void record_reference(bool in_assignee,
 207                          bool in_conditional_code_or_nested_loop,
 208                          ir_assignment *current_assignment);
 209 };
 210
 211
 212 class loop_terminator : public exec_node {
 213 public:
 214    loop_terminator()
 215       : ir(NULL), iterations(-1)
 216    {
 217    }
 218
 219    /**
 220     * Statement which terminates the loop.
 221     */
 222    ir_if *ir;
 223
 224    /**
 225     * The number of iterations after which the terminator is known to
 226     * terminate the loop (if that is a fixed value).  Otherwise -1.
 227     */
 228    int iterations;
 229 };
 230
 231
 232 class loop_state {
 233 public:
 234    ~loop_state();
 235
 236    /**
 237     * Get the loop variable state data for a particular loop
 238     */
 239    loop_variable_state *get(const ir_loop *);
 240
 241    loop_variable_state *insert(ir_loop *ir);
 242
 243    bool loop_found;
 244
 245 private:
 246    loop_state();
 247
 248    /**
 249     * Hash table containing all loops that have been analyzed.
 250     */
 251    hash_table *ht;
 252
 253    void *mem_ctx;
 254
 255    friend loop_state *analyze_loop_variables(exec_list *instructions);
 256 };
 257
 258 #endif /* LOOP_ANALYSIS_H */