src/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 sequences
  43  * in the loop of the form
  44  *
  45  *  (if (expression bool ...) (break))
  46  *
  47  * and fill in the \c ir_loop::from, \c ir_loop::to, and \c ir_loop::counter
  48  * fields of the \c ir_loop.
  49  *
  50  * In this process, some conditional break-statements may be eliminated
  51  * altogether.  For example, if it is provable that one loop exit condition will
  52  * always be satisfied before another, the unnecessary exit condition will be
  53  * removed.
  54  */
  55 extern bool
  56 set_loop_controls(exec_list *instructions, loop_state *ls);
  57
  58
  59 extern bool
  60 unroll_loops(exec_list *instructions, loop_state *ls, unsigned max_iterations);
  61
  62
  63 /**
  64  * Tracking for all variables used in a loop
  65  */
  66 class loop_variable_state : public exec_node {
  67 public:
  68    class loop_variable *get(const ir_variable *);
  69    class loop_variable *insert(ir_variable *);
  70    class loop_variable *get_or_insert(ir_variable *, bool in_assignee);
  71    class loop_terminator *insert(ir_if *);
  72
  73
  74    /**
  75     * Variables that have not yet been classified
  76     */
  77    exec_list variables;
  78
  79    /**
  80     * Variables whose values are constant within the body of the loop
  81     *
  82     * This list contains \c loop_variable objects.
  83     */
  84    exec_list constants;
  85
  86    /**
  87     * Induction variables for this loop
  88     *
  89     * This list contains \c loop_variable objects.
  90     */
  91    exec_list induction_variables;
  92
  93    /**
  94     * Simple if-statements that lead to the termination of the loop
  95     *
  96     * This list contains \c loop_terminator objects.
  97     *
  98     * \sa is_loop_terminator
  99     */
 100    exec_list terminators;
 101
 102    /**
 103     * Hash table containing all variables accessed in this loop
 104     */
 105    hash_table *var_hash;
 106
 107    /**
 108     * Maximum number of loop iterations.
 109     *
 110     * If this value is negative, then the loop may be infinite.  This actually
 111     * means that analysis was unable to determine an upper bound on the number
 112     * of loop iterations.
 113     */
 114    int max_iterations;
 115
 116    /**
 117     * Number of ir_loop_jump instructions that operate on this loop
 118     */
 119    unsigned num_loop_jumps;
 120
 121    /**
 122     * Whether this loop contains any function calls.
 123     */
 124    bool contains_calls;
 125
 126    loop_variable_state()
 127    {
 128       this->max_iterations = -1;
 129       this->num_loop_jumps = 0;
 130       this->contains_calls = false;
 131       this->var_hash = hash_table_ctor(0, hash_table_pointer_hash,
 132                                        hash_table_pointer_compare);
 133    }
 134
 135    ~loop_variable_state()
 136    {
 137       hash_table_dtor(this->var_hash);
 138    }
 139
 140    static void* operator new(size_t size, void *ctx)
 141    {
 142       void *lvs = ralloc_size(ctx, size);
 143       assert(lvs != NULL);
 144
 145       ralloc_set_destructor(lvs, (void (*)(void*)) destructor);
 146
 147       return lvs;
 148    }
 149
 150 private:
 151    static void
 152    destructor(loop_variable_state *lvs)
 153    {
 154       lvs->~loop_variable_state();
 155    }
 156 };
 157
 158
 159 class loop_variable : public exec_node {
 160 public:
 161    /** The variable in question. */
 162    ir_variable *var;
 163
 164    /** Is the variable read in the loop before it is written? */
 165    bool read_before_write;
 166
 167    /** Are all variables in the RHS of the assignment loop constants? */
 168    bool rhs_clean;
 169
 170    /**
 171     * Is there an assignment to the variable that is conditional, or inside a
 172     * nested loop?
 173     */
 174    bool conditional_or_nested_assignment;
 175
 176    /** Reference to the first assignment to the variable in the loop body. */
 177    ir_assignment *first_assignment;
 178
 179    /** Number of assignments to the variable in the loop body. */
 180    unsigned num_assignments;
 181
 182    /**
 183     * Increment values for loop induction variables
 184     *
 185     * Loop induction variables have a single increment of the form
 186     * \c b * \c biv + \c c, where \c b and \c c are loop constants and \c i
 187     * is a basic loop induction variable.
 188     *
 189     * If \c iv_scale is \c NULL, 1 is used.  If \c biv is the same as \c var,
 190     * then \c var is a basic loop induction variable.
 191     */
 192    /*@{*/
 193    ir_rvalue *iv_scale;
 194    ir_variable *biv;
 195    ir_rvalue *increment;
 196    /*@}*/
 197
 198
 199    inline bool is_loop_constant() const
 200    {
 201       const bool is_const = (this->num_assignments == 0)
 202          || ((this->num_assignments == 1)
 203              && !this->conditional_or_nested_assignment
 204              && !this->read_before_write
 205              && this->rhs_clean);
 206
 207       /* If the RHS of *the* assignment is clean, then there must be exactly
 208        * one assignment of the variable.
 209        */
 210       assert((this->rhs_clean && (this->num_assignments == 1))
 211              || !this->rhs_clean);
 212
 213       /* Variables that are marked read-only *MUST* be loop constant.
 214        */
 215       assert(!this->var->read_only || (this->var->read_only && is_const));
 216
 217       return is_const;
 218    }
 219
 220    void record_reference(bool in_assignee,
 221                          bool in_conditional_code_or_nested_loop,
 222                          ir_assignment *current_assignment);
 223 };
 224
 225
 226 class loop_terminator : public exec_node {
 227 public:
 228    ir_if *ir;
 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 */