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_terminator *insert(ir_if *);
  71
  72
  73    /**
  74     * Loop whose variable state is being tracked by this structure
  75     */
  76    ir_loop *loop;
  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     * Hash table containing all variables accessed in this loop
 108     */
 109    hash_table *var_hash;
 110
 111    /**
 112     * Maximum number of loop iterations.
 113     *
 114     * If this value is negative, then the loop may be infinite.  This actually
 115     * means that analysis was unable to determine an upper bound on the number
 116     * of loop iterations.
 117     */
 118    int max_iterations;
 119
 120    /**
 121     * Number of ir_loop_jump instructions that operate on this loop
 122     */
 123    unsigned num_loop_jumps;
 124
 125    loop_variable_state()
 126    {
 127       this->max_iterations = -1;
 128       this->num_loop_jumps = 0;
 129       this->var_hash = hash_table_ctor(0, hash_table_pointer_hash,
 130                                        hash_table_pointer_compare);
 131    }
 132
 133    ~loop_variable_state()
 134    {
 135       hash_table_dtor(this->var_hash);
 136    }
 137 };
 138
 139
 140 class loop_variable : public exec_node {
 141 public:
 142    /** The variable in question. */
 143    ir_variable *var;
 144
 145    /** Is the variable read in the loop before it is written? */
 146    bool read_before_write;
 147
 148    /** Are all variables in the RHS of the assignment loop constants? */
 149    bool rhs_clean;
 150
 151    /** Is there an assignment to the variable that is conditional? */
 152    bool conditional_assignment;
 153
 154    /** Reference to the first assignment to the variable in the loop body. */
 155    ir_assignment *first_assignment;
 156
 157    /** Number of assignments to the variable in the loop body. */
 158    unsigned num_assignments;
 159
 160    /**
 161     * Increment values for loop induction variables
 162     *
 163     * Loop induction variables have a single increment of the form
 164     * \c b * \c biv + \c c, where \c b and \c c are loop constants and \c i
 165     * is a basic loop induction variable.
 166     *
 167     * If \c iv_scale is \c NULL, 1 is used.  If \c biv is the same as \c var,
 168     * then \c var is a basic loop induction variable.
 169     */
 170    /*@{*/
 171    ir_rvalue *iv_scale;
 172    ir_variable *biv;
 173    ir_rvalue *increment;
 174    /*@}*/
 175
 176
 177    inline bool is_loop_constant() const
 178    {
 179       const bool is_const = (this->num_assignments == 0)
 180          || ((this->num_assignments == 1)
 181              && !this->conditional_assignment
 182              && !this->read_before_write
 183              && this->rhs_clean);
 184
 185       /* If the RHS of *the* assignment is clean, then there must be exactly
 186        * one assignment of the variable.
 187        */
 188       assert((this->rhs_clean && (this->num_assignments == 1))
 189              || !this->rhs_clean);
 190
 191       /* Variables that are marked read-only *MUST* be loop constant.
 192        */
 193       assert(!this->var->read_only || (this->var->read_only && is_const));
 194
 195       return is_const;
 196    }
 197 };
 198
 199
 200 class loop_terminator : public exec_node {
 201 public:
 202    ir_if *ir;
 203 };
 204
 205
 206 class loop_state {
 207 public:
 208    ~loop_state();
 209
 210    /**
 211     * Get the loop variable state data for a particular loop
 212     */
 213    loop_variable_state *get(const ir_loop *);
 214
 215    loop_variable_state *insert(ir_loop *ir);
 216
 217    bool loop_found;
 218
 219 private:
 220    loop_state();
 221
 222    /**
 223     * Hash table containing all loops that have been analyzed.
 224     */
 225    hash_table *ht;
 226
 227    void *mem_ctx;
 228
 229    friend class loop_analysis;
 230 };
 231
 232 #endif /* LOOP_ANALYSIS_H */