src/glsl/lower_instructions.cpp

   1 /*
   2  * Copyright © 2010 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  21  * DEALINGS IN THE SOFTWARE.
  22  */
  23
  24 /**
  25  * \file lower_instructions.cpp
  26  *
  27  * Many GPUs lack native instructions for certain expression operations, and
  28  * must replace them with some other expression tree.  This pass lowers some
  29  * of the most common cases, allowing the lowering code to be implemented once
  30  * rather than in each driver backend.
  31  *
  32  * Currently supported transformations:
  33  * - SUB_TO_ADD_NEG
  34  * - DIV_TO_MUL_RCP
  35  * - EXP_TO_EXP2
  36  * - POW_TO_EXP2
  37  * - LOG_TO_LOG2
  38  * - MOD_TO_FRACT
  39  *
  40  * SUB_TO_ADD_NEG:
  41  * ---------------
  42  * Breaks an ir_binop_sub expression down to add(op0, neg(op1))
  43  *
  44  * This simplifies expression reassociation, and for many backends
  45  * there is no subtract operation separate from adding the negation.
  46  * For backends with native subtract operations, they will probably
  47  * want to recognize add(op0, neg(op1)) or the other way around to
  48  * produce a subtract anyway.
  49  *
  50  * DIV_TO_MUL_RCP:
  51  * ---------------
  52  * Breaks an ir_unop_div expression down to op0 * (rcp(op1)).
  53  *
  54  * Many GPUs don't have a divide instruction (945 and 965 included),
  55  * but they do have an RCP instruction to compute an approximate
  56  * reciprocal.  By breaking the operation down, constant reciprocals
  57  * can get constant folded.
  58  *
  59  * EXP_TO_EXP2 and LOG_TO_LOG2:
  60  * ----------------------------
  61  * Many GPUs don't have a base e log or exponent instruction, but they
  62  * do have base 2 versions, so this pass converts exp and log to exp2
  63  * and log2 operations.
  64  *
  65  * POW_TO_EXP2:
  66  * -----------
  67  * Many older GPUs don't have an x**y instruction.  For these GPUs, convert
  68  * x**y to 2**(y * log2(x)).
  69  *
  70  * MOD_TO_FRACT:
  71  * -------------
  72  * Breaks an ir_unop_mod expression down to (op1 * fract(op0 / op1))
  73  *
  74  * Many GPUs don't have a MOD instruction (945 and 965 included), and
  75  * if we have to break it down like this anyway, it gives an
  76  * opportunity to do things like constant fold the (1.0 / op1) easily.
  77  */
  78
  79 #include "main/core.h" /* for M_LOG2E */
  80 #include "glsl_types.h"
  81 #include "ir.h"
  82 #include "ir_optimization.h"
  83
  84 class lower_instructions_visitor : public ir_hierarchical_visitor {
  85 public:
  86    lower_instructions_visitor(unsigned lower)
  87       : progress(false), lower(lower) { }
  88
  89    ir_visitor_status visit_leave(ir_expression *);
  90
  91    bool progress;
  92
  93 private:
  94    unsigned lower; /** Bitfield of which operations to lower */
  95
  96    void sub_to_add_neg(ir_expression *);
  97    void div_to_mul_rcp(ir_expression *);
  98    void mod_to_fract(ir_expression *);
  99    void exp_to_exp2(ir_expression *);
 100    void pow_to_exp2(ir_expression *);
 101    void log_to_log2(ir_expression *);
 102 };
 103
 104 /**
 105  * Determine if a particular type of lowering should occur
 106  */
 107 #define lowering(x) (this->lower & x)
 108
 109 bool
 110 lower_instructions(exec_list *instructions, unsigned what_to_lower)
 111 {
 112    lower_instructions_visitor v(what_to_lower);
 113
 114    visit_list_elements(&v, instructions);
 115    return v.progress;
 116 }
 117
 118 void
 119 lower_instructions_visitor::sub_to_add_neg(ir_expression *ir)
 120 {
 121    ir->operation = ir_binop_add;
 122    ir->operands[1] = new(ir) ir_expression(ir_unop_neg, ir->operands[1]->type,
 123                                            ir->operands[1], NULL);
 124    this->progress = true;
 125 }
 126
 127 void
 128 lower_instructions_visitor::div_to_mul_rcp(ir_expression *ir)
 129 {
 130    if (!ir->operands[1]->type->is_integer()) {
 131       /* New expression for the 1.0 / op1 */
 132       ir_rvalue *expr;
 133       expr = new(ir) ir_expression(ir_unop_rcp,
 134                                    ir->operands[1]->type,
 135                                    ir->operands[1],
 136                                    NULL);
 137
 138       /* op0 / op1 -> op0 * (1.0 / op1) */
 139       ir->operation = ir_binop_mul;
 140       ir->operands[1] = expr;
 141    } else {
 142       /* Be careful with integer division -- we need to do it as a
 143        * float and re-truncate, since rcp(n > 1) of an integer would
 144        * just be 0.
 145        */
 146       ir_rvalue *op0, *op1;
 147       const struct glsl_type *vec_type;
 148
 149       vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
 150                                          ir->operands[1]->type->vector_elements,
 151                                          ir->operands[1]->type->matrix_columns);
 152
 153       if (ir->operands[1]->type->base_type == GLSL_TYPE_INT)
 154          op1 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[1], NULL);
 155       else
 156          op1 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[1], NULL);
 157
 158       op1 = new(ir) ir_expression(ir_unop_rcp, op1->type, op1, NULL);
 159
 160       vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
 161                                          ir->operands[0]->type->vector_elements,
 162                                          ir->operands[0]->type->matrix_columns);
 163
 164       if (ir->operands[0]->type->base_type == GLSL_TYPE_INT)
 165          op0 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[0], NULL);
 166       else
 167          op0 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[0], NULL);
 168
 169       op0 = new(ir) ir_expression(ir_binop_mul, vec_type, op0, op1);
 170
 171       ir->operation = ir_unop_f2i;
 172       ir->operands[0] = op0;
 173       ir->operands[1] = NULL;
 174    }
 175
 176    this->progress = true;
 177 }
 178
 179 void
 180 lower_instructions_visitor::exp_to_exp2(ir_expression *ir)
 181 {
 182    ir_constant *log2_e = new(ir) ir_constant(float(M_LOG2E));
 183
 184    ir->operation = ir_unop_exp2;
 185    ir->operands[0] = new(ir) ir_expression(ir_binop_mul, ir->operands[0]->type,
 186                                            ir->operands[0], log2_e);
 187    this->progress = true;
 188 }
 189
 190 void
 191 lower_instructions_visitor::pow_to_exp2(ir_expression *ir)
 192 {
 193    ir_expression *const log2_x =
 194       new(ir) ir_expression(ir_unop_log2, ir->operands[0]->type,
 195                             ir->operands[0]);
 196
 197    ir->operation = ir_unop_exp2;
 198    ir->operands[0] = new(ir) ir_expression(ir_binop_mul, ir->operands[1]->type,
 199                                            ir->operands[1], log2_x);
 200    ir->operands[1] = NULL;
 201    this->progress = true;
 202 }
 203
 204 void
 205 lower_instructions_visitor::log_to_log2(ir_expression *ir)
 206 {
 207    ir->operation = ir_binop_mul;
 208    ir->operands[0] = new(ir) ir_expression(ir_unop_log2, ir->operands[0]->type,
 209                                            ir->operands[0], NULL);
 210    ir->operands[1] = new(ir) ir_constant(float(1.0 / M_LOG2E));
 211    this->progress = true;
 212 }
 213
 214 void
 215 lower_instructions_visitor::mod_to_fract(ir_expression *ir)
 216 {
 217    ir_variable *temp = new(ir) ir_variable(ir->operands[1]->type, "mod_b",
 218                                            ir_var_temporary);
 219    this->base_ir->insert_before(temp);
 220
 221    ir_assignment *const assign =
 222       new(ir) ir_assignment(new(ir) ir_dereference_variable(temp),
 223                             ir->operands[1], NULL);
 224
 225    this->base_ir->insert_before(assign);
 226
 227    ir_expression *const div_expr =
 228       new(ir) ir_expression(ir_binop_div, ir->operands[0]->type,
 229                             ir->operands[0],
 230                             new(ir) ir_dereference_variable(temp));
 231
 232    /* Don't generate new IR that would need to be lowered in an additional
 233     * pass.
 234     */
 235    if (lowering(DIV_TO_MUL_RCP))
 236       div_to_mul_rcp(div_expr);
 237
 238    ir_rvalue *expr = new(ir) ir_expression(ir_unop_fract,
 239                                            ir->operands[0]->type,
 240                                            div_expr,
 241                                            NULL);
 242
 243    ir->operation = ir_binop_mul;
 244    ir->operands[0] = new(ir) ir_dereference_variable(temp);
 245    ir->operands[1] = expr;
 246    this->progress = true;
 247 }
 248
 249 ir_visitor_status
 250 lower_instructions_visitor::visit_leave(ir_expression *ir)
 251 {
 252    switch (ir->operation) {
 253    case ir_binop_sub:
 254       if (lowering(SUB_TO_ADD_NEG))
 255          sub_to_add_neg(ir);
 256       break;
 257
 258    case ir_binop_div:
 259       if (lowering(DIV_TO_MUL_RCP))
 260          div_to_mul_rcp(ir);
 261       break;
 262
 263    case ir_unop_exp:
 264       if (lowering(EXP_TO_EXP2))
 265          exp_to_exp2(ir);
 266       break;
 267
 268    case ir_unop_log:
 269       if (lowering(LOG_TO_LOG2))
 270          log_to_log2(ir);
 271       break;
 272
 273    case ir_binop_mod:
 274       if (lowering(MOD_TO_FRACT))
 275          mod_to_fract(ir);
 276       break;
 277
 278    case ir_binop_pow:
 279       if (lowering(POW_TO_EXP2))
 280          pow_to_exp2(ir);
 281       break;
 282
 283    default:
 284       return visit_continue;
 285    }
 286
 287    return visit_continue;
 288 }