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 * - INT_DIV_TO_MUL_RCP 36 * - EXP_TO_EXP2 37 * - POW_TO_EXP2 38 * - LOG_TO_LOG2 39 * - MOD_TO_FRACT 40 * 41 * SUB_TO_ADD_NEG: 42 * --------------- 43 * Breaks an ir_binop_sub expression down to add(op0, neg(op1)) 44 * 45 * This simplifies expression reassociation, and for many backends 46 * there is no subtract operation separate from adding the negation. 47 * For backends with native subtract operations, they will probably 48 * want to recognize add(op0, neg(op1)) or the other way around to 49 * produce a subtract anyway. 50 * 51 * DIV_TO_MUL_RCP and INT_DIV_TO_MUL_RCP: 52 * -------------------------------------- 53 * Breaks an ir_binop_div expression down to op0 * (rcp(op1)). 54 * 55 * Many GPUs don't have a divide instruction (945 and 965 included), 56 * but they do have an RCP instruction to compute an approximate 57 * reciprocal. By breaking the operation down, constant reciprocals 58 * can get constant folded. 59 * 60 * DIV_TO_MUL_RCP only lowers floating point division; INT_DIV_TO_MUL_RCP 61 * handles the integer case, converting to and from floating point so that 62 * RCP is possible. 63 * 64 * EXP_TO_EXP2 and LOG_TO_LOG2: 65 * ---------------------------- 66 * Many GPUs don't have a base e log or exponent instruction, but they 67 * do have base 2 versions, so this pass converts exp and log to exp2 68 * and log2 operations. 69 * 70 * POW_TO_EXP2: 71 * ----------- 72 * Many older GPUs don't have an x**y instruction. For these GPUs, convert 73 * x**y to 2**(y * log2(x)). 74 * 75 * MOD_TO_FRACT: 76 * ------------- 77 * Breaks an ir_binop_mod expression down to (op1 * fract(op0 / op1)) 78 * 79 * Many GPUs don't have a MOD instruction (945 and 965 included), and 80 * if we have to break it down like this anyway, it gives an 81 * opportunity to do things like constant fold the (1.0 / op1) easily. 82 */ 83 84 #include "main/core.h" /* for M_LOG2E */ 85 #include "glsl_types.h" 86 #include "ir.h" 87 #include "ir_optimization.h" 88 89 class lower_instructions_visitor : public ir_hierarchical_visitor { 90 public: 91 lower_instructions_visitor(unsigned lower) 92 : progress(false), lower(lower) { } 93 94 ir_visitor_status visit_leave(ir_expression *); 95 96 bool progress; 97 98 private: 99 unsigned lower; /** Bitfield of which operations to lower */ 100 101 void sub_to_add_neg(ir_expression *); 102 void div_to_mul_rcp(ir_expression *); 103 void int_div_to_mul_rcp(ir_expression *); 104 void mod_to_fract(ir_expression *); 105 void exp_to_exp2(ir_expression *); 106 void pow_to_exp2(ir_expression *); 107 void log_to_log2(ir_expression *); 108 }; 109 110 /** 111 * Determine if a particular type of lowering should occur 112 */ 113 #define lowering(x) (this->lower & x) 114 115 bool 116 lower_instructions(exec_list *instructions, unsigned what_to_lower) 117 { 118 lower_instructions_visitor v(what_to_lower); 119 120 visit_list_elements(&v, instructions); 121 return v.progress; 122 } 123 124 void 125 lower_instructions_visitor::sub_to_add_neg(ir_expression *ir) 126 { 127 ir->operation = ir_binop_add; 128 ir->operands[1] = new(ir) ir_expression(ir_unop_neg, ir->operands[1]->type, 129 ir->operands[1], NULL); 130 this->progress = true; 131 } 132 133 void 134 lower_instructions_visitor::div_to_mul_rcp(ir_expression *ir) 135 { 136 assert(ir->operands[1]->type->is_float()); 137 138 /* New expression for the 1.0 / op1 */ 139 ir_rvalue *expr; 140 expr = new(ir) ir_expression(ir_unop_rcp, 141 ir->operands[1]->type, 142 ir->operands[1]); 143 144 /* op0 / op1 -> op0 * (1.0 / op1) */ 145 ir->operation = ir_binop_mul; 146 ir->operands[1] = expr; 147 148 this->progress = true; 149 } 150 151 void 152 lower_instructions_visitor::int_div_to_mul_rcp(ir_expression *ir) 153 { 154 assert(ir->operands[1]->type->is_integer()); 155 156 /* Be careful with integer division -- we need to do it as a 157 * float and re-truncate, since rcp(n > 1) of an integer would 158 * just be 0. 159 */ 160 ir_rvalue *op0, *op1; 161 const struct glsl_type *vec_type; 162 163 vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT, 164 ir->operands[1]->type->vector_elements, 165 ir->operands[1]->type->matrix_columns); 166 167 if (ir->operands[1]->type->base_type == GLSL_TYPE_INT) 168 op1 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[1], NULL); 169 else 170 op1 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[1], NULL); 171 172 op1 = new(ir) ir_expression(ir_unop_rcp, op1->type, op1, NULL); 173 174 vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT, 175 ir->operands[0]->type->vector_elements, 176 ir->operands[0]->type->matrix_columns); 177 178 if (ir->operands[0]->type->base_type == GLSL_TYPE_INT) 179 op0 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[0], NULL); 180 else 181 op0 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[0], NULL); 182 183 vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT, 184 ir->type->vector_elements, 185 ir->type->matrix_columns); 186 187 op0 = new(ir) ir_expression(ir_binop_mul, vec_type, op0, op1); 188 189 if (ir->operands[1]->type->base_type == GLSL_TYPE_INT) { 190 ir->operation = ir_unop_f2i; 191 ir->operands[0] = op0; 192 } else { 193 ir->operation = ir_unop_i2u; 194 ir->operands[0] = new(ir) ir_expression(ir_unop_f2i, op0); 195 } 196 ir->operands[1] = NULL; 197 198 this->progress = true; 199 } 200 201 void 202 lower_instructions_visitor::exp_to_exp2(ir_expression *ir) 203 { 204 ir_constant *log2_e = new(ir) ir_constant(float(M_LOG2E)); 205 206 ir->operation = ir_unop_exp2; 207 ir->operands[0] = new(ir) ir_expression(ir_binop_mul, ir->operands[0]->type, 208 ir->operands[0], log2_e); 209 this->progress = true; 210 } 211 212 void 213 lower_instructions_visitor::pow_to_exp2(ir_expression *ir) 214 { 215 ir_expression *const log2_x = 216 new(ir) ir_expression(ir_unop_log2, ir->operands[0]->type, 217 ir->operands[0]); 218 219 ir->operation = ir_unop_exp2; 220 ir->operands[0] = new(ir) ir_expression(ir_binop_mul, ir->operands[1]->type, 221 ir->operands[1], log2_x); 222 ir->operands[1] = NULL; 223 this->progress = true; 224 } 225 226 void 227 lower_instructions_visitor::log_to_log2(ir_expression *ir) 228 { 229 ir->operation = ir_binop_mul; 230 ir->operands[0] = new(ir) ir_expression(ir_unop_log2, ir->operands[0]->type, 231 ir->operands[0], NULL); 232 ir->operands[1] = new(ir) ir_constant(float(1.0 / M_LOG2E)); 233 this->progress = true; 234 } 235 236 void 237 lower_instructions_visitor::mod_to_fract(ir_expression *ir) 238 { 239 ir_variable *temp = new(ir) ir_variable(ir->operands[1]->type, "mod_b", 240 ir_var_temporary); 241 this->base_ir->insert_before(temp); 242 243 ir_assignment *const assign = 244 new(ir) ir_assignment(new(ir) ir_dereference_variable(temp), 245 ir->operands[1], NULL); 246 247 this->base_ir->insert_before(assign); 248 249 ir_expression *const div_expr = 250 new(ir) ir_expression(ir_binop_div, ir->operands[0]->type, 251 ir->operands[0], 252 new(ir) ir_dereference_variable(temp)); 253 254 /* Don't generate new IR that would need to be lowered in an additional 255 * pass. 256 */ 257 if (lowering(DIV_TO_MUL_RCP)) 258 div_to_mul_rcp(div_expr); 259 260 ir_rvalue *expr = new(ir) ir_expression(ir_unop_fract, 261 ir->operands[0]->type, 262 div_expr, 263 NULL); 264 265 ir->operation = ir_binop_mul; 266 ir->operands[0] = new(ir) ir_dereference_variable(temp); 267 ir->operands[1] = expr; 268 this->progress = true; 269 } 270 271 ir_visitor_status 272 lower_instructions_visitor::visit_leave(ir_expression *ir) 273 { 274 switch (ir->operation) { 275 case ir_binop_sub: 276 if (lowering(SUB_TO_ADD_NEG)) 277 sub_to_add_neg(ir); 278 break; 279 280 case ir_binop_div: 281 if (ir->operands[1]->type->is_integer() && lowering(INT_DIV_TO_MUL_RCP)) 282 int_div_to_mul_rcp(ir); 283 else if (ir->operands[1]->type->is_float() && lowering(DIV_TO_MUL_RCP)) 284 div_to_mul_rcp(ir); 285 break; 286 287 case ir_unop_exp: 288 if (lowering(EXP_TO_EXP2)) 289 exp_to_exp2(ir); 290 break; 291 292 case ir_unop_log: 293 if (lowering(LOG_TO_LOG2)) 294 log_to_log2(ir); 295 break; 296 297 case ir_binop_mod: 298 if (lowering(MOD_TO_FRACT) && ir->type->is_float()) 299 mod_to_fract(ir); 300 break; 301 302 case ir_binop_pow: 303 if (lowering(POW_TO_EXP2)) 304 pow_to_exp2(ir); 305 break; 306 307 default: 308 return visit_continue; 309 } 310 311 return visit_continue; 312 } 313
