src/mesa/drivers/dri/i965/brw_fs_cse.cpp

   1 /*
   2  * Copyright © 2012 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 DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include "brw_fs.h"
  25 #include "brw_cfg.h"
  26
  27 /** @file brw_fs_cse.cpp
  28  *
  29  * Support for local common subexpression elimination.
  30  *
  31  * See Muchnick's Advanced Compiler Design and Implementation, section
  32  * 13.1 (p378).
  33  */
  34
  35 namespace {
  36 struct aeb_entry : public exec_node {
  37    /** The instruction that generates the expression value. */
  38    fs_inst *generator;
  39
  40    /** The temporary where the value is stored. */
  41    fs_reg tmp;
  42 };
  43 }
  44
  45 static bool
  46 is_copy_payload(const fs_inst *inst)
  47 {
  48    const int reg = inst->src[0].reg;
  49    if (inst->src[0].reg_offset != 0)
  50       return false;
  51
  52    for (int i = 1; i < inst->sources; i++) {
  53       if (inst->src[i].reg != reg ||
  54           inst->src[i].reg_offset != i) {
  55          return false;
  56       }
  57    }
  58    return true;
  59 }
  60
  61 static bool
  62 is_expression(const fs_inst *const inst)
  63 {
  64    switch (inst->opcode) {
  65    case BRW_OPCODE_MOV:
  66    case BRW_OPCODE_SEL:
  67    case BRW_OPCODE_NOT:
  68    case BRW_OPCODE_AND:
  69    case BRW_OPCODE_OR:
  70    case BRW_OPCODE_XOR:
  71    case BRW_OPCODE_SHR:
  72    case BRW_OPCODE_SHL:
  73    case BRW_OPCODE_ASR:
  74    case BRW_OPCODE_CMP:
  75    case BRW_OPCODE_CMPN:
  76    case BRW_OPCODE_ADD:
  77    case BRW_OPCODE_MUL:
  78    case BRW_OPCODE_FRC:
  79    case BRW_OPCODE_RNDU:
  80    case BRW_OPCODE_RNDD:
  81    case BRW_OPCODE_RNDE:
  82    case BRW_OPCODE_RNDZ:
  83    case BRW_OPCODE_LINE:
  84    case BRW_OPCODE_PLN:
  85    case BRW_OPCODE_MAD:
  86    case BRW_OPCODE_LRP:
  87    case FS_OPCODE_UNIFORM_PULL_CONSTANT_LOAD:
  88    case FS_OPCODE_VARYING_PULL_CONSTANT_LOAD_GEN7:
  89    case FS_OPCODE_VARYING_PULL_CONSTANT_LOAD:
  90    case FS_OPCODE_CINTERP:
  91    case FS_OPCODE_LINTERP:
  92       return true;
  93    case SHADER_OPCODE_RCP:
  94    case SHADER_OPCODE_RSQ:
  95    case SHADER_OPCODE_SQRT:
  96    case SHADER_OPCODE_EXP2:
  97    case SHADER_OPCODE_LOG2:
  98    case SHADER_OPCODE_POW:
  99    case SHADER_OPCODE_INT_QUOTIENT:
 100    case SHADER_OPCODE_INT_REMAINDER:
 101    case SHADER_OPCODE_SIN:
 102    case SHADER_OPCODE_COS:
 103       return inst->mlen < 2;
 104    case SHADER_OPCODE_LOAD_PAYLOAD:
 105       return !is_copy_payload(inst);
 106    default:
 107       return inst->is_send_from_grf() && !inst->has_side_effects();
 108    }
 109 }
 110
 111 static bool
 112 is_expression_commutative(const fs_inst *inst)
 113 {
 114    switch (inst->opcode) {
 115    case BRW_OPCODE_AND:
 116    case BRW_OPCODE_OR:
 117    case BRW_OPCODE_XOR:
 118    case BRW_OPCODE_ADD:
 119    case BRW_OPCODE_MUL:
 120       return true;
 121    case BRW_OPCODE_SEL:
 122       /* MIN and MAX are commutative. */
 123       if (inst->conditional_mod == BRW_CONDITIONAL_GE ||
 124           inst->conditional_mod == BRW_CONDITIONAL_L) {
 125          return true;
 126       }
 127       /* fallthrough */
 128    default:
 129       return false;
 130    }
 131 }
 132
 133 static bool
 134 operands_match(const fs_inst *a, const fs_inst *b)
 135 {
 136    fs_reg *xs = a->src;
 137    fs_reg *ys = b->src;
 138
 139    if (a->opcode == BRW_OPCODE_MAD) {
 140       return xs[0].equals(ys[0]) &&
 141              ((xs[1].equals(ys[1]) && xs[2].equals(ys[2])) ||
 142               (xs[2].equals(ys[1]) && xs[1].equals(ys[2])));
 143    } else if (!is_expression_commutative(a)) {
 144       bool match = true;
 145       for (int i = 0; i < a->sources; i++) {
 146          if (!xs[i].equals(ys[i])) {
 147             match = false;
 148             break;
 149          }
 150       }
 151       return match;
 152    } else {
 153       return (xs[0].equals(ys[0]) && xs[1].equals(ys[1])) ||
 154              (xs[1].equals(ys[0]) && xs[0].equals(ys[1]));
 155    }
 156 }
 157
 158 static bool
 159 instructions_match(fs_inst *a, fs_inst *b)
 160 {
 161    return a->opcode == b->opcode &&
 162           a->saturate == b->saturate &&
 163           a->predicate == b->predicate &&
 164           a->predicate_inverse == b->predicate_inverse &&
 165           a->conditional_mod == b->conditional_mod &&
 166           a->dst.type == b->dst.type &&
 167           a->sources == b->sources &&
 168           (a->is_tex() ? (a->offset == b->offset &&
 169                           a->mlen == b->mlen &&
 170                           a->regs_written == b->regs_written &&
 171                           a->base_mrf == b->base_mrf &&
 172                           a->eot == b->eot &&
 173                           a->header_present == b->header_present &&
 174                           a->shadow_compare == b->shadow_compare)
 175                        : true) &&
 176           operands_match(a, b);
 177 }
 178
 179 bool
 180 fs_visitor::opt_cse_local(bblock_t *block)
 181 {
 182    bool progress = false;
 183    exec_list aeb;
 184
 185    void *cse_ctx = ralloc_context(NULL);
 186
 187    int ip = block->start_ip;
 188    foreach_inst_in_block(fs_inst, inst, block) {
 189       /* Skip some cases. */
 190       if (is_expression(inst) && !inst->is_partial_write() &&
 191           (inst->dst.file != HW_REG || inst->dst.is_null()))
 192       {
 193          bool found = false;
 194
 195          foreach_in_list_use_after(aeb_entry, entry, &aeb) {
 196             /* Match current instruction's expression against those in AEB. */
 197             if (instructions_match(inst, entry->generator)) {
 198                found = true;
 199                progress = true;
 200                break;
 201             }
 202          }
 203
 204          if (!found) {
 205             if (inst->opcode != BRW_OPCODE_MOV ||
 206                 (inst->opcode == BRW_OPCODE_MOV &&
 207                  inst->src[0].file == IMM &&
 208                  inst->src[0].type == BRW_REGISTER_TYPE_VF)) {
 209                /* Our first sighting of this expression.  Create an entry. */
 210                aeb_entry *entry = ralloc(cse_ctx, aeb_entry);
 211                entry->tmp = reg_undef;
 212                entry->generator = inst;
 213                aeb.push_tail(entry);
 214             }
 215          } else {
 216             /* This is at least our second sighting of this expression.
 217              * If we don't have a temporary already, make one.
 218              */
 219             bool no_existing_temp = entry->tmp.file == BAD_FILE;
 220             if (no_existing_temp && !entry->generator->dst.is_null()) {
 221                int written = entry->generator->regs_written;
 222                int dst_width = entry->generator->dst.width / 8;
 223                assert(written % dst_width == 0);
 224
 225                fs_reg orig_dst = entry->generator->dst;
 226                fs_reg tmp = fs_reg(GRF, virtual_grf_alloc(written),
 227                                    orig_dst.type, orig_dst.width);
 228                entry->tmp = tmp;
 229                entry->generator->dst = tmp;
 230
 231                fs_inst *copy;
 232                if (written > dst_width) {
 233                   fs_reg *sources = ralloc_array(mem_ctx, fs_reg, written / dst_width);
 234                   for (int i = 0; i < written / dst_width; i++)
 235                      sources[i] = offset(tmp, i);
 236                   copy = LOAD_PAYLOAD(orig_dst, sources, written / dst_width);
 237                } else {
 238                   copy = MOV(orig_dst, tmp);
 239                   copy->force_writemask_all =
 240                      entry->generator->force_writemask_all;
 241                }
 242                entry->generator->insert_after(block, copy);
 243             }
 244
 245             /* dest <- temp */
 246             if (!inst->dst.is_null()) {
 247                int written = inst->regs_written;
 248                int dst_width = inst->dst.width / 8;
 249                assert(written == entry->generator->regs_written);
 250                assert(dst_width == entry->generator->dst.width / 8);
 251                assert(inst->dst.type == entry->tmp.type);
 252                fs_reg dst = inst->dst;
 253                fs_reg tmp = entry->tmp;
 254                fs_inst *copy;
 255                if (written > dst_width) {
 256                   fs_reg *sources = ralloc_array(mem_ctx, fs_reg, written / dst_width);
 257                   for (int i = 0; i < written / dst_width; i++)
 258                      sources[i] = offset(tmp, i);
 259                   copy = LOAD_PAYLOAD(dst, sources, written / dst_width);
 260                } else {
 261                   copy = MOV(dst, tmp);
 262                   copy->force_writemask_all = inst->force_writemask_all;
 263                }
 264                inst->insert_before(block, copy);
 265             }
 266
 267             /* Set our iterator so that next time through the loop inst->next
 268              * will get the instruction in the basic block after the one we've
 269              * removed.
 270              */
 271             fs_inst *prev = (fs_inst *)inst->prev;
 272
 273             inst->remove(block);
 274             inst = prev;
 275          }
 276       }
 277
 278       foreach_in_list_safe(aeb_entry, entry, &aeb) {
 279          /* Kill all AEB entries that write a different value to or read from
 280           * the flag register if we just wrote it.
 281           */
 282          if (inst->writes_flag()) {
 283             if (entry->generator->reads_flag() ||
 284                 (entry->generator->writes_flag() &&
 285                  !instructions_match(inst, entry->generator))) {
 286                entry->remove();
 287                ralloc_free(entry);
 288                continue;
 289             }
 290          }
 291
 292          for (int i = 0; i < entry->generator->sources; i++) {
 293             fs_reg *src_reg = &entry->generator->src[i];
 294
 295             /* Kill all AEB entries that use the destination we just
 296              * overwrote.
 297              */
 298             if (inst->overwrites_reg(entry->generator->src[i])) {
 299                entry->remove();
 300                ralloc_free(entry);
 301                break;
 302             }
 303
 304             /* Kill any AEB entries using registers that don't get reused any
 305              * more -- a sure sign they'll fail operands_match().
 306              */
 307             if (src_reg->file == GRF && virtual_grf_end[src_reg->reg] < ip) {
 308                entry->remove();
 309                ralloc_free(entry);
 310                break;
 311             }
 312          }
 313       }
 314
 315       ip++;
 316    }
 317
 318    ralloc_free(cse_ctx);
 319
 320    return progress;
 321 }
 322
 323 bool
 324 fs_visitor::opt_cse()
 325 {
 326    bool progress = false;
 327
 328    calculate_live_intervals();
 329
 330    foreach_block (block, cfg) {
 331       progress = opt_cse_local(block) || progress;
 332    }
 333
 334    if (progress)
 335       invalidate_live_intervals();
 336
 337    return progress;
 338 }