src/intel/compiler/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 using namespace brw;
  36
  37 namespace {
  38 struct aeb_entry : public exec_node {
  39    /** The instruction that generates the expression value. */
  40    fs_inst *generator;
  41
  42    /** The temporary where the value is stored. */
  43    fs_reg tmp;
  44 };
  45 }
  46
  47 static bool
  48 is_expression(const fs_visitor *v, const fs_inst *const inst)
  49 {
  50    switch (inst->opcode) {
  51    case BRW_OPCODE_MOV:
  52    case BRW_OPCODE_SEL:
  53    case BRW_OPCODE_NOT:
  54    case BRW_OPCODE_AND:
  55    case BRW_OPCODE_OR:
  56    case BRW_OPCODE_XOR:
  57    case BRW_OPCODE_SHR:
  58    case BRW_OPCODE_SHL:
  59    case BRW_OPCODE_ASR:
  60    case BRW_OPCODE_CMP:
  61    case BRW_OPCODE_CMPN:
  62    case BRW_OPCODE_ADD:
  63    case BRW_OPCODE_MUL:
  64    case SHADER_OPCODE_MULH:
  65    case BRW_OPCODE_FRC:
  66    case BRW_OPCODE_RNDU:
  67    case BRW_OPCODE_RNDD:
  68    case BRW_OPCODE_RNDE:
  69    case BRW_OPCODE_RNDZ:
  70    case BRW_OPCODE_LINE:
  71    case BRW_OPCODE_PLN:
  72    case BRW_OPCODE_MAD:
  73    case BRW_OPCODE_LRP:
  74    case FS_OPCODE_FB_READ_LOGICAL:
  75    case FS_OPCODE_UNIFORM_PULL_CONSTANT_LOAD:
  76    case FS_OPCODE_VARYING_PULL_CONSTANT_LOAD_LOGICAL:
  77    case FS_OPCODE_LINTERP:
  78    case SHADER_OPCODE_FIND_LIVE_CHANNEL:
  79    case FS_OPCODE_LOAD_LIVE_CHANNELS:
  80    case SHADER_OPCODE_BROADCAST:
  81    case SHADER_OPCODE_MOV_INDIRECT:
  82    case SHADER_OPCODE_TEX_LOGICAL:
  83    case SHADER_OPCODE_TXD_LOGICAL:
  84    case SHADER_OPCODE_TXF_LOGICAL:
  85    case SHADER_OPCODE_TXL_LOGICAL:
  86    case SHADER_OPCODE_TXS_LOGICAL:
  87    case FS_OPCODE_TXB_LOGICAL:
  88    case SHADER_OPCODE_TXF_CMS_LOGICAL:
  89    case SHADER_OPCODE_TXF_CMS_W_LOGICAL:
  90    case SHADER_OPCODE_TXF_UMS_LOGICAL:
  91    case SHADER_OPCODE_TXF_MCS_LOGICAL:
  92    case SHADER_OPCODE_LOD_LOGICAL:
  93    case SHADER_OPCODE_TG4_LOGICAL:
  94    case SHADER_OPCODE_TG4_OFFSET_LOGICAL:
  95    case FS_OPCODE_PACK:
  96       return true;
  97    case SHADER_OPCODE_RCP:
  98    case SHADER_OPCODE_RSQ:
  99    case SHADER_OPCODE_SQRT:
 100    case SHADER_OPCODE_EXP2:
 101    case SHADER_OPCODE_LOG2:
 102    case SHADER_OPCODE_POW:
 103    case SHADER_OPCODE_INT_QUOTIENT:
 104    case SHADER_OPCODE_INT_REMAINDER:
 105    case SHADER_OPCODE_SIN:
 106    case SHADER_OPCODE_COS:
 107       return inst->mlen < 2;
 108    case SHADER_OPCODE_LOAD_PAYLOAD:
 109       return !is_coalescing_payload(v->alloc, inst);
 110    default:
 111       return inst->is_send_from_grf() && !inst->has_side_effects() &&
 112          !inst->is_volatile();
 113    }
 114 }
 115
 116 static bool
 117 operands_match(const fs_inst *a, const fs_inst *b, bool *negate)
 118 {
 119    fs_reg *xs = a->src;
 120    fs_reg *ys = b->src;
 121
 122    if (a->opcode == BRW_OPCODE_MAD) {
 123       return xs[0].equals(ys[0]) &&
 124              ((xs[1].equals(ys[1]) && xs[2].equals(ys[2])) ||
 125               (xs[2].equals(ys[1]) && xs[1].equals(ys[2])));
 126    } else if (a->opcode == BRW_OPCODE_MUL && a->dst.type == BRW_REGISTER_TYPE_F) {
 127       bool xs0_negate = xs[0].negate;
 128       bool xs1_negate = xs[1].file == IMM ? xs[1].f < 0.0f
 129                                           : xs[1].negate;
 130       bool ys0_negate = ys[0].negate;
 131       bool ys1_negate = ys[1].file == IMM ? ys[1].f < 0.0f
 132                                           : ys[1].negate;
 133       float xs1_imm = xs[1].f;
 134       float ys1_imm = ys[1].f;
 135
 136       xs[0].negate = false;
 137       xs[1].negate = false;
 138       ys[0].negate = false;
 139       ys[1].negate = false;
 140       xs[1].f = fabsf(xs[1].f);
 141       ys[1].f = fabsf(ys[1].f);
 142
 143       bool ret = (xs[0].equals(ys[0]) && xs[1].equals(ys[1])) ||
 144                  (xs[1].equals(ys[0]) && xs[0].equals(ys[1]));
 145
 146       xs[0].negate = xs0_negate;
 147       xs[1].negate = xs[1].file == IMM ? false : xs1_negate;
 148       ys[0].negate = ys0_negate;
 149       ys[1].negate = ys[1].file == IMM ? false : ys1_negate;
 150       xs[1].f = xs1_imm;
 151       ys[1].f = ys1_imm;
 152
 153       *negate = (xs0_negate != xs1_negate) != (ys0_negate != ys1_negate);
 154       if (*negate && (a->saturate || b->saturate))
 155          return false;
 156       return ret;
 157    } else if (!a->is_commutative()) {
 158       bool match = true;
 159       for (int i = 0; i < a->sources; i++) {
 160          if (!xs[i].equals(ys[i])) {
 161             match = false;
 162             break;
 163          }
 164       }
 165       return match;
 166    } else {
 167       return (xs[0].equals(ys[0]) && xs[1].equals(ys[1])) ||
 168              (xs[1].equals(ys[0]) && xs[0].equals(ys[1]));
 169    }
 170 }
 171
 172 static bool
 173 instructions_match(fs_inst *a, fs_inst *b, bool *negate)
 174 {
 175    return a->opcode == b->opcode &&
 176           a->force_writemask_all == b->force_writemask_all &&
 177           a->exec_size == b->exec_size &&
 178           a->group == b->group &&
 179           a->saturate == b->saturate &&
 180           a->predicate == b->predicate &&
 181           a->predicate_inverse == b->predicate_inverse &&
 182           a->conditional_mod == b->conditional_mod &&
 183           a->flag_subreg == b->flag_subreg &&
 184           a->dst.type == b->dst.type &&
 185           a->offset == b->offset &&
 186           a->mlen == b->mlen &&
 187           a->ex_mlen == b->ex_mlen &&
 188           a->sfid == b->sfid &&
 189           a->desc == b->desc &&
 190           a->size_written == b->size_written &&
 191           a->base_mrf == b->base_mrf &&
 192           a->check_tdr == b->check_tdr &&
 193           a->send_has_side_effects == b->send_has_side_effects &&
 194           a->eot == b->eot &&
 195           a->header_size == b->header_size &&
 196           a->shadow_compare == b->shadow_compare &&
 197           a->pi_noperspective == b->pi_noperspective &&
 198           a->target == b->target &&
 199           a->sources == b->sources &&
 200           operands_match(a, b, negate);
 201 }
 202
 203 static void
 204 create_copy_instr(const fs_builder &bld, fs_inst *inst, fs_reg src, bool negate)
 205 {
 206    unsigned written = regs_written(inst);
 207    unsigned dst_width =
 208       DIV_ROUND_UP(inst->dst.component_size(inst->exec_size), REG_SIZE);
 209    fs_inst *copy;
 210
 211    if (inst->opcode == SHADER_OPCODE_LOAD_PAYLOAD) {
 212       assert(src.file == VGRF);
 213       fs_reg *payload = ralloc_array(bld.shader->mem_ctx, fs_reg,
 214                                      inst->sources);
 215       for (int i = 0; i < inst->header_size; i++) {
 216          payload[i] = src;
 217          src.offset += REG_SIZE;
 218       }
 219       for (int i = inst->header_size; i < inst->sources; i++) {
 220          src.type = inst->src[i].type;
 221          payload[i] = src;
 222          src = offset(src, bld, 1);
 223       }
 224       copy = bld.LOAD_PAYLOAD(inst->dst, payload, inst->sources,
 225                               inst->header_size);
 226    } else if (written != dst_width) {
 227       assert(src.file == VGRF);
 228       assert(written % dst_width == 0);
 229       const int sources = written / dst_width;
 230       fs_reg *payload = ralloc_array(bld.shader->mem_ctx, fs_reg, sources);
 231       for (int i = 0; i < sources; i++) {
 232          payload[i] = src;
 233          src = offset(src, bld, 1);
 234       }
 235       copy = bld.LOAD_PAYLOAD(inst->dst, payload, sources, 0);
 236    } else {
 237       copy = bld.MOV(inst->dst, src);
 238       copy->group = inst->group;
 239       copy->force_writemask_all = inst->force_writemask_all;
 240       copy->src[0].negate = negate;
 241    }
 242    assert(regs_written(copy) == written);
 243 }
 244
 245 bool
 246 fs_visitor::opt_cse_local(const fs_live_variables &live, bblock_t *block, int &ip)
 247 {
 248    bool progress = false;
 249    exec_list aeb;
 250
 251    void *cse_ctx = ralloc_context(NULL);
 252
 253    foreach_inst_in_block(fs_inst, inst, block) {
 254       /* Skip some cases. */
 255       if (is_expression(this, inst) && !inst->is_partial_write() &&
 256           ((inst->dst.file != ARF && inst->dst.file != FIXED_GRF) ||
 257            inst->dst.is_null()))
 258       {
 259          bool found = false;
 260          bool negate = false;
 261
 262          foreach_in_list_use_after(aeb_entry, entry, &aeb) {
 263             /* Match current instruction's expression against those in AEB. */
 264             if (!(entry->generator->dst.is_null() && !inst->dst.is_null()) &&
 265                 instructions_match(inst, entry->generator, &negate)) {
 266                found = true;
 267                progress = true;
 268                break;
 269             }
 270          }
 271
 272          if (!found) {
 273             if (inst->opcode != BRW_OPCODE_MOV ||
 274                 (inst->opcode == BRW_OPCODE_MOV &&
 275                  inst->src[0].file == IMM &&
 276                  inst->src[0].type == BRW_REGISTER_TYPE_VF)) {
 277                /* Our first sighting of this expression.  Create an entry. */
 278                aeb_entry *entry = ralloc(cse_ctx, aeb_entry);
 279                entry->tmp = reg_undef;
 280                entry->generator = inst;
 281                aeb.push_tail(entry);
 282             }
 283          } else {
 284             /* This is at least our second sighting of this expression.
 285              * If we don't have a temporary already, make one.
 286              */
 287             bool no_existing_temp = entry->tmp.file == BAD_FILE;
 288             if (no_existing_temp && !entry->generator->dst.is_null()) {
 289                const fs_builder ibld = fs_builder(this, block, entry->generator)
 290                                        .at(block, entry->generator->next);
 291                int written = regs_written(entry->generator);
 292
 293                entry->tmp = fs_reg(VGRF, alloc.allocate(written),
 294                                    entry->generator->dst.type);
 295
 296                create_copy_instr(ibld, entry->generator, entry->tmp, false);
 297
 298                entry->generator->dst = entry->tmp;
 299             }
 300
 301             /* dest <- temp */
 302             if (!inst->dst.is_null()) {
 303                assert(inst->size_written == entry->generator->size_written);
 304                assert(inst->dst.type == entry->tmp.type);
 305                const fs_builder ibld(this, block, inst);
 306
 307                create_copy_instr(ibld, inst, entry->tmp, negate);
 308             }
 309
 310             /* Set our iterator so that next time through the loop inst->next
 311              * will get the instruction in the basic block after the one we've
 312              * removed.
 313              */
 314             fs_inst *prev = (fs_inst *)inst->prev;
 315
 316             inst->remove(block);
 317             inst = prev;
 318          }
 319       }
 320
 321       /* Discard jumps aren't represented in the CFG unfortunately, so we need
 322        * to make sure that they behave as a CSE barrier, since we lack global
 323        * dataflow information.  This is particularly likely to cause problems
 324        * with instructions dependent on the current execution mask like
 325        * SHADER_OPCODE_FIND_LIVE_CHANNEL.
 326        */
 327       if (inst->opcode == FS_OPCODE_DISCARD_JUMP ||
 328           inst->opcode == FS_OPCODE_PLACEHOLDER_HALT)
 329          aeb.make_empty();
 330
 331       foreach_in_list_safe(aeb_entry, entry, &aeb) {
 332          /* Kill all AEB entries that write a different value to or read from
 333           * the flag register if we just wrote it.
 334           */
 335          if (inst->flags_written()) {
 336             bool negate; /* dummy */
 337             if (entry->generator->flags_read(devinfo) ||
 338                 (entry->generator->flags_written() &&
 339                  !instructions_match(inst, entry->generator, &negate))) {
 340                entry->remove();
 341                ralloc_free(entry);
 342                continue;
 343             }
 344          }
 345
 346          for (int i = 0; i < entry->generator->sources; i++) {
 347             fs_reg *src_reg = &entry->generator->src[i];
 348
 349             /* Kill all AEB entries that use the destination we just
 350              * overwrote.
 351              */
 352             if (regions_overlap(inst->dst, inst->size_written,
 353                                 entry->generator->src[i],
 354                                 entry->generator->size_read(i))) {
 355                entry->remove();
 356                ralloc_free(entry);
 357                break;
 358             }
 359
 360             /* Kill any AEB entries using registers that don't get reused any
 361              * more -- a sure sign they'll fail operands_match().
 362              */
 363             if (src_reg->file == VGRF && live.vgrf_end[src_reg->nr] < ip) {
 364                entry->remove();
 365                ralloc_free(entry);
 366                break;
 367             }
 368          }
 369       }
 370
 371       ip++;
 372    }
 373
 374    ralloc_free(cse_ctx);
 375
 376    return progress;
 377 }
 378
 379 bool
 380 fs_visitor::opt_cse()
 381 {
 382    const fs_live_variables &live = live_analysis.require();
 383    bool progress = false;
 384    int ip = 0;
 385
 386    foreach_block (block, cfg) {
 387       progress = opt_cse_local(live, block, ip) || progress;
 388    }
 389
 390    if (progress)
 391       invalidate_analysis(DEPENDENCY_INSTRUCTIONS | DEPENDENCY_VARIABLES);
 392
 393    return progress;
 394 }