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