dfg/DFGArgumentsSimplificationPhase.cpp

   1 /*
   2  * Copyright (C) 2012, 2013 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "config.h"
  27 #include "DFGArgumentsSimplificationPhase.h"
  28
  29 #if ENABLE(DFG_JIT)
  30
  31 #include "DFGBasicBlock.h"
  32 #include "DFGGraph.h"
  33 #include "DFGInsertionSet.h"
  34 #include "DFGPhase.h"
  35 #include "DFGValidate.h"
  36 #include "DFGVariableAccessDataDump.h"
  37 #include "JSCInlines.h"
  38 #include <wtf/HashSet.h>
  39 #include <wtf/HashMap.h>
  40
  41 namespace JSC { namespace DFG {
  42
  43 namespace {
  44
  45 struct ArgumentsAliasingData {
  46     InlineCallFrame* callContext;
  47     bool callContextSet;
  48     bool multipleCallContexts;
  49
  50     bool assignedFromArguments;
  51     bool assignedFromManyThings;
  52
  53     bool escapes;
  54
  55     ArgumentsAliasingData()
  56         : callContext(0)
  57         , callContextSet(false)
  58         , multipleCallContexts(false)
  59         , assignedFromArguments(false)
  60         , assignedFromManyThings(false)
  61         , escapes(false)
  62     {
  63     }
  64
  65     void mergeCallContext(InlineCallFrame* newCallContext)
  66     {
  67         if (multipleCallContexts)
  68             return;
  69
  70         if (!callContextSet) {
  71             callContext = newCallContext;
  72             callContextSet = true;
  73             return;
  74         }
  75
  76         if (callContext == newCallContext)
  77             return;
  78
  79         multipleCallContexts = true;
  80     }
  81
  82     bool callContextIsValid()
  83     {
  84         return callContextSet && !multipleCallContexts;
  85     }
  86
  87     void mergeArgumentsAssignment()
  88     {
  89         assignedFromArguments = true;
  90     }
  91
  92     void mergeNonArgumentsAssignment()
  93     {
  94         assignedFromManyThings = true;
  95     }
  96
  97     bool argumentsAssignmentIsValid()
  98     {
  99         return assignedFromArguments && !assignedFromManyThings;
 100     }
 101
 102     bool isValid()
 103     {
 104         return callContextIsValid() && argumentsAssignmentIsValid() && !escapes;
 105     }
 106 };
 107
 108 } // end anonymous namespace
 109
 110 class ArgumentsSimplificationPhase : public Phase {
 111 public:
 112     ArgumentsSimplificationPhase(Graph& graph)
 113         : Phase(graph, "arguments simplification")
 114     {
 115     }
 116
 117     bool run()
 118     {
 119         if (!m_graph.m_hasArguments)
 120             return false;
 121
 122         bool changed = false;
 123
 124         // Record which arguments are known to escape no matter what.
 125         for (InlineCallFrameSet::iterator iter = m_graph.m_plan.inlineCallFrames->begin(); !!iter; ++iter)
 126             pruneObviousArgumentCreations(*iter);
 127         pruneObviousArgumentCreations(0); // the machine call frame.
 128
 129         // Create data for variable access datas that we will want to analyze.
 130         for (unsigned i = m_graph.m_variableAccessData.size(); i--;) {
 131             VariableAccessData* variableAccessData = &m_graph.m_variableAccessData[i];
 132             if (!variableAccessData->isRoot())
 133                 continue;
 134             if (variableAccessData->isCaptured())
 135                 continue;
 136             m_argumentsAliasing.add(variableAccessData, ArgumentsAliasingData());
 137         }
 138
 139         // Figure out which variables are live, using a conservative approximation of
 140         // liveness.
 141         for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex) {
 142             BasicBlock* block = m_graph.block(blockIndex);
 143             if (!block)
 144                 continue;
 145             for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
 146                 Node* node = block->at(indexInBlock);
 147                 switch (node->op()) {
 148                 case GetLocal:
 149                 case Flush:
 150                 case PhantomLocal:
 151                     m_isLive.add(node->variableAccessData());
 152                     break;
 153                 default:
 154                     break;
 155                 }
 156             }
 157         }
 158
 159         // Figure out which variables alias the arguments and nothing else, and are
 160         // used only for GetByVal and GetArrayLength accesses. At the same time,
 161         // identify uses of CreateArguments that are not consistent with the arguments
 162         // being aliased only to variables that satisfy these constraints.
 163         for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex) {
 164             BasicBlock* block = m_graph.block(blockIndex);
 165             if (!block)
 166                 continue;
 167             for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
 168                 Node* node = block->at(indexInBlock);
 169                 switch (node->op()) {
 170                 case CreateArguments: {
 171                     // Ignore this op. If we see a lone CreateArguments then we want to
 172                     // completely ignore it because:
 173                     // 1) The default would be to see that the child is a GetLocal on the
 174                     //    arguments register and conclude that we have an arguments escape.
 175                     // 2) The fact that a CreateArguments exists does not mean that it
 176                     //    will continue to exist after we're done with this phase. As far
 177                     //    as this phase is concerned, a CreateArguments only "exists" if it
 178                     //    is used in a manner that necessitates its existance.
 179                     break;
 180                 }
 181
 182                 case TearOffArguments: {
 183                     // Ignore arguments tear off, because it's only relevant if we actually
 184                     // need to create the arguments.
 185                     break;
 186                 }
 187
 188                 case SetLocal: {
 189                     Node* source = node->child1().node();
 190                     VariableAccessData* variableAccessData = node->variableAccessData();
 191                     VirtualRegister argumentsRegister =
 192                         m_graph.uncheckedArgumentsRegisterFor(node->origin.semantic);
 193                     if (source->op() != CreateArguments && source->op() != PhantomArguments) {
 194                         // Make sure that the source of the SetLocal knows that if it's
 195                         // a variable that we think is aliased to the arguments, then it
 196                         // may escape at this point. In future, we could track transitive
 197                         // aliasing. But not yet.
 198                         observeBadArgumentsUse(source);
 199
 200                         // If this is an assignment to the arguments register, then
 201                         // pretend as if the arguments were created. We don't want to
 202                         // optimize code that explicitly assigns to the arguments,
 203                         // because that seems too ugly.
 204
 205                         // But, before getting rid of CreateArguments, we will have
 206                         // an assignment to the arguments registers with JSValue().
 207                         // That's because CSE will refuse to get rid of the
 208                         // init_lazy_reg since it treats CreateArguments as reading
 209                         // local variables. That could be fixed, but it's easier to
 210                         // work around this here.
 211                         if (source->op() == JSConstant
 212                             && !source->valueOfJSConstant(codeBlock()))
 213                             break;
 214
 215                         // If the variable is totally dead, then ignore it.
 216                         if (!m_isLive.contains(variableAccessData))
 217                             break;
 218
 219                         if (argumentsRegister.isValid()
 220                             && (variableAccessData->local() == argumentsRegister
 221                                 || variableAccessData->local() == unmodifiedArgumentsRegister(argumentsRegister))) {
 222                             m_createsArguments.add(node->origin.semantic.inlineCallFrame);
 223                             break;
 224                         }
 225
 226                         if (variableAccessData->isCaptured())
 227                             break;
 228
 229                         // Make sure that if it's a variable that we think is aliased to
 230                         // the arguments, that we know that it might actually not be.
 231                         ArgumentsAliasingData& data =
 232                             m_argumentsAliasing.find(variableAccessData)->value;
 233                         data.mergeNonArgumentsAssignment();
 234                         data.mergeCallContext(node->origin.semantic.inlineCallFrame);
 235                         break;
 236                     }
 237                     if (argumentsRegister.isValid()
 238                         && (variableAccessData->local() == argumentsRegister
 239                             || variableAccessData->local() == unmodifiedArgumentsRegister(argumentsRegister))) {
 240                         if (node->origin.semantic.inlineCallFrame == source->origin.semantic.inlineCallFrame)
 241                             break;
 242                         m_createsArguments.add(source->origin.semantic.inlineCallFrame);
 243                         break;
 244                     }
 245                     if (variableAccessData->isCaptured()) {
 246                         m_createsArguments.add(source->origin.semantic.inlineCallFrame);
 247                         break;
 248                     }
 249                     ArgumentsAliasingData& data =
 250                         m_argumentsAliasing.find(variableAccessData)->value;
 251                     data.mergeArgumentsAssignment();
 252                     // This ensures that the variable's uses are in the same context as
 253                     // the arguments it is aliasing.
 254                     data.mergeCallContext(node->origin.semantic.inlineCallFrame);
 255                     data.mergeCallContext(source->origin.semantic.inlineCallFrame);
 256                     break;
 257                 }
 258
 259                 case GetLocal:
 260                 case Phi: /* FIXME: https://bugs.webkit.org/show_bug.cgi?id=108555 */ {
 261                     VariableAccessData* variableAccessData = node->variableAccessData();
 262                     if (variableAccessData->isCaptured())
 263                         break;
 264                     ArgumentsAliasingData& data =
 265                         m_argumentsAliasing.find(variableAccessData)->value;
 266                     data.mergeCallContext(node->origin.semantic.inlineCallFrame);
 267                     break;
 268                 }
 269
 270                 case Flush: {
 271                     VariableAccessData* variableAccessData = node->variableAccessData();
 272                     if (variableAccessData->isCaptured())
 273                         break;
 274                     ArgumentsAliasingData& data =
 275                         m_argumentsAliasing.find(variableAccessData)->value;
 276                     data.mergeCallContext(node->origin.semantic.inlineCallFrame);
 277
 278                     // If a variable is used in a flush then by definition it escapes.
 279                     data.escapes = true;
 280                     break;
 281                 }
 282
 283                 case SetArgument: {
 284                     VariableAccessData* variableAccessData = node->variableAccessData();
 285                     if (variableAccessData->isCaptured())
 286                         break;
 287                     ArgumentsAliasingData& data =
 288                         m_argumentsAliasing.find(variableAccessData)->value;
 289                     data.mergeNonArgumentsAssignment();
 290                     data.mergeCallContext(node->origin.semantic.inlineCallFrame);
 291                     break;
 292                 }
 293
 294                 case GetByVal: {
 295                     if (node->arrayMode().type() != Array::Arguments) {
 296                         observeBadArgumentsUses(node);
 297                         break;
 298                     }
 299
 300                     // That's so awful and pretty much impossible since it would
 301                     // imply that the arguments were predicted integer, but it's
 302                     // good to be defensive and thorough.
 303                     observeBadArgumentsUse(node->child2().node());
 304                     observeProperArgumentsUse(node, node->child1());
 305                     break;
 306                 }
 307
 308                 case GetArrayLength: {
 309                     if (node->arrayMode().type() != Array::Arguments) {
 310                         observeBadArgumentsUses(node);
 311                         break;
 312                     }
 313
 314                     observeProperArgumentsUse(node, node->child1());
 315                     break;
 316                 }
 317
 318                 case Phantom:
 319                 case HardPhantom:
 320                     // We don't care about phantom uses, since phantom uses are all about
 321                     // just keeping things alive for OSR exit. If something - like the
 322                     // CreateArguments - is just being kept alive, then this transformation
 323                     // will not break this, since the Phantom will now just keep alive a
 324                     // PhantomArguments and OSR exit will still do the right things.
 325                     break;
 326
 327                 case CheckStructure:
 328                 case StructureTransitionWatchpoint:
 329                 case CheckArray:
 330                     // We don't care about these because if we get uses of the relevant
 331                     // variable then we can safely get rid of these, too. This of course
 332                     // relies on there not being any information transferred by the CFA
 333                     // from a CheckStructure on one variable to the information about the
 334                     // structures of another variable.
 335                     break;
 336
 337                 case MovHint:
 338                     // We don't care about MovHints at all, since they represent what happens
 339                     // in bytecode. We rematerialize arguments objects on OSR exit anyway.
 340                     break;
 341
 342                 default:
 343                     observeBadArgumentsUses(node);
 344                     break;
 345                 }
 346             }
 347         }
 348
 349         // Now we know which variables are aliased to arguments. But if any of them are
 350         // found to have escaped, or were otherwise invalidated, then we need to mark
 351         // the arguments as requiring creation. This is a property of SetLocals to
 352         // variables that are neither the correct arguments register nor are marked as
 353         // being arguments-aliased.
 354         for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex) {
 355             BasicBlock* block = m_graph.block(blockIndex);
 356             if (!block)
 357                 continue;
 358             for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
 359                 Node* node = block->at(indexInBlock);
 360                 if (node->op() != SetLocal)
 361                     continue;
 362                 Node* source = node->child1().node();
 363                 if (source->op() != CreateArguments)
 364                     continue;
 365                 VariableAccessData* variableAccessData = node->variableAccessData();
 366                 if (variableAccessData->isCaptured()) {
 367                     // The captured case would have already been taken care of in the
 368                     // previous pass.
 369                     continue;
 370                 }
 371
 372                 ArgumentsAliasingData& data =
 373                     m_argumentsAliasing.find(variableAccessData)->value;
 374                 if (data.isValid())
 375                     continue;
 376
 377                 m_createsArguments.add(source->origin.semantic.inlineCallFrame);
 378             }
 379         }
 380
 381         InsertionSet insertionSet(m_graph);
 382
 383         for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex) {
 384             BasicBlock* block = m_graph.block(blockIndex);
 385             if (!block)
 386                 continue;
 387             for (unsigned indexInBlock = 0; indexInBlock < block->size(); indexInBlock++) {
 388                 Node* node = block->at(indexInBlock);
 389                 switch (node->op()) {
 390                 case SetLocal: {
 391                     Node* source = node->child1().node();
 392                     if (source->op() != CreateArguments)
 393                         break;
 394
 395                     if (m_createsArguments.contains(source->origin.semantic.inlineCallFrame))
 396                         break;
 397
 398                     VariableAccessData* variableAccessData = node->variableAccessData();
 399
 400                     if (variableAccessData->mergeIsArgumentsAlias(true)) {
 401                         changed = true;
 402
 403                         // Make sure that the variable knows, that it may now hold non-cell values.
 404                         variableAccessData->predict(SpecEmpty);
 405                     }
 406
 407                     // Make sure that the SetLocal doesn't check that the input is a Cell.
 408                     if (node->child1().useKind() != UntypedUse) {
 409                         node->child1().setUseKind(UntypedUse);
 410                         changed = true;
 411                     }
 412                     break;
 413                 }
 414
 415                 case Flush: {
 416                     VariableAccessData* variableAccessData = node->variableAccessData();
 417
 418                     if (variableAccessData->isCaptured()
 419                         || !m_argumentsAliasing.find(variableAccessData)->value.isValid()
 420                         || m_createsArguments.contains(node->origin.semantic.inlineCallFrame))
 421                         break;
 422
 423                     RELEASE_ASSERT_NOT_REACHED();
 424                     break;
 425                 }
 426
 427                 case Phantom:
 428                 case HardPhantom: {
 429                     // It's highly likely that we will have a Phantom referencing either
 430                     // CreateArguments, or a local op for the arguments register, or a
 431                     // local op for an arguments-aliased variable. In any of those cases,
 432                     // we should remove the phantom reference, since:
 433                     // 1) Phantoms only exist to aid OSR exit. But arguments simplification
 434                     //    has its own OSR exit story, which is to inform OSR exit to reify
 435                     //    the arguments as necessary.
 436                     // 2) The Phantom may keep the CreateArguments node alive, which is
 437                     //    precisely what we don't want.
 438                     for (unsigned i = 0; i < AdjacencyList::Size; ++i)
 439                         detypeArgumentsReferencingPhantomChild(node, i);
 440                     break;
 441                 }
 442
 443                 case CheckStructure:
 444                 case StructureTransitionWatchpoint:
 445                 case CheckArray: {
 446                     // We can just get rid of this node, if it references a phantom argument.
 447                     if (!isOKToOptimize(node->child1().node()))
 448                         break;
 449                     node->convertToPhantom();
 450                     break;
 451                 }
 452
 453                 case GetByVal: {
 454                     if (node->arrayMode().type() != Array::Arguments)
 455                         break;
 456
 457                     // This can be simplified to GetMyArgumentByVal if we know that
 458                     // it satisfies either condition (1) or (2):
 459                     // 1) Its first child is a valid ArgumentsAliasingData and the
 460                     //    InlineCallFrame* is not marked as creating arguments.
 461                     // 2) Its first child is CreateArguments and its InlineCallFrame*
 462                     //    is not marked as creating arguments.
 463
 464                     if (!isOKToOptimize(node->child1().node()))
 465                         break;
 466
 467                     insertionSet.insertNode(
 468                         indexInBlock, SpecNone, Phantom, node->origin, node->child1());
 469
 470                     node->child1() = node->child2();
 471                     node->child2() = Edge();
 472                     node->setOpAndDefaultFlags(GetMyArgumentByVal);
 473                     changed = true;
 474                     --indexInBlock; // Force reconsideration of this op now that it's a GetMyArgumentByVal.
 475                     break;
 476                 }
 477
 478                 case GetArrayLength: {
 479                     if (node->arrayMode().type() != Array::Arguments)
 480                         break;
 481
 482                     if (!isOKToOptimize(node->child1().node()))
 483                         break;
 484
 485                     insertionSet.insertNode(
 486                         indexInBlock, SpecNone, Phantom, node->origin, node->child1());
 487
 488                     node->child1() = Edge();
 489                     node->setOpAndDefaultFlags(GetMyArgumentsLength);
 490                     changed = true;
 491                     --indexInBlock; // Force reconsideration of this op noew that it's a GetMyArgumentsLength.
 492                     break;
 493                 }
 494
 495                 case GetMyArgumentsLength:
 496                 case GetMyArgumentsLengthSafe: {
 497                     if (m_createsArguments.contains(node->origin.semantic.inlineCallFrame)) {
 498                         ASSERT(node->op() == GetMyArgumentsLengthSafe);
 499                         break;
 500                     }
 501                     if (node->op() == GetMyArgumentsLengthSafe) {
 502                         node->setOp(GetMyArgumentsLength);
 503                         changed = true;
 504                     }
 505
 506                     NodeOrigin origin = node->origin;
 507                     if (!origin.semantic.inlineCallFrame)
 508                         break;
 509
 510                     // We know exactly what this will return. But only after we have checked
 511                     // that nobody has escaped our arguments.
 512                     insertionSet.insertNode(
 513                         indexInBlock, SpecNone, CheckArgumentsNotCreated, origin);
 514
 515                     m_graph.convertToConstant(
 516                         node, jsNumber(origin.semantic.inlineCallFrame->arguments.size() - 1));
 517                     changed = true;
 518                     break;
 519                 }
 520
 521                 case GetMyArgumentByVal:
 522                 case GetMyArgumentByValSafe: {
 523                     if (m_createsArguments.contains(node->origin.semantic.inlineCallFrame)) {
 524                         ASSERT(node->op() == GetMyArgumentByValSafe);
 525                         break;
 526                     }
 527                     if (node->op() == GetMyArgumentByValSafe) {
 528                         node->setOp(GetMyArgumentByVal);
 529                         changed = true;
 530                     }
 531                     if (!node->origin.semantic.inlineCallFrame)
 532                         break;
 533                     if (!node->child1()->hasConstant())
 534                         break;
 535                     JSValue value = node->child1()->valueOfJSConstant(codeBlock());
 536                     if (!value.isInt32())
 537                         break;
 538                     int32_t index = value.asInt32();
 539                     if (index < 0
 540                         || static_cast<size_t>(index + 1) >=
 541                             node->origin.semantic.inlineCallFrame->arguments.size())
 542                         break;
 543
 544                     // We know which argument this is accessing. But only after we have checked
 545                     // that nobody has escaped our arguments. We also need to ensure that the
 546                     // index is kept alive. That's somewhat pointless since it's a constant, but
 547                     // it's important because this is one of those invariants that we like to
 548                     // have in the DFG. Note finally that we use the GetLocalUnlinked opcode
 549                     // here, since this is being done _after_ the prediction propagation phase
 550                     // has run - therefore it makes little sense to link the GetLocal operation
 551                     // into the VariableAccessData and Phi graphs.
 552
 553                     NodeOrigin origin = node->origin;
 554                     AdjacencyList children = node->children;
 555
 556                     node->convertToGetLocalUnlinked(
 557                         VirtualRegister(
 558                             origin.semantic.inlineCallFrame->stackOffset +
 559                             m_graph.baselineCodeBlockFor(origin.semantic)->argumentIndexAfterCapture(index)));
 560
 561                     insertionSet.insertNode(
 562                         indexInBlock, SpecNone, CheckArgumentsNotCreated, origin);
 563                     insertionSet.insertNode(
 564                         indexInBlock, SpecNone, Phantom, origin, children);
 565
 566                     changed = true;
 567                     break;
 568                 }
 569
 570                 case TearOffArguments: {
 571                     if (m_createsArguments.contains(node->origin.semantic.inlineCallFrame))
 572                         continue;
 573
 574                     node->convertToPhantom();
 575                     break;
 576                 }
 577
 578                 default:
 579                     break;
 580                 }
 581             }
 582             insertionSet.execute(block);
 583         }
 584
 585         for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex) {
 586             BasicBlock* block = m_graph.block(blockIndex);
 587             if (!block)
 588                 continue;
 589             for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
 590                 Node* node = block->at(indexInBlock);
 591                 if (node->op() != CreateArguments)
 592                     continue;
 593                 // If this is a CreateArguments for an InlineCallFrame* that does
 594                 // not create arguments, then replace it with a PhantomArguments.
 595                 // PhantomArguments is a non-executing node that just indicates
 596                 // that the node should be reified as an arguments object on OSR
 597                 // exit.
 598                 if (m_createsArguments.contains(node->origin.semantic.inlineCallFrame))
 599                     continue;
 600                 insertionSet.insertNode(
 601                     indexInBlock, SpecNone, Phantom, node->origin, node->children);
 602                 node->setOpAndDefaultFlags(PhantomArguments);
 603                 node->children.reset();
 604                 changed = true;
 605             }
 606             insertionSet.execute(block);
 607         }
 608
 609         for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex) {
 610             BasicBlock* block = m_graph.block(blockIndex);
 611             if (!block)
 612                 continue;
 613             for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
 614                 Node* node = block->at(indexInBlock);
 615                 if (node->op() != Phantom)
 616                     continue;
 617                 for (unsigned i = 0; i < AdjacencyList::Size; ++i)
 618                     detypeArgumentsReferencingPhantomChild(node, i);
 619             }
 620         }
 621
 622         if (changed) {
 623             m_graph.dethread();
 624             m_graph.m_form = LoadStore;
 625         }
 626
 627         return changed;
 628     }
 629
 630 private:
 631     HashSet<InlineCallFrame*,
 632             DefaultHash<InlineCallFrame*>::Hash,
 633             NullableHashTraits<InlineCallFrame*>> m_createsArguments;
 634     HashMap<VariableAccessData*, ArgumentsAliasingData,
 635             DefaultHash<VariableAccessData*>::Hash,
 636             NullableHashTraits<VariableAccessData*>> m_argumentsAliasing;
 637     HashSet<VariableAccessData*> m_isLive;
 638
 639     void pruneObviousArgumentCreations(InlineCallFrame* inlineCallFrame)
 640     {
 641         ScriptExecutable* executable = m_graph.executableFor(inlineCallFrame);
 642         if (m_graph.m_executablesWhoseArgumentsEscaped.contains(executable)
 643             || executable->isStrictMode())
 644             m_createsArguments.add(inlineCallFrame);
 645     }
 646
 647     void observeBadArgumentsUse(Node* node)
 648     {
 649         if (!node)
 650             return;
 651
 652         switch (node->op()) {
 653         case CreateArguments: {
 654             m_createsArguments.add(node->origin.semantic.inlineCallFrame);
 655             break;
 656         }
 657
 658         case GetLocal: {
 659             VirtualRegister argumentsRegister =
 660                 m_graph.uncheckedArgumentsRegisterFor(node->origin.semantic);
 661             if (argumentsRegister.isValid()
 662                 && (node->local() == argumentsRegister
 663                     || node->local() == unmodifiedArgumentsRegister(argumentsRegister))) {
 664                 m_createsArguments.add(node->origin.semantic.inlineCallFrame);
 665                 break;
 666             }
 667
 668             VariableAccessData* variableAccessData = node->variableAccessData();
 669             if (variableAccessData->isCaptured())
 670                 break;
 671
 672             ArgumentsAliasingData& data = m_argumentsAliasing.find(variableAccessData)->value;
 673             data.escapes = true;
 674             break;
 675         }
 676
 677         default:
 678             break;
 679         }
 680     }
 681
 682     void observeBadArgumentsUses(Node* node)
 683     {
 684         for (unsigned i = m_graph.numChildren(node); i--;)
 685             observeBadArgumentsUse(m_graph.child(node, i).node());
 686     }
 687
 688     void observeProperArgumentsUse(Node* node, Edge edge)
 689     {
 690         if (edge->op() != GetLocal) {
 691             // When can this happen? At least two cases that I can think
 692             // of:
 693             //
 694             // 1) Aliased use of arguments in the same basic block,
 695             //    like:
 696             //
 697             //    var a = arguments;
 698             //    var x = arguments[i];
 699             //
 700             // 2) If we're accessing arguments we got from the heap!
 701
 702             if (edge->op() == CreateArguments
 703                 && node->origin.semantic.inlineCallFrame
 704                     != edge->origin.semantic.inlineCallFrame)
 705                 m_createsArguments.add(edge->origin.semantic.inlineCallFrame);
 706
 707             return;
 708         }
 709
 710         VariableAccessData* variableAccessData = edge->variableAccessData();
 711         if (edge->local() == m_graph.uncheckedArgumentsRegisterFor(edge->origin.semantic)
 712             && node->origin.semantic.inlineCallFrame != edge->origin.semantic.inlineCallFrame) {
 713             m_createsArguments.add(edge->origin.semantic.inlineCallFrame);
 714             return;
 715         }
 716
 717         if (variableAccessData->isCaptured())
 718             return;
 719
 720         ArgumentsAliasingData& data = m_argumentsAliasing.find(variableAccessData)->value;
 721         data.mergeCallContext(node->origin.semantic.inlineCallFrame);
 722     }
 723
 724     bool isOKToOptimize(Node* source)
 725     {
 726         if (m_createsArguments.contains(source->origin.semantic.inlineCallFrame))
 727             return false;
 728
 729         switch (source->op()) {
 730         case GetLocal: {
 731             VariableAccessData* variableAccessData = source->variableAccessData();
 732             VirtualRegister argumentsRegister =
 733                 m_graph.uncheckedArgumentsRegisterFor(source->origin.semantic);
 734             if (!argumentsRegister.isValid())
 735                 break;
 736             if (argumentsRegister == variableAccessData->local())
 737                 return true;
 738             if (unmodifiedArgumentsRegister(argumentsRegister) == variableAccessData->local())
 739                 return true;
 740             if (variableAccessData->isCaptured())
 741                 break;
 742             ArgumentsAliasingData& data =
 743                 m_argumentsAliasing.find(variableAccessData)->value;
 744             if (!data.isValid())
 745                 break;
 746
 747             return true;
 748         }
 749
 750         case CreateArguments: {
 751             return true;
 752         }
 753
 754         default:
 755             break;
 756         }
 757
 758         return false;
 759     }
 760
 761     void detypeArgumentsReferencingPhantomChild(Node* node, unsigned edgeIndex)
 762     {
 763         Edge edge = node->children.child(edgeIndex);
 764         if (!edge)
 765             return;
 766
 767         switch (edge->op()) {
 768         case GetLocal: {
 769             VariableAccessData* variableAccessData = edge->variableAccessData();
 770             if (!variableAccessData->isArgumentsAlias())
 771                 break;
 772             node->children.child(edgeIndex).setUseKind(UntypedUse);
 773             break;
 774         }
 775
 776         case PhantomArguments: {
 777             node->children.child(edgeIndex).setUseKind(UntypedUse);
 778             break;
 779         }
 780
 781         default:
 782             break;
 783         }
 784     }
 785 };
 786
 787 bool performArgumentsSimplification(Graph& graph)
 788 {
 789     SamplingRegion samplingRegion("DFG Arguments Simplification Phase");
 790     return runPhase<ArgumentsSimplificationPhase>(graph);
 791 }
 792
 793 } } // namespace JSC::DFG
 794
 795 #endif // ENABLE(DFG_JIT)
 796
 797