kc3-lang/angle/src/compiler/translator/UnfoldShortCircuitToIf.cpp

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• Hash : d4f303ee
  Author :
  Date : 2015-05-20T17:09:06
  

  Refactoring: Make creating temporary symbols in AST traversal reusable
  
  Temporary symbols will also be needed to store temporary arrays when complex
  array expressions are unfolded.
  
  Also clear tree update related structures at the end of updateTree(), so that
  the traverser can be reused for several rounds of replacement more easily, and
  remove unnecessary InVisit step from UnfoldShortCircuitToIf.
  
  BUG=angleproject:971
  TEST=angle_end2end_tests, WebGL conformance tests
  
  Change-Id: Iecdd3008d43f01b02fe344ccde8614f70e6c0c65
  Reviewed-on: https://chromium-review.googlesource.com/272121
  Reviewed-by: Zhenyao Mo <zmo@chromium.org>
  Tested-by: Olli Etuaho <oetuaho@nvidia.com>
  

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• src/compiler/translator/UnfoldShortCircuitToIf.cpp

• //
  // Copyright (c) 2002-2013 The ANGLE Project Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  //
  // UnfoldShortCircuitToIf is an AST traverser to convert short-circuiting operators to if-else statements.
  // The results are assigned to s# temporaries, which are used by the main translator instead of
  // the original expression.
  //
  
  #include "compiler/translator/UnfoldShortCircuitToIf.h"
  
  #include "compiler/translator/IntermNode.h"
  
  namespace
  {
  
  // Traverser that unfolds one short-circuiting operation at a time.
  class UnfoldShortCircuitTraverser : public TIntermTraverser
  {
    public:
      UnfoldShortCircuitTraverser();
  
      void traverse(TIntermNode *node);
      bool visitBinary(Visit visit, TIntermBinary *node) override;
      bool visitAggregate(Visit visit, TIntermAggregate *node) override;
      bool visitSelection(Visit visit, TIntermSelection *node) override;
  
      void nextIteration();
      bool foundShortCircuit() const { return mFoundShortCircuit; }
  
    protected:
      // Marked to true once an operation that needs to be unfolded has been found.
      // After that, no more unfolding is performed on that traversal.
      bool mFoundShortCircuit;
  };
  
  UnfoldShortCircuitTraverser::UnfoldShortCircuitTraverser()
      : TIntermTraverser(true, false, true),
        mFoundShortCircuit(false)
  {
  }
  
  bool UnfoldShortCircuitTraverser::visitBinary(Visit visit, TIntermBinary *node)
  {
      if (mFoundShortCircuit)
          return false;
      // If our right node doesn't have side effects, we know we don't need to unfold this
      // expression: there will be no short-circuiting side effects to avoid
      // (note: unfolding doesn't depend on the left node -- it will always be evaluated)
      if (!node->getRight()->hasSideEffects())
      {
          return true;
      }
  
      switch (node->getOp())
      {
        case EOpLogicalOr:
          mFoundShortCircuit = true;
  
          // "x || y" is equivalent to "x ? true : y", which unfolds to "bool s; if(x) s = true; else s = y;",
          // and then further simplifies down to "bool s = x; if(!s) s = y;".
          {
              TIntermSequence insertions;
              TType boolType(EbtBool, EbpUndefined, EvqTemporary);
  
              ASSERT(node->getLeft()->getType() == boolType);
              insertions.push_back(createTempInitDeclaration(node->getLeft()));
  
              TIntermAggregate *assignRightBlock = new TIntermAggregate(EOpSequence);
              ASSERT(node->getRight()->getType() == boolType);
              assignRightBlock->getSequence()->push_back(createTempAssignment(node->getRight()));
  
              TIntermUnary *notTempSymbol = new TIntermUnary(EOpLogicalNot, boolType);
              notTempSymbol->setOperand(createTempSymbol(boolType));
              TIntermSelection *ifNode = new TIntermSelection(notTempSymbol, assignRightBlock, nullptr);
              insertions.push_back(ifNode);
  
              insertStatementsInParentBlock(insertions);
  
              NodeUpdateEntry replaceVariable(getParentNode(), node, createTempSymbol(boolType), false);
              mReplacements.push_back(replaceVariable);
          }
          return false;
        case EOpLogicalAnd:
          mFoundShortCircuit = true;
  
          // "x && y" is equivalent to "x ? y : false", which unfolds to "bool s; if(x) s = y; else s = false;",
          // and then further simplifies down to "bool s = x; if(s) s = y;".
          {
              TIntermSequence insertions;
              TType boolType(EbtBool, EbpUndefined, EvqTemporary);
  
              ASSERT(node->getLeft()->getType() == boolType);
              insertions.push_back(createTempInitDeclaration(node->getLeft()));
  
              TIntermAggregate *assignRightBlock = new TIntermAggregate(EOpSequence);
              ASSERT(node->getRight()->getType() == boolType);
              assignRightBlock->getSequence()->push_back(createTempAssignment(node->getRight()));
  
              TIntermSelection *ifNode = new TIntermSelection(createTempSymbol(boolType), assignRightBlock, nullptr);
              insertions.push_back(ifNode);
  
              insertStatementsInParentBlock(insertions);
  
              NodeUpdateEntry replaceVariable(getParentNode(), node, createTempSymbol(boolType), false);
              mReplacements.push_back(replaceVariable);
          }
          return false;
        default:
          return true;
      }
  }
  
  bool UnfoldShortCircuitTraverser::visitSelection(Visit visit, TIntermSelection *node)
  {
      if (mFoundShortCircuit)
          return false;
  
      // Unfold "b ? x : y" into "type s; if(b) s = x; else s = y;"
      if (visit == PreVisit && node->usesTernaryOperator())
      {
          mFoundShortCircuit = true;
          TIntermSequence insertions;
  
          TIntermSymbol *tempSymbol = createTempSymbol(node->getType());
          TIntermAggregate *tempDeclaration = new TIntermAggregate(EOpDeclaration);
          tempDeclaration->getSequence()->push_back(tempSymbol);
          insertions.push_back(tempDeclaration);
  
          TIntermAggregate *trueBlock = new TIntermAggregate(EOpSequence);
          TIntermBinary *trueAssignment = createTempAssignment(node->getTrueBlock()->getAsTyped());
          trueBlock->getSequence()->push_back(trueAssignment);
  
          TIntermAggregate *falseBlock = new TIntermAggregate(EOpSequence);
          TIntermBinary *falseAssignment = createTempAssignment(node->getFalseBlock()->getAsTyped());
          falseBlock->getSequence()->push_back(falseAssignment);
  
          TIntermSelection *ifNode = new TIntermSelection(node->getCondition()->getAsTyped(), trueBlock, falseBlock);
          insertions.push_back(ifNode);
  
          insertStatementsInParentBlock(insertions);
  
          TIntermSymbol *ternaryResult = createTempSymbol(node->getType());
          NodeUpdateEntry replaceVariable(getParentNode(), node, ternaryResult, false);
          mReplacements.push_back(replaceVariable);
          return false;
      }
  
      return true;
  }
  
  bool UnfoldShortCircuitTraverser::visitAggregate(Visit visit, TIntermAggregate *node)
  {
      if (visit == PreVisit && mFoundShortCircuit)
          return false; // No need to traverse further
  
      if (node->getOp() == EOpComma)
      {
          ASSERT(visit != PreVisit || !mFoundShortCircuit);
  
          if (visit == PostVisit && mFoundShortCircuit)
          {
              // We can be sure that we arrived here because there was a short-circuiting operator
              // inside the sequence operator since we only start traversing the sequence operator in
              // case a short-circuiting operator has not been found so far.
              // We need to unfold the sequence (comma) operator, otherwise the evaluation order of
              // statements would be messed up by unfolded operations inside.
              // Don't do any other unfolding on this round of traversal.
              mReplacements.clear();
              mMultiReplacements.clear();
              mInsertions.clear();
  
              TIntermSequence insertions;
              TIntermSequence *seq = node->getSequence();
  
              TIntermSequence::size_type i = 0;
              ASSERT(!seq->empty());
              while (i < seq->size() - 1)
              {
                  TIntermTyped *child = (*seq)[i]->getAsTyped();
                  insertions.push_back(child);
                  ++i;
              }
  
              insertStatementsInParentBlock(insertions);
  
              NodeUpdateEntry replaceVariable(getParentNode(), node, (*seq)[i], false);
              mReplacements.push_back(replaceVariable);
          }
      }
      return true;
  }
  
  void UnfoldShortCircuitTraverser::nextIteration()
  {
      mFoundShortCircuit = false;
      nextTemporaryIndex();
  }
  
  } // namespace
  
  void UnfoldShortCircuitToIf(TIntermNode *root, unsigned int *temporaryIndex)
  {
      UnfoldShortCircuitTraverser traverser;
      ASSERT(temporaryIndex != nullptr);
      traverser.useTemporaryIndex(temporaryIndex);
      // Unfold one operator at a time, and reset the traverser between iterations.
      do
      {
          traverser.nextIteration();
          root->traverse(&traverser);
          if (traverser.foundShortCircuit())
              traverser.updateTree();
      }
      while (traverser.foundShortCircuit());
  }
  

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