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

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• Author : Olli Etuaho
  Date : 2015-11-02 12:26:02
  Hash : 3fed4306
  Message : Unfold short-circuiting operators in loop conditions correctly Sometimes short-circuiting operators need to be unfolded to if statements. If the unfolded operator is inside a loop condition or expression, it needs to be evaluated repeatedly inside the loop. Add logic to UnfoldShortCircuitToIf that can move or copy the unfolded part of loop conditions or expressions to inside the loop. The exact changes that need to be done depend on the type of the loop. For loops may require also moving the initializer to outside the loop. The unfolded expression inside a loop condition or expression is moved or copied to inside the loop on the first traversal of the loop node, and unfolding to if is deferred until a second traversal. This keeps the code relatively simple. BUG=angleproject:1167 TEST=WebGL 2 conformance tests, dEQP-GLES2.functional.shaders.*select_iteration_count* Change-Id: Ieffc0ea858186054378d387dca9aa64a5fa95137 Reviewed-on: https://chromium-review.googlesource.com/310230 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org> Tested-by: Olli Etuaho <oetuaho@nvidia.com>

• 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();
  
      bool visitBinary(Visit visit, TIntermBinary *node) override;
      bool visitAggregate(Visit visit, TIntermAggregate *node) override;
      bool visitSelection(Visit visit, TIntermSelection *node) override;
      bool visitLoop(Visit visit, TIntermLoop *node) override;
  
      void nextIteration();
      bool foundShortCircuit() const { return mFoundShortCircuit; }
  
    protected:
      // Check if the traversal is inside a loop condition or expression, in which case the unfolded
      // expression needs to be copied inside the loop. Returns true if the copying is done, in which
      // case no further unfolding should be done on the same traversal.
      // The parameters are the node that will be unfolded to multiple statements and so can't remain
      // inside a loop condition, and its parent.
      bool copyLoopConditionOrExpression(TIntermNode *parent, TIntermTyped *node);
  
      // 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;
  
      // Set to the loop node while a loop condition or expression is being traversed.
      TIntermLoop *mParentLoop;
      // Parent of the loop node while a loop condition or expression is being traversed.
      TIntermNode *mLoopParent;
  
      bool mInLoopCondition;
      bool mInLoopExpression;
  };
  
  UnfoldShortCircuitTraverser::UnfoldShortCircuitTraverser()
      : TIntermTraverser(true, false, true),
        mFoundShortCircuit(false),
        mParentLoop(nullptr),
        mLoopParent(nullptr),
        mInLoopCondition(false),
        mInLoopExpression(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;
          if (!copyLoopConditionOrExpression(getParentNode(), node))
          {
              // "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;
          if (!copyLoopConditionOrExpression(getParentNode(), node))
          {
              // "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;
          if (!copyLoopConditionOrExpression(getParentNode(), node))
          {
              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();
  
              if (!copyLoopConditionOrExpression(getParentNode(), node))
              {
                  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;
  }
  
  bool UnfoldShortCircuitTraverser::visitLoop(Visit visit, TIntermLoop *node)
  {
      if (visit == PreVisit)
      {
          if (mFoundShortCircuit)
              return false;  // No need to traverse further
  
          mLoopParent = getParentNode();
          mParentLoop = node;
          incrementDepth(node);
  
          if (node->getInit())
          {
              node->getInit()->traverse(this);
              if (mFoundShortCircuit)
              {
                  decrementDepth();
                  return false;
              }
          }
  
          if (node->getCondition())
          {
              mInLoopCondition = true;
              node->getCondition()->traverse(this);
              mInLoopCondition = false;
  
              if (mFoundShortCircuit)
              {
                  decrementDepth();
                  return false;
              }
          }
  
          if (node->getExpression())
          {
              mInLoopExpression = true;
              node->getExpression()->traverse(this);
              mInLoopExpression = false;
  
              if (mFoundShortCircuit)
              {
                  decrementDepth();
                  return false;
              }
          }
  
          if (node->getBody())
              node->getBody()->traverse(this);
  
          decrementDepth();
      }
      return false;
  }
  
  bool UnfoldShortCircuitTraverser::copyLoopConditionOrExpression(TIntermNode *parent,
                                                                  TIntermTyped *node)
  {
      if (mInLoopCondition)
      {
          mReplacements.push_back(
              NodeUpdateEntry(parent, node, createTempSymbol(node->getType()), false));
          TIntermAggregate *body = mParentLoop->getBody();
          TIntermSequence empty;
          if (mParentLoop->getType() == ELoopDoWhile)
          {
              // Declare the temporary variable before the loop.
              TIntermSequence insertionsBeforeLoop;
              insertionsBeforeLoop.push_back(createTempDeclaration(node->getType()));
              insertStatementsInParentBlock(insertionsBeforeLoop);
  
              // Move a part of do-while loop condition to inside the loop.
              TIntermSequence insertionsInLoop;
              insertionsInLoop.push_back(createTempAssignment(node));
              mInsertions.push_back(NodeInsertMultipleEntry(body, body->getSequence()->size() - 1,
                                                            empty, insertionsInLoop));
          }
          else
          {
              // The loop initializer expression and one copy of the part of the loop condition are
              // executed before the loop. They need to be in a new scope.
              TIntermAggregate *loopScope = new TIntermAggregate(EOpSequence);
  
              TIntermNode *initializer = mParentLoop->getInit();
              if (initializer != nullptr)
              {
                  // Move the initializer to the newly created outer scope, so that condition can
                  // depend on it.
                  mReplacements.push_back(NodeUpdateEntry(mParentLoop, initializer, nullptr, false));
                  loopScope->getSequence()->push_back(initializer);
              }
  
              loopScope->getSequence()->push_back(createTempInitDeclaration(node));
              loopScope->getSequence()->push_back(mParentLoop);
              mReplacements.push_back(NodeUpdateEntry(mLoopParent, mParentLoop, loopScope, true));
  
              // The second copy of the part of the loop condition is executed inside the loop.
              TIntermSequence insertionsInLoop;
              insertionsInLoop.push_back(createTempAssignment(node->deepCopy()));
              mInsertions.push_back(NodeInsertMultipleEntry(body, body->getSequence()->size() - 1,
                                                            empty, insertionsInLoop));
          }
          return true;
      }
  
      if (mInLoopExpression)
      {
          TIntermTyped *movedExpression = mParentLoop->getExpression();
          mReplacements.push_back(NodeUpdateEntry(mParentLoop, movedExpression, nullptr, false));
          TIntermAggregate *body = mParentLoop->getBody();
          TIntermSequence empty;
          TIntermSequence insertions;
          insertions.push_back(movedExpression);
          mInsertions.push_back(
              NodeInsertMultipleEntry(body, body->getSequence()->size() - 1, empty, insertions));
          return true;
      }
      return false;
  }
  
  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());
  }