UnfoldShortCircuitToIf.cpp

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Author : Olli Etuaho
Date : 2015-05-13 14:51:59
Hash : 0ea959f4
Message : Unfold sequence operator when operations inside need unfolding Unfolding the sequence operator ensures correct evaluation order when parts of the expression need to get hoisted out of the expression to the surrounding scope. BUG=angleproject:1001 TEST=WebGL conformance tests Change-Id: Ifd3093c9fb63d3e9842ebb4b9531b2f46875ad8a Reviewed-on: https://chromium-review.googlesource.com/270660 Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>
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/InfoSink.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:
    int mTemporaryIndex;

    // 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;

    struct ParentBlock
    {
        ParentBlock(TIntermAggregate *_node, TIntermSequence::size_type _pos)
            : node(_node),
              pos(_pos)
        {
        }

        TIntermAggregate *node;
        TIntermSequence::size_type pos;
    };
    std::vector<ParentBlock> mParentBlockStack;

    TIntermSymbol *createTempSymbol(const TType &type);
    TIntermAggregate *createTempInitDeclaration(const TType &type, TIntermTyped *initializer);
    TIntermBinary *createTempAssignment(const TType &type, TIntermTyped *rightNode);
};

UnfoldShortCircuitTraverser::UnfoldShortCircuitTraverser()
    : TIntermTraverser(true, true, true),
      mTemporaryIndex(0),
      mFoundShortCircuit(false)
{
}

TIntermSymbol *UnfoldShortCircuitTraverser::createTempSymbol(const TType &type)
{
    // Each traversal uses at most one temporary variable, so the index stays the same within a single traversal.
    TInfoSinkBase symbolNameOut;
    symbolNameOut << "s" << mTemporaryIndex;
    TString symbolName = symbolNameOut.c_str();

    TIntermSymbol *node = new TIntermSymbol(0, symbolName, type);
    node->setInternal(true);
    return node;
}

TIntermAggregate *UnfoldShortCircuitTraverser::createTempInitDeclaration(const TType &type, TIntermTyped *initializer)
{
    ASSERT(initializer != nullptr);
    TIntermSymbol *tempSymbol = createTempSymbol(type);
    TIntermAggregate *tempDeclaration = new TIntermAggregate(EOpDeclaration);
    TIntermBinary *tempInit = new TIntermBinary(EOpInitialize);
    tempInit->setLeft(tempSymbol);
    tempInit->setRight(initializer);
    tempInit->setType(type);
    tempDeclaration->getSequence()->push_back(tempInit);
    return tempDeclaration;
}

TIntermBinary *UnfoldShortCircuitTraverser::createTempAssignment(const TType &type, TIntermTyped *rightNode)
{
    ASSERT(rightNode != nullptr);
    TIntermSymbol *tempSymbol = createTempSymbol(type);
    TIntermBinary *assignment = new TIntermBinary(EOpAssign);
    assignment->setLeft(tempSymbol);
    assignment->setRight(rightNode);
    assignment->setType(type);
    return assignment;
}

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);

            insertions.push_back(createTempInitDeclaration(boolType, node->getLeft()));

            TIntermAggregate *assignRightBlock = new TIntermAggregate(EOpSequence);
            assignRightBlock->getSequence()->push_back(createTempAssignment(boolType, node->getRight()));

            TIntermUnary *notTempSymbol = new TIntermUnary(EOpLogicalNot, boolType);
            notTempSymbol->setOperand(createTempSymbol(boolType));
            TIntermSelection *ifNode = new TIntermSelection(notTempSymbol, assignRightBlock, nullptr);
            insertions.push_back(ifNode);

            NodeInsertMultipleEntry insert(mParentBlockStack.back().node, mParentBlockStack.back().pos, insertions);
            mInsertions.push_back(insert);

            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);

            insertions.push_back(createTempInitDeclaration(boolType, node->getLeft()));

            TIntermAggregate *assignRightBlock = new TIntermAggregate(EOpSequence);
            assignRightBlock->getSequence()->push_back(createTempAssignment(boolType, node->getRight()));

            TIntermSelection *ifNode = new TIntermSelection(createTempSymbol(boolType), assignRightBlock, nullptr);
            insertions.push_back(ifNode);

            NodeInsertMultipleEntry insert(mParentBlockStack.back().node, mParentBlockStack.back().pos, insertions);
            mInsertions.push_back(insert);

            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->getType(), node->getTrueBlock()->getAsTyped());
        trueBlock->getSequence()->push_back(trueAssignment);

        TIntermAggregate *falseBlock = new TIntermAggregate(EOpSequence);
        TIntermBinary *falseAssignment = createTempAssignment(node->getType(), node->getFalseBlock()->getAsTyped());
        falseBlock->getSequence()->push_back(falseAssignment);

        TIntermSelection *ifNode = new TIntermSelection(node->getCondition()->getAsTyped(), trueBlock, falseBlock);
        insertions.push_back(ifNode);

        NodeInsertMultipleEntry insert(mParentBlockStack.back().node, mParentBlockStack.back().pos, insertions);
        mInsertions.push_back(insert);

        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() == EOpSequence)
    {
        if (visit == PreVisit)
        {
            mParentBlockStack.push_back(ParentBlock(node, 0));
        }
        else if (visit == InVisit)
        {
            ++mParentBlockStack.back().pos;
        }
        else
        {
            ASSERT(visit == PostVisit);
            mParentBlockStack.pop_back();
        }
    }
    else 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;
            }

            NodeInsertMultipleEntry insert(mParentBlockStack.back().node, mParentBlockStack.back().pos, insertions);
            mInsertions.push_back(insert);
            NodeUpdateEntry replaceVariable(getParentNode(), node, (*seq)[i], false);
            mReplacements.push_back(replaceVariable);
        }
    }
    return true;
}

void UnfoldShortCircuitTraverser::nextIteration()
{
    mFoundShortCircuit = false;
    mTemporaryIndex++;
    mReplacements.clear();
    mMultiReplacements.clear();
    mInsertions.clear();
}

} // namespace

void UnfoldShortCircuitToIf(TIntermNode *root)
{
    UnfoldShortCircuitTraverser traverser;
    // 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());
}
kc3-lang/angle/src/compiler/translator/UnfoldShortCircuitToIf.cpp

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