RewriteElseBlocks.cpp

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//

// Copyright 2014 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.

//

// RewriteElseBlocks.cpp: Implementation for tree transform to change

//   all if-else blocks to if-if blocks.

//

#include "compiler/translator/tree_ops/d3d/RewriteElseBlocks.h"

#include "compiler/translator/Compiler.h"

#include "compiler/translator/IntermNode.h"

#include "compiler/translator/SymbolTable.h"

#include "compiler/translator/tree_util/IntermNode_util.h"

#include "compiler/translator/tree_util/NodeSearch.h"

namespace sh

namespace

class ElseBlockRewriter : public TIntermTraverser

  public:

    ElseBlockRewriter(TSymbolTable *symbolTable);

  protected:

    bool visitFunctionDefinition(Visit visit, TIntermFunctionDefinition *aggregate) override;

    bool visitBlock(Visit visit, TIntermBlock *block) override;

  private:

    TIntermNode *rewriteIfElse(TIntermIfElse *ifElse);

    const TType *mFunctionType;

};

ElseBlockRewriter::ElseBlockRewriter(TSymbolTable *symbolTable)

    : TIntermTraverser(true, false, true, symbolTable), mFunctionType(nullptr)

{}

bool ElseBlockRewriter::visitFunctionDefinition(Visit visit, TIntermFunctionDefinition *node)

    // Store the current function context (see comment below)

    mFunctionType = ((visit == PreVisit) ? &node->getFunctionPrototype()->getType() : nullptr);

    return true;

bool ElseBlockRewriter::visitBlock(Visit visit, TIntermBlock *node)

    if (visit == PostVisit)

        for (size_t statementIndex = 0; statementIndex != node->getSequence()->size();

             statementIndex++)

            TIntermNode *statement = (*node->getSequence())[statementIndex];

            TIntermIfElse *ifElse  = statement->getAsIfElseNode();

            if (ifElse && ifElse->getFalseBlock() != nullptr)

                (*node->getSequence())[statementIndex] = rewriteIfElse(ifElse);

    return true;

TIntermNode *ElseBlockRewriter::rewriteIfElse(TIntermIfElse *ifElse)

    ASSERT(ifElse != nullptr);

    TIntermDeclaration *storeCondition = nullptr;

    TVariable *conditionVariable =

        DeclareTempVariable(mSymbolTable, ifElse->getCondition(), EvqTemporary, &storeCondition);

    TIntermBlock *falseBlock = nullptr;

    TType boolType(EbtBool, EbpUndefined, EvqTemporary);

    if (ifElse->getFalseBlock())

        TIntermBlock *negatedElse = nullptr;

        // crbug.com/346463

        // D3D generates error messages claiming a function has no return value, when rewriting

        // an if-else clause that returns something non-void in a function. By appending mock

        // returns (that are unreachable) we can silence this compile error.

        if (mFunctionType && mFunctionType->getBasicType() != EbtVoid)

            TIntermNode *returnNode = new TIntermBranch(EOpReturn, CreateZeroNode(*mFunctionType));

            negatedElse             = new TIntermBlock();

            negatedElse->appendStatement(returnNode);

        TIntermSymbol *conditionSymbolElse = CreateTempSymbolNode(conditionVariable);

        TIntermUnary *negatedCondition =

            new TIntermUnary(EOpLogicalNot, conditionSymbolElse, nullptr);

        TIntermIfElse *falseIfElse =

            new TIntermIfElse(negatedCondition, ifElse->getFalseBlock(), negatedElse);

        falseBlock = EnsureBlock(falseIfElse);

    TIntermSymbol *conditionSymbolSel = CreateTempSymbolNode(conditionVariable);

    TIntermIfElse *newIfElse =

        new TIntermIfElse(conditionSymbolSel, ifElse->getTrueBlock(), falseBlock);

    TIntermBlock *block = new TIntermBlock();

    block->getSequence()->push_back(storeCondition);

    block->getSequence()->push_back(newIfElse);

    return block;

}  // anonymous namespace

bool RewriteElseBlocks(TCompiler *compiler, TIntermNode *node, TSymbolTable *symbolTable)

    ElseBlockRewriter rewriter(symbolTable);

    node->traverse(&rewriter);

    return compiler->validateAST(node);

}  // namespace sh