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      1 //
      2 // Copyright (c) 2014 The ANGLE Project Authors. All rights reserved.
      3 // Use of this source code is governed by a BSD-style license that can be
      4 // found in the LICENSE file.
      5 //
      6 // RewriteElseBlocks.cpp: Implementation for tree transform to change
      7 //   all if-else blocks to if-if blocks.
      8 //
      9 
     10 #include "compiler/translator/RewriteElseBlocks.h"
     11 #include "compiler/translator/NodeSearch.h"
     12 #include "compiler/translator/SymbolTable.h"
     13 
     14 namespace sh
     15 {
     16 
     17 namespace
     18 {
     19 
     20 class ElseBlockRewriter : public TIntermTraverser
     21 {
     22   public:
     23     ElseBlockRewriter();
     24 
     25   protected:
     26     bool visitAggregate(Visit visit, TIntermAggregate *aggregate);
     27 
     28   private:
     29     int mTemporaryIndex;
     30     const TType *mFunctionType;
     31 
     32     TIntermNode *rewriteSelection(TIntermSelection *selection);
     33 };
     34 
     35 TIntermSymbol *MakeNewTemporary(const TString &name, TBasicType type)
     36 {
     37     TType variableType(type, EbpHigh, EvqInternal);
     38     return new TIntermSymbol(-1, name, variableType);
     39 }
     40 
     41 TIntermBinary *MakeNewBinary(TOperator op, TIntermTyped *left, TIntermTyped *right, const TType &resultType)
     42 {
     43     TIntermBinary *binary = new TIntermBinary(op);
     44     binary->setLeft(left);
     45     binary->setRight(right);
     46     binary->setType(resultType);
     47     return binary;
     48 }
     49 
     50 TIntermUnary *MakeNewUnary(TOperator op, TIntermTyped *operand)
     51 {
     52     TIntermUnary *unary = new TIntermUnary(op, operand->getType());
     53     unary->setOperand(operand);
     54     return unary;
     55 }
     56 
     57 ElseBlockRewriter::ElseBlockRewriter()
     58     : TIntermTraverser(true, false, true, false),
     59       mTemporaryIndex(0),
     60       mFunctionType(NULL)
     61 {}
     62 
     63 bool ElseBlockRewriter::visitAggregate(Visit visit, TIntermAggregate *node)
     64 {
     65     switch (node->getOp())
     66     {
     67       case EOpSequence:
     68         if (visit == PostVisit)
     69         {
     70             for (size_t statementIndex = 0; statementIndex != node->getSequence()->size(); statementIndex++)
     71             {
     72                 TIntermNode *statement = (*node->getSequence())[statementIndex];
     73                 TIntermSelection *selection = statement->getAsSelectionNode();
     74                 if (selection && selection->getFalseBlock() != NULL)
     75                 {
     76                     // Check for if / else if
     77                     TIntermSelection *elseIfBranch = selection->getFalseBlock()->getAsSelectionNode();
     78                     if (elseIfBranch)
     79                     {
     80                         selection->replaceChildNode(elseIfBranch, rewriteSelection(elseIfBranch));
     81                         delete elseIfBranch;
     82                     }
     83 
     84                     (*node->getSequence())[statementIndex] = rewriteSelection(selection);
     85                     delete selection;
     86                 }
     87             }
     88         }
     89         break;
     90 
     91       case EOpFunction:
     92         // Store the current function context (see comment below)
     93         mFunctionType = ((visit == PreVisit) ? &node->getType() : NULL);
     94         break;
     95 
     96       default: break;
     97     }
     98 
     99     return true;
    100 }
    101 
    102 TIntermNode *ElseBlockRewriter::rewriteSelection(TIntermSelection *selection)
    103 {
    104     ASSERT(selection != NULL);
    105 
    106     TString temporaryName = "cond_" + str(mTemporaryIndex++);
    107     TIntermTyped *typedCondition = selection->getCondition()->getAsTyped();
    108     TType resultType(EbtBool, EbpUndefined);
    109     TIntermSymbol *conditionSymbolInit = MakeNewTemporary(temporaryName, EbtBool);
    110     TIntermBinary *storeCondition = MakeNewBinary(EOpInitialize, conditionSymbolInit,
    111                                                   typedCondition, resultType);
    112     TIntermNode *negatedElse = NULL;
    113 
    114     TIntermSelection *falseBlock = NULL;
    115 
    116     if (selection->getFalseBlock())
    117     {
    118         // crbug.com/346463
    119         // D3D generates error messages claiming a function has no return value, when rewriting
    120         // an if-else clause that returns something non-void in a function. By appending dummy
    121         // returns (that are unreachable) we can silence this compile error.
    122         if (mFunctionType && mFunctionType->getBasicType() != EbtVoid)
    123         {
    124             TString typeString = mFunctionType->getStruct() ? mFunctionType->getStruct()->name() :
    125                 mFunctionType->getBasicString();
    126             TString rawText = "return (" + typeString + ")0";
    127             negatedElse = new TIntermRaw(*mFunctionType, rawText);
    128         }
    129 
    130         TIntermSymbol *conditionSymbolElse = MakeNewTemporary(temporaryName, EbtBool);
    131         TIntermUnary *negatedCondition = MakeNewUnary(EOpLogicalNot, conditionSymbolElse);
    132         falseBlock = new TIntermSelection(negatedCondition,
    133                                           selection->getFalseBlock(), negatedElse);
    134     }
    135 
    136     TIntermSymbol *conditionSymbolSel = MakeNewTemporary(temporaryName, EbtBool);
    137     TIntermSelection *newSelection = new TIntermSelection(conditionSymbolSel,
    138                                                           selection->getTrueBlock(), falseBlock);
    139 
    140     TIntermAggregate *declaration = new TIntermAggregate(EOpDeclaration);
    141     declaration->getSequence()->push_back(storeCondition);
    142 
    143     TIntermAggregate *block = new TIntermAggregate(EOpSequence);
    144     block->getSequence()->push_back(declaration);
    145     block->getSequence()->push_back(newSelection);
    146 
    147     return block;
    148 }
    149 
    150 }
    151 
    152 void RewriteElseBlocks(TIntermNode *node)
    153 {
    154     ElseBlockRewriter rewriter;
    155     node->traverse(&rewriter);
    156 }
    157 
    158 }
    159