Line data    Source code

       1             : //
       2             : // Copyright (c) 2002-2013 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             : // UnfoldShortCircuitToIf is an AST traverser to convert short-circuiting operators to if-else statements.
       7             : // The results are assigned to s# temporaries, which are used by the main translator instead of
       8             : // the original expression.
       9             : //
      10             : 
      11             : #include "compiler/translator/UnfoldShortCircuitToIf.h"
      12             : 
      13             : #include "compiler/translator/IntermNode.h"
      14             : #include "compiler/translator/IntermNodePatternMatcher.h"
      15             : 
      16             : namespace sh
      17             : {
      18             : 
      19             : namespace
      20             : {
      21             : 
      22             : // Traverser that unfolds one short-circuiting operation at a time.
      23           0 : class UnfoldShortCircuitTraverser : public TIntermTraverser
      24             : {
      25             :   public:
      26             :     UnfoldShortCircuitTraverser();
      27             : 
      28             :     bool visitBinary(Visit visit, TIntermBinary *node) override;
      29             :     bool visitTernary(Visit visit, TIntermTernary *node) override;
      30             : 
      31             :     void nextIteration();
      32           0 :     bool foundShortCircuit() const { return mFoundShortCircuit; }
      33             : 
      34             :   protected:
      35             :     // Marked to true once an operation that needs to be unfolded has been found.
      36             :     // After that, no more unfolding is performed on that traversal.
      37             :     bool mFoundShortCircuit;
      38             : 
      39             :     IntermNodePatternMatcher mPatternToUnfoldMatcher;
      40             : };
      41             : 
      42           0 : UnfoldShortCircuitTraverser::UnfoldShortCircuitTraverser()
      43             :     : TIntermTraverser(true, false, true),
      44             :       mFoundShortCircuit(false),
      45           0 :       mPatternToUnfoldMatcher(IntermNodePatternMatcher::kUnfoldedShortCircuitExpression)
      46             : {
      47           0 : }
      48             : 
      49           0 : bool UnfoldShortCircuitTraverser::visitBinary(Visit visit, TIntermBinary *node)
      50             : {
      51           0 :     if (mFoundShortCircuit)
      52           0 :         return false;
      53             : 
      54           0 :     if (visit != PreVisit)
      55           0 :         return true;
      56             : 
      57           0 :     if (!mPatternToUnfoldMatcher.match(node, getParentNode()))
      58           0 :         return true;
      59             : 
      60             :     // If our right node doesn't have side effects, we know we don't need to unfold this
      61             :     // expression: there will be no short-circuiting side effects to avoid
      62             :     // (note: unfolding doesn't depend on the left node -- it will always be evaluated)
      63           0 :     ASSERT(node->getRight()->hasSideEffects());
      64             : 
      65           0 :     mFoundShortCircuit = true;
      66             : 
      67           0 :     switch (node->getOp())
      68             :     {
      69             :       case EOpLogicalOr:
      70             :       {
      71             :           // "x || y" is equivalent to "x ? true : y", which unfolds to "bool s; if(x) s = true;
      72             :           // else s = y;",
      73             :           // and then further simplifies down to "bool s = x; if(!s) s = y;".
      74             : 
      75           0 :           TIntermSequence insertions;
      76           0 :           TType boolType(EbtBool, EbpUndefined, EvqTemporary);
      77             : 
      78           0 :           ASSERT(node->getLeft()->getType() == boolType);
      79           0 :           insertions.push_back(createTempInitDeclaration(node->getLeft()));
      80             : 
      81           0 :           TIntermBlock *assignRightBlock = new TIntermBlock();
      82           0 :           ASSERT(node->getRight()->getType() == boolType);
      83           0 :           assignRightBlock->getSequence()->push_back(createTempAssignment(node->getRight()));
      84             : 
      85           0 :           TIntermUnary *notTempSymbol = new TIntermUnary(EOpLogicalNot, createTempSymbol(boolType));
      86           0 :           TIntermIfElse *ifNode       = new TIntermIfElse(notTempSymbol, assignRightBlock, nullptr);
      87           0 :           insertions.push_back(ifNode);
      88             : 
      89           0 :           insertStatementsInParentBlock(insertions);
      90             : 
      91           0 :           queueReplacement(node, createTempSymbol(boolType), OriginalNode::IS_DROPPED);
      92           0 :           return false;
      93             :       }
      94             :       case EOpLogicalAnd:
      95             :       {
      96             :           // "x && y" is equivalent to "x ? y : false", which unfolds to "bool s; if(x) s = y;
      97             :           // else s = false;",
      98             :           // and then further simplifies down to "bool s = x; if(s) s = y;".
      99           0 :           TIntermSequence insertions;
     100           0 :           TType boolType(EbtBool, EbpUndefined, EvqTemporary);
     101             : 
     102           0 :           ASSERT(node->getLeft()->getType() == boolType);
     103           0 :           insertions.push_back(createTempInitDeclaration(node->getLeft()));
     104             : 
     105           0 :           TIntermBlock *assignRightBlock = new TIntermBlock();
     106           0 :           ASSERT(node->getRight()->getType() == boolType);
     107           0 :           assignRightBlock->getSequence()->push_back(createTempAssignment(node->getRight()));
     108             : 
     109             :           TIntermIfElse *ifNode =
     110           0 :               new TIntermIfElse(createTempSymbol(boolType), assignRightBlock, nullptr);
     111           0 :           insertions.push_back(ifNode);
     112             : 
     113           0 :           insertStatementsInParentBlock(insertions);
     114             : 
     115           0 :           queueReplacement(node, createTempSymbol(boolType), OriginalNode::IS_DROPPED);
     116           0 :           return false;
     117             :       }
     118             :       default:
     119           0 :           UNREACHABLE();
     120             :           return true;
     121             :     }
     122             : }
     123             : 
     124           0 : bool UnfoldShortCircuitTraverser::visitTernary(Visit visit, TIntermTernary *node)
     125             : {
     126           0 :     if (mFoundShortCircuit)
     127           0 :         return false;
     128             : 
     129           0 :     if (visit != PreVisit)
     130           0 :         return true;
     131             : 
     132           0 :     if (!mPatternToUnfoldMatcher.match(node))
     133           0 :         return true;
     134             : 
     135           0 :     mFoundShortCircuit = true;
     136             : 
     137             :     // Unfold "b ? x : y" into "type s; if(b) s = x; else s = y;"
     138           0 :     TIntermSequence insertions;
     139             : 
     140           0 :     TIntermDeclaration *tempDeclaration = createTempDeclaration(node->getType());
     141           0 :     insertions.push_back(tempDeclaration);
     142             : 
     143           0 :     TIntermBlock *trueBlock       = new TIntermBlock();
     144           0 :     TIntermBinary *trueAssignment = createTempAssignment(node->getTrueExpression());
     145           0 :     trueBlock->getSequence()->push_back(trueAssignment);
     146             : 
     147           0 :     TIntermBlock *falseBlock       = new TIntermBlock();
     148           0 :     TIntermBinary *falseAssignment = createTempAssignment(node->getFalseExpression());
     149           0 :     falseBlock->getSequence()->push_back(falseAssignment);
     150             : 
     151             :     TIntermIfElse *ifNode =
     152           0 :         new TIntermIfElse(node->getCondition()->getAsTyped(), trueBlock, falseBlock);
     153           0 :     insertions.push_back(ifNode);
     154             : 
     155           0 :     insertStatementsInParentBlock(insertions);
     156             : 
     157           0 :     TIntermSymbol *ternaryResult = createTempSymbol(node->getType());
     158           0 :     queueReplacement(node, ternaryResult, OriginalNode::IS_DROPPED);
     159             : 
     160           0 :     return false;
     161             : }
     162             : 
     163           0 : void UnfoldShortCircuitTraverser::nextIteration()
     164             : {
     165           0 :     mFoundShortCircuit = false;
     166           0 :     nextTemporaryIndex();
     167           0 : }
     168             : 
     169             : } // namespace
     170             : 
     171           0 : void UnfoldShortCircuitToIf(TIntermNode *root, unsigned int *temporaryIndex)
     172             : {
     173           0 :     UnfoldShortCircuitTraverser traverser;
     174           0 :     ASSERT(temporaryIndex != nullptr);
     175           0 :     traverser.useTemporaryIndex(temporaryIndex);
     176             :     // Unfold one operator at a time, and reset the traverser between iterations.
     177           0 :     do
     178             :     {
     179           0 :         traverser.nextIteration();
     180           0 :         root->traverse(&traverser);
     181           0 :         if (traverser.foundShortCircuit())
     182           0 :             traverser.updateTree();
     183             :     }
     184             :     while (traverser.foundShortCircuit());
     185           0 : }
     186             : 
     187             : }  // namespace sh