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

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• Hash : 590f6235
  Author :
  Date : 2017-07-21T11:10:26
  

  Fix getting temporary id in RewriteDoWhile
  
  There's been a long-standing bug in RewriteDoWhile where it would only
  call nextTemporaryId() after it had created the temporary variable.
  This escalated into a null pointer dereference in the recent symbol
  table refactoring, and initializing the traverser with the symbol
  table was also missing.
  
  BUG=chromium:747244
  TEST=angle_unittests
  
  Change-Id: I8987a609bb5d7d49e3c3e284fc42a2e53e38dafa
  Reviewed-on: https://chromium-review.googlesource.com/580887
  Commit-Queue: Jamie Madill <jmadill@chromium.org>
  Reviewed-by: Jamie Madill <jmadill@chromium.org>
  

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• src/compiler/translator/RewriteDoWhile.cpp

• //
  // Copyright (c) 2015 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.
  //
  
  // RewriteDoWhile.cpp: rewrites do-while loops using another equivalent
  // construct.
  
  #include "compiler/translator/RewriteDoWhile.h"
  
  #include "compiler/translator/IntermTraverse.h"
  
  namespace sh
  {
  
  namespace
  {
  
  // An AST traverser that rewrites loops of the form
  //   do {
  //     CODE;
  //   } while (CONDITION)
  //
  // to loops of the form
  //   bool temp = false;
  //   while (true) {
  //     if (temp) {
  //       if (!CONDITION) {
  //         break;
  //       }
  //     }
  //     temp = true;
  //     CODE;
  //   }
  //
  // The reason we don't use a simpler form, with for example just (temp && !CONDITION) in the
  // while condition, is that short-circuit is often badly supported by driver shader compiler.
  // The double if has the same effect, but forces shader compilers to behave.
  //
  // TODO(cwallez) when UnfoldShortCircuitIntoIf handles loops correctly, revisit this as we might
  // be able to use while (temp || CONDITION) with temp initially set to true then run
  // UnfoldShortCircuitIntoIf
  class DoWhileRewriter : public TIntermTraverser
  {
    public:
      DoWhileRewriter(TSymbolTable *symbolTable) : TIntermTraverser(true, false, false, symbolTable)
      {
      }
  
      bool visitBlock(Visit, TIntermBlock *node) override
      {
          // A well-formed AST can only have do-while inside TIntermBlock. By doing a prefix traversal
          // we are able to replace the do-while in the sequence directly as the content of the
          // do-while will be traversed later.
  
          TIntermSequence *statements = node->getSequence();
  
          // The statements vector will have new statements inserted when we encounter a do-while,
          // which prevents us from using a range-based for loop. Using the usual i++ works, as
          // the (two) new statements inserted replace the statement at the current position.
          for (size_t i = 0; i < statements->size(); i++)
          {
              TIntermNode *statement = (*statements)[i];
              TIntermLoop *loop      = statement->getAsLoopNode();
  
              if (loop == nullptr || loop->getType() != ELoopDoWhile)
              {
                  continue;
              }
  
              // Found a loop to change.
              nextTemporaryId();
  
              TType boolType = TType(EbtBool);
  
              // bool temp = false;
              TIntermDeclaration *tempDeclaration = nullptr;
              {
                  TConstantUnion *falseConstant = new TConstantUnion();
                  falseConstant->setBConst(false);
                  TIntermTyped *falseValue = new TIntermConstantUnion(falseConstant, boolType);
  
                  tempDeclaration = createTempInitDeclaration(falseValue);
              }
  
              // temp = true;
              TIntermBinary *assignTrue = nullptr;
              {
                  TConstantUnion *trueConstant = new TConstantUnion();
                  trueConstant->setBConst(true);
                  TIntermTyped *trueValue = new TIntermConstantUnion(trueConstant, boolType);
  
                  assignTrue = createTempAssignment(trueValue);
              }
  
              // if (temp) {
              //   if (!CONDITION) {
              //     break;
              //   }
              // }
              TIntermIfElse *breakIf = nullptr;
              {
                  TIntermBranch *breakStatement = new TIntermBranch(EOpBreak, nullptr);
  
                  TIntermBlock *breakBlock = new TIntermBlock();
                  breakBlock->getSequence()->push_back(breakStatement);
  
                  TIntermUnary *negatedCondition =
                      new TIntermUnary(EOpLogicalNot, loop->getCondition());
  
                  TIntermIfElse *innerIf = new TIntermIfElse(negatedCondition, breakBlock, nullptr);
  
                  TIntermBlock *innerIfBlock = new TIntermBlock();
                  innerIfBlock->getSequence()->push_back(innerIf);
  
                  breakIf = new TIntermIfElse(createTempSymbol(boolType), innerIfBlock, nullptr);
              }
  
              // Assemble the replacement loops, reusing the do-while loop's body and inserting our
              // statements at the front.
              TIntermLoop *newLoop = nullptr;
              {
                  TConstantUnion *trueConstant = new TConstantUnion();
                  trueConstant->setBConst(true);
                  TIntermTyped *trueValue = new TIntermConstantUnion(trueConstant, boolType);
  
                  TIntermBlock *body = loop->getBody();
                  if (body == nullptr)
                  {
                      body = new TIntermBlock();
                  }
                  auto sequence = body->getSequence();
                  sequence->insert(sequence->begin(), assignTrue);
                  sequence->insert(sequence->begin(), breakIf);
  
                  newLoop = new TIntermLoop(ELoopWhile, nullptr, trueValue, nullptr, body);
              }
  
              TIntermSequence replacement;
              replacement.push_back(tempDeclaration);
              replacement.push_back(newLoop);
  
              node->replaceChildNodeWithMultiple(loop, replacement);
          }
          return true;
      }
  };
  
  }  // anonymous namespace
  
  void RewriteDoWhile(TIntermNode *root, TSymbolTable *symbolTable)
  {
      DoWhileRewriter rewriter(symbolTable);
  
      root->traverse(&rewriter);
  }
  
  }  // namespace sh
  

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