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

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• Hash : cccf2b00
  Author :
  Date : 2017-07-05T14:50:54
  

  Reorganize AST traversal utility code
  
  Define TIntermTraverser and TIntermLValueTrackingTraverser in a
  separate header file. hash() function is moved out from
  TIntermTraverser as it is not related to the core functionality
  of traversing and transforming ASTs.
  
  Also reorganize some traversers to follow common conventions:
  
  - Intermediate output is now in OutputTree.h/.cpp
  - Max tree depth check is now in IsASTDepthBelowLimit.h/.cpp
  
  BUG=angleproject:1490
  TEST=angle_unittests
  
  Change-Id: Id4968aa9d4e24d0c5bac90dc147fc9f310de0184
  Reviewed-on: https://chromium-review.googlesource.com/559531
  Reviewed-by: Jamie Madill <jmadill@chromium.org>
  Reviewed-by: Corentin Wallez <cwallez@chromium.org>
  Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
  

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• src/compiler/translator/BreakVariableAliasingInInnerLoops.cpp

• //
  // Copyright (c) 2016 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.
  //
  
  // BreakVariableAliasingInInnerLoops.h: To optimize simple assignments, the HLSL compiler frontend
  //      may record a variable as aliasing another. Sometimes the alias information gets garbled
  //      so we work around this issue by breaking the aliasing chain in inner loops.
  
  #include "BreakVariableAliasingInInnerLoops.h"
  
  #include "compiler/translator/IntermTraverse.h"
  
  // A HLSL compiler developer gave us more details on the root cause and the workaround needed:
  //     The root problem is that if the HLSL compiler is applying aliasing information even on
  //     incomplete simulations (in this case, a single pass). The bug is triggered by an assignment
  //     that comes from a series of assignments, possibly with swizzled or ternary operators with
  //     known conditionals, where the source is before the loop.
  //     So, a workaround is to add a +0 term to variables the first time they are assigned to in
  //     an inner loop (if they are declared in an outside scope, otherwise there is no need).
  //     This will break the aliasing chain.
  
  // For simplicity here we add a +0 to any assignment that is in at least two nested loops. Because
  // the bug only shows up with swizzles, and ternary assignment, whole array or whole structure
  // assignment don't need a workaround.
  
  namespace sh
  {
  
  namespace
  {
  
  class AliasingBreaker : public TIntermTraverser
  {
    public:
      AliasingBreaker() : TIntermTraverser(true, false, true) {}
  
    protected:
      bool visitBinary(Visit visit, TIntermBinary *binary)
      {
          if (visit != PreVisit)
          {
              return false;
          }
  
          if (mLoopLevel < 2 || !binary->isAssignment())
          {
              return true;
          }
  
          TIntermTyped *B = binary->getRight();
          TType type      = B->getType();
  
          if (!type.isScalar() && !type.isVector() && !type.isMatrix())
          {
              return true;
          }
  
          if (type.isArray() || IsSampler(type.getBasicType()))
          {
              return true;
          }
  
          // We have a scalar / vector / matrix assignment with loop depth 2.
          // Transform it from
          //    A = B
          // to
          //    A = (B + typeof<B>(0));
  
          TIntermBinary *bPlusZero = new TIntermBinary(EOpAdd, B, TIntermTyped::CreateZero(type));
          bPlusZero->setLine(B->getLine());
  
          binary->replaceChildNode(B, bPlusZero);
  
          return true;
      }
  
      bool visitLoop(Visit visit, TIntermLoop *loop)
      {
          if (visit == PreVisit)
          {
              mLoopLevel++;
          }
          else
          {
              ASSERT(mLoopLevel > 0);
              mLoopLevel--;
          }
  
          return true;
      }
  
    private:
      int mLoopLevel = 0;
  };
  
  }  // anonymous namespace
  
  void BreakVariableAliasingInInnerLoops(TIntermNode *root)
  {
      AliasingBreaker breaker;
      root->traverse(&breaker);
  }
  
  }  // namespace sh
  

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