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

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• Hash : 3272a6d3
  Author :
  Date : 2016-08-29T17:54:50
  

  Promote and fold indexing nodes similarly to other binary ops
  
  Indexing nodes now get their type set in TIntermBinary::promote, same
  as math and logic ops. They are also constant folded through
  TIntermBinary::fold() instead of having special functions for constant
  folding them in ParseContext.
  
  Index nodes for struct and interface block member access now always
  have integer type, instead of sometimes having the type of the field
  they were used to access.
  
  Usage of TIntermBinary constructor is cleaned up so only the
  constructor that takes in left and right operands is used. The type
  of TIntermBinary nodes is always determined automatically.
  
  Together these changes make the code considerably cleaner.
  
  Note that the code for constant folding for array indexing is actually
  never hit because constant folding array constructors is still
  intentionally disabled in the code.
  
  BUG=angleproject:1490
  TEST=angle_unittests
  
  Change-Id: Ifcec45257476cdb0d495c7d72e3cf2f83388e8c5
  Reviewed-on: https://chromium-review.googlesource.com/377961
  Reviewed-by: Jamie Madill <jmadill@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/IntermNode.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
  {
  
  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
  
  namespace sh
  {
  
  void BreakVariableAliasingInInnerLoops(TIntermNode *root)
  {
      AliasingBreaker breaker;
      root->traverse(&breaker);
  }
  
  }  // namespace sh
  

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