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

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• Author : Stuart Morgan
  Date : 2019-08-14 12:25:12
  Hash : 9d737966
  Message : Standardize copyright notices to project style For all "ANGLE Project" copyrights, standardize to the format specified by the style guide. Changes: - "Copyright (c)" and "Copyright(c)" changed to just "Copyright". - Removed the second half of date ranges ("Y1Y1-Y2Y2"->"Y1Y1"). - Fixed a small number of files that had no copyright date using the initial commit year from the version control history. - Fixed one instance of copyright being "The ANGLE Project" rather than "The ANGLE Project Authors" These changes are applied both to the copyright of source file, and where applicable to copyright statements that are generated by templates. BUG=angleproject:3811 Change-Id: I973dd65e4ef9deeba232d5be74c768256a0eb2e5 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1754397 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>

• src/compiler/translator/tree_ops/BreakVariableAliasingInInnerLoops.cpp

• //
  // Copyright 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/tree_util/IntermNode_util.h"
  #include "compiler/translator/tree_util/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, CreateZeroNode(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