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

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• Hash : 472c74c6
  Author :
  Date : 2019-08-19T16:32:13
  

  Translator: Allow tree validation in children of TCompiler
  
  This is to be able to perform validation inside TranslatorVulkan, even
  if it's through ASSERTs.
  
  Additionally, every transformation is changed such that they do their
  validation themselves.  TIntermTraverser::updateTree() performs the
  validation, which indirectly validates many of three tree
  transformations.  Some of the more ancient transformations that don't
  use this function directly call TCompiler::validateAST.
  
  Bug: angleproject:2733
  Change-Id: Ie4af029d34e053c5ad1dc8c2c2568eecd625d344
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1761149
  Reviewed-by: Geoff Lang <geofflang@chromium.org>
  Reviewed-by: Jamie Madill <jmadill@chromium.org>
  Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
  

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• 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/Compiler.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
  
  bool BreakVariableAliasingInInnerLoops(TCompiler *compiler, TIntermNode *root)
  {
      AliasingBreaker breaker;
      root->traverse(&breaker);
  
      return compiler->validateAST(root);
  }
  
  }  // namespace sh
  

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