kc3-lang/angle/src/compiler/translator/TranslatorMetalDirect/GuardFragDepthWrite.cpp

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• Hash : 45237a04
  Author :
  Date : 2022-01-11T00:14:01
  

  Metal: Fix undefined behavior of depth write
  
  Writing to an unbound depth attachment is undefined behavior in Metal.
  Fix this by emitting a function constant to guard depth buffer use
  in fragment shaders.
  
  Bug: angleproject:6865
  Change-Id: Id7c10d0aeb349aacfe09c397bc292a71199ab50a
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3380304
  Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
  Reviewed-by: Kenneth Russell <kbr@chromium.org>
  Commit-Queue: Kenneth Russell <kbr@chromium.org>
  

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• src/compiler/translator/TranslatorMetalDirect/GuardFragDepthWrite.cpp

• //
  // Copyright 2022 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.
  //
  // GuardFragDepthWrite: Guards use of frag depth behind the function constant
  // ANGLEDepthWriteEnabled to ensure it is only used when a valid depth buffer
  // is bound.
  
  #include "compiler/translator/TranslatorMetalDirect/GuardFragDepthWrite.h"
  #include "compiler/translator/TranslatorMetalDirect/AstHelpers.h"
  #include "compiler/translator/tree_util/BuiltIn.h"
  #include "compiler/translator/tree_util/IntermRebuild.h"
  
  using namespace sh;
  
  ////////////////////////////////////////////////////////////////////////////////
  
  namespace
  {
  
  class Rewriter : public TIntermRebuild
  {
    public:
      Rewriter(TCompiler &compiler) : TIntermRebuild(compiler, false, true) {}
  
      PostResult visitBinaryPost(TIntermBinary &node) override
      {
          if (TIntermSymbol *leftSymbolNode = node.getLeft()->getAsSymbolNode())
          {
              if (leftSymbolNode->getType().getQualifier() == TQualifier::EvqFragDepth)
              {
                  // This transformation leaves the tree in an inconsistent state by using a variable
                  // that's defined in text, outside of the knowledge of the AST.
                  // FIXME(jcunningham): remove once function constants (specconst) are implemented
                  // with the metal translator.
                  mCompiler.disableValidateVariableReferences();
  
                  TSymbolTable *symbolTable = &mCompiler.getSymbolTable();
  
                  // Create kDepthWriteEnabled variable reference.
                  TType *boolType = new TType(EbtBool);
                  boolType->setQualifier(EvqConst);
                  TVariable *depthWriteEnabledVar = new TVariable(
                      symbolTable, sh::ImmutableString(sh::mtl::kDepthWriteEnabledConstName),
                      boolType, SymbolType::AngleInternal);
  
                  TIntermBlock *innerif = new TIntermBlock;
                  innerif->appendStatement(&node);
  
                  TIntermSymbol *depthWriteEnabled = new TIntermSymbol(depthWriteEnabledVar);
                  TIntermIfElse *ifCall = new TIntermIfElse(depthWriteEnabled, innerif, nullptr);
                  return ifCall;
              }
          }
  
          return node;
      }
  };
  
  }  // anonymous namespace
  
  ////////////////////////////////////////////////////////////////////////////////
  
  bool sh::GuardFragDepthWrite(TCompiler &compiler, TIntermBlock &root)
  {
      Rewriter rewriter(compiler);
      if (!rewriter.rebuildRoot(root))
      {
          return false;
      }
      return true;
  }
  

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