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

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• Author : Shahbaz Youssefi
  Date : 2021-01-19 12:48:15
  Hash : 9f4b159b
  Message : Translator: Avoid vector copies with multi-replacement Turns push_backs into emplace_backs and changes the TIntermSequence constructor argument to &&. Bug: angleproject:5535 Change-Id: I640ce879b6ade48a28dea6385ebb7a95cb8304ff Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2636680 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com>

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

• //
  // Copyright 2018 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.
  //
  // PruneEmptyCases.cpp: The PruneEmptyCases function prunes cases that are followed by nothing from
  // the AST.
  
  #include "compiler/translator/tree_ops/PruneEmptyCases.h"
  
  #include "compiler/translator/Symbol.h"
  #include "compiler/translator/tree_util/IntermTraverse.h"
  
  namespace sh
  {
  
  namespace
  {
  
  bool AreEmptyBlocks(TIntermSequence *statements);
  
  bool IsEmptyBlock(TIntermNode *node)
  {
      TIntermBlock *asBlock = node->getAsBlock();
      if (asBlock)
      {
          return AreEmptyBlocks(asBlock->getSequence());
      }
      // Empty declarations should have already been pruned, otherwise they would need to be handled
      // here. Note that declarations for struct types do contain a nameless child node.
      ASSERT(node->getAsDeclarationNode() == nullptr ||
             !node->getAsDeclarationNode()->getSequence()->empty());
      // Pure literal statements should also already be pruned.
      ASSERT(node->getAsConstantUnion() == nullptr);
      return false;
  }
  
  // Return true if all statements in "statements" consist only of empty blocks and no-op statements.
  // Returns true also if there are no statements.
  bool AreEmptyBlocks(TIntermSequence *statements)
  {
      for (size_t i = 0u; i < statements->size(); ++i)
      {
          if (!IsEmptyBlock(statements->at(i)))
          {
              return false;
          }
      }
      return true;
  }
  
  class PruneEmptyCasesTraverser : private TIntermTraverser
  {
    public:
      ANGLE_NO_DISCARD static bool apply(TCompiler *compiler, TIntermBlock *root);
  
    private:
      PruneEmptyCasesTraverser();
      bool visitSwitch(Visit visit, TIntermSwitch *node) override;
  };
  
  bool PruneEmptyCasesTraverser::apply(TCompiler *compiler, TIntermBlock *root)
  {
      PruneEmptyCasesTraverser prune;
      root->traverse(&prune);
      return prune.updateTree(compiler, root);
  }
  
  PruneEmptyCasesTraverser::PruneEmptyCasesTraverser() : TIntermTraverser(true, false, false) {}
  
  bool PruneEmptyCasesTraverser::visitSwitch(Visit visit, TIntermSwitch *node)
  {
      // This may mutate the statementList, but that's okay, since traversal has not yet reached
      // there.
      TIntermBlock *statementList = node->getStatementList();
      TIntermSequence *statements = statementList->getSequence();
  
      // Iterate block children in reverse order. Cases that are only followed by other cases or empty
      // blocks are marked for pruning.
      size_t i                       = statements->size();
      size_t lastNoOpInStatementList = i;
      while (i > 0)
      {
          --i;
          TIntermNode *statement = statements->at(i);
          if (statement->getAsCaseNode() || IsEmptyBlock(statement))
          {
              lastNoOpInStatementList = i;
          }
          else
          {
              break;
          }
      }
      if (lastNoOpInStatementList == 0)
      {
          // Remove the entire switch statement, extracting the init expression if needed.
          TIntermTyped *init = node->getInit();
          if (init->hasSideEffects())
          {
              queueReplacement(init, OriginalNode::IS_DROPPED);
          }
          else
          {
              TIntermSequence emptyReplacement;
              ASSERT(getParentNode()->getAsBlock());
              mMultiReplacements.emplace_back(getParentNode()->getAsBlock(), node,
                                              std::move(emptyReplacement));
          }
          return false;
      }
      if (lastNoOpInStatementList < statements->size())
      {
          statements->erase(statements->begin() + lastNoOpInStatementList, statements->end());
      }
  
      return true;
  }
  
  }  // namespace
  
  bool PruneEmptyCases(TCompiler *compiler, TIntermBlock *root)
  {
      return PruneEmptyCasesTraverser::apply(compiler, root);
  }
  
  }  // namespace sh