kc3-lang/angle/src/compiler/translator/tree_ops/apple/RewriteDoWhile.cpp

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• Hash : b8d6f8aa
  Author :
  Date : 2021-07-22T22:31:29
  

  Translator: Facilitate integration in FireFox
  
  Instead of relying on is_apple to build workarounds applied on apple
  hardware, a new build argument is added for this purpose.  This allows
  FireFox to more easily include these files in their build system (which
  builds every workaround on every platform).
  
  The workarounds are reorganized too and moved from tree_ops/gl/mac to
  tree_ops/apple.  RewriteRowMajorMatrices is moved there too as it's now
  used by both gl and metal.  This workaround is large, and removing it
  from non-apple builds improves binary size (~40KB on Linux).
  
  Bug: angleproject:6188
  Change-Id: I8e1dab44d0235bb6b8341d53721bdd0d157d46c6
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3047385
  Reviewed-by: Jeff Gilbert <jgilbert@mozilla.com>
  Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
  Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
  

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• src/compiler/translator/tree_ops/apple/RewriteDoWhile.cpp

• //
  // Copyright 2015 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.
  //
  
  // RewriteDoWhile.cpp: rewrites do-while loops using another equivalent
  // construct.
  
  #include "compiler/translator/tree_ops/apple/RewriteDoWhile.h"
  
  #include "compiler/translator/Compiler.h"
  #include "compiler/translator/StaticType.h"
  #include "compiler/translator/tree_util/IntermNode_util.h"
  #include "compiler/translator/tree_util/IntermTraverse.h"
  
  namespace sh
  {
  
  namespace
  {
  
  // An AST traverser that rewrites loops of the form
  //   do {
  //     CODE;
  //   } while (CONDITION)
  //
  // to loops of the form
  //   bool temp = false;
  //   while (true) {
  //     if (temp) {
  //       if (!CONDITION) {
  //         break;
  //       }
  //     }
  //     temp = true;
  //     CODE;
  //   }
  //
  // The reason we don't use a simpler form, with for example just (temp && !CONDITION) in the
  // while condition, is that short-circuit is often badly supported by driver shader compiler.
  // The double if has the same effect, but forces shader compilers to behave.
  //
  // TODO(cwallez) when UnfoldShortCircuitIntoIf handles loops correctly, revisit this as we might
  // be able to use while (temp || CONDITION) with temp initially set to true then run
  // UnfoldShortCircuitIntoIf
  class DoWhileRewriter : public TIntermTraverser
  {
    public:
      DoWhileRewriter(TSymbolTable *symbolTable) : TIntermTraverser(true, false, false, symbolTable)
      {}
  
      bool visitBlock(Visit, TIntermBlock *node) override
      {
          // A well-formed AST can only have do-while inside TIntermBlock. By doing a prefix traversal
          // we are able to replace the do-while in the sequence directly as the content of the
          // do-while will be traversed later.
  
          TIntermSequence *statements = node->getSequence();
  
          // The statements vector will have new statements inserted when we encounter a do-while,
          // which prevents us from using a range-based for loop. Using the usual i++ works, as
          // the (two) new statements inserted replace the statement at the current position.
          for (size_t i = 0; i < statements->size(); i++)
          {
              TIntermNode *statement = (*statements)[i];
              TIntermLoop *loop      = statement->getAsLoopNode();
  
              if (loop == nullptr || loop->getType() != ELoopDoWhile)
              {
                  continue;
              }
  
              // Found a loop to change.
              const TType *boolType = StaticType::Get<EbtBool, EbpUndefined, EvqTemporary, 1, 1>();
              TVariable *conditionVariable = CreateTempVariable(mSymbolTable, boolType);
  
              // bool temp = false;
              TIntermDeclaration *tempDeclaration =
                  CreateTempInitDeclarationNode(conditionVariable, CreateBoolNode(false));
  
              // temp = true;
              TIntermBinary *assignTrue =
                  CreateTempAssignmentNode(conditionVariable, CreateBoolNode(true));
  
              // if (temp) {
              //   if (!CONDITION) {
              //     break;
              //   }
              // }
              TIntermIfElse *breakIf = nullptr;
              {
                  TIntermBranch *breakStatement = new TIntermBranch(EOpBreak, nullptr);
  
                  TIntermBlock *breakBlock = new TIntermBlock();
                  breakBlock->getSequence()->push_back(breakStatement);
  
                  TIntermUnary *negatedCondition =
                      new TIntermUnary(EOpLogicalNot, loop->getCondition(), nullptr);
  
                  TIntermIfElse *innerIf = new TIntermIfElse(negatedCondition, breakBlock, nullptr);
  
                  TIntermBlock *innerIfBlock = new TIntermBlock();
                  innerIfBlock->getSequence()->push_back(innerIf);
  
                  breakIf = new TIntermIfElse(CreateTempSymbolNode(conditionVariable), innerIfBlock,
                                              nullptr);
              }
  
              // Assemble the replacement loops, reusing the do-while loop's body and inserting our
              // statements at the front.
              TIntermLoop *newLoop = nullptr;
              {
                  TIntermBlock *body = loop->getBody();
                  if (body == nullptr)
                  {
                      body = new TIntermBlock();
                  }
                  auto sequence = body->getSequence();
                  sequence->insert(sequence->begin(), assignTrue);
                  sequence->insert(sequence->begin(), breakIf);
  
                  newLoop = new TIntermLoop(ELoopWhile, nullptr, CreateBoolNode(true), nullptr, body);
              }
  
              TIntermSequence replacement;
              replacement.push_back(tempDeclaration);
              replacement.push_back(newLoop);
  
              node->replaceChildNodeWithMultiple(loop, replacement);
          }
          return true;
      }
  };
  
  }  // anonymous namespace
  
  bool RewriteDoWhile(TCompiler *compiler, TIntermNode *root, TSymbolTable *symbolTable)
  {
      DoWhileRewriter rewriter(symbolTable);
  
      root->traverse(&rewriter);
  
      return compiler->validateAST(root);
  }
  
  }  // namespace sh
  

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