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

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• Hash : 197beb4d
  Author :
  Date : 2024-02-13T15:47:32
  

  Metal: Crash if for loop body is optimized away
  
  Loops might have their bodies optimized away.
  For case like `for(;;) if(false);` the constant pruning happens at
  parse phase. The else branch (e.e. no else branch, nullptr) would be
  selected as the body.
  
  Some code treated the body as optional, some code treated it as
  required. Define it as required, and remove all conditional code
  related to the loop body.
  
  Bug: angleproject:8532
  Change-Id: Ic35f1bf78e63ceb2cee7b96ba99e788efc282e6f
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5291554
  Auto-Submit: Kimmo Kinnunen <kkinnunen@apple.com>
  Commit-Queue: Kimmo Kinnunen <kkinnunen@apple.com>
  Reviewed-by: Kenneth Russell <kbr@chromium.org>
  

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• src/compiler/translator/tree_ops/glsl/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/glsl/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();
                  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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