compilerplugins/clang/postfixincrementfix.cxx

   1 /*
   2  * This file is part of the LibreOffice project.
   3  *
   4  * Based on LLVM/Clang.
   5  *
   6  * This file is distributed under the University of Illinois Open Source
   7  * License. See LICENSE.TXT for details.
   8  *
   9  */
  10
  11 #include "postfixincrementfix.hxx"
  12
  13 /*
  14 This is a rewriter.
  15
  16 Change all postfix ++ operators of non-trivial types to prefix if possible.
  17 */
  18
  19 namespace loplugin
  20 {
  21
  22 PostfixIncrementFix::PostfixIncrementFix( CompilerInstance& compiler, Rewriter& rewriter )
  23     : RewritePlugin( compiler, rewriter )
  24     {
  25     }
  26
  27 void PostfixIncrementFix::run()
  28     {
  29     TraverseDecl( compiler.getASTContext().getTranslationUnitDecl());
  30     }
  31
  32 bool PostfixIncrementFix::VisitFunctionDecl( const FunctionDecl* declaration )
  33     {
  34     if( ignoreLocation( declaration ))
  35         return true;
  36     if( !declaration->doesThisDeclarationHaveABody())
  37         return true;
  38     StmtParents parents;
  39     fixPostfixOperators( declaration->getBody(), parents );
  40     return true;
  41     }
  42
  43 void PostfixIncrementFix::fixPostfixOperators( const Stmt* stmt, StmtParents& parents )
  44     {
  45     if( const CXXOperatorCallExpr* op = dyn_cast<CXXOperatorCallExpr>( stmt ))
  46         { // postfix ++ has two arguments (the operand and the hidden extra int)
  47         if( op->getOperator() == OO_PlusPlus && op->getNumArgs() == 2 )
  48             fixPostfixOperator( op, parents );
  49         }
  50     // For primitive types it would be UnaryOperatorExpr, but probably no good reason to change those.
  51     parents.push_back( stmt );
  52     for( ConstStmtIterator it = stmt->child_begin();
  53          it != stmt->child_end();
  54          ++it )
  55         {
  56         if( *it != NULL ) // some children can be apparently NULL
  57             fixPostfixOperators( *it, parents );
  58         }
  59     assert( parents.back() == stmt );
  60     parents.pop_back();
  61     }
  62
  63 void PostfixIncrementFix::fixPostfixOperator( const CXXOperatorCallExpr* op, StmtParents& parents )
  64     {
  65     if( !canChangePostfixToPrefix( op, parents, parents.size() - 1 ))
  66         return;
  67     if( !shouldDoChange( op->getArg( 0 )))
  68         return;
  69     // Adding spaces around the moved ++ should not be necessary
  70     // (there might a problem with e.g. a+b++ -> a+++b (i.e. a++ +b),
  71     // but we don't change such expressions).
  72     if( insertText( op->getLocStart(), "++" )) // insert is intentionally first, in case it fails
  73         removeText( op->getCallee()->getSourceRange());
  74     }
  75
  76 bool PostfixIncrementFix::canChangePostfixToPrefix( const CXXOperatorCallExpr* op, StmtParents& parents, int parent_pos )
  77     {
  78     // check if foo++ can be safely replaced by ++foo
  79     switch( parents[ parent_pos ]->getStmtClass())
  80         {
  81         case Stmt::CompoundStmtClass:
  82             return true;
  83         // these mean somebody is going to use it
  84         case Stmt::ImplicitCastExprClass:
  85         case Stmt::MaterializeTemporaryExprClass:
  86         case Stmt::BinaryOperatorClass:
  87         case Stmt::UnaryOperatorClass:
  88         case Stmt::CallExprClass:
  89         case Stmt::CXXOperatorCallExprClass:
  90             return false;
  91         case Stmt::CXXBindTemporaryExprClass:
  92             // tricky, it may just mean the temporary will be cleaned up
  93             // (by ExprWithCleanups), ignore and go up
  94             assert( parent_pos > 0 ); // should not happen
  95             return canChangePostfixToPrefix( op, parents, parent_pos - 1 );
  96         case Stmt::ExprWithCleanupsClass:
  97             // cleanup of a temporary, should be harmless (if the use
  98             // of the postfix ++ operator here relies on the fact that
  99             // the dtor for the object will be called, that's pretty insane
 100             // code). Ignore and go up.
 101             assert( parent_pos > 0 ); // should not happen
 102             return canChangePostfixToPrefix( op, parents, parent_pos - 1 );
 103         case Stmt::ParenExprClass: // parentheses, go up
 104             assert( parent_pos > 0 );
 105             return canChangePostfixToPrefix( op, parents, parent_pos - 1 );
 106         case Stmt::IfStmtClass:
 107             return canChangeInConditionStatement( op, cast< IfStmt >( parents[ parent_pos ] )->getCond(),
 108                 parents, parent_pos );
 109         case Stmt::WhileStmtClass:
 110             return canChangeInConditionStatement( op, cast< WhileStmt >( parents[ parent_pos ] )->getCond(),
 111                 parents, parent_pos );
 112         case Stmt::DoStmtClass:
 113             return canChangeInConditionStatement( op, cast< DoStmt >( parents[ parent_pos ] )->getCond(),
 114                 parents, parent_pos );
 115         case Stmt::ForStmtClass:
 116             return canChangeInConditionStatement( op, dyn_cast< ForStmt >( parents[ parent_pos ] )->getCond(),
 117                 parents, parent_pos );
 118         default:
 119             report( DiagnosticsEngine::Fatal, "cannot analyze operator++ (plugin needs fixing)",
 120                 op->getLocStart()) << parents[ parent_pos ]->getSourceRange();
 121 //            parents[ parent_pos ]->dump();
 122 //            parents[ std::max( parent_pos - 3, 0 ) ]->dump();
 123             return false;
 124         }
 125     }
 126
 127 bool PostfixIncrementFix::canChangeInConditionStatement( const CXXOperatorCallExpr* op, const Expr* condition,
 128     const StmtParents& parents, unsigned int parent_pos )
 129     {
 130     // cannot be changed in condition, can be changed in statements
 131     if( parent_pos == parents.size() - 1 )
 132         return op != condition;
 133     else
 134         { // indirect child
 135         assert( parent_pos + 1 < parents.size());
 136         return parents[ parent_pos + 1 ] != condition;
 137         }
 138     }
 139
 140 bool PostfixIncrementFix::shouldDoChange( const Expr* operand )
 141     {
 142     // TODO Changing 'a->b++' to '++a->b' is technically the same, but the latter probably looks confusing,
 143     // so either avoid that, or add parentheses. Avoid for now.
 144     const Expr* expr = const_cast< Expr* >( operand )->IgnoreImplicit(); // does not have const version
 145     switch( expr->getStmtClass())
 146         {
 147         case Stmt::ParenExprClass:
 148             return true; // there are already parentheses, ok to move the ++
 149         case Stmt::MemberExprClass:
 150             return false; // ++a->b , avoid
 151         case Stmt::DeclRefExprClass:
 152             return true;
 153         default:
 154             {
 155             report( DiagnosticsEngine::Fatal, "cannot analyze operator++ (plugin needs fixing)",
 156                 expr->getLocStart()) << operand->getSourceRange();
 157             expr->dump();
 158             operand->dump();
 159             return false;
 160             }
 161         }
 162     }
 163
 164 static Plugin::Registration< PostfixIncrementFix > X( "postfixincrementfix" );
 165
 166 } // namespace