[cfe-dev] Clang does not rewrite expressions with NULL

[Douglas Gregor]

On Jun 26, 2011, at 3:44 PM, Andrey Tarasevich wrote:

> Hello!
> 
> I'm currently doing some source-to-source manipulations mainly on C
> code. I found a problem with NULL macro. I'm using Ubuntu 10.04 64bit.
> 
> Here is a simple code I'm parsing
> 
> #include <stdlib.h>
> 
> int main()
> {
>    int n;
>    int* p;
>    if(p == NULL)
> 	n = 0;
>    else
>        n = 1;
> }
> 
> 
> I initialize the compiler in the following way
> 
> void startProcessing(string inFile, string outFile)
> {
> 	auto_ptr<CompilerInstance> compiler(new CompilerInstance);
> 	compiler->createDiagnostics(0, NULL);
> 
> 	const char *args[] =
> 	{
> 	  "-cc1",
> 	  "/home/sevich/master/list.c"
> 	};
> 
> 	clang::CompilerInvocation::CreateFromArgs(
> 	  compiler->getInvocation(),
> 	  args,
> 	  args + 2,
> 	  compiler->getDiagnostics());
> 
> 	llvm::OwningPtr<clang::ASTFrontendAction> action(new ASTMutationAction(inFile,
> 			outFile));
> 	compiler->ExecuteAction(*action);
> }
> 
> The ASTConsumer I use is a modified version of the RewriteOBjC class.
> The main work it does is negation of the if statement condition in the
> following way
> 
>  void RewriteIfStatement(clang::IfStmt *is)
>  {
> 	  Expr* oldCond = is->getCond();
> 	  ParenExpr* pe = new (context) ParenExpr(is->getLocStart(),
> is->getLocEnd(), oldCond);
> 	  Expr* uo = new (context) UnaryOperator(pe, UO_LNot,
> 		                                     context->getPointerType(pe->getType()),
> 											 VK_RValue,
> 											 OK_Ordinary,
> 											 SourceLocation());
> 	  bool result = rewriter.ReplaceStmt(oldCond, uo);
>  }
> 
> So the problem is whenever I meet the NULL in the if condition it
> never gets rewritten. I found out, that source range of the condition
> expression with NULL is wrong, for instance It starts with 373 and
> ends at 2147677727, what is obviously wrong and rewriter does not do
> anything. Clang didn't signalize any errors for this code sample.
> 
> So my question is following. Am I doing something wrong or this is a
> problem of the clang?

Neither. Clang's source locations keep track of macro instantiation history. The 2147677727 location is the encoding for a macro instantiation; see the SourceManager class and (especially) SourceManager::getInstantiationLoc().

> And one more question also. Is it possible to force clang to process
> code as C-code? Since I only saw a options for C++ and ObjC.

-x c

	- Doug