[cfe-dev] parsing of self-referring vardecls

[Chris Lattner]

On Sep 11, 2007, at 11:28 AM, Ted Kremenek wrote:
> I'm not certain if vardecls are being correctly parsed.  Consider the
> following program (self-decl.c):

You're right, this looks like a bug in the initializer parsing  
stuff.  "var" should be added to the scope chain before the  
initializer for var is parsed.  This will require some juggling of  
the actions hooks though, so it will be non-trivial.

Steve, can you add this to your todo list?

-Chris

> #include <stdio.h>
>
> int foo(int var)
> {
>    {  // note the extra scope
> L1:
>      int var = var+1;
>      return var;
>    }
> }
>
> int main() {
>    printf("%d\n",foo(10));
>    return 0;
> }
>
> The output of this program is not what you might expected:
>
> (kremenek at grue:tmp)$ gcc -o self-decl self-decl.c
> (kremenek at grue:tmp)$ ./self-decl
> 1
>
>
> What happens is that the declaration of "var" at label "L1" refers to
> itself, and thus is undefined.  This is because "var" comes into scope
> before its initialization.  I wrote a checker to look for such cases,
> but it isn't flagging any warnings because the initialization is
> falsely referring to the decl in the enclosing scope.  This can be
> seen from a dump of the AST:
>
> int foo(int var)
> (CompoundStmt 0x710fd0 </tmp/self-decl.c:3:18, line:8:1>
>    (CompoundStmt 0x710f60 <line:4:3, line:7:3>
>      (DeclStmt 0x70f210 <:0:0>
>        0x710f00 "int var =
>          (BinaryOperator 0x710ee0 </tmp/t2.c:5:15, col:19> 'int' '+'
>            (DeclRefExpr 0x70ec50 <col:15> 'int' ParmVariable='var'
> 0x710e90)
>            (IntegerLiteral 0x710ec0 <col:19> 'int' 1))")
>      (ReturnStmt 0x710f50 <line:6:5, col:12>
>        (DeclRefExpr 0x710f30 <col:12> 'int' BlockVariable='var'
> 0x710f00))))
>
> Notice the "DeclRefExpr" refers to the ParmVariable, not a VarDecl
> (the choice of using a parameter in this case just easily
> disambiguates this case, but "var" could have been a variable declared
> in any enclosing scope).
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