Re: [CIL users] Simplification of variable declarations and definitions

[Matt H. <ma...@cs...>]

Hi Chris,

In C, "int i;" and "extern int i;" are both just declarations. Extern 
linkage is a property of the global variable, not any particular 
declaration, so CIL puts the linkage in the varinfo structure 
(vstorage).  The result of parsing

   extern int i;
   ...
   int i;

into CIL would be

   GVarDecl(i)
   ...
   GVarDecl(i)

where i has no storage specifier, since the NoStorage version overrides 
the Extern.  The second declaration is redundant, however, so cabs2cil 
ignores it.  So we get

   int i;
   ...

like you said.  Note that if the second declaration had an explicit 
initializer, then cabs2cil wouldn't delete it.  Is this translation ever 
wrong?


As for your analysis that needs to know about every declaration:  One 
thing you can do is modify createGlobal in cabs2cil.ml, which says
         if not alreadyInEnv then begin (* Only one declaration *)
           cabsPushGlobal (GVarDecl (vi, !currentLoc));
           vi
	end
Removing the conditional will add a GVarDecl even for redundant 
declarations.  It would be harder to make a distinction between 
declarations with different storage modifiers, since those are stored in 
the varinfo.  You could have createGlobal call back into your analysis 
to announce that a variable was declared with storage X at location Y. 
But are you sure it matters whether a declaration uses extern or not?

Cheers,
Matt


Christoph Spiel wrote:
> Hi All!
> 
>     We would like to run an analysis that relies
> on the declaration and definition points of
> variables.  However, CIL simplifies the code by
> replacing the first declaration with a
> definition and droping all later declarations or
> definitions.  There is no way to switch off this
> "feature".
> 
> For example
>     extern int i;
> 
>     int i;
> 
>     void
>     f(void)
>     {
>         i = 1;
>     }
> 
> becomes
>     /* Generated by CIL v. 1.3.5 */
>     /* print_CIL_Input is true */
> 
>     #line 1 "def-vs-decl.c"
>     int i ;
>     #line 5 "def-vs-decl.c"
>     void f(void)
>     {
> 
>       {
>     #line 8
>       i = 1;
>     #line 9
>       return;
>     }
>     }
> 
> whereas we would prefer
>     #line 1 "def-vs-decl.c"
>     extern int i ;
>     #line 3 "def-vs-decl.c"
>     int i ;
>     #line 5 "def-vs-decl.c"
>     void f(void)
>     {
> 
>       {
>     #line 8
>       i = 1;
>     #line 9
>       return;
>     }
>     }
> 
> We did wade through the sources, however we
> could not spot the piece of code that is
> respsonsible for this simplification.  Can
> anyone please point us to the relevant
> function[s]?
> 
> 
> TIA,
>     Chris
> 
> --
> Dr. Christoph L. Spiel
> BMW Forschungs- und Innovationszentrum, EA-410
> Lauchstaedter Strasse 5, 80995 Muenchen
> 
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