Re: [CIL users] constant folding: partial work

[Nathan C. <co...@cs...>]

The constant folder in CIL only folds over the bitwise and operation 
when both operands are constant.  Otherwise, it leaves the expression 
alone.  There are a couple of places (such as here and multiplying by 
zero) when the constant folder is sound but not maximally precise. 


My guess is that if you add a line in constFoldBinOp to handle bitwise 
and-ing with zero, then you will get the desired behavior.  In other 
words, the conditional expression will get folded to 0 and then the 
partial evaluation will remove the if statement.


In answer to your other quesion about who is working on this kind of 
stuff:  I am working on an interprocedural dataflow analyzer in CIL that 
includes a constant propagator.  It will be released in the not too 
distant future, but you can get an early version directly from me if you 
want. 


Nathan


Shahar Golan wrote:

> *Hello,*
> ** 
> *I'm trying the following code with cil:*
>
>     *int main() {
>       volatile int i;*
>      
>     *  if (0 & i)
>         return i;
>       else
>         return 0;
>       } *
>
> *And this is what I get:*
>
>     *int main(void)
>     { int volatile   i ;*
>      
>     *  {
>       if (0 & (int )i) {
>         return ((int )i);
>       } else {
>         return (0);
>       }
>     }
>     } *
>
> 	*S H A H A R
> TOOLS GROUP LEADER
> TEL +972 (9) 7766336 * 	*G O L A N
> SOFTIER IL LTD
> EXT 8940 *
> *Needless to say that I would expect:*
>
>     *
>     *int main(void)
>     { int volatile   i ;*
>      
>     *  {
>          return (0);
>       }
>     }
>     }*
>     *
>
> *BTW, "--domakeCFG --dopartial" don't do the trick.*
> *
> ** 
> *Is anyone doing any work on improving the constant folding mechanism, 
> or should I?*
> ** 
> *Anyone sees any reason why I shouldn't have expected the dead code 
> removal?*
> *
> ** 
>
> **