On Fri, Aug 15, 2008 at 10:58 AM, Daniel Berlin <[EMAIL PROTECTED]> wrote:
> On Fri, Aug 15, 2008 at 8:06 AM, Manuel López-Ibáñez
> <[EMAIL PROTECTED]> wrote:
>> 2008/8/14 Daniel Berlin <[EMAIL PROTECTED]>:
>>> 1. You can't assume VUSE's are must-aliases. The fact that there is a
>>> vuse for something does not imply it is must-used, it implies it is
>>> may-used.
>>>
>>> We do not differentiate may-use from must-use in our alias system. You
>>> can do some trivial must-use analysis if you like (by computing
>>> cardinality of points-to set as either single or multiple and
>>> propagating/meeting it in the right place).
>>>
>>> Must-use is actually quite rare.
>>
>> Then, is it impossible to distinguish the following testcase and the
>> one from my previous mail with the current infrastructure?
>
> If by current you mean "code that already exists", then yes :)
> You could write code to do further analysis, but with the existing
> code, it will not work.
FWIW, it is actually worse than the cases you have posited so far.
Consider the following simple case (which are different from yours in
that the conditionals are not dependent on maybe uninitialized
variables), where you will miss an obvious warning.
extern int foo(int *);
extern int bar(int);
int main(int argc, char **argv)
{
int a;
if (argc)
foo (&a)
/* VUSE of a will be a phi node, but it still may be used uninitialized. */
bar(a);
}
Realistically, to get good results, you would have to track may-use vs
must-use and also propagate where the default def is being used when
the default_def is not from a parameter.
(noticing that the a is a must-use there and comes from a phi node
whose arguments contain the default def would prove it is
uninitialized along some path)
--Dan
