Re: RFA: New pass to delete unexecutable paths in the CFG

[Richard Guenther <richard.guenther@gmail.com>]

On Mon, Nov 7, 2011 at 4:43 PM, Jeff Law <law@redhat.com> wrote:
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> On 11/07/11 06:53, Tom Tromey wrote:
>>>>>>> "Jeff" == Jeff Law <law@redhat.com> writes:
>>
>> Jeff> First, it's perfectly fine to have a NULL pointer dereference
>> in a Jeff> program as long as that code is never executed.  Once
>> the code is Jeff> executed, we've entered the realm of undefined
>> behavior.
>>
>> Jeff> Thus in a conforming program we can safely assume that a
>> provable NULL Jeff> pointer dereference can never be executed at
>> runtime.  This implies Jeff> there is a path through the CFG that
>> is unexecutable.
>>
>> IIUC, then this isn't true for Java.  In Java the attempt to
>> dereference NULL throws a NullPointerException, which can be
>> caught, etc.  It isn't undefined.
> So, presumably there's no way to know we're throwing to
> NullPointerException from the exception information attached to the
> statement or BB?  If not I could disable if the statement with the
> memory op throws anywhere.  It's not ideal, but conservatively correct.

Well, stmt_could_throw_p says that (java has non-call exceptions).

OTOH I'm not sure we want to change a possible trap (And thus
program abort) to a fallthru ...

Richard.