Make tree-ssa-strlen.c handle partial unterminated strings

[Jakub Jelinek]

On Fri, May 05, 2017 at 10:28:45AM -0600, Martin Sebor wrote:
> There have been requests for a warning to diagnose invalid uses
> of character arrays that are not nul-terminated, such as arguments
> to functions that expect a (nul-terminated) string.  For example:
> 
>     char *p = (char*)malloc (20);
>     memcpy (p, "/tmp/", 5);
>     strcat (p, "file.text");   // << warn here
> 
> It would be helpful to diagnose such cases (while avoiding false
> positives on the indeterminate cases you mention, of course).

One thing here is that there is a function known to require a null
terminated function, not arbitrary other function that may or might not
need it.
And another thing is that in the tree-ssa-strlen.c framework known
records can be invalidated at any time and you then don't know,
it is an optimization, not a warning framework.
So, for the warning you'd need to track whether there have been any
invalidation and just punt in that case.

	Jakub