Re: [PATCH] avoid assuming known string length is constant (PR 83896)

[Martin Sebor]

On 01/16/2018 02:26 PM, Jakub Jelinek wrote:

On Tue, Jan 16, 2018 at 07:37:30PM +0000, Richard Sandiford wrote:

-/* Check if RHS is string_cst possibly wrapped by mem_ref.  */
+/* If RHS, either directly or indirectly, refers to a string of constant
+   length, return it.  Otherwise return a negative value.  */
+
 static int
 get_string_len (tree rhs)
 {

I think this should be returning HOST_WIDE_INT given the unconstrained
tree_to_shwi return.  Same type change for rhslen in the caller.

(Not my call, but it might be better to have a more specific function name,
given that the file already had "get_string_length" before this function
was added.)

Yeah, certainly for both.

@@ -2789,7 +2791,8 @@ get_string_len (tree rhs)
              if (idx > 0)
                {
                  strinfo *si = get_strinfo (idx);
-                 if (si && si->full_string_p)
+                 if (si && si->full_string_p
+                     && TREE_CODE (si->nonzero_chars) == INTEGER_CST)
                    return tree_to_shwi (si->nonzero_chars);

tree_fits_shwi_p?

Surely that instead of TREE_CODE check, but even that will not make sure it
fits into host int, so yes, it should be HOST_WIDE_INT and the code should
make sure it is also >= 0.

I made these changes except for the last part:  How/when can
the length be negative?

Martin