Per your comments, the updated gimple-fold.c is like the following:
FWIW, I suspect Richard is thinking of VLAs with the INTEGER_CST
comment above. This is the case we discussed in private. It is
handled either way but the handling could be improved by determining
the size of the VLA from the first __builtin_alloca_with_align
argument and using it or its range as the minimum and maximum.
With that, the range of string lengths that fit in vla in
the following could be determined and the sprintf call could
be diagnosed:
char d[30];
void f (unsigned n)
{
if (n < 32)
{
char vla[n];
__builtin_sprintf (d, "%s", vla);
}
}
I think this would be a nice enhancement to add on top of yours,
not just for VLAs but for dynamically allocated arrays as well,
and not just for the sprintf pass but also for the strlen pass
to optimize cases like:
void f (unsigned n)
{
if (n < 32)
{
char vla[n];
fgets (vla, n, stdin);
unsigned len = strlen (vla);
if (len >= n) // cannot hold
abort (); // can be eliminated
}
}
That said, at some point, it might make more sense to change
those passes to start tracking these things as they traverse
the CFG rather than having get_range_strlen() do the work.
Martin
diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index 353a46e..0500fba 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -1323,6 +1323,19 @@ get_range_strlen (tree arg, tree length[2],
bitmap *visited, int type,
the array could have zero length. */
*minlen = ssize_int (0);
}
+
+ if (VAR_P (arg)
+ && TREE_CODE (TREE_TYPE (arg)) == ARRAY_TYPE)
+ {
+ val = TYPE_SIZE_UNIT (TREE_TYPE (arg));
+ if (!val || TREE_CODE (val) != INTEGER_CST ||
integer_zerop (val))
+ return false;
+ val = fold_build2 (MINUS_EXPR, TREE_TYPE (val), val,
+ build_int_cst (TREE_TYPE (val), 1));
+ /* Set the minimum size to zero since the string in
+ the array could have zero length. */
+ *minlen = ssize_int (0);
+ }
}
if (!val)
let me know any further issue with the above.
thanks a lot.
Qing