Hi, Martin,
thanks for the suggestion, this might be a good enhancement for
get_range_strlen for a future work.
my understanding is, the current get_range_strlen does not use value range
info yet, and also does not handle VLA.
we can improve it from both aspects in a later work.
Qing
>>
>> 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
