What about ptr + intptr_t? I guess we should check nonnegative for op1 then?
-Manish
On Thu, Jun 30, 2016 at 5:25 PM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Thu, Jun 30, 2016 at 1:17 PM, Manish Goregaokar <man...@mozilla.com> wrote:
>> gcc/ChangeLog:
>> PR c/71699
>> * fold-const.c (tree_binary_nonzero_warnv_p): Allow
>> pointer addition to also be considered nonzero.
>> ---
>> gcc/fold-const.c | 20 +++++++++++++-------
>> 1 file changed, 13 insertions(+), 7 deletions(-)
>>
>> diff --git a/gcc/fold-const.c b/gcc/fold-const.c
>> index 3b9500d..eda713e 100644
>> --- a/gcc/fold-const.c
>> +++ b/gcc/fold-const.c
>> @@ -13200,16 +13200,22 @@ tree_binary_nonzero_warnv_p (enum tree_code code,
>> {
>> case POINTER_PLUS_EXPR:
>> case PLUS_EXPR:
>> - if (ANY_INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_UNDEFINED (type))
>> + if ((ANY_INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_UNDEFINED (type))
>> + || POINTER_TYPE_P (type))
>> {
>> + /* Pointers are always nonnegative, check integers. */
>> + if (ANY_INTEGRAL_TYPE_P (type))
>> + {
>> + sub_strict_overflow_p = false;
>> + if (!tree_expr_nonnegative_warnv_p (op0,
>> + &sub_strict_overflow_p)
>> + || !tree_expr_nonnegative_warnv_p (op1,
>> + &sub_strict_overflow_p))
>> + return false;
>> + }
>> /* With the presence of negative values it is hard
>> to say something. */
>> - sub_strict_overflow_p = false;
>> - if (!tree_expr_nonnegative_warnv_p (op0,
>> - &sub_strict_overflow_p)
>> - || !tree_expr_nonnegative_warnv_p (op1,
>> - &sub_strict_overflow_p))
>> - return false;
>> +
>
> Hmm, note that op1 of POINTER_PLUS_EXPR _is_ an integer that needs to be
> treated
> as signed.
>
> POINTER_PLUS_EXPR is special in other ways in that iff
> flag_delete_null_pointer_checks
> is set we can assume that ptr + non-zero is never zero. Thus simply do
>
> case POINTER_PLUS_EXPR:
> return flag_delete_null_pointer_checks
> && (tree_expr_nonzero_warnv_p (op0, strict_overflow_p)
> || tree_expr_nonzero_warnv_p (op1, strict_overflow_p));
>
> OTOH ptr + -(uintptr_t)ptr is valid from a POINTER_PLUS_EXPR
> perspective as GCC does
> not have a special tree code for pointer subtraction (but IIRC it uses
> MINUS_EXPR on integers
> for this).
>
> Richard.
>
>
>> /* One of operands must be positive and the other non-negative. */
>> /* We don't set *STRICT_OVERFLOW_P here: even if this value
>> overflows, on a twos-complement machine the sum of two
>> --
>> 2.8.3
