Alright, the following patch was tested and it works
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 3b9500d..0d82018 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -13199,6 +13199,9 @@ tree_binary_nonzero_warnv_p (enum tree_code code,
switch (code)
{
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));
case PLUS_EXPR:
if (ANY_INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_UNDEFINED (type))
{
--
2.8.3
-Manish
On Thu, Jun 30, 2016 at 6:45 PM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Thu, Jun 30, 2016 at 2:03 PM, Manish Goregaokar <man...@mozilla.com> wrote:
>> What about ptr + intptr_t? I guess we should check nonnegative for op1 then?
>
> op1 will always be nonnegative as it is forced to sizetype type (which
> is unsigned).
>
> Richard.
>
>> -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
