On Fri, Jul 25, 2014 at 1:35 PM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Thu, Jul 17, 2014 at 11:08 AM, Bin Cheng <bin.ch...@arm.com> wrote:
>> Hi,
>> As quoted from the function difference_cannot_overflow_p,
>>
>> /* TODO: deeper inspection may be necessary to prove the equality. */
>> switch (code)
>> {
>> case PLUS_EXPR:
>> return expr_equal_p (e1, offset) || expr_equal_p (e2, offset);
>> case POINTER_PLUS_EXPR:
>> return expr_equal_p (e2, offset);
>>
>> default:
>> return false;
>> }
>>
>> The overflow check can be improved by using deeper inspection to prove the
>> equality. This patch deals with that by making below two improvements:
>> a) Handles constant cases.
>> b) Uses affine expansion as deeper inspection to check the equality.
>>
>> As a result, functions strip_wrap_conserving_type_conversions and
>> expr_equal_p can be removed now. A test case is also added to illustrate iv
>> elimination opportunity captured by this patch.
>>
>> Thanks,
>> bin
>
> You add special casing for constants but I don't see any testcases for that.
> Specifically
>
> + /* No overflow if offset is zero. */
> + if (offset == integer_zero_node)
> return true;
>
> is a bogus check (use integer_zerop). Apart from the special-casing of
Will be changed.
> constants the patch looks good to me.
>
Ah, Now I can see that handling of constants (here the zero offset
case) is to make the 3rd patch to work. I should include this part of
code in the 3rd patch. Also I will try to reduce testcase for other
non-zero constant scenarios
Thanks,
bin
