[LLVMdev] new LLVM IR features

[Dan Gohman]

On Jul 29, 2009, at 9:41 AM, David Greene wrote:


> On Wednesday 29 July 2009 11:25, Dan Gohman wrote:
>
>
>> Getelementptr now has an optional flag: inbounds.  WIth this flag,
>>
>> if the result of a getelementptr is not in bounds of an allocated
>>
>> object,
>>
>> the result value is undefined.  Note the the new getelementptr rule
>>
>> applies regardless of whether the keyword is present.
>>
>
> How do the semantics of "inbounds" differ from the new GEP rules?

In summary:

The new GEP rule says that you can't dereference a pointer within an
object if it was computed from a GEP based on a different object.

The optional inbounds flag further constrains a GEP by saying that
the integer arithmetic implied by a GEP won't overflow.

Dan