[llvm] r188507 - Don't do FoldCmpLoadFromIndexedGlobal for non inbounds GEPs

[Dan Gohman]

That's actually not valid with either kind of getelementptr.

See "Can I compute the distance between two objects, and add that value to
one address to compute the other address?" in the GetElementPtr FAQ.

Dan

On Fri, Aug 16, 2013 at 6:30 PM, Eli Friedman <eli.friedman at gmail.com>wrote:

> Because if we don't have inbounds, it could point at a different object in
> a defined way, e.g. "x[(uintptr_t)&y - (uintptr_t)&x]".
>
> -Eli
>
>
> On Fri, Aug 16, 2013 at 6:24 PM, Dan Gohman <dan433584 at gmail.com> wrote:
>
>> In that case, why do you need to check inbounds at all?
>>
>> Dan
>>
>>
>> On Fri, Aug 16, 2013 at 5:40 PM, Matt Arsenault <
>> Matthew.Arsenault at amd.com> wrote:
>>
>>>  On 08/16/2013 11:40 AM, Dan Gohman wrote:
>>>
>>> On Thu, Aug 15, 2013 at 4:11 PM, Matt Arsenault <
>>> Matthew.Arsenault at amd.com> wrote:
>>>
>>>> Author: arsenm
>>>> Date: Thu Aug 15 18:11:07 2013
>>>> New Revision: 188507
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=188507&view=rev
>>>> Log:
>>>> Don't do FoldCmpLoadFromIndexedGlobal for non inbounds GEPs
>>>>
>>>
>>>  I don't see how inbounds is meaningful here. inbounds includes "one
>>> past the end" pointers, so there is no guarantee that a load from an
>>> inbounds getelementptr pointer value will load from within the bounds of
>>> the object.
>>>
>>>  Dan
>>>
>>>    If you actually load past the end of the object it's undefined, so
>>> it doesn't matter
>>>
>>
>>
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>>
>
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