[LLVMdev] memory lifetime and invariance

[Nick Lewycky]

Chris Lattner wrote:
> On May 19, 2009, at 7:58 PM, Nick Lewycky wrote:
> 
>> Chris Lattner wrote:
>>> On May 19, 2009, at 12:32 AM, Nick Lewycky wrote:
>>>
>>>> Chris Lattner wrote:
>>>>> FYI, I wrote up some thoughts on this here:
>>>>> http://nondot.org/sabre/LLVMNotes/MemoryUseMarkers.txt
>>>>>
>>>>> The intention is to allow front-ends to express things like "I know
>>>>> this memory is a constant in this region" and to allow the  
>>>>> optimizer/
>>>>> codegen to perform more aggressive stack slot merging.
>>>> Very nice!
>>>>
>>>> Why does @llvm.invariant.end restate the size when it already takes
>>>> the
>>>> call to @llvm.invariant.start as its first argument? Did you really
>>>> mean
>>>> to allow for the case where part of an object is still invariant and
>>>> part isn't? If so, isn't it missing an offset as well?
>>> It is basically because the invariant.start may not be the immediate
>>> operand of the invariant.end.  You may end up having phi nodes
>>> connecting the two when various phi translation cases occur.
>> The verifier rejects phi nodes of {} type. Do you actually have a case
>> where you want this to happen?
> 
> That sounds like a serious bug then: {} should be a first class value  
> just like {i32}.

Okay then. I've just posted a patch to llvm-commits which would do that:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20090518/077934.html

Nick