[llvm-dev] Return on nocapture pointer

Hal Finkel via llvm-dev llvm-dev at lists.llvm.org
Fri Apr 28 08:58:14 PDT 2017

On 04/28/2017 10:22 AM, Piotr Padlewski via llvm-dev wrote:
> Hi,
> I have a question about semantics of nocapture attribute:
> "This indicates that the callee does not make any copies of the 
> pointer that outlive the callee itself. "
> Is returing a pointer considered outliving callee? For example is this 
> code valid:

Yes, it includes returning the pointer. The code below is invalid. The 
return value outlives the callee itself.

> define i8* @foo(i8* nocapture %p)
>   ret i8* %p
> }
> The documentation also mention that "This is not a valid attribute for 
> return values.", but I interpret that it is is about this case:
> declare i8* nocapture @bar(i8* %p)



> Piotr
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Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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