[PATCH] D63067: [Attributor] NoAlias on return values.

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a comment.

In D63067#1538120 <https://reviews.llvm.org/D63067#1538120>, @lebedev.ri wrote:

> In D63067#1538100 <https://reviews.llvm.org/D63067#1538100>, @sstefan1 wrote:
>
> > > Why should the return values in nonnull.ll be noalias?
> >
> > All functions returning pointer never actually capture it, or they return null.  Isn't that enough?
>
>
> This doesn't seem sufficient to me.
> Consider:
>
>   file1.c
>   int* getter();
>   int* callee0() { // will get marked as noalias
>     return getter();
>   }
>   int* callee1() { // will get marked as noalias
>     return getter();
>   }
>   int entry() {
>     int* p0 = callee0();
>     int* p1 = callee1();
>     // do p0 and p1 alias?
>   }
>  
>   file2.c
>   int* global;
>   int* getter() { return global; } // oops
>  
>


The problem is the pointers returned need to be `noalias` return pointers as well (that is the missing sufficient condition).


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