[PATCH] D67604: [Attributor] Use Alias Analysis in noalias callsite argument deduction

[Hideto Ueno via Phabricator via llvm-commits]

uenoku added inline comments.


================
Comment at: llvm/test/Transforms/FunctionAttrs/noalias_returned.ll:266
 ; FIXME: This should be @two_args(i8* noalias %A_0, i8* noalias %B_0)
-; CHECK: tail call void @two_args(i8* %A_0, i8* %B_0)
   tail call void @two_args(i8* %A_0, i8* %B_0)
----------------
jdoerfert wrote:
> Why didn't this get resolved?
This is because, for now, we check noalias for the floating value firsthand: 
```
// (i) Check whether noalias holds in the definition.

    auto &NoAliasAA = A.getAAFor<AANoAlias>(*this, IRP);

    if (!NoAliasAA.isAssumedNoAlias())
      return indicatePessimisticFixpoint();
```
And GEP is not looked in AANoaliasFloaitingValue so `A_0` and `B_0` can't be deduced in this point.
I think it is too conservative but without this, at least global variable might be deduced as noalias in the current implementation.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D67604/new/

https://reviews.llvm.org/D67604