[llvm] [Attributor] Fix an issue that an access is skipped by mistake (PR #101862)

[Shilei Tian via llvm-commits]

shiltian wrote:

> > > Testcase?
> > 
> > 
> > Well, the thing is, this can only be exposed in an Attributor use that doesn't have `AAInterFnReachability`. Regular `AttributorPass` will not have this issue. Only `AMDGPUAttributorPass` can do this, but the enabling of `AAIndirectCallInfo ` has been reverted so even that can't expose it.
> 
> I'm not very familiar with these APIs, but is this something that would be easier to test with a C++ unit test? I see there are already some [attributor unit tests](https://github.com/llvm/llvm-project/blob/main/llvm/unittests/Transforms/IPO/AttributorTest.cpp).

Yes, that's a good point. However, this issue requires a target where a stack variable is not accessible by other threads (effectively a GPU). I can't add target triple in the unit test because it will break a build if the target is not enabled.

https://github.com/llvm/llvm-project/pull/101862