[Reland][IPO] Added attributor for identifying invariant loads (#146584)

Patched and tested the `AAInvariantLoadPointer` attributor from #141800,
which identifies pointers whose loads are eligible to be marked as
`!invariant.load`.

The bug in the attributor was due to `AAMemoryBehavior` always
identifying pointers obtained from `alloca`s as having no writes. I'm
not entirely sure why `AAMemoryBehavior` behaves this way, but it seems
to be beceause it identifies the scope of an `alloca` to be limited to
only that instruction (and, certainly, no memory writes occur within the
`alloca` instructin). This patch just adds a check to disallow all loads
from `alloca` pointers from being marked `!invariant.load` (since any
well-defined program will have to write to stack pointers at some
point).

0 files changed, 0 insertions, 0 deletions