[GlobalsAA] Loosen an overly conservative bailout

[GlobalsAA] Loosen an overly conservative bailout

Instead of bailing out when we see loads, analyze them. If we can prove that the loaded-from address must escape, then we can conclude that a load from that address must escape too and therefore cannot alias a non-addr-taken global.

When checking if a Value can alias a non-addr-taken global, if the Value is a LoadInst of a non-global, recurse instead of bailing.

If we can follow a trail of loads up to some base that is captured, we know by inference that all the loads we followed are also captured.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251017 91177308-0d34-0410-b5e6-96231b3b80d8