[RS4GC] Drop invalid metadata after pointers are relocated

Summary:
After RS4GC, we should drop metadata that is no longer valid. These metadata
is used by optimizations scheduled after RS4GC, and can cause a miscompile.
One such metadata is invariant.load which is used by LICM sinking transform.
After rewriting statepoints, the address of a load maybe relocated. With
invariant.load metadata on a load instruction, LICM sinking assumes the
loaded value (from a dererenceable address) to be invariant, and
rematerializes the load operand and the load at the exit block.
This transforms the IR to have an unrelocated use of the
address after a statepoint, which is incorrect.
Other metadata we conservatively remove are related to
dereferenceability and noalias metadata.

This patch drops such metadata on store and load instructions after
rewriting statepoints.

Reviewers: reames, sanjoy, apilipenko

Reviewed by: reames

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33756

llvm-svn: 305234