[TRE] Improve code motion in TRE, use AA to tell whether a load can be moved...

[TRE] Improve code motion in TRE, use AA to tell whether a load can be moved before a call that writes to memory.

Summary: use AA to tell whether a load can be moved before a call that writes to memory.

Reviewers: dberlin, davide, sanjoy, hfinkel

Reviewed By: hfinkel

Subscribers: hfinkel, llvm-commits

Differential Revision: https://reviews.llvm.org/D34115

llvm-svn: 305698