Recommit r333268: [IPSCCP] Use PredicateInfo to propagate facts from cmp instructions.

Recommit r333268: [IPSCCP] Use PredicateInfo to propagate facts from cmp instructions.

This version of the patch fixes cleaning up ssa_copy intrinsics, so it does not
crash for instructions in blocks that have been marked unreachable.

This patch updates IPSCCP to use PredicateInfo to propagate
facts to true branches predicated by EQ and to false branches
predicated by NE.

As a follow up, we should be able to extend it to also propagate additional
facts about nonnull.

Reviewers: davide, mssimpso, dberlin, efriedma

Reviewed By: davide, dberlin

Differential Revision: https://reviews.llvm.org/D45330

llvm-svn: 340525