Add a testcase for the changes in r199938.

<rdar://problem/15611947>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200027 91177308-0d34-0410-b5e6-96231b3b80d8
InstCombine: Don't try to use aggregate elements of ConstantExprs.

PR18600.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200028 91177308-0d34-0410-b5e6-96231b3b80d8
Verify that attributes are not lost during linking.

We don't want to lose attributes when a function decl without them is merged
with a function decl that has them.
PR2382

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200030 91177308-0d34-0410-b5e6-96231b3b80d8