[AMDGPU] Testcase for computeKnownBits recursion. NFC.

Testcase for rL312364:
[AMDGPU] Prevent infinite recursion in DAG.computeKnownBits()

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312388 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed