[SystemZ] Implementation of getUnrollingPreferences().

This commit enables more unrolling for SystemZ by implementing the
SystemZTargetTransformInfo::getUnrollingPreferences() method.

It has been found that it is better to only unroll moderately, so the
DefaultUnrollRuntimeCount has been moved into UnrollingPreferences in order
to set this to a lower value for SystemZ (4).

Reviewers: Evgeny Stupachenko, Ulrich Weigand.
https://reviews.llvm.org/D24451

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282570 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed