Codegen: Tail Merge: Be less aggressive with special cases.

This change makes it possible for tail-duplication and tail-merging to
be disjoint. By being less aggressive when merging during layout, there are no
overlapping cases between tail-duplication and tail-merging, provided the
thresholds are disjoint.

There is a remaining TODO to benchmark the succ_size() test for non-layout tail
merging.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278265 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed