[MachineOutliner] NFC: Split up getOutliningBenefit

This is some more cleanup in preparation for some actual
functional changes. This splits getOutliningBenefit into
two cost functions: getOutliningCallOverhead and
getOutliningFrameOverhead. These functions return the
number of instructions that would be required to call
a specific function and the number of instructions
that would be required to construct a frame for a
specific funtion. The actual outlining benefit logic
is moved into the outliner, which calls these functions.

The goal of refactoring getOutliningBenefit is to:

- Get us closer to getting rid of the IsTailCall flag

- Further split up "target-specific" things and
"general algorithm" things




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309356 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed