Add new pass LazyMachineBlockFrequencyInfo

And use it in MachineOptimizationRemarkEmitter.  A test will follow on top of
Justin's changes to enable MachineORE in AsmPrinter.

The approach is similar to the IR-level pass.  It's a bit simpler because BPI
is immutable at the Machine level so we don't need to make that lazy.

Because of this, a new function mapping is introduced (BPIPassTrait::getBPI).
This function extracts BPI from the pass.  In case of the lazy pass, this is
when the calculation of the BFI occurs.  For Machine-level, this is the
identity function.

Differential Revision: https://reviews.llvm.org/D29836

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295072 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed