A previous PR introduced a threshold where we would mask out a LR that
had been evicted a certain number of times to combat pathological
compile time cases with a somewhat adversarial model. However, this
patch did not take into account urgent LRs which led to compilation
failures when greedy would expect us to provide an eviction and we could
not due to the newly introduced logic.
This patch adds a threshold flag, -mlregalloc-max-cascade, to prevent
live ranges from being evicted more than is necessary.
After deploying a new regalloc model, we ran into some pathological
cases where the model decided it wanted to ping-pong evictions, taking
up a large amount of compile time. This threshold is mostly a stop gap
while we continue to investigate other solutions and work on
minimizing/constructing test cases.
- Add `MachineBlockFrequencyAnalysis`.
- Add `MachineBlockFrequencyPrinterPass`.
- Use `MachineBlockFrequencyInfoWrapperPass` in legacy pass manager.
- `LazyMachineBlockFrequencyInfo::print` is empty, drop it due to new
pass manager migration.
