Currently MachineLoopInfo is used in only two places:
- for computing IsBasicBlockInsideInnermostLoop field of MCCodePaddingContext, and it is never used.
- in emitBasicBlockLoopComments, which is called only if isVerbose() is true.
Despite that, we currently have a dependency on MachineLoopInfo, which makes
pass manager to compute it and MachineDominator Tree. This patch removes the
use (1) and makes the use (2) lazy, thus avoiding some redundant