PassManager should minimize number of LoopPassManagers

[llvmbot]

Bugzilla Link	9184
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor

Extended Description

Currently, this analysis usage (taken from LoopStrengthReduce)

AU.addRequired();
AU.addRequiredID(LoopSimplifyID);
AU.addRequired();
AU.addRequired();
AU.addRequired();

causes this pass order:

 Natural Loop Information
  Loop Pass Manager
    Canonicalize natural loops
  Scalar Evolution Analysis
  Loop Pass Manager
    Induction Variable Users
    Canonicalize natural loops
    Induction Variable Users
    Loop Strength Reduction

The PassManager should move ScalarEvolution before all of the loop passes, since they all preserve ScalarEvolution. It is easy enough to fix this by changing the pass ordering, but in the future this could be done automatically.