Added a SimplifyIndVar utility to simplify induction variable users

based on ScalarEvolution without changing the induction variable phis.

This utility is the main tool of IndVarSimplifyPass, but the pass also
restructures induction variables in strange ways that are sensitive to
pass ordering. This provides a way for other loop passes to simplify
new uses of induction variables created during transformation. The
utility may be used by any pass that preserves ScalarEvolution. Soon
LoopUnroll will use it.

The net effect in this checkin is to cleanup the IndVarSimplify pass
by factoring out the SimplifyIndVar algorithm into a standalone utility.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137197 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/IVUsers.h

@@ -140,6 +140,8 @@ public:
   static char ID; // Pass ID, replacement for typeid
   IVUsers();
 
+  Loop *getLoop() const { return L; }
+
   /// AddUsersIfInteresting - Inspect the specified Instruction.  If it is a
   /// reducible SCEV, recursively add its users to the IVUsesByStride set and
   /// return true.  Otherwise, return false.