[LoopAccesses] Add canAnalyzeLoop

This allows the analysis to be attempted with any loop.  This feature
will be used with -analysis.  (LV only requests the analysis on loops
that have already satisfied these tests.)

This is part of the patchset that converts LoopAccessAnalysis into an
actual analysis pass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229895 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/LoopAccessAnalysis.h

@@ -181,6 +181,10 @@ private:
   /// \brief Analyze the loop.  Substitute symbolic strides using Strides.
   void analyzeLoop(ValueToValueMap &Strides);
 
+  /// \brief Check if the structure of the loop allows it to be analyzed by this
+  /// pass.
+  bool canAnalyzeLoop();
+
   void emitAnalysis(VectorizationReport &Message);
 
   /// We need to check that all of the pointers in this list are disjoint