Add VectorTargetTransform::getNumberOfParts.

As discussed on IRC, add VectorTargetTransform::getNumberOfParts
to provide a stable interface to the vector legalization splitting factor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166751 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/TargetTransformInfo.h

@@ -156,6 +156,11 @@ public:
     return 1;
   }
 
+  /// Returns the number of pieces into which the provided type must be
+  /// split during legalization. Zero is returned when the answer is unknown.
+  virtual unsigned getNumberOfParts(Type *Tp) const {
+    return 0;
+  }
 };
 
 } // End llvm namespace