Add a ConstantDataVector::getSplatValue() method, for parity with

ConstantVector.  Fix some outright bugs in the implementation of
ConstantArray and Constant struct, which would cause us to not make
one big UndefValue when asking for an array/struct with all undef
elements.  Enhance Constant::isAllOnesValue to work with
ConstantDataVector.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149021 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Constants.h

@@ -766,6 +766,10 @@ public:
   /// i32/i64/float/double) and must be a ConstantFP or ConstantInt.
   static Constant *getSplat(unsigned NumElts, Constant *Elt);
 
+  /// getSplatValue - If this is a splat constant, meaning that all of the
+  /// elements have the same value, return that value. Otherwise return NULL.
+  Constant *getSplatValue() const;
+  
   /// getType - Specialize the getType() method to always return a VectorType,
   /// which reduces the amount of casting needed in parts of the compiler.
   ///