For PR778:

Move file-scoped documentation to class-scoped so it is more readily
accessible.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28689 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Constant.h

@@ -18,6 +18,23 @@
 
 namespace llvm {
 
+/// This is an important base class in LLVM. It provides the common facilities
+/// of all constant values in an LLVM program. A constant is a value that is
+/// immutable at runtime. Functions are constants because their address is
+/// immutable. Same with global variables. 
+/// 
+/// All constants share the capabilities provided in this class. All constants
+/// can have a null value. They can have an operand list. Constants can be
+/// simple (integer and floating point values), complex (arrays and structures),
+/// or expression based (computations yielding a constant value composed of 
+/// only certain operators and other constant values).
+/// 
+/// Note that Constants are immutable (once created they never change) 
+/// and are fully shared by structural equivalence.  This means that two 
+/// structurally equivalent constants will always have the same address.  
+/// Constant's are created on demand as needed and never deleted: thus clients 
+/// don't have to worry about the lifetime of the objects.
+/// @brief LLVM Constant Representation
 class Constant : public User {
   void operator=(const Constant &);     // Do not implement
   Constant(const Constant &);           // Do not implement