Wrap MVT::ValueType in a struct to get type safety

and better control the abstraction.  Rename the type
to MVT.  To update out-of-tree patches, the main
thing to do is to rename MVT::ValueType to MVT, and
rewrite expressions like MVT::getSizeInBits(VT) in
the form VT.getSizeInBits().  Use VT.getSimpleVT()
to extract a MVT::SimpleValueType for use in switch
statements (you will get an assert failure if VT is
an extended value type - these shouldn't exist after
type legalization).
This results in a small speedup of codegen and no
new testsuite failures (x86-64 linux).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52044 91177308-0d34-0410-b5e6-96231b3b80d8

docs/CodeGenerator.html

@@ -790,7 +790,8 @@ to the node defining the used value.  Because nodes may define multiple values,
 edges are represented by instances of the <tt>SDOperand</tt> class, which is 
 a <tt>&lt;SDNode, unsigned&gt;</tt> pair, indicating the node and result
 value being used, respectively.  Each value produced by an <tt>SDNode</tt> has
-an associated <tt>MVT::ValueType</tt> indicating what type the value is.</p>
+an associated <tt>MVT</tt> (Machine Value Type) indicating what the type of the
+value is.</p>
 
 <p>SelectionDAGs contain two different kinds of values: those that represent
 data flow and those that represent control flow dependencies.  Data values are