Add some comments explaining what MVT and EVT are, and how they differ.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118014 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/ValueTypes.h b/include/llvm/CodeGen/ValueTypes.h
index 292423e272387b7a29aece6f775ef94850adb5aa..9e583ef4d69c7991e08031ab67c5c3c995d78ec7 100644 (file)
--- a/include/llvm/CodeGen/ValueTypes.h
+++ b/include/llvm/CodeGen/ValueTypes.h
@@ -26,7 +26,10 @@ namespace llvm {
   class LLVMContext;
   struct EVT;
 
-  class MVT { // MVT = Machine Value Type
+  /// MVT - Machine Value Type.  Every type that is supported natively by some
+  /// processor targeted by LLVM occurs here.  This means that any legal value
+  /// type can be represented by a MVT.
+  class MVT {
   public:
     enum SimpleValueType {
       // If you change this numbering, you must change the values in
@@ -158,7 +161,7 @@ namespace llvm {
       return !(NElts & (NElts - 1));
     }
 
-    /// getPow2VectorType - Widens the length of the given vector EVT up to
+    /// getPow2VectorType - Widens the length of the given vector MVT up to
     /// the nearest power of 2 and returns that type.
     MVT getPow2VectorType() const {
       if (isPow2VectorType())
@@ -353,7 +356,11 @@ namespace llvm {
     }
   };
 
-  struct EVT { // EVT = Extended Value Type
+
+  /// EVT - Extended Value Type.  Capable of holding value types which are not
+  /// native for any processor (such as the i12345 type), as well as the types
+  /// a MVT can represent.
+  struct EVT {
   private:
     MVT V;
     const Type *LLVMTy;