Teach TableGen to automatically generate missing SubRegIndex instances.

The RegisterInfo.td file should only specify the indexes that sources need to
refer to. The rest is inferred.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131058 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/CodeGenTarget.h b/utils/TableGen/CodeGenTarget.h
index 4e04154..891b2d5 100644
--- a/utils/TableGen/CodeGenTarget.h
+++ b/utils/TableGen/CodeGenTarget.h
@@ -121,6 +121,9 @@
     return (i - SubRegIndices.begin()) + 1;
   }
 
+  // Create a new SubRegIndex with the given name.
+  Record *createSubRegIndex(const std::string &Name);
+
   const std::vector<CodeGenRegisterClass> &getRegisterClasses() const {
     if (RegisterClasses.empty()) ReadRegisterClasses();
     return RegisterClasses;