Implement a !subst operation simmilar to $(subst) in GNU make to do
def/var/string substitution on generic pattern templates.  For example:

def Type;
def v4f32 : Type;
def TYPE : Type;

class GenType<Type t> {
  let type = !(subst TYPE, v4f32, t);
}

def TheType : GenType<TYPE>;


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@71801 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/TGLexer.cpp b/utils/TableGen/TGLexer.cpp
index 43afae9..264be4b 100644
--- a/utils/TableGen/TGLexer.cpp
+++ b/utils/TableGen/TGLexer.cpp
@@ -447,7 +447,7 @@
   if (Len == 3  && !memcmp(Start, "shl", 3)) return tgtok::XSHL;
   if (Len == 9  && !memcmp(Start, "strconcat", 9))   return tgtok::XStrConcat;
   if (Len == 10 && !memcmp(Start, "nameconcat", 10)) return tgtok::XNameConcat;
-//   if (Len == 5 && !memcmp(Start, "subst", 5)) return tgtok::XSubst;
+  if (Len == 5 && !memcmp(Start, "subst", 5)) return tgtok::XSubst;
 //   if (Len == 7 && !memcmp(Start, "foreach", 7)) return tgtok::XForEach;
   if (Len == 4 && !memcmp(Start, "cast", 4)) return tgtok::XCast;