[TableGen] Make sure EnforceSameSize populates the type sets if necessary.

This was found by another commit I'm working on.

llvm-svn: 295578
diff --git a/llvm/utils/TableGen/CodeGenDAGPatterns.cpp b/llvm/utils/TableGen/CodeGenDAGPatterns.cpp
index 4eec2e6..22c3d49 100644
--- a/llvm/utils/TableGen/CodeGenDAGPatterns.cpp
+++ b/llvm/utils/TableGen/CodeGenDAGPatterns.cpp
@@ -644,6 +644,12 @@
 
   bool MadeChange = false;
 
+  if (isCompletelyUnknown())
+    MadeChange = FillWithPossibleTypes(TP);
+
+  if (VTOperand.isCompletelyUnknown())
+    MadeChange = VTOperand.FillWithPossibleTypes(TP);
+
   // If we know one of the types, it forces the other type agree.
   if (isConcrete()) {
     MVT IVT = getConcrete();