add scaffolding for target-specific MCExprs.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95559 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCExpr.cpp b/lib/MC/MCExpr.cpp
index 1ee1b1b..07546c1 100644
--- a/lib/MC/MCExpr.cpp
+++ b/lib/MC/MCExpr.cpp
@@ -17,6 +17,8 @@
 
 void MCExpr::print(raw_ostream &OS) const {
   switch (getKind()) {
+  case MCExpr::Target:
+    return cast<MCTargetExpr>(this)->PrintImpl(OS);
   case MCExpr::Constant:
     OS << cast<MCConstantExpr>(*this).getValue();
     return;
@@ -131,6 +133,7 @@
   return Create(Ctx.GetOrCreateSymbol(Name), Ctx);
 }
 
+MCTargetExpr::~MCTargetExpr() {}
 
 /* *** */
 
@@ -168,6 +171,9 @@
 
 bool MCExpr::EvaluateAsRelocatable(MCValue &Res) const {
   switch (getKind()) {
+  case Target:
+    return cast<MCTargetExpr>(this)->EvaluateAsRelocatableImpl(Res);
+      
   case Constant:
     Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
     return true;