[IR] Add support for empty tokens

When working with tokens, it is often the case that one has instructions
which consume a token and produce a new token.  Currently, we have no
mechanism to represent an initial token state.

Instead, we can create a notional "empty token" by inventing a new
constant which captures the semantics we would like.  This new constant
is called ConstantTokenNone and is written textually as "token none".

Differential Revision: http://reviews.llvm.org/D14581

llvm-svn: 252811

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index aabd9716118..2c6e8081c13 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -2622,6 +2622,7 @@ bool LLParser::ParseValID(ValID &ID, PerFunctionState *PFS) {
   case lltok::kw_null: ID.Kind = ValID::t_Null; break;
   case lltok::kw_undef: ID.Kind = ValID::t_Undef; break;
   case lltok::kw_zeroinitializer: ID.Kind = ValID::t_Zero; break;
+  case lltok::kw_none: ID.Kind = ValID::t_None; break;
 
   case lltok::lbrace: {
     // ValID ::= '{' ConstVector '}'
@@ -4255,6 +4256,11 @@ bool LLParser::ConvertValIDToValue(Type *Ty, ValID &ID, Value *&V,
       return Error(ID.Loc, "invalid type for null constant");
     V = Constant::getNullValue(Ty);
     return false;
+  case ValID::t_None:
+    if (!Ty->isTokenTy())
+      return Error(ID.Loc, "invalid type for none constant");
+    V = Constant::getNullValue(Ty);
+    return false;
   case ValID::t_Constant:
     if (ID.ConstantVal->getType() != Ty)
       return Error(ID.Loc, "constant expression type mismatch");