[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

4 files changed, 17 insertions, 10 deletions

diff --git a/llvm/lib/AsmParser/LLLexer.cpp b/llvm/lib/AsmParser/LLLexer.cpp
index 91ce1fd7669..372c5658886 100644
--- a/llvm/lib/AsmParser/LLLexer.cpp
+++ b/llvm/lib/AsmParser/LLLexer.cpp
@@ -523,6 +523,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(zeroinitializer);
   KEYWORD(undef);
   KEYWORD(null);
+  KEYWORD(none);
   KEYWORD(to);
   KEYWORD(caller);
   KEYWORD(tail);
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");
diff --git a/llvm/lib/AsmParser/LLParser.h b/llvm/lib/AsmParser/LLParser.h
index 24ff8e75023..d4384db9bf0 100644
--- a/llvm/lib/AsmParser/LLParser.h
+++ b/llvm/lib/AsmParser/LLParser.h
@@ -46,15 +46,15 @@ namespace llvm {
   /// or a symbolic (%var) reference.  This is just a discriminated union.
   struct ValID {
     enum {
-      t_LocalID, t_GlobalID,      // ID in UIntVal.
-      t_LocalName, t_GlobalName,  // Name in StrVal.
-      t_APSInt, t_APFloat,        // Value in APSIntVal/APFloatVal.
-      t_Null, t_Undef, t_Zero,    // No value.
-      t_EmptyArray,               // No value:  []
-      t_Constant,                 // Value in ConstantVal.
-      t_InlineAsm,                // Value in FTy/StrVal/StrVal2/UIntVal.
-      t_ConstantStruct,           // Value in ConstantStructElts.
-      t_PackedConstantStruct      // Value in ConstantStructElts.
+      t_LocalID, t_GlobalID,           // ID in UIntVal.
+      t_LocalName, t_GlobalName,       // Name in StrVal.
+      t_APSInt, t_APFloat,             // Value in APSIntVal/APFloatVal.
+      t_Null, t_Undef, t_Zero, t_None, // No value.
+      t_EmptyArray,                    // No value:  []
+      t_Constant,                      // Value in ConstantVal.
+      t_InlineAsm,                     // Value in FTy/StrVal/StrVal2/UIntVal.
+      t_ConstantStruct,                // Value in ConstantStructElts.
+      t_PackedConstantStruct           // Value in ConstantStructElts.
     } Kind = t_LocalID;
 
     LLLexer::LocTy Loc;
diff --git a/llvm/lib/AsmParser/LLToken.h b/llvm/lib/AsmParser/LLToken.h
index 6980790c098..6a9a1de0b85 100644
--- a/llvm/lib/AsmParser/LLToken.h
+++ b/llvm/lib/AsmParser/LLToken.h
@@ -49,7 +49,7 @@ namespace lltok {
     kw_external, kw_thread_local,
     kw_localdynamic, kw_initialexec, kw_localexec,
     kw_zeroinitializer,
-    kw_undef, kw_null,
+    kw_undef, kw_null, kw_none,
     kw_to,
     kw_caller,
     kw_tail,