Make TableGen definitions clearer and add additional assertions

Author: bozicrHT

clang/include/clang/Basic/BuiltinsBase.td

@@ -33,16 +33,15 @@ def NoThrow : Attribute<"n">;
 def Pure : Attribute<"U">;
 def ReturnsTwice : Attribute<"j">;
 
-class NonNullOptMode {
-  int value;
+class NonNullOptMode<int mode> {
+  int value = mode;
 }
 
-def NonOptimizing : NonNullOptMode { let value = 0; }
-def Optimizing    : NonNullOptMode { let value = 1; }
+def NonOptimizing : NonNullOptMode<0>;
+def Optimizing    : NonNullOptMode<1>;
 
-class NonNull<NonNullOptMode Mode, list<int> Is> : MultiIndexAttribute<"N", Is> {
+class NonNull<NonNullOptMode Mode, list<int> Is> : MultiIndexAttribute<"N:" # Mode.value # ":", Is> {
   int optMode = Mode.value;
-  let Mangling = "N:" # Mode.value # ":";
 }
 
 // builtin-specific attributes

clang/lib/Basic/Builtins.cpp

@@ -320,14 +320,18 @@ bool Builtin::Context::isNonNull(unsigned ID, llvm::SmallVectorImpl<int> &Indxs,
   if (!AttrPos)
     return false;
 
-  AttrPos += 2; // skip 'N' and ':'
+  ++AttrPos;
+  assert(*AttrPos == ':' && "Format specifier must be followed by a ':'");
+  ++AttrPos;
   if (*AttrPos == '0')
     Mode = Info::NonNullMode::NonOptimizing;
   else if (*AttrPos == '1')
     Mode = Info::NonNullMode::Optimizing;
   else
     llvm_unreachable("Unrecognized NonNull optimization mode");
-  AttrPos += 2; // skip mode and ':'
+  ++AttrPos; // skip mode
+  assert(*AttrPos == ':' && "Mode must be followed by a ':'");
+  ++AttrPos;
 
   parseCommaSeparatedIndices(AttrPos, Indxs);