TableGen: Explicitly forbid self-references to field members

[nhaehnle]

Summary

Otherwise, patterns like in the test case produce cryptic error
messages about fields being resolved incompletely.

Change-Id: I713c0191f00fe140ad698675803ab1f8823dc5bd

include/llvm/TableGen/Record.h

public:
   static FieldInit *get(Init *R, StringInit *FN);
 
   Init *getRecord() const { return Rec; }
   StringInit *getFieldName() const { return FieldName; }
 
   Init *getBit(unsigned Bit) const override;
 
   Init *resolveReferences(Resolver &R) const override;
-  Init *Fold() const;
+  Init *Fold(Record *CurRec) const;
 
   std::string getAsString() const override {
     return Rec->getAsString() + "." + FieldName->getValue().str();
   }
 };
 
 /// (v a, b) - Represent a DAG tree value.  DAG inits are required
 /// to have at least one value then a (possibly empty) list of arguments.  Each

lib/TableGen/Record.cpp

Init *FieldInit::getBit(unsigned Bit) const {
   if (getType() == BitRecTy::get())
     return const_cast<FieldInit*>(this);
   return VarBitInit::get(const_cast<FieldInit*>(this), Bit);
 }
 
 Init *FieldInit::resolveReferences(Resolver &R) const {
   Init *NewRec = Rec->resolveReferences(R);
   if (NewRec != Rec)
-    return FieldInit::get(NewRec, FieldName)->Fold();
+    return FieldInit::get(NewRec, FieldName)->Fold(R.getCurrentRecord());
   return const_cast<FieldInit *>(this);
 }
 
-Init *FieldInit::Fold() const {
+Init *FieldInit::Fold(Record *CurRec) const {
   if (DefInit *DI = dyn_cast<DefInit>(Rec)) {
-    Init *FieldVal = DI->getDef()->getValue(FieldName)->getValue();
+    Record *Def = DI->getDef();
+    if (Def == CurRec)
+      PrintFatalError(CurRec->getLoc(),
+                      Twine("Attempting to access field '") +
+                      FieldName->getAsUnquotedString() + "' of '" +
+                      Rec->getAsString() + "' is a forbidden self-reference");
+    Init *FieldVal = Def->getValue(FieldName)->getValue();
     if (FieldVal->isComplete())
       return FieldVal;
   }
   return const_cast<FieldInit *>(this);
 }
 
 static void ProfileDagInit(FoldingSetNodeID &ID, Init *V, StringInit *VN,
                            ArrayRef<Init *> ArgRange,

lib/TableGen/TGParser.cpp

case tgtok::period: {
         return nullptr;
       }
       StringInit *FieldName = StringInit::get(Lex.getCurStrVal());
       if (!Result->getFieldType(FieldName)) {
         TokError("Cannot access field '" + Lex.getCurStrVal() + "' of value '" +
                  Result->getAsString() + "'");
         return nullptr;
       }
-      Result = FieldInit::get(Result, FieldName)->Fold();
+      Result = FieldInit::get(Result, FieldName)->Fold(CurRec);
       Lex.Lex();  // eat field name
       break;
     }
 
     case tgtok::paste:
       SMLoc PasteLoc = Lex.getLoc();
 
       // Create a !strconcat() operation, first casting each operand to

test/TableGen/self-reference-recursion.td

+// RUN: not llvm-tblgen %s 2>&1 | FileCheck %s
+// XFAIL: vg_leak
+
+class A<string self> {
+  int x = !cast<A>(self).x;
+}
+
+// CHECK: error: Attempting to access field 'x' of 'A0' is a forbidden self-reference
+def A0 : A<"A0">;